MINI PROJECTGenerator Protection

MINI PROJECT ON

GENERATORS AND ITS PROTECTION IN VIJJESWARAM POWER PLANT

A Study report submitted in partial fulfilment of the requirement for the award of the degree

BACHELOR OF TECHNOLOGY IN

ELECTRICAL AND ELECTRONICS ENGINEERING

Submitted by

N.BHAGYASRI (08221A0237)

G.SAINATH (08221A0214) V.SAMPATH (08221A0262)

S.SWAROOP (08221A0256) G.RAJU (08221A0213)

Under the esteemed guidance of

Electrical EngineerG.T.P.S

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

B.V.C Engineering College

(Affiliated to JNTU, Kakinada, A.P)

ODALAREVU, ALLAVARAM MANDAL-533210.

CERTIFICATE

This is to certify that the following students,

N.BHAGYASRI 08221A0237

G.SAINATH 08221A0214

V.SAMPATH 08221A0262

S.SWAROOP 08221A0256

G.RAJU 08221A0213

Have undergone industrial training at GTPS, Vijjeswaram in partial fulfilment of the industrial training of bachelor of technology in the department of ELECTRICAL AND ELECTRONICS ENGINEERING, IN BONAM VENKATA CHALAMAYYA ENGINEERING COLLEGE and is a bonified work carried out of them under my guidance and supervision during the academic year 2011

ACKNOWLEDGMENT

We sincerely and whole heartedly express our gratitude to our BVC ENGINEERING COLLEGE, ODALAREVU for the care they showed on us. We also thank our HOD Mr.J.V.G.RAMARAO for his constant support during our MINI PROJECT as well as study period.

We take great pleasure to express our sincere gratitude to SRI.M.CHITTIBABU, General Manager(operational), AP gas power corporation Ltd., who gave this opportunity to do project work at GTPS, Vijjeswaram,

ACHANTA. SRINIVAS, PLANT MANAGER.

G.SRINIVAS RAO, OPERATIONAL MANAGER.

O&M SOLUTIONS LIMITED.

We special thank the staff in our department and at GTPS

for their co-operation help & guidance in our completion of this mini project

PROJECT MEMBERS

N.BHAGYASRI 08221A0237

G.SAINATH 08221A0214

V.SAMPATH 08221A0262

S.SWAROOP 08221A0256

G.RAJU 08221A0213

INDEX

INTRODUCTION

SINGLE LINE DIAGRAMS OF S.T.G & G.T.G

GENERATOR AND ITS FUNCTION

CONSTRUCTION

COOLING SYSTEM

EXCITATION

SYNCHRONIZATION

RATINGS

PROTECTION SCHEMES

CONCLUSION

INTRODUCTION:

Power is most essential commodity today to one and all in the universe.

The economical growth of the country depends on only one factor i.e., growth of power i.e., installed capacity of the power generation

Andhra Pradesh Gas Power Corporation Ltd., (APGPCL) is a company promoted by ANDHRA Pradesh State Electricity Board (APSEB) in association with industries in the private and public sector to supplement power supply from the grid. The pioneering effort has come in to being weft 31.10.88 paving way for many more Gas based stations around the region. It was among the first companies to be permitted in the private sector after the electricity laws in the country restricted entry only government bodies and/or government owned companies in to power generation and before the opening up in 1991.

Gas Turbo Power Generation, Vijjeswaram owned by M/S.APGPCL is existing in an island amidst the Godavari water of the western delta canal and navigation canal branching out from the great river Godavari at Sitampet village of Kovvur Mandal in west Godavari District of A.P.

The objectives of the company are:

Supplementing power from grid. Meet the demands of energy of the participating

industries without restrictions. Enabling cheaper and reliable source of power to all

its participating industries than what a captive generation plant would give them. Ensuring appreciations on the investment

made by the company.

GTPS has generation capacity of 272MW in two stages. Stage-I is of 100MW and stage-II is of 172MW.

STAGE 1:

The company installed a 100MW Gas based combined cycle power plant comprising two Gas Turbines.

Generations of 33MW each and one steam turbine generator of 34MW capacity with natural gas as main fuel .M/S.BHEL had under taken to execute the most recent combined cycle plant indigenously built 33MW Gas Turbine Generator units for the first gas project in Andhra Pradesh at Vijjeswaram. The company successfully commissioned first phase of the plant containing 2 nos. gas turbine generators and 1 no. steam turbine generator on 31.08.1990, 02.03.1991 and 17.03.1992 respectively.

STAGE 2: The second stage installed capacity is 172MW with total capacity is 272MW in combined cycle as a natural gas as prime fuel. The plant containing 1 no. 112MW Gas turbine of GE, USA Make, model frame 9E and 1no. 60MW steam turbine of GE, USA make at site conditions. The plant engineering and design was commissioned on 31.03.1997 and steam turbine was commissioned on 22.12.1997.

The GTPS is the first gas based power plant come up in south-India and commissioned its first gas turbine in the year 1990.

The fuel for gas turbine is natural gas/clean liquid fuel viz.naphtha/HSD. The gas resources of KG basin are near to supplement the short fall of natural gas or as a base fuel supplied by M/S HPCL either from kakinada/gummaladobbi(60/25km away from GTPS)

The water required for condenser cooling for both the stage 1 and stage 2 is available from the sir Arthur cotton Barrage on river Godavari.

The gas turbo power station at Vijjeswaram was constructed under the technical supervision of APGENCO.APGENCO is the operation and maintenance contractor for the plant from its inspection. APGENCO is operating the plant at its best .The GTPS has awarded Gold Medals for its best performance off identical gas based power plants throughout India for the years 2002-2003 and 2003-2004.

GENERATOR AND ITS FUNCTION:

Generator is an Electro magnetic device that converts mechanical energy into electrical energy in the form of alternating current.

A.C. generators or alternators (as they are usually called) operate on the same fundamental principles of electromagnetic induction as D.C. generators.

Alternating voltage may be generated by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends on-

The number of turns in the coil.

Strength of the field. The speed at which the coil or magnetic field rotates.

Generator parts and their function:

The generator frame provides the structural strength and rigidity for the generator and serves as a housing to guide cooling air or gas flow.

The inner shield is a baffle used to form a path for cooled air or gas.

The generator fan mounted on the rotating field causes continuous of cooling air or gas

The rotating field forms a strong polarized, rotating magnetic field when energized by an external source of dc power.

The stator core carries the stationary high voltage windings and forms a magnetic path for magnetic fields.

The air gap is the radial clearance between the rotating field and the stator core.

Stator core spring bars act as somewhat flexible support for the stator core assembly.

Stator coil end turns are formed when coils leave one slot in the stator core and are returned to a different slot.

The end turn support structure provides for bracing and ties to secure the stator coil end turns against magnetic forces.

The high voltage terminal leads serve to conduct the three phase voltage and current flow from the generator stator to the external system.

Collector rings are used to provide a connection and path for dc power into the rotating field windings.

The outboard end stub shaft is sometimes used to drive a small dc generator used to supply dc power to the rotating field.

Field conductor end turns are securely blocked and serve as connection points for the dc power applied to the field windings.

The main coupling is bolted to the driving turbine shaft.

Generator coolers serve to remove heat from the generator cooling air or gas after it has passed over a through the stator and rotating field.

Cooling water connections are supplied to the generator air coolers.

CONSTRUCTION:

The generator construction will with stand all normal conditions

of operation and three-phase short circuits and their associated

suddenly applied loads without harm.

Generator frame and supports:

The generator frame is provided with four mounting feet

which are installed directly on the foundation. The generator is

shipped with the rotor in place. Each end of the rotor is supported

by a suitable journal bearing mounted in the end shield. Four

vertical hydrogen coolers are arranged symmetrically in the gas

stream within the gas-tight generator casing.

STATOR:

A. Stator frame supports:

The stator frame consists of a gas-tight cylindrical casing

of welded plate construction, reinforced internally in the radial

direction by stationary web plates, and in the axial direction by

spring bars and braces.

B. Stator core:

The stator core is made up of segmented, annealed,

insulated punching of preferred grain-oriented, high-quality

silicon steel to give minimum electrical loss.

C. Stator winding:

The stator winding is composed of insulated bars assembled

in the stator slots, joints at the ends to form coils and

connected in the proper phase belts by bus rings. Each phase is

split into groups of coils 180 degrees apart.

ROTOR:

A. General:

The rotor is machine from single alloy steel forging which

has passed extensive tests to assure that the forging meets

the required physical and metallurgical properties.

B. Bearings:

The rotor is supported and rotates in elliptical journal

bearings mounted in the generator end shields. The bearing

and the shaft seal housing at the collector end of the

generator are insulated from the generator frame to prevent

the flow of shaft currents.

C. End shields:

The end shields are split on the horizontal centre line to

facilitate their removal. Inner end shields are located

between the ends of the armature windings and the outer

end shields to separate the gas discharged from the fans

from the gas entering the fans.

D. Shaft seals:

This arrangement permits inspection of the generator

bearings without removing gas from the machine. The shaft

seal housing at the collector end of the machine is insulated

from the generator frame to prevent the flow of shaft

currents.

E. Field winding and Retaining Rings:

The field winding consists of rectangular copper bars,

fabricated into coils. End turns are held in place against

centrifugal force by heavy retaining rings machined from the

high strength, heat treated alloy steel forgings which shrunk

and locked on the centering rings.

Typical Generator assembly

GENERATOR COLLECTOR RINGS AND BRUSHES:

It consists of

A. Collector and Collector Connections

B. Brush Rigging

C. Shaft Grounding Brushes

GENERATOR VENTILATION:

Rotor fans circulate hydrogen gas within the generator. They

are axial flow type with individual blades fastened to fan hubs

near the end of the rotor. The entrance conditions of the gas to

the fans is controlled by an inlet nozzle.

COOLING SYSTEM:

The cooling system employed in this generator is Hydrogen

cooling system. Four Hydrogen gas coolers are mounted vertically

within cooler support rails inside cooler towers located at the four

corners of the generator frame. Each Hydrogen cooler section

consists of a water headers, tube sheets, round tubes with plate

fins, all supported by a frame. These sections should be piped in

parallel for water flow.

Ventilating system for a typical hydrogen-cooled

generator

1. Cooler Frame:

The frame is of welded steel construction and consists of two-channel-shaped side plates forming a box like structure with end plates at each end. Strength is provided by diagonal pipe braces welded to the corner bars and extending across the two open sides of the frame.

Vertical cooler for hydrogen-cooled Turbine generators

2. Cooler Tubes:

The tubes are of condenser tube quality as described by ASTM specification B-111.

The extended surface on the outside of the tube consists of continuous plate fin with a shoulder formed at the tube holes for stacking as required. Both ends of the each tube are roller-expanded into the tube sheets. The length of the rolled joint should equal approximately 90% of the tube sheet thickness measured from the front face of the tube sheet.

3. Tube sheets:

In addition to the normal functions, the tube sheets of the vertical hydrogen cooler support the cooler at the extended end edges and provides a hydrogen seal between the cooler and the generator frame. The gas seal at the floating end is provided by a compressed ring gasket which bears on the edge of the floating end tube sheet. The edges of the floating end tube sheet are machined accurately to provide good sealing surfaces.

4. Water boxes:

The water boxes or headers and covers are bolted to the tube sheets with bolts or studs which thread into bottom-taped holes in the tube sheets. Four studs located at the corner of the lower water boxes are fitted with jamb nuts, which holds the lower water boxes in place when the cover is removed.

5. Gaskets:

Gaskets are provided in the joints between covers and water boxes, and between water boxes and tube sheets.

EXCITATION:

Generator requires direct current to energise its magnetic field. The dc field current is obtained from a separate source called an exciter.

When the magnetic field around a conductor changes a current is induced in the conductor. Typically a rotating magnet called the rotator turns with in a stationary set of conductors generates an induced E.M.F, as the mechanical input causes the

rotor to turn. The rotating magnetic field induces an AC voltage in the stationary winding. The magnetic field may be produced by

Permanent magnets

Field coils

In case of machine with field coils in rotor winding, a current must flow in the coils to generate the field. The rotor winding is energised with dc through slip rings and brushes. In case of machine with permanent magnet, the rotor magnetic field may be produced by inductance through “permanent magnet”. Either rotating (or) static excitation system are used in power generation system Rotating type Stationary type

Brush type . Field flash voltage from Storage battery

Brush less type . voltage from system of solid state component

ROTATING TYPE: There are two types of excitation system in G.T.P.S, they are 1)Brush type excitation system. 2)Brush less type excitation system.

1)Brush type excitation: In this excitation system stationary brushes are used to transfer the DC exciting current to the rotating generator field. Current transfer is made on rotating slip ring (collector rings) that are in contact with the brushes.

Two collector rings are used on each exciter which are fully insulated from shaft and each other.

The inner ring is usually wired with negative polarity and the outer ring is with positive polarity.

2) Brush less type excitation:

In this excitation system the brush and slip rings are replaced by a rotatory solid state rectifier assembly. The exciter (armature), generator rotating assembly &RRA are mounted on a common shaft.

STATIONARY TYPE: It doesn’t contain any moving part. A portion of the AC voltage from each phase of generator output is feed back to the field winding, as Dc excitation, through a source of Transformer, rectifier, and reactor. An excitation source of dc is necessary for initial excitation of the field winding.

Main features of the excitation system: Controlling terminal voltage with suitable accessory.

Ensures stable operation with network.

Contributes to transient stability subsequent to a fault.

Variable dc current with short time over load capability.

Synchronization:

The process of connecting an AC generator (alternator) to other AC generators is known as synchronization and is crucial for the generation of AC electrical power.

A DC generator can be connected to a power network by adjusting its open-circuit terminal voltage to match the network voltage by either adjusting its speed or its field excitation; the exact engine speed is not critical. However, an AC machine must match both the amplitude and the timing of the network voltage, which requires both speed and excitation to be systematically and closely controlled for synchronization.

Conditions:

There are five conditions that must be met before the synchronization process takes place. The alternator must have equal line voltage, frequency, phase sequence, phase angle and waveform to that of the system to which it is being synchronized. Waveform and phase sequence are fixed by the construction of the generator and its connections to the system, but voltage, frequency and phase angle must be controlled each time a generator is to be connected to a grid.

RATINGS: STAGE II:GENERATORS AND TURBINES:DETAILS GAS TURBINE STEAM TURBINEFUEL NATURAL

GAS/NAPTHA/HSD/MIXEDFUEL

STEAM

SPEED 3000 RPM 3000 RPMOUTLETTEMPERATURE

554 C 135 C-150 C

KVA 151000 81300ARMATUREVOLTAGE

11.5 KV 11.5 KV

AMPS 7581 A 4082 ACONNECTION Y YFREQUENCY 50 50SPEED 3000 3000COOLING HYDROGEN TEWACPF 0.8 LAG 0.8 LAGEXCITATION BRUSH TYPE BRUSHLESSEFFICENCYATFULL LOAD

98.5% 98.52%

EXICTERVOLTAGE

240 V

GTG:a) GENERATOR DATA Make : GENERAL ELECTRICSl. No. : 335X982Poles : TwoPhase : ThreeConnection : WYEFrequency : 50 HzSpeed : 3000 RpmTemperature at rated output : 40ºCMethod of cooling : Hydrogen

RATINGKVA : 151,000Armature amperes : 7,581Armature volts : 11,500Field amperes : 1604 Exciter volts : 425Power factor : 0.8(LAG)No load field amperes : 440Efficiency at full load : 98.59%

COLLECTOR AND BRUSH DATA:No. of collector brushes : 50%Collector min. safe operating diameter : 13 inchesNo. of shaft grounding brushes : 2%Grade of brushes : National Carbon 634

GAS COOLER DATAInlet water temperature : 35ºCWater flow at rated load : 1,215 GPMHead loss through cooler : 34 ftGas flow through generator : 55,290 cfmGas space in generator : 1,640 ft³

b) EXCITATION SYSTEM AND AVR:

i) EXCITATION SYSTEM 1) Type : Static Bus Fed 2) Field at no load, rated voltage : 127 V , 486 A

3) Field at rated load, voltage and Power factor : 418 V , 1,604 A

4) Excitation transformer :-(i)Type : Dry(ii)Power : 1,050KVA(iii)Ratio : 11.5 / 0.6 KV (iv)Insulation class : F

ii) VOLTAGE REGULATOR 1) Type : EX2000 (Digital) 2) Range of voltage level setting (a) Auto : 90-110% (b) Manual : 20-120% 3) Features Available: (a) Minimum excitation limiter (b) Maximum rotor current limiter (c) Maximum excitation limiter (d) Volts/Hertz limiter (e) Reactive drop compensatorc) HYDROGEN SYSTEM Min. purity of Hydrogen in storage : 99.6%Hydrogen purity in generator casing :

98.0%Co2 required for removing air from casing :

2,050 ft³Co2 required for removing Hydrogen from casing :

3,280 ft³Hydrogen required to fill casing to 90% purity at 0.5 psi :

2,870 ft³Rate of flow of liquid through gas generator :

65,800 ft³/minRate of flow of liquid through gas coolers :

1,250 ft³/minHead loss through cooler : 34 ft

Total Hydrogen required to reach30 psi : 8,382 ft³40 psi : 10,617 ft³

HYDROGEN REQUIRED OF GENERATOR IN NORMAL OPERATION:At 5 psi : 50 ft³ / dayAt 15 psi : 125 ft³ / dayAt 30 psi : 250 ft³ / dayMAXIMUM SEAL OIL FLOW FOR 110ºF INLET TEMPERATURETotal oil flow (each end) at 5 psi : 7.3 gal/minTotal oil flow (each end) at 15 psi : 11.6 gal/minTotal oil flow (each end) at 30 psi : 17.4 gal/minH2 side flow only : 1.2 gal/min

DIFFERENTIAL BETWEEN SEAL OIL AND CASING HYDROGEN PRESSURETurbine end : 4.5 psiCollector end : 4.5 psi

GENERATOR CURRENT TRANSFORMERS :

DESCRIPTION RATIO PURPOSE

CT 1, 2, 3 10,000 / 5 A

Generator Motor , Transducer for Mark V

CT 4, 5, 6 10,000 / 5 A

Digital, Generator protection

CT 7, 8, 9 10,000 / 5 A

Overall Differential protection

CT 13, 14, 15 10,000 / 5 A

Digital Feeder protection

CT 16, 17, 18 10,000 / 5 A

Spare

CT 19A, 19C 10,000 / 5 A

Excitater Regulator , EX 2000

CT 21, 22, 23 10,000 / 5 A

Digital Generator protection

GENERATOR PROTECTION TRANSFORMERS:

DESCRIPTION

RATIO PURPOSE

VT 2 12,000 / 120 V

Digital Generator protection, Generator Meter, Mark V for synchronizing

VT 4 12,000 / 120 V

Mark V Transducer, Digital Feeder protection, Low forward power Relay, Impedance Relay

NETURAL GROUNDING TRANSFORMER:

DESCRIPTION RATIO PURPOSE

10 KVA 8,000 / 240 V


STG:GENERATOR DATA

Make : GENERAL ELECTRICSl. No. : 316X947Poles : TwoPhase : ThreeConnection : WYEFrequency : 50 HzSpeed : 3000 RpmTemperature at rated output : 120ºCCold gas/Air temperature : 48ºCMethod of cooling : TEWAC (Totally enclosed water to air cooled)

RATING:KVA : 81,300Armature amperes : 4,082Armature volts : 11,500Field amperes : 858Exciter volts : 240Power factor : 0.8(LAG)No load field amperes : 3.2Efficiency at full load : 98.52%

EXCITATION SYSTEM AND AVR:a)EXCITATION SYSTEM:1) Type : Brushless2) Field at no load , rated voltage : 86 V , 313 A3) Field at rated load, voltage and

power factor : 236 V , 858 A4) Excitation transformers:-(i)Type : Dry(ii)Power : 4KVA(iii)Ratio : 480 / 240 V (iv)Insulation class : F

b)VOLTAGE REGULATOR: 1) Type : EX2000 R (Digital) 2) Range of voltage level settings (a) Auto : 90-110% (b) Manual : 20-120% 3) Features Available: (a) Minimum excitation limiter (b) Maximum rotor current limiter (c) Maximum excitation limiter (d) Volts/Hertz limiter (e) Reactive drop compensator

c) GAS COOLER Type : DUPLEX COOLERInlet water temperature : 36ºCWater flow : 900 GPMHead loss through cooler : 8 ftAir flow through generator : 47,500 cfm

GENERATOR CURRENT TRANSFORMERS:DESCRIPTION RATIO PURPOSE

CT 1, 2, 3 6,000 / 5 A

Generator Motor , Transducer for Mark V

CT 4, 5, 6 6,000 / 5 A


Digital Feeder protection

CT 7, 8, 9 6,000 / 5 A

Overall Differential protection

CT 13, 14, 15 6,000 / 5 A


CT 19A, 19C 10,000 / 5 A

Excitater Regulator , EX 2000

GENERATOR PROTECTION TRANSFORMERS

DESCRIPTION

RATIO PURPOSE

VT 2 12,000 / 120 V

Digital Generator protection, Generator Meter, Mark V for synchronizing

VT 4 12,000 / 120 V

Mark V Transducer, Digital Feeder protection, Low forward power Relay, Impedance Relay, Distance Relay

GENERATOR PROTECTION SCHEMES:

Introduction:

Protection system is essential to protect the generator against internal or external faults. The protection relays can trip the generator i.e., disconnected from the system of shutdown whenever it detects abnormality in machine parameters. As the generator protection is a large and complex subject, the instructions were written here to provide information on protection schemes only. It is an operator’s responsibility to decide what corrective action is required and to take it. The timely taken action can avert serious damage or failure of the generator, which in turn saves a lot of revenue and time.

The following are the main protection schemes adopted for our generator.

1. Generator Differential Protection (87G)2. Generator & Transformer Differential Protection (87GT)3. Loss of Field or Loss of Excitation Protection (40G)4. Negative Sequence or Current Unbalance Protection (46G)5. Over Fluxing or Over Excitation Protection (99GT)6. Over Current Protection (51G)7. Stator Earth Fault Protection (64G)8. Rotor Earth Fault Protection (64R)

9. Restricted Earth Fault Protection (64GTR)10. Backup Impedance Protection (21G)11. Low Forward Power Protection (37G)12. Reverse Power Protection (32G)13. Pole Slip Protection (98G)14. Pole Discrepancy Protection (47)15. Local Breaker Back Protection (50Z)16. Bus Bar Protection (BB)17. Over Frequency Protection (81)18. Under Frequency Protection (81)19. Over Voltage Protection (59G)20. Under Voltage Protection (27G)

1. GENERATOR DIFFERENTIAL PROTECTION (87G):

Setting: 0.5 Amp Time: Instantaneous

It is one of the important protections to protect generator winding against internal faults such as phase-to-phase and three phase-to-ground faults. This type of fault is very serious because very large current can flow and produce large amounts of damage to the winding if it is allowed to persist. One set current transformers of the generator on neutral and phase side, is exclusively used for this protection. The differential protection cannot detect turn-to-turn fault and phase to ground within one winding for high impedance neutral grounding generator such as ours. Upon the detection of a phase-to-phase fault in the winding, the unit is tripped without time delay.

Relays acted : a. Flag operation at Protection panel.b. Acting of Master relay 86Uc. Indication at Annunciation Panel.

Consequences: a. Tripping of 220KV breakerb. Tripping of Field breakerc. Stop command to Turbine thro’ Mark-IV

Status : a. Unit is at coasting down.Once the differential protection operated, the unit

cannot be taken into service unless the generator winding is thoroughly examined by the maintenance staff of any internal faults.

2. GENERATOR-TRANSFORMER DIFFERENTIAL PROTECTION (87GT):

Setting : 0.75 Amp Time: Instantaneous

If protects 11KV bus duct, 11/0.440KV unit auxiliary transformer, 11/20KV step-up transformer against internal faults such as phase-to-phase and three phase-to-ground faults. This type of fault is very serious because very large current can flow and produce large amounts of damage to the winding if it is allowed to persist. One set current transformers of the generator on neutral side and another set current transformer on 220KV side after transformer, is exclusively used for the protection. Upon the detection of difference in current between these current transformers, the unit is tripped with out time delay.

Relays acted : a. Flag operation at Protection panel.

b. Acting of Master relay 86U

c. Indication at Annunciation Panel.

Consequences : a. Tripping of 220KV breaker

b. Tripping of Field breaker

c. Stop command to Turbine thro’ Mark-IV

Status : a. Unit is at coasting down.

One the generator-transformer differential protection operated, the unit cannot be taken into service unless the 11KV bus duct, unit auxiliary transformer, power transformer are thoroughly examined by the maintenance staff for any internal faults.

3. LOSS OF FIELD OR EXCITATION PROTECTION (40G):

Setting: K1-2, K2-1, K3-2 Trip after 2 Sec.

When the synchronous machine with excitation, is connected to the grid, it generates reactive power along with active power to the grid and the rotor speed is same as that of grid frequency. Loss of field or loss of excitation results in loss of synchronism between rotor flux & stator flux. The synchronous machine operates as an induction machine at higher speed and draws reactive power from the grid. This will result in the flow of slip frequency currents in the rotor body as well as severe torque oscillations in the rotor shaft. As the rotor is not designed to sustain such currents or to withstand the high alternating torques which results in rotor overheating, coupling slippage and even rotor failure.

A loss of excitation normally indicates a problem with the excitation system. Sometimes it may be due to inadvertent tripping of filed breaker, open or short circuit of field winding or loss of source to the exciter. If the generator is not disconnected immediately when it loses excitation wide spread instability may very quickly develop and major system shutdown may occur.

When loss of excitation alarm annunciates at annunciation panel, the machine may probably be running with less excitation at leading MVAR power. Increase the excitation on the machine until it reaches on lagging MVAR power. The machine trips on the same protection along with alarm resynchronize the machine and try to stabilize at required MVAR power. If not possible, trip the machine immediately and inform to the maintenance staff for thorough checking of the Automatic Voltage Regulator (AVR) and its associated parts.




Consequences : a. Tripping of 220KV breaker




4. NEGATIVE SEQUENCE OR CURRENT UNBALANCE PROTECTION (46G):

Setting: Alarm – 75% of 12s Time - 5 Sec.

Trip – 75% of 12s Time- 300 Sec.

When the machine delivering the equal currents in three phases, no unbalance or negative phase sequence current is produced as the vector sum of these currents is zero, when the generator is supplying an unbalanced load to a system, a negative phase sequence current is imposed on the generator. The system unbalance may be due to opening of lines, breaker failures or system faults. The negative sequence current in the stator winding creates a magnetic flux wave in the air gap which rotates in opposite direction to that of rotor synchronous speed. This flux induces currents in the rotor body, wedges, retaining rings at twice the line frequency.

Heating occurs in these areas and the resulting temperatures depend upon the level and duration of the unbalanced currents. Under these conditions it is possible to reach temperatures at which the rotor material no longer contain the centrifugal forces imposed on them resulting in serious damage to the turbine-generator set. Any machine as per design data will permit some level of negative sequence currents for continuous period.

An alarm will annunciate at annunciation panel if negative sequence currents exceeds a normal level. Reduce the MVAR power on the machine if necessary load also and keep the machine for some time till the alarm vanishes at annunciation panel. If the machine trips on the Negative sequence protection never take the machine into service until the temperatures on the rotor parts settle down to its lower value. Resynchronize the machine to the grid after considerable time under grid & feeder parameters are within limits. If the unit trips again on the same protection, stop the machine after consideration time so as to

cool down the rotor parts and inform to the maintenance staff for thorough examination of the system.

Relays acted : a. Flag operation at Protection panel.b. Acting of Master relay 86Uc. Indication at Annunciation Panel.

Consequences:a. Tripping of 220KV breakerb. Tripping of Field breaker

Status: a. Unit is at FSNL.

5. OVER FLUXING OR EXCITATION OR VOLTS PER HERTZ PROTECTION (99GT):

Setting: Alarm – 1.17 Time - 10 Sec.

Trip– 1.17 Time-30 Sec.

Per unit voltage divided by per unit frequency commonly called Volts/Hertz is a measurable quantity that is proportional to flux in the generator or step-up transformer cores. Moderate over fluxing (105-110%) increases core loss resulting in increase of core temperatures due to hysterics & eddy currents loss. Long term operation at elevated temperatures can shorten the life of the stator insulation. Severe over fluxing can breakdown inter-laminar insulation followed by rapid local core melting. Over fluxing normally can be caused by over speed of the turbine or over excitation during Off-line condition, and load rejection or AVR mal-functioning during On-line condition.

If alarm annunciation panel, Increase/Reduce the speed of the turbine to rated generator speed (3000RPM) and reduce the generator voltage to rated during Off-line condition. Reduce the MVAR power on the generator during On-line condition. If the machine trips on over fluxing protection during On-line, Keep the machine at FSNL till the grid parameters stabilize and resins. Again the machine trips on the same stop the machine for examination of the AVR & Governor systems by maintenance staff.

Relays acted : a. Flag operation at Protection panel. b. Acting of Master relay 86U c. Indication at Annunciation Panel.

Consequences: a. Tripping of 220KV breaker b. Tripping of Field breaker c. Stop command to Turbine thro’ Mark-IV

Status: a. Unit is at coasting down.

6. OVER CURRENT WITH VOLTAGE RESTRAINT PROTECTION (51V) :

Setting: Alarm – 85% Time -10 Sec.

Trip – 100% Time- 0.5 Sec.

Normally generators are designed to operate continuously at rated MVA, frequency and power factor over a range of 95 to 105% rated voltage. Operating the generator at rated MVA with 95% voltage, 105% stator current is permissible. Operating of the generator beyond rated KVA may result in harmful stator over current. A consequence of over current in winding is stator core over heating and leads to failure of insulation.

If alarm annunciates at annunciation panel, Reduce the stator current to the below the rated by reducing the MVAR power on the machine. When the trips on the same protection, Resins the machine after keeping the machine at FSNL for some time, and keep the stator current below the rated.

Relays acted : a. Flag operation at Protection panel. b. Acting of Master relay 86U

c. Indication at Annunciation Panel.Consequences : a. Tripping of 220KV breaker

b. Tripping of Field breakerStatus : a. Unit is at FSNL.

7. STATOR EARTH FAULT PROTECTION (64G):Setting : 70% Time- 5 Sec.

Normally the generator stator neutral operates at a potential close to ground. If a faulty phase winding connected to

ground, the normal low neutral voltage could rise as high as line-to-neutral voltage depending on the fault location. Although a single ground fault will not necessarily cause immediate damage, the presence of one increases the probability of a second. A second fault even if detected by differential relay, may cause serious damage. The usual method of detection fault is by measuring the voltage across the secondary of neutral grounding transformer (NGT). Here are two over lapping zones to detect stator ground faults in a high impedance grounded generator system, the two zones are put together cover 100% stator winding for earth faults. A fundamental frequency neutral over voltage relay covers about 0-95% of the stator zonal winding for all faults except those near the neutral. Another third harmonic neutral under voltage relay covers remaining 96-100% of the stator zone 2 winding on neutral side.

Relays acted : a. Flag operation at Protection panel. b. Acting of Master relay 86U c. Indication at Annunciation Panel.

Consequences: a. Tripping of 220KV breaker b. Tripping of Field breaker c. Stop command to Turbine thro’ Mark-IV


8. ROTOR EARTH FAULT PROTECTION (64R) :

Settings: Less than 80K ohm

Any rotor field winding of the generator is electrically isolated from the ground. Therefore the existence of one ground fault in the field winding will usually not damage the rotor. However the presence of two or more ground faults in the winding will cause magnetic and thermal imbalance plus localized heating and damage to the rotor metallic parts. The rotor earth fault may be caused due to insulation failure of winding or inter-turn fault followed by localized heat.




Consequences: a. Tripping of 220KV breaker




9. RESTRICTED EARTH FAULT PROTECTION (64GTR) :

Settings: 0.1 Amps. Time: Instantaneous

It is similar to generator differential protection in working. It protects the high voltage winding of 11/220KV power transformer against internal faults. One set current transformers of the power transformer on neutral and phase side, is exclusively used for this protection. The protection can not detect turn-to-turn fault within one winding. Upon the detection of a phase-to-phase or phase-to-ground fault in the winding, the unit to be tripped without time delay.








Once the restricted earth fault protection operated, the unit can not be taken into service unless the transformer winding is thoroughly examined by the maintenance staff for any internals faults.

10. BACKUP IMPEDANCE PROTECTION (21G) :

Settings: K1-3, K2-0.71 Time – 1.5 Sec.

As in name implies, it is used to protect the generator from supplying the over loaded or faulty system. It is backup protection of the generator over current protection. In measures ratio of the voltage and current supplied by the generator and initiates trip signal when the measured impedance is less than the preset value.

If the machine trips on the Backup protection, never take the machine into service until the temperatures of the generator settle down to its lower value. Resynchronize the machine to the grid after considerable time when grid & feeder parameters are within limits.




Consequences:a. Tripping of 220KV breaker




11. LOW FORWARD POWER PROTECTION (37G) :

Setting: 0.5% Time: 1 Sec.

The generator will not develop output power when turbine input is less than the no load losses and motoring action develops on the turbine. The generator is able to generate power, usually 55 to 10% of generator capacity, within pre-determined time after closing of 220KV breaker.


b. Acting of Master relay 86G



Status : a. Unit is at FSNL with potential.

The unit trips on the low forward protection, Resins the machine and increase input power to the turbine as quickly as possible within low forward power time setting. Even after two to three attempts, the machine is tripping on the same protection; probably the governor of turbine is faulty. Inform to maintenance staff for rectification of the same.

12. REVERSE POWER PROTECTION (32G) :

Setting: 0.5% Time-2.0 Sec.

It is backup protection to the low forward protection. Motoring of a generator will occur when turbine output is reduced such that it develops less than no-load losses while the generator is still on-line, the generator will operate as a synchronous motor and driving the turbine. The generator will not be harmed by synchronous motoring and a steam turbine can be harmed through over heating during synchronous motoring if continued long enough. The motoring of the turbine output can be detected by reverse power protection. The avoid false tripping due to power swings a time delay is incorporated before tripping signal is generated.








The unit trips on the reverse power protection. Resins the machine and increase the input power to the turbine as

quickly as possible within low forward power time setting. Even after two to three attempts, the machine is tripping on the same protection; probably the governor of turbine is faulty. Inform to maintenance staff for rectification of the same.

13. POLE SLIP OR OUT-OF-STEP PROTECTION (98W) :

Setting: 6.9 ohm.

When a generator loses synchronism, the resulting high current peaks and off-frequency operation may cause winding stresses, pulsation torques and mechanical resonances that have the potential danger to turbine generator. Therefore, to minimize the possibility of damage, it is generally accepted that the machine should be tripped without time delay preferably during the first half-slip cycle of the loss of synchronism condition. The electrical center during loss-of-synchronous conditions can occur in the generator as a result of increased impedance of the generator while decrease system impedance. The protections normally applied in the generator zone such as back-up impedance, loss of excitation etc., will not protect a generator during loss of synchronism under normal generator conditions.








The unit trips on the Pole slip protection, Resynchronising the machine after stabilization of the grid parameters.

14. POLE DISCREPANCY PROTECITON (47) :

Setting: 0.5 Sec.

If One or two poles of generator breaker fail to close during synchronization, all poles of the breaker trip on this protection. It may be due to mechanical failure of the breaker un equal distribution of closing signal to the breaker from protection system.

Relays acted : a. Flag operation at 220KV Breaker panel.

b. Indication at Annunciation Panel.

Consequences : a. tripping of 220KV breaker

Status : a. Unit is at FSNL with potential.

The generator breaker trips on the pole discrepancy protection, Resynch the generator. Even after two to three attempts, the machine is tripping on the same protection, probably the generator breaker is faulty. Inform to maintenance staff for rectification of the same.

15. LOCAL BREAKER BACKUP PROTECTION (50Z) :

Setting: 25% Time: 0.8 Sec.

For most of the faults, the generator breaker involves tripping the generator from the system. Failure of the breaker to open probably results in loss of protection and other problems such as motoring action or single phasing, If one or two poles of the generator breaker fail to open due to mechanical failure in breaker mechanism, the result can be a single phasing and negative phase sequence currents inducted on the rotor. The LBB protection is energized when the breaker trip is initiated after a suitable time interval if confirmation of the confirmation of breaker tripping from three poles is not received. The energized tripping signal from LBB protection will trip all 220KV generator breakers and all 220KV feeder breakers through Bus-bar protection.


b. Acting of Master relay 86G for all units.



b. Tripping of Field breaker of all units.

Status : a. all Units are at FSNL.

Once the LBB protection operated, the entire station is in dark. First restore all essential services to all units such as lube oil system and turning gear etc., from battery backup and 6.6/0.44KV Stage-II reserve power supply. Checkup the faulty 220KV breaker and isolate the breaker from the system by opening the both side of the isolators. After restoring all services from station supply, Close 220KV feeder breakers first and take all units into service one after the other duly co-coordinating with the DE/LD.

Since it involves complex operation, it is necessary to get help from maintenance staff for restoring the normally in the station. Never attempt to close the faulty 220KV generator in panic as it causes permanent damage to the generator and transformer.

16. BUS BAR PROTECTION (BB):

Setting: 0.8 Amps.

There are mainly three protection zones namely called generator zone, bus duct transformer zone, 220KV breakers zone. The protection of generator zone and bus duct & transformer zone are covered in previous schemes. All 220KV breakers at switchyard will come under Bus-Bar protection. Functioning of this scheme is similar to the generator differential protection or generator-transformer differential protection. It measures all incoming currents from the generators at 220KV side and all outgoing currents in 220KV feeders, and initiates trip signal if it detects any deviation more than the preset value as the algebraic sum of all currents at 220KV bus must be less than the preset value. It isolates all 220KV generator breakers and all 220KV feeder breakers connected to 220KV bus.


b. Acting of Master relay 86G for all units.



b. Tripping of Field breaker of all units.

Status : a. all Units are at FSNL.

Once the Bus-Bar protection operated, the entire station is in dark. First restore all essential services to all units such as lube oil system and turning gear etc., from battery backup and 6.6/0.44KV Stage – II reserve power supply. Check-up the entire 220KV switch yard for any wire snapping or equipment damage.

After restoring all services from station supply, Close 220KV feeder breakers first and take all units into service one after the other duly co-ordinating with the DE/LD. Since it involves complex operation, it is necessary to get help from maintenance staff for restoring the normalcy in the station. Never attempt to restore the 220KV supply at switch yard in panic unless the entire system is thoroughly examined and satisfy yourself as it causes permanent damage to the equipment or injury/death to the person working at switch yard.

17. OVER FREQUENCY PROTECTION (81) :

Setting: 52 Hz Time - 2 Sec.

For a generator connected to a system, abnormal frequency operation is a result of a severe system disturbance. The generator can tolerate moderate over frequency operation provided voltage is within an acceptable limits. The machine operated at higher speeds at which the rotor material no longer contain the centrifugal forces imposed on them resulting in serious damage to the turbine-generator set. The abnormal over frequency on the machine may be due to improper speed control adjustment or disoperation of the speed controller or severe grid disturbance or sudden load through off.








The unit trips on the over frequency protection, Resins the machine. Even after two to three attempts, the machine is tripping on the same protection; probably the governor of turbine is faulty. Inform to maintenance staff for rectification of the same.

18. UNDER FREQUENCY PROTECTION (81) :

Setting: 48 Hz Time: 2.0 Sec.

For a generator connected to a system, under frequency operation is a result of a severe system disturbance. The generator can tolerate moderate under frequency operation provided voltage is within an acceptable limits. The machine operated at lower higher speeds causes severe over fluxing in the generator-transformer. The abnormal under frequency on the machine may be due to improper speed control adjustment or disoperation of the speed controller.


b. Indication at Annunciation Panel

Consequences:a. NIL

Status : a. Unit is at lower speed with potential.

Increase governor speed until machine reaches full speed. Even after two to three attempts, the machine are running at lower speed, probably the governor of turbine is faulty. Inform to maintenance staff for rectification of the same.

19. OVER VOLTAGE PROTECTION (59G) :

Setting: a.110% Time - 2.0 Sec.

b.120% Time - 0.3 Sec.

Generator voltage is at present value under normal operating conditions as selected by operator in AVR. If it parts from preset value, May be due to AVR mal-functioning or a system disturbance. Severe over voltage can cause over fluxing and winding insulation failure. The over voltage protection can be considered as a backup to the Volts-per-Hertz protection.


b. Acting of Master relay 86G




Status : a. Unit is at FSNL without potential.

Raise the generator voltage slowly with manual mode in AVR and keep generator voltage within the limits of normal voltage. If it is unable to control the generator voltage, trip the field breaker and inform to the maintenance staff for rectification of the AVR.

CONCLUSION

The mini project opportunity given to us by the authorities of APGPCL and O&M SOLUTIONS at their gas turbo power station, Vijjeswaram at the request of our B.V.C. ENGINEERING COLLEGE, ODALAREVU is much useful.

In this mini project we had linked up the project work as practical oriented with full pledge involvement with Operations &

Maintenance team.. We had studied the working of generator and its protection schemes designed in stage2 of Vijjeswaram power plant. And we also studied how the electrical power generated & exported in the combined cycle power plant.

So we may conclude that this training is much helpful and useful for the students like us. It is also useful in our future and even after completion of our Engineering graduation.

AND ALSO SPECIAL THANKS TO GTPS STAFF.

MINI PROJECTGenerator Protection

Documents

g generator

bhagyasri 08221a0237

swaroop 08221a0256 g

growth of power

power supply

supplementing power

vijjeswaram power plant

gas turbo power generation