Existing Distribution System and Protection Using Numerical Relay

Existing Distribution System &Protection using Numerical Relay Project- 2010

1. BRIEF HISTORY OF BPCL -KR

BPCL Kochi Refinery earlier known as Cochin Refineries Limited was incorporated

as a Public Limited Company in September 1963, with technical collaboration &

financial participation from Philips Petroleum Company of USA.

The refinery was commissioned in 1966. Initially it had an installed capacity to process

2.3 Million Metric Tonnes Per Annum (MMTPA) of Agha Jari Crude (Light Iranian

Crude). It commenced crude processing on 23rd September 1966.From the date of

commissioning to-date, the refinery undertook 3 expansions in refining capacity and

installation of Secondary Processing Facilities.

The capacity was first expanded from 2.5 MMTPA to 3.3 MMTPA in September

1973.The production of LPG and Aviation Turbine fuel (ATF) commenced after this

expansion. Bombay High Crude was first processed in 1977.Crude processing capacity

of Kochi Refinery was further increased from 3.3 MMTPA by revamping the crude

unit in the year 1984.

A substantial portion of the atmospheric residue, which varies 30% to 45% of the crude

throughput, depending on the crude, was converted to furnace oil by vibrating or

yielded as Low Sulphur Heavy Stock Oil (LSHS) in the initial setup. The original

scheme was conceived at a time when the price of crude oil was only $1 per barrel

which has now gone up to about $18 per barrel. With the steep rise in the price of crude

oil and petroleum products in the part few years & the country’s policy of conservation

of non-renewable resources out which petroleum resources form the single largest

fraction, it became necessary to review the utilization of atmospheric residue more

economically. Further increased processing of Bombay High Crude generates

substantial quantity of LSHS with subsequent disposal problems. The consumption

pattern of petroleum products in India is such that there is a deficit of middle distillates

and LPG.

In this context, a secondary processing scheme at Kochi Refinery was thought of in

order to produce additional middle distillates and LPG out of atmospheric residue. The

SCMS School of Engineering Dept. of Electrical & Electronics& Technology 1


proposed secondary processing facility was to utilize the Vacuum Gas Oil (VGO)

derived from a mixture of 3.5 MMTPA of Bombay High and 1.0 MMTPA of Basrah

crude with flexibility to process 100% Bombay High or 100% Middle East Crude at a

total crude throughput of 4.5 million tonnes per annum.

With the above considerations, Fluid Catalytic Cracking Process was selected for KRL.

FCC technology is process one and a number of units are in operation in the country.

LPG yield from FCC from FCC unit is quite high and operation can be adjusted for

lower seventy to give increased yields of middle distillates and lower yields of

gasoline. With this in mind, an FCC unit with a capacity for processing 1.0 MMTPA of

Vacuum Gas Oil was set up along with the revamp in 1985.

Conventional Bitumen Unit with capacity of 42.7TPH commissioned by Kochi

Refinery in 1985. Later then Bitumen Unit utilized to produce 60-70 and 80-100

penetration grade bitumen product. In house off gas treatment incorporated with this

Bitumen Unit.

The crude capacity was further revamped to 7.5MMTPA (3.5 MMTPA BH and

4.0MMTPA PG), in the year 1994, with the addition of a new crude unit and

consequently the FCC capacity was further increased to 1.4MMTPA in order to process

the increased quantity of VGO generated. The revamped FCC unit is designed to

process VGO derived from 100% BH crude oil or 32% BH and 68% PG crude oil.

During the year 1989 , the company commissioned an Aromatic Recovery Unit with a

design capacity of 87200 Tonnes Per annum(TPA) of Benzene and 12000 TPA of

Toluene, marking Kochi Refinery’s entry into petrochemicals. A captive Power Plant

of 26.3 MW ISO rating was commissioned in March 1991 in order to meet power

requirements of Kochi Refinery.

A light Ends Field Preparation Unit (LEFPU) to supply feedstock to (poly iso butane)

PIBU was commissioned in March 1993. PIBU plant was commissioned in 1994 as a

joint venture company between KRL and Ballmer Lawri. On 19/4/2001, this company

was taken over by KRL.

The PIB plant was designed to produce poly iso butane grades of PIB24, PIB32, and

PIB28 using chevron processing technology. PIB is a feedstock for manufacturing oil



additives, adhesives, coatings and films. Feedstocks, oefin& Butane are supplied by

LEFPU-1&2 in FCCU unit.

Kochi Refinery also commissioned a Rafffinate Purification Unit for manufacture of

8800 TPA of petroleum hydrocarbon solvent in January 1994. A fuel gas

desulphurization Unit, forming part of capacity expansion to 7.5 MMTPA and as a part

of environment protection was commissioned in March 1995.

During the year2000, the company commissioned diesel hydro desulphurization unit

(DHDS) OF 2.0 MMTPA capacities along with Hydrogen generation unit, Amine

Regeneration Unit to meet the specification of High Speed Diesel (HSD) recommended

by Ministry of Environment and Forest to make it more eco friendly.



2. PLANT OVERVIEW

There are five sections under the manufacturing department , four out of which

corresponds to four process unit block. They are

1. Crude Distillation Unit I ( CDU I)

2. Crude Distillation Unit II (CDU II)

3. Fluidized Catalystic Cracking unit (FCCU)

4. Diesel Hydro De- sulphurisation.

CRUDE DISTILLATION UNIT I

The design of CDU-I is a primary unit and mainly meant for preventing LPG

components, which was going to fuel gas header along with the crude column over

head gas. Other features include optimization of the heat recovery system, qualitative

improvement of products from the crude atmospheric column and increase in crude

through put.

The crude after desalting process is heated to a required temperature in the heater and

is fed to the prefractioner. The over head product obtained here is Naphtha. The over

head product (light naphtha) is fed to LPG recovery unit in Naphtha stabiliser, light

naphtha from the crude prefractioner contains lighter components such as LPG and fuel

gas. This naphtha as such cannot be routed to store due to its high vapour pressure. The

naphtha is stabilized by separating out and recovering the LPG component in the LPG

recovery unit.

The pre-treated crude from the prefractionator column bottom is sent to crude

column after being heated in the crude preheat train in the crude charge heater for

further distillation process. The distilled products are drawn from the different sections

of the columns depending upon their boiling range. Heavy naphtha, kero-1.kero-2 and

diesel are side products. The remaining portion of crude is drawn from the column

bottom and reduced crude oil (RCO) are routed to FCCU block for further separation.



CRUDE DISTILLATION UNIT - II

The installed capacity of CDU-II is 3MMPTA. The plant is designed to process

362.3 TPH of BH crude with light ends at 2.2 wt% or Arabian Mix crude.

Crude from storage is pumped through a feed preheat train and preheated to 135

degree Celsius. Stripped water from sour water stripes unit is injected into the crude

and the mixed crude is sent to a desalter for removing salts. A high voltage electric

field in the desalter breaks the emulsion and the brine water is separated.

The desalted crude is pumped through another preheat exchanger and then split

into two streams for further preheating in the second and third chains of preheat train.

The preheated crude is finally heated in the charge furnace to 360 degree Celsius and

introduced into the flash zone of the atmospheric column.

The atmospheric column over-head vapours are condensed and received in an

accumulator and overheat steam is sent to naphtha stabilizer. A small quantity of fuel

gas is generated which is burned off in the crude heater.

Heavy gas oil (HGO). Light gas oil (LGO),kerosene and heavy naphtha are

withdrawn as side streams and are steam stripped in stripper columns. Heavy naphtha is

cooled and routed to gas oil stream. Provision is also given to route heavy naphtha

along with stabilized naphtha. Kerosene after steam stripping is cooled and routed to

storage.

HGO,LGO streams are mixed after cooling and the gas oil streams is further

cooled and its routed to storage and the vacuum diesel from VDU joins gas oil at

battery limit. Provision is given to blend kerosene and LVGO also with gas oil. Gas oil

along with other blend streams goes to the diesel pool as a combined diesel stream.

RCO from the crude column bottom is send to VDU. A part from top reflux

cooling and condensation of vapours at various stages of the column is achieved by



means of the pump around streams of kerosene, LGO and HGO. The heat content of

the pump around streams are mostly recovered in crude preheat trains. LGO is used as

heating medium for stabilizer reboiler.

FCCU BLOCK

The FCCU was commissioned in 1985 with the design capacity of 1MMTPA. Feed

preparation unit (FPU) is a main unit in the FCCU block. The purpose of the feed

preparation unit is to make feed of required quality to be processed in FCC. In this unit

RCO is distilled under vacuum into four different cuts namely vacuum diesel oil

(VDU), Light vacuum gas oil (LVGO), Heavy vacuum gas oil (HVGO) and vacuum

residence. The VDO cut is normally routed to diesel pool. LVGO and HVGO

combined having boiling range approximately between 360C and 555C is the feed of

FCC.

By maintaining the end point VGO below 550C, the metal content like Ni, vanadium

etc and the carbon residue are reduced to an acceptable level. The metals if present in

VGO are poisons to the FCC catalysts. FCCU converts VGO into higher value products

such as LPG, gasoline and diesel by cracking of heavier hydrocarbon molecules of

VGO to lighter components. Silica-alumina catalyst in powder form is used for

promoting the cracking reactions. Reaction takes place at higher temperature and at

pressure above atmospheric pressure.

During cracking. Heavy hydrocarbon molecular of VGO are converted to lower

molecular weight components such as LPG, gasoline etc . Coke is formed as side

product. The entire coke formed is deposited on the catalyst surface, using exothermic

reaction and regenerate the catalyst. H2S present in the LPG is removed by absorbing

in diethanol amine in an absorption column in the amine unit.



DIESEL HYDRO DE-SULPHURISTAION UNIT (DHDS)

DHDS unit is designed to desulphurise diesel blend stock and reduce the sulphur

content to less than 0.05wt%. this is achieved by passing a preheated diesel steam along

with hydrogen over two reactors in series containing beds of Nickel-Molybdenum

catalyst. Sulphur compounds in the feed diesel react with hydrogen to form hydrogen

sulphide. Any unsaturated hydrogen in the feedstock also get saturated, which helps in

improving the ignition quality of diesel.

The sulphur recovery unit convert and separate H2S contained in the sour gas and acid

gas streams from sour water stripping unit and amine regeneration unit in the form of

solid element sulphur. The sour water stripping unit function is to treat sour water

generated from DHDS/hydrogen units.



3. BPCL-KR PRODUCTS

Liquefied petroleum gas & kerosene for households and industrial uses.

Natural rubber modified bitumen ( Rubberized bitumen)

Petrol and diesel for automobiles.

Naphtha, major raw material for fertilizer and petrochemical industries.

Benzene for manufacture of caprolactum, phenol, insecticides and other

chemicals.

Furnace oil and low sulphur heavy stock for fuel in industries.

Aviation turbine fuel (ATF) for aircrafts.

Bitumen and Natural Rubber Modified Bitumen (NRMB) for road paving.

Special boiling point spirit used as solvent in tyre industry.

Toluene for manufacture of solvents and insecticides, pharmaceuticals and

paint.

Polyisobutenes for manufacture of lubricants, cable jelly etc.

Sulphur for use in fertilizer, sugar, chemical and tyre industry.



4. EXISTING DISRIBUTION SYSTEM

The Captive Power Plant (CPP) was set up in 1990 with one 22MW Gas Turbine

Generator (GTG). This machine is capable of using the Refinery Fuel Gas (RFG) as

one of its fuel. If RFG is not available to the requirement levels, the remaining fuel

requirement is met from diesel. The waste heat from the turbine is utilized to produce

steam using a Heat Recovery Steam Generator (HRSG). The GTG generates power at

11KV level and is supplied to the 11KV switchgear-200 at the CPP Substation.

To augment the capacity of CPP, a new Steam Turbo Generator (STG) of 17.8MW

capacity was added to the system in 1998.This generator is producing power at 11KV

level and is also feeding to the 11KV switchgear-200 at the CPP Substation.

In KR, steam consumption in process units are from MP steam header of 18 Kg/cm2

and LP steam header of 4.5 Kg/cm2. But the steam generated in CO Boiler and HRSG

are at a pressure level of 38 Kg/cm2 that envisaged a co-generation of power with

another TG set of 2.5MW and it generates power at a 3.3KV level.

KR receives power from KSEB with a contract of Maximum Demand 20 MVA. Two

66KV feeders Line-1 and Line-2 are tapped from Kalamassery-Vytilla No.1 feeder and

Kalamassery-Vytilla No.2 feeder respectively and are fed to the 66KV switchyard at

CPP. The power at 66KV is stepped down to 11KV by two 35MVA, 66/11KV

transformers and is fed to the 11KV switchgear-2101 at New MRS substation.

The two 11KV switchgears i.e. SWGR-2101 and SWGR-200 are linked together by

two link circuits, Link-1 and Link-2 so that operational flexibility is assured.

Synchronizing with the state grid is done to draw power as and when required.

The power is distributed from the 11KV switchgears to a number of substations

through cables. The substations feeding to various process plants cater the energy needs

of the process units at different levels of 11KV, 3.3KV, 415V etc i.e. the power is



distributed from 11kv switchgear to Power Motor Control Centre (PMCC) at 415V

then to the Motor Control Centre (MCC) at 415V and then finally to Motor/LDB (Light

Distribution Board ). The present power demand of the refinery is to the tune of 31MW

and everyday KR consumes approximately 7lakhs Kilowatt-hour of electrical energy.



FIG : 4.1



BLOCK DIAGRAM OF DISTRIBUTION SYSTEM

FIG: 4.2



5. CAPTIVE POWER PLANT

A captive power plant of 22MW was commissioned in 1990. An additional power plant

of 17.8 MW was commissioned in 1998.

Captive Power Plant (CPP) is the heart of KR. It has as gas turbine generator (GTG)

and a steam turbine generator (STG) which caters the electrical load of refinery. BPCL-

KR also has 66KV feeders from KSEB, Kalamassery Substation with a contact

maximum demand of 20 MVA. The 66KV feeder’s line 1 and 2 are tapped from

(Kalamassery- Vytilla) No:1 feeder and ( Kalamassery- Vytilla) No:2 feeder

respectively. The total running load of BPCL-KR comes to around 36MW out of which

5MW is being continuously drawn from KSEB and remaining 31MW will be shared by

GTG.,STG and TG. KSEB power being unstable used for feeding non critical loads and

captive generation is used for feeding critical loads. The BPCL-KR consumes about 7.5

lakhs units of electrical energy on an average per day. The generated/ imported from

KSEB at captive power plant is distributed to different plants using XPLE cables at

11KV level through two substations namely CPP substation and New MRS substation.

Process substation, FCCU, revamp substation, ACTP substation, CPP offsite

substation, unit station transformers receives power from CPP substation. 11KV

switchgear and CDU-2 substation, ARU substation, Naphtha revamp substation, PIB

substation and colony sector-1 substation receives power from New MRS substation.

BPCL-KR electrical system also consists of around 2500 motors, 80 transformers, and

40 substations/MCC rooms.



6. STG DESCRIPTION

6.1 STG Generator Construction

Construction of Stator

Outer frame is of steel plate welded construction of high quality and is of rigid

design. At the inner side of outer frame, stator core is tightened and fitted at ample

pressure by core bolts through the media of stator core clamps.

Stator core is formed by laminating silicon steel sheets of high quality and little iron

loss, ventilation ducts are provided for each proper length in axial direction for the

purpose of effectively cooling the interior. Stator coil is entirely immersed F type

varnish on its which is mainly made of mica and coated special finish coating which

possesses heat resistance, humidity resistance and oil resistance along with sufficient

insulating intensity.

Construction of rotor

Shaft is made of forged steel and field core is formed by laminating steel

sheets. At every suitable length in its axial direction, duct pieces are welded forming

ventilating duct to effectively cool the interior.

Excitation device

Alternating current from three phase AC rectifier is rectified to DC by the

rotary rectifier with silicon rectifier. Then, that DC electric source excites the field coil

of generator. Therefore the generator does not have brush and slip ring.

The AC exciter is revolving armature type i.e. the field is frame side and the armature is

rotor side. The rotary rectifier consists of silicon rectifier, protecting condenser and

attachment ring. The attachment ring keeps the silicon rectifier and condenser against

the centrifugal force.



7. BRUSHLESS EXCITATION SYSTEM

FIG: 7.1

The shaft is connected to prime mover. At first when shaft rotates the rotor of the PM

generator also rotates. It results an AC voltage induced in stator of PM generator. The

AC voltage induced is given to an Automatic Voltage Regulator (AVR). It rectifies AC

to DC and is given to the stator of main exciter. At same time the rotor winding rotating

in the main exciter field induces a voltage and is given to the diode wheel through

internal wiring. Here the AC is again converted into DC. It is given to the rotor of main

generator. The stator of this generator induces three phase AC as shown in figure.



8. WHY PROTECTION IS NEEDED?

Protection is installed to detect faults occurrences and isolate the faulty

equipments so that the damage to the faulty equipment is limited and disruption of

supplies to the adjacent unaffected equipment is minimized.

In a power system consisting of generators, motors, transformers etc, it is

inevitable that sooner or later some fault may occur. When a fault occurs it must be

quickly detected and the faulty equipment must be disconnected from the system. If

fault are not detected it cause unnecessary interruption of service to the customers and

damage to other connected equipments.

Generally fuse performs the function of detection and interruption but it is limited

only to low voltage circuits. For high voltage circuits. Relays and circuit breakers are

used.

So protection must detect faults and abnormal working conditions and isolate the

faulty working conditions and isolate the faulty equipment so as to limit damage caused

by fault energy and to limit effect on rest of the system.

8.1 Fault Risks

Severe damage to the faulted equipment

Excessive current may flow

Causes burning of conductors or equipment winding.

Arcing-energy dissipation.

Risk of explosion for oil filled switch area or when in hazardous

environments.

Damage to adjacent plants

Damage to staff or personnel.

Disruption to adjacent plants

Prolonged voltage dips cause other equipment to stall.



Loss of synchronism for synchronous generators/ motors

9. ASPECTS OF PROTECTION SYSTEM

Dependability/Reliability

Protection must operate when required

Failure to operate can be extremely damaging and disruptive

Faults are rare: Protection must operate even after years of inactivity

Improved by use of back up protection and duplicate protection

Security/Stability

Protection must not operate when not required to e.g., due to

Load switching

Faults on other parts of the system

Recoverable process swings

Speed

Fast operation

Minimizes damages and danger

Minimizes system instability

Discrimination and security can be costly to achieve as it generally

involves additional signalling/communication equipment

Cost

The cost of protection is equivalent to an insurance policy against

damage to plant and loss of supply and customer goodwill

Acceptable cost is based on a balance of economics and technical

factors. Cost of protection should be balanced against cost of

potential hazards

There is an economic limit on what we can spend



10. CLASSIFICATION OF PROTECTIVE SCHEMES

A protective scheme is used to protect equipment or a section of the line. It includes

one or more relays of the same or different types. The following are the most common

protective schemes, which are usually used for the protection of a modern power

system.

OVERCURRENT PROTECTION

This scheme of protection is used for the protection of distribution lines, large motors,

equipments etc. It includes one or more over current relays. An over current relay

operates when the current exceeds its pick up value.

DISTANCE PROTECTION

Distance protection is used for the protection of transmission line; usually 33kV, 66kV

lines. It includes a number of relays of same or different types. A distance between the

relay location and the point of fault in terms of impedance, reactance etc. The relay

operates if the point of fault lies within the protected section of the line. There are

various kinds of distance relays. The important types are impedance, reactance mho

type. An impedance relay measures the line impedance between the fault point and

relay location; a reactance relay measures reactance and mho relay measures a

component of admittance.

CARRIER CURRENT PROTECTION

This scheme of protection is used for the protection of EHV and UHV lines generally

132kV and above. A carrier signal in the range 50-500 kc/sec is generated for the

purpose. A transmitter and receiver are installed at each end of transmission line to be

protected. Information regarding the direction of the fault current is transmitted from

one end of the line section to the other. Depending on the information relays placed at



each end trip if the fault lies within their protected section. Relays do not trip in case of

external faults. The relays are of distance type and their tripping operation is controlled

by their carrier signal.

DIFFERERNTIAL PROTECTION

This scheme of protection is used for the protection of generators, transformers, motors

of very large size, bus zones etc. C.Ts is placed on both sides of each winding of a

machine. The outputs of their secondaries are applied to the relay coils. The relay

compares the current entering a machine winding and leaving the same. Under normal

conditions or during any external faults, the current entering the winding is equal to the

current leaving the winding. But in the case of an internal fault of the winding these are

not equal. This difference in current actuates the relay. Thus the relay operates for

internal faults and remains in operation under normal conditions or during external

faults. In case of bus zone protection C.T are placed on both sides of the bus bar.



11. PROTECTIVE RELAYS

A relay is an automatic device by means of which an electric circuit is indirectly

controlled and is governed by a change in the same or another electrical circuit. It

detects an abnormal condition in an electrical circuit and causes a circuit breaker to

isolate the faulty element of the system. In some cases, it may give an alarm or visible

indication to alert the operator.

The Function of Protective Relaying

The function of protective relaying is to cause the prompt removal from service of any

element of power system when it suffers a short circuit, or when it starts to operate in

any abnormal manner that might cause damage or otherwise interfere with the effective

operation of the rest of the system. The relaying equipment is aided in this task by

circuit breakers that are capable of disconnecting the faulty elements when they are

called upon to do so by the relaying equipment.

Circuit breakers are generally located so that each generator, transformer, bus,

transmission line etc can be completely disconnected from the rest of the system. These

circuit breakers must have sufficient capacity so that they can carry momentarily the

maximum short circuit current that can flow through them, and then interrupt this

current; they must also withstand closing in on such a short circuit and then interrupting

it according to certain prescribed standards.

Although the principle function of protective relaying is to mitigate the effects of short

circuits, other abnormal operating conditions arise that also require the services of

protective relaying. This is particularly true of generators and motors.

A secondary function of protective relaying is to provide indication of the location and

type of failure. Such data not only assist in expediting repair but also, by comparison

with human observation and automatic oscillograph records, they provide means for

analyzing the effectiveness of the fault-prevention and mitigation features including the

protective relaying itself.



Automatic Reclosure

About 90% of faults on overhead lines are of transient nature. Transient faults are

caused by lightning or external bodies falling on the lines. Such faults are always

associated with arcs. If the line is disconnected from the system for a time the arc is

extinguished and the fault disappears. Immediately after this the circuit breaker can be

reclosed automatically to restore the supply.

Most faults on EHV lines are caused by lightning. Flashover across insulators takes

place due to overvoltage caused by lightning and short time. Hence only one

instantaneous reclosure is used in the case of EHV lines. There is no need for more than

one reclosure for such a situation. For EHV lines one reclosure is 12 cycles is

recommended. A fast reclosure is desired from the stability point of view. Statistical

reports show that over 80% faults are cleared after the first reclosure, 10% requires the

second reclosure and 2% need the third reclosure, while the remaining 8% are

permanent faults. If the fault is not cleared after 3 reclosures, it indicates that the fault is

of permanent nature. Automatic reclosure are not used on cables as the breakdown of

insulation cable causes a permanent fault.

Back-up Relaying

Back-up relaying is employed only for protection against short circuits. Because short

circuits are the preponderant type of power failure, there are more opportunities for

failure in short primary relaying. Experience has shown that back-up relaying for other

than short circuits is not economically justifiable.

Auxiliary relays

Auxiliary relays assist protective relays. They repeat operations of protective relays,

control switches etc. They relieve the protective relays of duties like tripping, time lag,

sounding an alarm etc. They may be instantaneous or may have a time delay.

Under voltage relay

A relay which operates when the system voltage falls below certain preset value.



Time Delay Relay

A time delay operates after a certain preset time delay. The time delay may be due to

its inherent design features or may be due to the presence of a time delay component.

Such relays are used in the protection schemes as a means of time discrimination. They

are frequently used in control and alarm schemes.

Differential Relay:

A relay which operates in response to the difference of two actuating quantities.

Earth fault Relay:

A relay used for the protection of an element of a power system against earth faults is

known as an earth relay.

Over current Relay:

A relay which operates when actuating current exceeds a certain preset value. The

value of preset current above which the relay operates is known as its pick up value.

This is used for protection of distribution lines, large motors, power equipments etc.



12. CLASSIFICATION OF PROTECTIVE RELAYS BASED ON TECHNOLOGY

Protective relays can be broadly classified into the following categories

depending on the technology they use for their construction and operation.

1. Electromagnetic Relays

2. Static Relays

3. Numerical Relay

12.1 ELECTROMAGNETIC RELAYS

Electromagnetic relays include attracted armature, moving coil, and induction disc

induction cup type relays. Electromagnetic relays contain an electromagnet (or a

permanent magnet) and a moving part. When the actuating quantity exceeds a certain

predetermined value, an operating torque is developed which is applied on the moving

part. This causes the moving part to travel and to finally close a contact to energise the

tripcoil of the breaker.

LIMITATIONS OF ELECTRO MAGNETIC RELAYS

The protective system works with the help of electromagnetic relays which have less

accuracy.

Fault events analysis is difficult

Slow response of faulty condition.

Different elements are required for different predictions.

Limited load shedding facility.

Increased electrical noise during switching.

Decreased lifetime due to the fact of moving parts and thus causes wear.



12.2 STATIC RELAYS

Static relays contain electronic circuit, which may be transistors, ICs, Diodes and other

electronic components, there is a comparator circuit in the relay, which compares two

or more currents or voltages and gives an output, which is applied to either a slave relay

or a thyristor circuit. The slave relay is an electromagnetic relay, is a semi-static relay.

A relay using a thyristor circuit is a wholly static relay. Static relay possess the

advantage of having low burden on CT and PT, fast operation, absence of mechanical

inertia and contact trouble, long life and less maintenance. Static relays have proved to

be superior to electromagnetic relays and they are being used for the protection of

important lines, power station and substations. Yet they have not completely replaced

electromagnetic relays. Static relays are treated as a family of relays. Electromagnetic

relays continue to be in use because of their simplicity and low cost. Their maintenance

can be done by less qualified personnel whereas the maintenance and repair of static

relays require personnel’s in solid state devices.

12.3 MICROPROCESSOR BASED PROTECTIVE RELAYS

Microprocessor based protective relays are the latest development in this field. With

the development in VLSI technology, sophisticated and fast microprocessors are

coming up. Their application to the problems of protective relaying schemes is of

current interest, to power engineers. The inherit advantages of microprocessor based

over static relay with or a very limited range of applications, are attractive flexibility

due to their programmable approach. Microprocessor based protective provides

protection at low cost and compete with conventional relays. The present downward

trend in the cost of large scale integrated circuits will encourage wide applications of

microprocessor based relays for the protection of the modern complex power networks.



13. FAULT IN POWER SYSTEM

Fault occurs when two or more conductors that normally operate with potential

difference coming contact with each other. These faults may be caused by sudden

failure of piece of equipment, accidental damage or short circuit to overhead lines, or

by insulation failure resulting from lightning surges. The faults generally occurring in

power system are

1.Over current

It occurs mainly due to short circuit/leakage due to corona effect sometimes due to

overload on the supply system.

2.Under voltage

It occurs either on short circuits because of more voltage drop in lines and machines

or on failure of alternators field.

3.Unbalance

Occurs either on grounding of one or two phases or on short circuit of two phases or

breaking of one of the conductors. In such cases different current flow through different

phases and fault is known as unbalanced fault.

4.Reverse Power

This fault occurs only in inter-connected systems. A generator, on failure of its field,

start working as a motor and takes power instead of delivering power ie, the flow of

power is reversed. Similarly in case of feeders connected in parallel. whenever some

fault occurs on any one of the feeders, the fault is fed from both ends ie, again direction

of flow of power in faulty feeder is reversed.



5.Surges

Whenever lightning takes place or severe fault occurs in the neighbouring circuits,

some short lived waves of very high voltage and current are set up in lines. Such fault

is known as surge and it may be considered as high voltage of very high frequency.



14. EXISTING PROTECTION SYSTEM IN BPCL-KR

14.1 Relays used in STG

Negative sequence over current relay

Relay type MCND 04 is a negative phase sequence over current relay and is

intended primarily for the unbalance protection of generator. Unbalanced loads or

faults in the system can cause negative sequence currents in stator and this induced

double frequency eddy current in rotor of generator. Heating of the rotor is proportional

to its AC resistance at twice system frequencies and even a modest value of negative

sequence current can cause serious over heating. The purpose of the relay is to

disconnect the generator before an excessive temperature is reached.

In order to avoid unnecessary tripping, the operating time characteristic of the

relay must match with the negative sequence characteristic of the generator. The type

MCND 04 relay has an adjustable time or current characteristic, which make it suitable

for generator of different designs.

Field failure relay

The type MYTU 04 relay detects the loss of field supply or reduction in the

field current or synchronous generator beyond the stability limits of the machine.

Loss of field supply to the synchronous generator can be caused by a fault in

the field circuit or by incorrect opening of the field circuit breaker. On loss of field, the

machine operates as an induction generator excited by reactive power drawn from the

system to which is connected. This could result in instability of power in a system and

over heating of rotor, especially if the machine is of cylindrical rotor type without

damping winding in the pole phases. The relay operation is blocked when the value of

input voltage falls below .2Vn or .4Vn. to avoid mal operation due to synchronising

surges and transient conditions, the relay is provided with an inbuilt timer with

adjustable setting. The delay may be arranged to initiate alarm or tripping if adverse



field conditions persist longer than a safe period. A front plate mounted LED is

available to indicate relay operation. A push button is provided for resetting the LED

indication . Operation of the relay can be tested by means of test push button , which

causes the comparator to operate the LED to indicate after the set time delay. The

output relay is however prevented from operating during the test. Access to the test

push button requires removal of the front cover.

Trip circuit supervision relays

These type MVAX relay supervises the trip circuit of a circuit breaker. Initiating

audible alarm and visual indication if the trip circuit fails or the mechanism does not

operate. Four types are available giving supervision as follows.

Relay type Faults detected

MVAX 12 Failure of trip supply only.

MVAX 21 Failure of trip supply.

MVAX 31 Open circuit trip coil or trip circuit wiring.

MVAX 91 Failure of circuit breaking tripping

Mechanism.

Type MVAX 31 gives supervision with the circuit breaker in either state, and

type MVAX 21 with circuit breaker closed only. If required, the alarm units of types

MVAX 21 and MVAX 31 can be operated via pilot wires. Type MVAX 91, three

separate MVAX 31’s in a size 8 case.

Definite time delayed voltage relays

The MVTU range of relays provides definite time voltage protection. The

MVTU 13 is a definite time delays neutral displacement relay,which is included

primarily for the earth fault protection of alternator stator windings where the neutral is

earthed. The relay is designed such that its response to third harmonic frequencies is

suppressed, thus making it inoperative to the third harmonic loads unbalance which



normally flows in the generator neutral. The application of the relay also includes

protection against unbalanced condition in capacitor banks and the detection of earth

fault is impedance earthed, solidly earthed or unearthed system. The MVTU 18 is a

definite time delayed neutral displacement relay.

Tripping and control relays

These relays are suitable for use in high security CB tripping circuits. In

particular they can be used in distributed ripping or control relays contact logic scheme,

where the initiating contact may be remote from the relay. The relays have a high

burden, which is either cut off at operation or economized to a low figure, either

instantaneously or after a time delay.

The high burden provides immunity to capacitance discharge currents,

which can result at the inception of an earth fault on battery wiring and immunity to the

subsequent leakage current. The high burden also permits the use of supervision relays

such as repeat type MVAJ relays, which can be provided with a time delayed

economizing feature.

Directional over current relays

KCEG relays include directional elements which can be selectively used to any

over current or earth fault element. These relays may be applied where directionality is

required to ensure full operation co-ordination. They are particularly cost effective

where both directional and non directional protection is needed at one point on a power

system. Start elements which might be interlocking the high speed elements of adjacent

relays, can be directionalised where necessary.

In some applications it may be required to select directionally for the fault

protection of a KCEG relay. For a resistance-earthed cable power system, where

capacitance current may be high in relation to the limited earth fault current, it may be

necessary to control earth fault elements with a leading directional element

characteristic. This prevents sympathetic operation of healthy circuit earth fault



elements in the event of an earth fault on another circuit. When non-directionalised, the

KCG over current elements will perform in the same manner as KCEG elements.

Pole slipping protection

The KCEG 140 relay is a three phase over current and earth fault relay. The relay

uses a common measuring element for all the three phases and a separate element to

monitor the residual current. The phase volt settings and earth fault settings are

completely separate. Both the fault element and the earth fault element have 3 tripping

stages, which can be enabled and disabled as required. The relay also features an

alternating setting group, in which 3 tripping stages for both the phase over current and

earth fault element can be enabled or disabled differently to that implemented with the

first setting group. The relay has programmable output relay and opt-isolated digital

inputs.

Rotor Earth Fault Protection Relay

The type DBAE relay is applied to detect each leakage in alternator field circuits

which are fully isolated from earth. It is suitable for use with thyristors excitation

system. The auxiliary AC bias supply is rectified to establish a small bias on alternator

field circuits so that all points are negative with respective to earth. In the event of earth

leakage current flows in the bias circuit and is detected by the sensitive Db coil as

additional safe guard, the relay functions as a self powered rotor earth fault relay in the

absence of injection supply, effectively covering a large protection of the field winding.

The actual protection covered depends upon the ratio of field voltage to relay rated

voltage and may be high as 95%. The external resistance, supposed with the relay

limits the fault current flowing in the DB coil.

Digital definite time frequency relay

These type MFVU 14 frequency relay consist of two independent frequency

monitoring circuit, one for one unit and other for over frequency measurement. Relay



operation is blocked when there is an abnormal fall of the monitored voltage to be less

than 40% of rated value.

The relay is suitable for any application in industrial plants and for generators where

definite time under or over frequency protection is required. In addition, multi stage

schemes using several relays can be provided for load shedding and reconnection

applications. Integral timers are provided for each operating circuit and a separate

electromagnetic auxiliary relays ensures maximum flexibility of applications.

Voltage selection relay

MVAP 22 is essentially a fuse failure relay with change over output contact enabling

its use for either voltage selection or fuse failure protection. A typical application as a

voltage selection relay is the automatic connection of the metering equipments to an

alternative supply if the normal or perfect supply fails. As a fuse failure relay it will

monitor the output of a voltage transformer and give an alarm or disconnect protection

circuit for VT fuse failure.

The relay monitors the three phase voltage supply if the supply is interrupted or

becomes unbalanced due to the failure of the voltage transformers primary or secondary

fuses.

Forward and reverse power relay

The MWTU 11 is suitable for the following applications.

Reverse power protection of a generator against monitoring

The relay has sensitive settings and operates accurately for boundary

conditions upto +/- 87.10(0.05pf). the definite time characteristic ensures that

mal operations does not occur due to momentary power reversals during

synchronizing and power swings on the system.

Limitations of power imported from a consumer by a utility power supply



This application is an over power or forward power functions in which

higher settings are required. The directional discrimination is not required at

such low pf for reactive components as high as 60% of the generator rating. The

operation time of the relay is not critical as fast tripping times are covered by

fault detecting relays.

Over current for phase and earth faults

The relay can be used in applications where time graded over current and earth

fault operation is required. The relay can be used to provide selective protection for

over head and under ground distribution feeders. Other applications include back up

protection for transformers, generators, and HV feeder circuits and protection of neutral

earthing resistors.

High stability circulating current relay

When circulating current protection schemes are subjected to heavy through

faults, the sudden and often asymmetrical growth in the system current can cause the

protective current transformer to approach or even reach saturating level. Because of

the variations in the magnetizing characteristics of the transformer a high unbalance

current may result to ensure stability under the condition, it is modern practice to use a

voltage operated, high impedance relay, set to operate at a voltage slightly higher than

that developed by the current transformers under maximum external fault conditions.

The MCAG 14 relay, used for applications where sensitive settings with stability on

heavy through faults are required, and is recommended for balance and restricted earth

fault, bus zone and certain forms of differential protection for transformers, reactors

and motors.

Voltage dependent over current relay



For back up over current protection of generators ordinary over current relays

are sometimes difficult to apply, due to the decaying characteristics of the fault current.

The value of the fault current will be progressively reduced due to the reaction, to a

value less than the full load current. Therefore, normal over current relays, set above

the load current or maximum permissible overload cannot be applied to provide time

delayed protection as they will not operate for fault conditions. For successful

application of generators backup protection, the relay is required to be a function of

voltage and current. There are two types of relays that are customarily used for these

applications, namely voltage restrained and voltage controlled over current relays.

With voltage restrained over current relays, when the voltage falls below a set

values, the operating time of the over current characteristics is continuously reduced

with declining voltage. In voltage controlled over current relays, the operating time

characteristic is changed from the load characteristics to the fault characteristics when

voltage falls below the set level. The MCVG 61 is a three phase voltage dependent over

current relay with both voltage restrained and voltage control characteristics available

from the same relay. A switch on the front panel of the relay selects the desired mode.



15. NUMERICAL RELAY

15.1 ARCHITECTURE

The analog to digital (AD) stage consists of memory components, a multiplexer and an

analog to digital (A/D) converter. The A/D converter processes the analog signals from

the IA stage. The digital signals from the converter are input to the microcomputer

system where they are processed as numerical values in the residing algorithms.

Microcomputer System

The actual protection and control functions of the 7SJ62/63/64 are processed in the

microcomputer system. In addition, the microcontroller controls the measured

quantities. Specifically, the microcontroller performs:

Filtering and preparation of the measured quantities

Continuous monitoring of the measured quantities

Monitoring of the pickup conditions for the individual elements and functions

Evaluation of limit values and sequences in time

Control of signals for the logic functions

Decision for trip, close and other control commands

Output of control commands for switching devices(output contacts)

Recording of messages and data for events, alarms, faults and control actions

and provisions of their data for analysis

Management of the operating system and the associated functions such as data

recording, real time clock, communications, interfaces etc.

Binary Inputs and Outputs



The microcomputer obtains external information through the binary inputs such as

blocking commands for protective elements or position indications of CB. The

microcomputer issues commands to external equipments via output contacts. These

output commands are generally used to operate CB’s or other switching devices. They

can also be connected to other protective devices or external carrier equipments for use

in pilot relaying schemes.

Front Elements

The devices with integrated or detached operator panel light emitting diodes (LED) and

displays screen (LCD) on the front panel providing information such as messages

related to events and functional status of the device.

The integrated control and numerical keys in conjunction with the LCD facilitates

local operation with the numerical relay. All information of the device can be accessed

using the integrated control and numerical keys. The information includes protective

and a control settings operating and fault messages and metering values. The settings

can be modified; in addition, control of CB and other equipment is possible from the

front panel.

Serial Interfaces

A serial PC port on device is provided for local communication with the relay through a

personal computer. Convenient operation of all functions of the device is possible. The

operating system facilitates a comfortable handling of all device functions.

A separate service port can be provided for remote communication in a modem or

substation. The operating program is required. The port is especially well suited for the

fixed wiring of the devices to the PC or operation via a modem. The service port can

also be used to connect a RTD-Box for entering external temperature (for overload

protection). The additional port is exclusively designed for the connection of a RTD-

Box for entering external temperature.

All relay data can be transferred to a central control and monitor system through the

SCADA port. Various protocols and physical interfaces are available to suit the

particular operation.



A further port is provided for the time synchronization of the internal clock via external

synchronization sources.Further communication protocols can be realized via

additional interface modules.

Power Supply

The relay can be supplied with any of the common power supply voltages from 24V

DC to 250V DC. The device can also be supplied with 115V AC. Momentary dips of

the supply voltage upto 50ms are bridged by a capacitor. Voltage dips can occur if the

voltage supply system becomes short circuited or experiences a source variation in

load.



FIG: 15.1 HARDWARE STRUCTURE OF NUMERICAL RELAY



15.2 APPLICATIONS

The numerical, multifunctional SIPROTEC 4 relay is a versatile device designed for

many applications. The relay can be used as a protective, control and monitoring device

for distribution feeders and transmission lines of any voltage in networks that are

grounded or of a compensated neutral point structures, the devices are suited for

networks that are radial or looped, and for lines in single or multi-terminal feed; the

relays are equipped with motor protection available for asynchronous machines of all

sizes.

The relay includes the functions that are necessary for protection, monitoring of circuit

breaker position and control of the circuit breaker in straight bus application or breaker

and a half configuration; therefore the devices can be inversely employed. The relay

provides excellent backup facilities of differential protective scheme of lines,

transformers, generators, motors and bus bars of all voltages.

A.Protective Functions

Non directional over current protection is the basis of the numerical relay. Four definite

over current protective elements exists, two for the phase and two for ground current.

The elements can set with time delay where instantaneous tripping is decided. Inverse

time over current protective elements are also available for both the phase and ground

currents.

Depending on the version of the device that is used, the non-directional over current

protection can be supplemented with directional over current protection, breaker failure

protection and sensitive ground fault detection for high resistance ground fault or

system datas are resistively ground. The highly sensitive ground fault detection,

directional or non-directional, include negative sequence current protection, automatic

reclosing, thermal overload protection, over voltage protection, under voltage

protection and over/under frequency protection. For another port, under current

monitoring are optionally available. Finally the relay is equipped with a fault locater.



A port feature can be ordered for the detection of intermittent ground faults which

detects and accumulate transient ground fault. External detectors account for ambient

temperature or coolant temperature. Before re-closing after 3 pole tripping, relay can

verify the validity of the re-closure by voltage check and/or synchronous check. The

sign function can also be controlled externally.

B.Control Functions

The relay supports all control monitoring functions that are required for operating

medium to high voltage substation. Major applications are the reliable control of

switchgear or CB’s. Such control can be accomplished through the integrated operation

panel, the system interface, binary inputs and the serial port using a PC with DIGSI.

The status of the equipment or auxiliary devices can be transmitted to the relay via

auxiliary contacts connected to the binary input. The present status of the primary

equipment can be displayed on the relay. Only the quantity of the binary input and

output available in the numerical relay limits the number of primary devices that can be

operated. Depending on the equipment being controlled, 1 binary input or 2 binary

input can be used in the position monitoring process.

The capability of switching primary equipment can be restricted by a setting associated

with switching authority-local, DIGSI 4 or remote and by the operating mode

interlocked or non-interlocked with password request.

C. Messages and Measured Values; Recording of Event and Fault data

The operating message provides information about condition in the power system and

the relay. Measurement quantities and values that are calculated can be displayed

locally and communicate via the serial interfaces.

Messages of the relay can be indicated via a number of programmable LED’s of the

front panel externally processed through programmable output contacts and

communicate via the serial interface.



D. Communication

Serial interfaces are available for communication with PC’s, RTU’s and SCADA

systems. A 9-pin D-sub miniature female connector on the front panel is used for local

communication with personal computer. DIGSI 4 software is required to communicate

via this port. Using this, settings and configurations can be made to the relay, real-time

operating quantities can be viewed, waveform capture and event by records can be

displayed and controls can be issued. A DIGSI 4 service interface port, a system port

and a time synchronize port are optionally available on the rear of the device.

A rear service interface can be supplied as RS-232, RS-485 or multimode fibre optics

type ST.DIGSI 4 software is required to communicate via this port. This additional port

is designed exclusively for connection of RTD-Box for entering external temperature.

It can also be operated via data lines or fibre optic cables.

15.3 CHARACTERISTICS

General Characteristics

Powerful 32 bit microprocessor system

Complete digital processing and control of measured values, from the

sampling of the analog input quantities to the initiation of the outputs.

Total electrical separation between the processing stages of the relay and the

external transformer circuits, control circuits and DC supply circuit.

Complete set of functions necessary for the proper protection of lines,

feeders, motors and bus-bars.

Continuous calculation and display of measured quantities on the front of

the device.

Storage of Min/Max measured values and storage of long term mean values.

Recording of event data, fault data and waveform capture.

Constant monitoring of the measured quantities as well as continuous self

diagnostics covering the hardware and software

Communication with SCADA or substation controller equipment via serial

interfaces through the choice of data cable, modem or optical fibres.



Recording of CB statistics including the number of trip signals sent and the

accumulated, interrupted currents of each pole of the CB

Tracking of operating hours of the equipment being protected.

Commissioning aids such as connection check, direction determination,

status indication of all binary i/o and display of test recordings.



16. SIPROTEC 4 7UM62

FIG :16

The SIPROTEC 4 7UM62 protection relays can do more than just

protect. They also offer numerous additional functions. Be it earth faults, short-circuits,

overloads, overvoltage, overfrequency or underfrequency asynchronous conditions,

protection relays assure continued operation of power stations. The SIPROTEC 4

7UM62 protection relay is a compact unit which has been specially developed and



designed for the protection of small, medium-sized and large generators. They integrate

all the necessary protection functions and are particularly suited for the protection of:

Hydro and pumped-storage generators

Co-generation stations

Private power stations using regenerative energy sources such as wind or

biogases

Diesel generator stations

Gas-turbine power stations

Industrial power stations

Conventional steam power stations

The SIPROTEC 4 7UM62 includes all necessary protection functions for large

synchronous and asynchronous motors and for transformers. The integrated

programmable logic functions (continuous function chart CFC) offer the user high

flexibility so that adjustments can easily be made to the varying power station

requirements on the basis of special system conditions. The flexible communication

interfaces are open for modern communication architectures with the control system.

The following basic functions are available for all versions:

Current differential protection for generators, motors and transformers, stator earth-

fault protection, sensitive earth-fault protection, stator overload protection, overcurrent-

time protection (either definite time or inverse time), definite-time over current

protection with directionality, under voltage and overvoltage protection,

underfrequency and overfrequency protection, overexcitation and underexcitation

protection, external trip coupling, forward-power and reverse power protection,

negative-sequence protection, breaker failure protection, rotor earth-faults protection

(fn, R-measuring), motor starting time supervision and restart inhibit for motors.



16.1 PROTECTION FUNCTIONS

Numerous protection functions are necessary for reliable protection of electrical

machines. Their extent and combination are determined by a variety of factors, such as

machine size, mode of operation, plant configuration, availability requirements,

experience and design philosophy. This results in multifunctionality, which is

implemented in outstanding fashion by numerical technology. In order to satisfy

differing requirements, the combination of functions is scalable (see Table 1). Selection

is facilitated by division into five groups.

GENERATOR BASIC

One application concentrates on small and medium generators for which differential

protection is required. The function mix is also suitable as backup protection.

Protection of synchronous motors is a further application.

GENERATOR STANDARD

In the case of medium-size generators (10 to 100 MVA) in a unit connection, this scope

of functions offers all necessary protection functions. Besides inadvertent energization

protection, it also includes powerful backup protection for the transformer or the power

system. The scope of protection is also suitable for units in the second protection group.

GENERATOR FULL

Here, all protection functions are available and the main application focuses on large

block units (more than 100 MVA). The function mix includes all necessary protection

functions for the generator as well as backup protection for the block transformer

including the power system. Additional functions such as protection during start-up for

generators with starting converters are also included. The scope of functions can be



used for the second protection group, and functions that are not used, can be masked

out.

ASYNCHRONOUS MOTOR

Besides differential protection, this function package includes all protection functions

needed to protect large asynchronous motors (more than 1 MVA). Stator and bearing

temperatures are measured by a separate thermo-box and are transmitted serially to the

protection unit for evaluation.

TRANSFORMER

This scope of functions not only includes differential and overcurrent protection, but

also a number of protection functions that permit monitoring of voltage and frequency

stress, for instance. The reverse power protection can be used for energy recovery

monitoring of parallel-connected transformers



TABLE -16.1-1



CURRENT DIFFERENTIAL PROTECTION (ANSI 87G, 87M, 87T)

This function provides undelayed short-circuit protection for generators, motors and

transformers, and is based on the current differential protection principle (Kirchhoff’s

current law). The differential and restraint (stabilization) current are calculated on the

basis of the phase currents. Optimized digital filters reliably attenuate disturbances such

as aperiodic component and harmonics. The high resolution of measured quantities

permits recording of low differential currents (10% of IN) and thus a very high

sensitivity. An adjustable restraint characteristic permits optimum adaptation to the

conditions of the protected object. Software is used to correct the possible mismatch of

the current transformers and the phase angle rotation through the transformer (vector

group). Thanks to harmonic analysis of the differential current, inrush (second

harmonic) and overexcitation (fifth harmonic) are reliably detected, and unwanted

operation of the differential protection is prevented. The current of internal short-

circuits is reliably measured by a fast measuring stage, which operates with two

mutually complementary measuring processes. An external short-circuit with

transformer saturation is picked up by a saturation detector with time and status

monitoring. It becomes active when the differential current (IDiff) moves out of the

add-on restraint area. If a motor is connected, this is detected by monitoring the

restraint current and the restraint characteristic is briefly raised. This prevents false

tripping in the event of unequal current transmission by the current transformers. Figure

shows the restraint characteristic and various areas.

FIG : 16.1-1 Restraint characteristic of current differential protection



EARTH CURRENT DIFFERENTIAL PROTECTION (ANSI

87GN,87TN)

The earth-current differential protection permits high sensitivity to single-pole faults.

The zero currents are compared. On the one hand, the zero-sequence current is

calculated on the basis of the phase currents and on the other hand, the earth current is

measured directly at the star-point current transformer. The differential and restraint

quantity is generated and fitted into the restraint characteristic. DC components in

particular are suppressed by means of specially dimensioned filters. A number of

monitoring processes avoid unwanted operation in the event of external short-circuits.

In the case of a sensitive setting, multiple measurement ensures the necessary

reliability. However, attention must be drawn to the fact that the sensitivity limits are

determined by the current transformers. The protection function is only used on

generators when the neutral point is earthed with a low impedance. In the case of

transformers, it is connected on the neutral side. Low impedance or solid earthing is

also required.

DEFINITE- TIME OVERCURRENTPROTECTION I>,I>>

(ANSI50,51,67)

This protection function comprises the short-circuit protection for the generator

and also the backup protection for upstream devices such as transformers or power

system protection. An undervoltage stage at I> maintains the pickup when, during the

fault, the current drops below the threshold. In the event of a voltage drop on the

generator terminals, the static excitation system can no longer be sufficiently supplied.

This is one reason for the decrease of the short-circuit current.

The I>> stage can be implemented as high-set instantaneous trip stage. With the

integrated directional function it can be used as backup protection on the transformer

high-voltage side. With the information of the directional element, impedance

protection can be controlled via the CFC.



INVERSE- TIME OVERCURRENT PROTECTION (ANSI 51V)

This function also comprises short-circuit and backup protection and is used for power

system protection with current protection dependent protection devices. IEC and ANSI

characteristics can be selected from the table given below.

Available inverse- time characteristics

TABLE: 16.1-2

The current function can be controlled by evaluating the generator terminal voltage.

The “controlled” version releases the sensitive set current stage. With the “restraint”

version, the pickup value of the current is lowered linearly with decreasing voltage. The

fuse failure monitor prevents unwanted operation.

STATOR OVERLOAD PROTECTION (ANSI 49)

The task of the overload protection is to protect the stator windings of generators and

motors from high, continuous overload currents. All load variations are evaluated by a

mathematical model. The thermal effect of the r.m.s. current value forms the basis of

the calculation. This conforms to IEC 60255-8. In dependency of the current, the

cooling time constant is automatically extended. If the ambient temperature or the

temperature of the coolant is injected via a transducer (TD2) or PROFIBUS-DP, the

model automatically adapts to the ambient conditions; otherwise a constant ambient

temperature is assumed.



NEGATIVE SEQUENCE PROTECTION (ANSI 46)

Asymmetrical current loads in the three phases of a generator cause a temperature rise

in the rotor because of the negative sequence field produced. This protection detects an

asymmetrical load in three-phase generators. It functions on the basis of symmetrical

components and evaluates the negative sequence of the phase currents. The thermal

processes are taken into account in the algorithm and form the inverse characteristic. In

addition, the negative sequence is evaluated by an independent stage (alarm and trip)

which is supplemented by a time-delay element .In the case of motors, the protection

function is also used to monitor a phase failure.

UNDEREXCITATION PROTECTION

(LOSS OFFIELD PROTECTION) (ANSI 40)

Derived from the generator terminal voltage and current, the complex admittance is

calculated and corresponds to the generator diagram scaled in per unit. This protection

prevents damage due to loss of synchronism resulting from underexcitation. The

protection function provides three characteristics for monitoring static and dynamic

stability. Via a transducer, the excitation voltage can be injected and, in the event of

failure, a swift reaction of the protection function can be achieved by timer changeover.

The straight-line characteristics allow the protection to be optimally adapted to the

generator diagram (see Fig16.1-2).The per-unit-presentation of the diagram allows the

setting values to be directly read out. The positive-sequence systems of current and

voltage are used to calculate the admittance. This ensures that the protection always

operates correctly even with asymmetrical network conditions. If the voltage deviates

from the rated voltage, the admittance calculation has the advantage that the

characteristics move in the same direction as the generator diagram.



FIG: 16.1-2 Characteristic of under excitation protection

REVERSE-POWER PROTECTION (ANSI 32R)

The reverse-power protection monitors the direction of active power flow and picks up

when the mechanical energy fails. This function can be used for operational shutdown

(sequential tripping) of the generator but also prevents damage to the steam turbines.

The reverse power is calculated from the positive-sequence systems of current and

voltage. Asymmetrical power system faults therefore do not cause reduced measuring

accuracy. The position of the emergency trip valve is injected as binary information and

is used to switch between two trip command delays. When applied for motor

protection, the sign (±) of the active power can be reversed via parameters.

FORWARD-POWER PROTECTION (ANSI 32F)

Monitoring of the active power produced by a generator can be useful for starting up

and shutting down generators. One stage monitors exceeding of a limit value, while

another stage monitors falling below another limit value. The power is calculated using

the positive sequence component of current and voltage. The function can be used to

shut down idling motors.



IMPEDANCE PROTECTION (ANSI 21)

This fast short-circuit protection protects the generator and the unit transformer and is a

backup protection for the power system. This protection has two settable impedance

stages; in addition, the first stage can be switched over via binary input. With the

circuit- breaker in the “open” position the impedance measuring range can be extended

(see Fig 16.1-3). The overcurrent pickup element with undervoltage seal-in ensures a

reliable pickup and the loop selection logic ensures a reliable detection of the faulty

loop. With this logic it is possible to perform correct measurement via the unit

transformer

.

FIG : 16.1-3 Grading of impedance protection

UNDERVOLTAGE PROTECTION (ANSI 27)

The undervoltage protection evaluates the positive-sequence components of the

voltages and compares them with the threshold values. There are two stages available.

The undervoltage function is used for asynchronous motors and pumped-storage

stations and prevents the voltage-related instability of such machines. The function can

also be used for monitoring purposes.



OVERVOLTAGE PROTECTION (ANSI 59)

This protection prevents insulation faults that result when the voltage is too high. Either

the maximum line-to-line voltages or the phase-to-earth voltages (for low voltage

generators) can be evaluated. The measuring results of the line-to-line voltages are

independent of the neutral point displacement caused by earth faults.

FREQUENCY PROTECTION (ANSI 81)

The frequency protection prevents impermissible stress of the equipment (e.g. turbine)

in case of under or overfrequency. It also serves as a monitoring and control element.

The function has four stages; the stages can be implemented either as underfrequency

or overfrequency protection. Each stage can be delayed separately. Even in the event of

voltage distortion, the frequency measuring algorithm reliably identifies the

fundamental waves and determines the frequency extremely precisely. Frequency

measurement can be blocked by using an undervoltage stage.

OVEREXCITATION PROTECTION Volt/Hertz (ANSI 24)

The overexcitation protection serves for detection of an unpermissible high induction

(proportional to V/f) in generators or transformers, which leads to thermal overloading.

This may occur when starting up, shutting down under full load, with weak systems or

under isolated operation. The inverse characteristic can be set via eight points derived

from the manufacturer data. In addition, a definite-time alarm stage and an

instantaneous stage can be used.

For calculation of the V/f ratio, frequency and also the highest of the three line-to line

voltages are used. The frequency range that can be monitored comprises 11 to 69 Hz.



SENSITIVE EARTH FAULT PROTECTION (ANSI 50/51 GN, 64R)

The sensitive earth-current input can also be used as separate earth-fault protection. It is

of two-stage form. Secondary earth currents of 2 mAor higher can be reliably handled.

Alternatively, this input is also suitable as rotor earth-fault protection. A voltage with

rated frequency (50 or 60 Hz) is connected in the rotor circuit via the interface unit

7XR61. If a higher earth current is flowing, a rotor earth fault has occurred. Measuring

circuit monitoring is provided for this application.

BREAKER FAILURE PROTECTION (ANSI 50BF)

In the event of scheduled downtimes or a fault in the generator, the generator can

remain on line if the circuit-breaker is defective and could suffer substantial damage.

Breaker failure protection evaluates a minimum current and the circuit-breaker

auxiliary contact. It can be started by internal protective tripping or externally via

binary input. Two-channel activation avoids overfunction.

INADVERTANT ENERGIZATION PROTECTION (ANSI 50,27)

This protection has the function of limiting the damage of the generator in the event of

an unintentional switch-on of the circuit breaker, whether the generator is standing still

or rotating without being excited or synchronized. If the power system voltage is

connected, the generator starts as an asynchronous machine with a large slip and this

leads to excessively high currents in the rotor. A logic circuit consisting of sensitive

current measurement for each phase, measured value detector, time control and

blocking as of a minimum voltage, leads to an instantaneous trip command. If the fuse

failure monitor responds, this function is ineffective.

ROTOR EARTH-FAULT PROTECTION (ANSI 64R)

This protection function can be realized in three ways with the 7UM62. The simplest

form is the method of rotor-current measurement (ie, sensitive earth-current

measurement).



Resistance measurement at system frequency voltage

The second form is rotor earth resistance measurement with voltage at system

frequency. This protection measures the voltage injected and the flowing rotor earth

current. Taking into account the complex impedance from the coupling device

(7XR61), the rotor earth resistance is calculated by way of a mathematical model. By

means of this method, the disturbing influence of the rotor earth capacitance is

eliminated, and sensitivity is increased. Fault resistance values up to 30 kΩ can be

measured if the excitation voltage is without disturbances. Thus, a two-stage protection

function, which features a warning and a tripping stage, can be realized. An

additionally implemented undercurrent stage monitors the rotor circuit for open circuit

and issues an alarm.

Resistance measurement with a square wave voltage of 1 to 3 Hz

A higher sensitivity is required for larger generators. On the one hand, the disturbing

influence of the rotor earth capacitance must be eliminated more effectively and, on the

other hand, the noise ratio with respect to the harmonics (e.g. sixth harmonic) of the

excitation equipment must be increased. Injecting a low-frequency square wave voltage

into the rotor circuit has proven itself excellently here. The square wave voltage

injected through the controlling unit 7XT71 leads to permanent recharging of the rotor

earth capacitance. By way of a shunt in the controlling unit, the flowing earth current is

measured and is injected into the protection unit (measurement input). In the absence of

a fault (RE≈∞), the rotor earth current after charging of the earth capacitance is close to

zero. In the event of an earth fault, the fault resistance including the coupling resistance

(7XR6004), and also the injecting voltage,defines the stationary current. The current

square wave voltage and the frequency are measured via the second input (control

input). Fault resistance values upto 80 kΩ can be measured by this measurement

principle. The rotor earth circuit is monitored for discontinuities by evaluation of the

current during the polarity reversals.



DC VOLTAGE TIME PROTECTION/ DC CURRENT TIME

PROTECTION (ANSI 59N(DC), 51N(DC)

Hydroelectric generators or gas turbines are started by way of frequency starting

converters. An earth fault in the intermediate circuit of the frequency starting converter

causes DC voltage displacement and thus a direct current. As the neutral or earthing

transformers have a lower ohmic resistance than the voltage transformers, the largest

part of the direct current flows through them, thus posing a risk of destruction from

thermal overloading.

OVER CURRENT PROTECTION DURING START-UP(ANSI 51)

Gas turbines are started by means of frequency starting converters. Overcurrent

protection during start-up measures short circuits in the lower frequency level (as from

about 5 Hz) and is designed as independent overcurrent-time protection. The pickup

value is set below the rated current. The function is only active during start-up. If

frequencies are higher than 10 Hz, sampling frequency correction takes effect and the

further short-circuit protection functions are active.

OUT-OF-STEP PROTECTION (ANSI 78)

This protection function serves to measure power swings in the system. If generators

feed to a system short-circuit for too long, low frequency transient phenomena (active

power swings) between the system and the generator may occur after fault clearing. If

the center of power swing is in the area of the block unit, the “active power surges”

lead to unpermissible mechanical stressing of the generator and the turbine. As the

currents and voltages are symmetrical, the positive-sequence impedance is calculated

on the basis of their positive sequence components and the impedance trajectory is

evaluated. Symmetry is also monitored by evaluation of the negative phase- sequence

current. Two characteristics in the R/X diagram describe the active range (generator,

unit transformer or power system) of the out-of-step protection. The associated

counters are incremented depending on the range of the



characteristic in which the impedance vector enters or departs. Tripping occurs when

the set counter value is reached.

The counters are automatically reset if power swing no longer occurs after a set time.

By means of an adjustable pulse, every power swing can be signaled. Expansion of the

characteristic in the R direction defines the power swing angle that can be measured.

An angle of 120 ° is practicable. The characteristic can be tilted over an adjustable

angle to adapt to the conditions prevailing when several parallel generators feed into

the system.

FIG: 16.1-4 Ranges of the characteristic and possible oscillation profiles

INVERSE UNDERVOLTAGE PROTECTION (ANSI 27)

Motors tend to fall out of step when their torque is less than the breakdown torque.

This, in turn, depends on the voltage. On the one hand, it is desirable to keep the motors

connected to the system for as long as possible while, on the other hand, the torque

should not fall below the breakdown level. This protection task is realized by inverse

undervoltage protection. The inverse characteristic is started if the voltage is less than

the pickup threshold Vp<. The tripping time is inversely proportional to the voltage dip

(see equation). The protection function uses the positive-sequence voltage, for the

protection decision.



RATE OF FREQUENCY CHANGE PROTECTION (ANSI 81)

The frequency difference is determined on the basis of the calculated frequency over a

time interval. It corresponds to the momentary rate-of-frequency change. The function

is designed so that it reacts to both positive and negative rate-of frequency changes.

Exceeding of the permissible rate-of-frequency change is monitored constantly. Release

of the relevant direction depends on whether the actual frequency is above or below the

rated frequency. In total, four stages are available, and can be used optionally.

VECTOR JUMP

Monitoring the phase angle in the voltage is a criterion for identifying an interrupted

infeed. If the incoming line should fail, the abrupt current discontinuity leads to a phase

angle jump in the voltage. This is measured by means of a delta process. The command

for opening the generator or coupler circuit-breaker is issued if the set threshold is

exceeded.

SENSITIVE EARTH-FAULT PROTECTION B (ANSI 51 GN)

The IEE-B sensitive earth-fault protection feature of 7UM62 provides greater

flexibility and can be used for the following applications:

Any kind of earth-fault current supervision to detect earth faults (fundamental

and 3rd harmonics)

Protection against load resistances

Shaft current protection in order to detect shaft currents of the generator shaft

and prevent that bearings take damage



The sensitive earth-current protection IEE-B uses either the hardware input IEE1 or

IEE2. These inputs are designed in a way that allows them to cut off currents greater

than 1.6 A (thermal limit, see technical data).This has to be considered for the

applications or for the selection of the current transformers. The shaft current protection

function is of particular interest in conjunction with hydroelectric generators. Due to

their construction, the hydroelectric generators have relatively long shafts. A number of

factors such as friction, magnetic fields of the generators and others can build up a

voltage across the shaft which then acts as voltage source (electro-motive force-emf).

This inducted voltage of approx. 10 to 30 V is dependent on the load, the system and

the machine. If the oil film covering a bearing is too thin, breakdown can occur. Due to

the low resistance (shaft, bearing and earthing), high currents may flow that destroy the

bearing. Past experience has shown that currents greater than 1 A are critical for the

bearings. As different bearings can be affected, the current entering the shaft is detected

by means of a special transformer (folding transformer).

INTERTURN PROTECTION (ANSI 59N (IT))

The interturn fault protection detects faults between turns within a generator winding

(phase). This situation may involve relatively high circulating currents that flow in the

short-circuited turns and damage the winding and the stator. The protection function is

characterized by a high sensitivity. The displacement voltage is measured at the open

delta winding by means of 3 two-phase isolated voltage transformers. So as to be

insensitive towards earth faults, the isolated voltage transformer star point has to be

connected to the generator star point by means of a high-voltage cable. The voltage

transformer star point must not be earthed since this implies that the generator star

point, too, would be earthed with the consequence that each fault would lead to a

single-pole earth fault. In the event of an interturn fault, the voltage in the affected

phase will be reduced causing a displacement voltage that is detected at the broken

delta winding. The sensitivity is limited rather by the winding asymmetries than by the

protection unit.



An FIR filter determines the fundamental component of the voltage based and the

scanned displacement voltage. Selecting an appropriate window function has the effect

that the sensitivity towards higher-frequency oscillations is improved and the disturbing

influence of the third harmonic is eliminated while achieving the required measurement

sensitivity.

EXTERNAL TRIP COUPLING

For recording and processing of external trip information, there are 4 binary inputs.

They are provided for information from the Buchholz relay or generator-specific

commands and act like a protection function. Each input initiates a fault event and can

be individually delayed by a timer.

TRIP CIRCUIT SUPERVISION (ANSI 74TC)

One or two binary inputs can be used for monitoring the circuit-breaker trip coil

including its incoming cables. An alarm signal occurs whenever the circuit is

interrupted.

PHASE ROTATION REVERSAL

If the relay is used in a pumped-storage power plant, matching to the prevailing rotary

field is possible via a binary input (generator/motor operation via phase rotation

reversal).

LOCKOUT (ANSI 86)

All binary outputs (alarm or trip relays) can be stored like LEDs and reset using the

LED reset key. The lockout state is also stored in the event of supply voltage failure.

Reclosure can only occur after the lockout state is reset.



FUSE FAILURE AND OTHER MONITORING

The relay comprises high-performance monitoring for the hardware and software. The

measuring circuits, analog-digital conversion, power supply voltages, memories and

software sequence (watch-dog) are all monitored. The fuse failure function detects

failure of the measuring voltage due to short-circuit or open circuit of the wiring or VT

and avoids overfunction of the undervoltage elements in the protection functions. The

positive and negative-sequence system (voltage and current) are evaluated.



16.2 DIRECT GENERATOR BUS BAR CONNECTION

WITH LOW RESISTANCE EARTHING

FIG: 16.2



If the generator neutral point has low-resistance earthing, the connection illustrated in

Fig 16.2 is recommended. In the case of several generators, the resistance must be

connected to only one generator, in order to prevent circulating currents (3rd

harmonic). For selective earth-fault detection, the earth-current input should be looped

into the common return conductor of the two current transformer sets (differential

connection). The current transformers must be earthed at only one point. The

displacement voltage VE is utilized as an additional enabling criterion. Balanced

current transformers (calibration of windings) are desirable with this form of

connection. In the case of higher generator power (for example, IN approximately2000

A), current transformers with a secondary rated current of 5 A are recommended. Earth

current differential protection can be used as an alternative.



17. ADVANTAGES AND DISADVANTAGES

ADVANTAGES

Mechanical and solid-state (static) relays have been almost completely phased out of

our production because numerical relays are now preferred by the users due to their

decisive

advantages:

Compact design and lower costs due to integration of many functions into one

relay

High availability even with less maintenance due to integral self-monitoring

No drift (aging) of measuring characteristics due to fully numerical processing

High measuring accuracy due to digital filtering and optimized measuring

algorithms

Many integrated add-on functions, for example, for load-monitoring,

event/fault recording and thermal monitoring.

Local operation keypad and display designed to modern ergonomic criteria.

Easy and reliable read-out of information via serial interfaces with a PC,

locally or remotely with DIGSI (one tool for all relays).

Possibility to communicate with higher-level control systems using

standardized

DISADVANTAGES

Software intensive

Serial nature

Obsolescence rate

EMI/EMC problems



18. CONCLUSION

In this project we conducted a detailed study of existing distribution system of BPCL-

KR. We also analysed and studied the existing generating protection relays used in

BPCL-KR. Their different types of protection employ different types of relays. From

our analysis on various relays in generator protection, we suggest using one numerical

relays instead of all existing electromechanical relays.



REFERENCES

1. Newark,NJ Applied Protective Relaying.: Westinghouse Electric

Corporation

2. The Art of Protective Relaying, Philadelphia, PA: General Electric

Company, Bulletin 1768

3. MASON,C.R “ The Art and science of protective relaying”. New York.

Wiley,1956.



APPENDIX- A

A-1 Technical Particulars of STG

a) Type of generator : GGAK517A-B01A-F01

b) Output Apparent power : 22.25 MVA

c) Output active power : 17.8MW

d) Voltage : 11KV

e) Armature current : 1168 A

f) Frequency : 50 Hz

g) Generator speed : 1500rpm

h) No. of phases : 3

I) No. of poles : 4

j) Power Factor : 0.8 (lag)

k) Insulation class : Stator: F

: Rotor: F

l) Rating : Continuous

m) Type of outer housing : Totally enclosed, internal cooling type (With air Cooler)

n) Ventilation type : Self-ventilation

o) Field type : Rotating field type

p) Bearing : Automatic canter aligning type

Cylindrical bearing

q) Bearing oil feed system : Forced oil feed

r) Guaranteed over speed : 1800 rpm for 2 minutes



s) Applicable standard : JEC-114 (1979)

t) Exciting method : Brushless exciting system

u) Turbine speed : 4988rpm

v) Inlet steam pressure : 39kg/hr

w) Inlet steam temperature : 370°C

x) Normal lube oil pressure : 1 to 1.2kg/cm2

y) Exhaust steam temperature : 150°C

z) Normal control oil pressure : 13 to 14kg/cm2

A-2 Particulars of STG AC Exciter

STG Exciter is a 3 phase AC Exciter.

a) Type of generator : GZA7312S-C02A-G03

b) Output : 115 KVA

c) Voltage : 165 Volts

D Current : 402 A

e) Frequency : 75 Hz

f) Revolutions : 1500 rpm

g) No. of phases : 3

h) No. of poles : 6

I) Power factor : 0.95 (lag)

j) Insulation class : F

k) Rating : Continuous

l) Type of outer hosing : Open



m) Armature : Revolving armature type

n) Bearing : None

o) Guaranteed over speed : 1800 rpm for 2 minutes

p) Applicable standard : JEC-114 (1979)

q) Exciting system : Separate excitation (stator side)



APPENDIX- B

B-1 STG Relay Settings

(1) Thermal Replica MCHD 4:Set at 5 Amps, 110 Volts 10 minutes

Trip K= set at 1.1 (0.9 – 1.1)

I=Is X K

Is=0.8 Im

(2) Negative Sequence over current MCD 04:

Trip K = 16 (0 – 40)

Is = 18% (6 – 20%)

Alarm I2 = 0.8Is

Time, t=4.8 seconds (1.6 – 17.6 seconds)

(3) Field failure (5 Amps, 110 Volts) MITU04:

Trip 4.8 seconds (0.8 – 8.8 seconds)

Z1=2.2 Ohms (1.76 – 8.8 Ohms)

(4) Definite time U/V MVTU11:

Time = 2seconds, 86 Volts

(5) Definite time O/V MVTU12:

Time = 2 seconds, 135 Volts

6 Pole slipping relay: set at 1.48 Amps



7 High Stability Circulating Current Relay (Bus Line):

Set at 0.5 Amps (0.5 – 2 Amps)

8 Rotor E/F MRSU;

Set at 5 Ohms (1 – 5 Ohms), t = 10 seconds

9 Rotor E/F DBAE4:

Set at 1.25 ma

1) Definite Time frequency relay MFVU 14:

F1 > 51.5 Hz, 2 seconds

F2 < 47 Hz, 2 seconds

2) Reverse power MWTU11

Set at Ps=5.5

t=2 Sec

3) E/F O/C MCGG 22:

Set at 5 Amps, Is = 0.2 Im, t=0.5seconds, I.inst = 19Is

4) High Stability Circulating Current Relay (SG): Set at 0.5 Amps

5) Voltage dependent O/C MCVG 61:

Vs = 80%, Is=0.6In, I> (Is + Is), Is= 20%In, t=1 second



APPENDIX – C

C-1 TECHNICAL DATA



APPENDIX- D

D-1 SINGLE LINE DIAGRAMS














Existing Distribution System and Protection Using Numerical Relay

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