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Seminar Report On NUMERICAL RELAY Submitted in partial fulfilment of the requirement For the award of the degree of Bachelor of Technology In Electrical Engineering Of Biju PatTnaik University of Technology By ANURAG SAHOO BPUT Registration No: 0501212561
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Page 1: Seminar

Seminar Report

On

NUMERICAL RELAY

Submitted in partial fulfilment of the requirement

For the award of the degree of

Bachelor of Technology

In

Electrical Engineering

Of

Biju PatTnaik University of Technology

By

ANURAG SAHOO

BPUT Registration No: 0501212561

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Department of Electrical Engineering

Institute of technical education and research

BHUBANESWAR, ORISSA

(An affiliated to Biju Pattnaik University of Technology, approved by AICTE)

CERTIFICATEThis is to certify that the seminar report entitled “NUMERICAL RELAY” is

the bona fide work of ANURAG SAHOO bearing Regn. No. 0501212561, a student of 8th Semester, Electrical Engineering.

...................................................

PROF. B.B. SAHU

(H.O.D, ELECTRICAL)

…………………………………….. ……………………………………..

Mr.Shubhranshu Mohan Parida Miss.J.SURYAPRABHA

(SEMINAR IN-CHARGE) (SEMINAR IN-CHARGE)

BHUBANESWAR, ORISSA

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Acknowledgement

The satisfaction that accompanies the successful completion of the task would be incomplete without the mention of the people who made it possible whose constant guidance crowns all effort with success.

I express my deep sense of gratitude Miss J.Suryaprabha, Mr.Shubhranshu Mohan parida of Electrical Engineering for their initiative and constant inspiration.

Lastly I express my gratitude to all the lectures and friends for their cooperation and valuable suggestion during the preparation of the seminar report.

Thanks to all...

Name: Anurag Sahoo Regd. no. :

0501212561 Branch: Electrical Engg.

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CONTENT

Introduction Relay Basic operation Numerical relay Development cycle of a numerical relay Block diagram of a numerical relay Basic principle Fundamental requirements of numerical relay Advantages and special features of numerical relay Protective elements type Manufacturers Applications Service life of numerical relay Conclusion Reference

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Introduction

Numerical relays have revolutionized protection, control, metering

and communication in power systems. Functional integration, new

methods of communication, reduced physical size, and an enormous

amount of available information are but a few of the benefits of this

revolution. Having made the initial conceptual adjustment of relating

objects from electromechanical technology such as rotating discs

and moving armatures to such electronic technology as analog to

digital converters and comparators protection practitioners then

must deal with programming a relay. Initially programming was no

more than selecting values for relay settings. Further advancement

in digital technology, however has made possible advanced and

sophisticated programming of logical functions and analog

quantities.

A good understanding of relay programming is

necessary to take full advantage of the many functions integrated

into numerical relays and use these functions in different

applications to enhance operation of a power network. Unfortunately

many users avoid relay programming, considering it too complex.

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Because of this perceived complexity, not all users investigate the

use of relay programming to realize automation and control

applications. Many cost saving opportunities and simple engineering

solutions to automation applications are reliably achieved by using

the protection relay programming features.

Relay

Relay is an automatic device which senses the faults and recloses its

contacts and gives adequate alarm and trip signal.

Basic Operation

A simple electromagnetic relay, such as the one taken from a car in

the first picture, is an adaptation of an electromagnet. It consists of

a coil of wire surrounding a soft iron core, an iron yoke, which

provides a low reluctance path for magnetic flux, a moveable

iron armature, and a set, or sets, of contacts; two in the relay

pictured. The armature is hinged to the yoke and mechanically

linked to a moving contact or contacts. It is held in place by

a spring so that when the relay is de-energised there is an air gap in

the magnetic circuit. In this condition, one of the two sets of

contacts in the relay pictured is closed, and the other set is open.

Other relays may have more or fewer sets of contacts depending on

their function. The relay in the picture also has a wire connecting the

armature to the yoke. This ensures continuity of the circuit between

the moving contacts on the armature, and the circuit track on

the Printed Circuit Board (PCB) via the yoke, which is soldered to the

PCB.

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When an electric current is passed through the coil, the

resulting magnetic field attracts the armature and the consequent

movement of the movable contact or contacts either makes or

breaks a connection with a fixed contact. If the set of contacts was

closed when the relay was de-energized, then the movement opens

the contacts and breaks the connection, and vice versa if the

contacts were open. When the current to the coil is switched off, the

armature is returned by a force, approximately half as strong as the

magnetic force, to its relaxed position. Usually this force is provided

by a spring, but gravity is also used commonly in industrial motor

starters. Most relays are manufactured to operate quickly. In a low

voltage application, this is to reduce noise. In a high voltage or high

current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across

the coil, to dissipate the energy from the collapsing magnetic field at

deactivation, which would otherwise generate a voltage

spike dangerous to circuit components. Some automotive relays

already include that diode inside the relay case. Alternatively a

contact protection network, consisting of a capacitor and resistor in

series, may absorb the surge. If the coil is designed to be energized

with AC, a small copper ring can be crimped to the end of the

solenoid. This "shading ring" creates a small out-of-phase current,

which increases the minimum pull on the armature during the AC

cycle.

By analogy with the functions of the original electromagnetic device,

a solid-state relay is made with a thyristor or other solid-state

switching device. To achieve electrical isolation an optocoupler can

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be used which is a light-emitting diode (LED) coupled with a photo

transistor.

Circuit diagram of a typical relay

Numerical relay

A numerical relay utilizes a microcontroller with software based

protection algorithms for the detection of electrical faults.

Description and definition

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The numerical relay, also called a digital relay by some

manufacturers and resources, refers to a protective relay that uses

an advanced microprocessor to analyze power system voltages and

currents for the purpose of detection of faults in an electric power

system. There are gray areas on what constitutes a digital/numeric

relay, but most engineers will recognize the design as having the

majority of these attributes:

The relay applies A/D (analog/digital) conversion processes to

the incoming voltages and currents.

The relay analyzes the A/D converter output to extract, as a

minimum, magnitude of the incoming quantity; most commonly

using Fourier transform concepts (RMS and some form of

averaging are used in basic products). Further, the Fourier

transform is commonly used to extract the signal's phase angle

relative to some reference, except in the most basic

applications.

The relay is capable of applying advanced logic. It is capable of

analyzing whether the relay should trip or restrain from tripping

based on current and/or voltage magnitude (and angle in some

applications), complex parameters set by the user, relay

contact inputs, and in some applications, the timing and order

of event sequences.

The logic is user-configurable at a level well beyond simply

changing front panel switches or moving of jumpers on a circuit

board.

The relay has some form of advanced event recording. The

event recording would include some means for the user to see

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the timing of key logic decisions, relay I/O (input/output)

changes, and see in an oscillographic fashion at least the

fundamental frequency component of the incoming AC

waveform.

The relay has an extensive collection of settings, beyond what

can be entered via front panel knobs and dials, and these

settings are transferred to the relay via an interface with a PC

(personal computer), and this same PC interface is used to

collect event reports from the relay.

The more modern versions of the digital relay will contain

advanced metering and communication protocol ports, allowing

the relay to become a focal point in a SCADA system.

Numerical relay

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Development cycle of a numerical relay

Block diagram of a numerical relay

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Basic principle

Low voltage and low current signals (i.e., at the secondary of a VT

and CT) are brought into a low pass filter that removes frequency

content above about 1/3 of the sampling frequency (a relay A/D

converter needs to sample faster than 2x per cycle of the highest

frequency that it is to monitor). The AC signal is then sampled by the

relay's analog to digital converter at anywhere from about 4 to 64

(varies by relay) samples per power system cycle. In some relays,

the entire sampled data is kept for oscillographic records, but in the

relay, only the fundamental component is needed for most

protection algorithms, unless a high speed algorithm is used that

uses sub cycle data to monitor for fast changing issues. The sampled

data is then passed through a low pass filter that numerically

removes the frequency content that is above the fundamental

frequency of interest (i.e., nominal system frequency), and uses

Fourier transform algorithms to extract the fundamental frequency

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magnitude and angle. Next the microprocessor passes the data into

a set of protection algorithms, which are a set of logic equations in

part designed by the protection engineer, and in part designed by

the relay manufacturer, that monitor for abnormal conditions that

indicate a fault. If a fault condition is detected, output contacts

operate to trip the associated circuit breaker(s).

Fundamental requirements of numerical relay

SPEED: The relay system should disconnect the faulty section

as fast as possible for the following reasons:

Electrical apparatus may be damaged if they are made to carry

the fault current for a long time.

A failure on the system leads to a great reduction in the system

voltage. As a result the system may become unstable.

The high speed relay system decreases the possibility of

development of one type of fault into the other more severe

type.

SENSITIVITY: It is the ability of the relay system to operate

with low value of actuating quantity.

RELIABILITY: It is the ability of the relay system to operate

under the pre-determined conditions, without reliability the

protection would be rendered largely in effective and could

even become a liability.

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SELECTIVITY: It is the ability of the protective system to select

correctly that part of the system in trouble and disconnect the

faulty part without disturbing the rest of the system.

SIMPLICITY: The relaying system should be simple so that it can

be easily maintained. Reliability is closely related to simplicity.

The simpler the protection scheme the greater will be its

reliability.

ECONOMY: The most important factor in the choice of a

particular protection scheme is the economic aspect.

Sometimes it is economically unjustified to use an ideal scheme

of protection and a compromise method has to be adopted. As

a rule, the protective gear should not cost more than 5% of the

total cost.

Advantages and special features of Numerical relay

Ability to combine a large number of protective and

monitoring functions in a single relay unit. In the earlier

protection systems, separate relay units were necessary for

each main function resulting in more number of units, more

wiring, and lesser reliability. Measured values are processed

digitally by microprocessor.

High level of flexibility: the relay meets the most complex

protective and monitoring requirements.

Various protective functions can be freely selected and

allocated to the various auxiliary relays by means of software

tripping matrix.

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The memory of the relay enables the relay to retain the values

of variables responsible for tripping, time taken to operate etc.

No need for measuring instruments at the output as data can

be seen digitally.

Comprehensive self-monitoring self-checking feature.

Increased reliability due to self-checking.

Data interface access – increased communication ability. These

relays can communicate with other

Relays, protected equipments, and control and protection

devices in the substation.

User friendly, yet highly capable.

Relay provides fault designations and information.

High speed.

Save quantized data from faults and disturbances.

Adaptive protection: Numerical relays can be designed to

include abilities to change their settings automatically. Some of

the functions that can be made adaptive are:

Using the most appropriate algorithms during a disturbance.

Changing settings of relays of a disturbance network as the

system loads or configuration change.

Changing the settings of second and third zone disturbance

relays as the system operating state changes.

Compensating for the CT & PT errors.

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Changing the allowable overload of circuits and equipment as

the ambient conditions, especially the temperature change.

Changing the circuit auto-reclosers delays to ensure that the

circuit is reclosed after the arc is extinguished.

Fiber optical communication with substation LAN.

Adaptive relaying scheme.

Permit historical data storage.

Allow GPS (Geographical positioning system) time stamping.

Protective elements type

Protective Elements refer to the overall logic surrounding the

electrical condition that is being monitored. For instance, a

differential element refers to the logic required to monitor two (or

more) currents, find their difference, and trip if the difference is

beyond certain parameters. The term element and function are quite

interchangeable in many instances.

For simplicity on one-lines, the element/function is usually identified

by what is referred to as an ANSI device number, and hence there

are three terms (element, function, device number) in use for

approximately the same concept. In the era of electromechanical

and solid state relays, any one relay could implement only one or

two protective elements/functions, so a complete protection system

may have many relays on its panel. In a digital/numeric relay, many

functions/elements are implemented by the microprocessor

programming. Any one digital/numeric relay may implement one or

all of these device numbers/functions/elements.

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A relatively complete listing of device numbers is found at the

site ANSI Device Numbers. A summary of some common device

numbers seen in digital relays is:

21 - Impedance (21G implies ground impedance)

27 - Under Voltage (27LL = line to line, 27LN = line to

neutral/ground)

32 - Directional Power Element

46 - Negative sequence current

47 - Negative sequence voltage

50 - Instantaneous Over Current (subscript N or G implies

Ground)

51 - Inverse Time Over current (subscript N or G implies

Ground)

59 - Over Voltage (59LL = line to line, 59LN = line to

neutral/ground)

67 - Directional Over Current (typically controls a 50/51

element)

79 - Auto-reclosure

81 - Under/Over Frequency

87 - Current Differential (87L=transmission line diff;

87T=transformer diff; 87G=generator diff)

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Manufacturers

There are many more than listed here. This especially becomes true

when one includes relays manufactured for niche or regional

markets, and manufactures that offer relays in part hidden and

buried within a larger product mix.

GE Multilin

ABB

AREVA T&D

Basler

Bresler

Beckwith

Cooper

Cutler Hammer

DEIF

General Electric

RFL

Schneider Electric

Schweitzer

Siemens

Orion Italia

VAMP

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ZIV

NARI

Applications

Relays are used to and for:

Control a high-voltage circuit with a low-voltage signal, as in

some types of modems or audio amplifiers,

Control a high-current circuit with a low-current signal, as in

the starter solenoid of an automobile,

Detect and isolate faults on transmission and distribution lines

by opening and closing circuit breakers (protection relays)

Isolate the controlling circuit from the controlled circuit when

the two are at different potentials, for example when

controlling a mains-powered device from a low-voltage switch.

The latter is often applied to control office lighting as the low

voltage wires are easily installed in partitions, which may be

often moved as needs change. They may also be controlled by

room occupancy detectors in an effort to conserve energy,

Logic functions. For example, the Boolean AND function is

realised by connecting normally open relay contacts in series,

the OR function by connecting normally open contacts in

parallel. The change-over or Form C contacts perform the XOR

(exclusive or) function. Similar functions for NAND and NOR are

accomplished using normally closed contacts. The Ladder

programming language is often used for designing relay logic

networks.

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Early computing. Before vacuum tubes and transistors, relays

were used as logical elements in digital computers. See ARRA

(computer), Harvard Mark II, Zuse Z2, and Zuse Z3.

Safety-critical logic. Because relays are much more resistant

than semiconductors to nuclear radiation, they are widely used

in safety-critical logic, such as the control panels of radioactive

waste-handling machinery.

Time delay functions. Relays can be modified to delay opening

or delay closing a set of contacts. A very shorts (a fraction of a

second) delay would use a copper disk between the armature

and moving blade assembly. Current flowing in the disk

maintains magnetic field for a short time, lengthening release

time. For a slightly longer (up to a minute) delay, a dashpot is

used. A dashpot is a piston filled with fluid that is allowed to

escape slowly. The time period can be varied by increasing or

decreasing the flow rate. For longer time periods, a mechanical

clockwork timer is installed.

Service life of Numerical relay

A typical service life of numerical relays is between fifteen and

twenty years. For comparison electro mechanical relays had a

service life of 20years.Numerical relays are sophisticated devices

with printed circuit board. In case of hardware faults the relay has to

be replaced because of computer technology. For errors in software

the requirement is to download a correct or a new version of relay

software into the relay hardware. When feeder protection has to be

updated or modified, it is easier to replace all protection especially if

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the different manufacturer employed for protection modification.

Some times the numerical protection is replaced a few years after

the first installation. Rapid changes in computer technology causes a

shorter life of current numerical relays because of requirements for

relay replacements when other protection and control assets are

being replaced. Once when the computer technology stabilises the

real service life of the numerical relays will be available.

Conclusion

Numerical relays are highly compact devices, characterised with fast

operation, high sensitivity, self monitoring, and low maintenance.

Online remote data exchange between numerical relays and

remotely located devices offers remote relay settings applications,

data processing for network operations and maintenance or

remotely analysing recorded fault data. With numerical protection

because of the numerous and complex settings to be entered it is

important to have procedures, processes and standards in place to

ensure careful management of the modern numerical relay. It has

been found possible to standardise on the large number of settings

entered, leaving a few site specific settings to be determined. It is

important that the settings are not entered manually on site, but

downloaded into the relay after careful checking and factory tests.

Numerical relays are environment friendly because of very small

amount of raw material used for their manufacturing easy

dismantling and the good component rate of recovery and recycling.

Only printed circuit boards have to be separated and processed

separately.

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References

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CIRED 19th international conference on electricity distribution,

Vienna 21-24 MAY, 2007.

Fundamental of power system protection-Y.G.Paithankar

http://en.wikipedia.org/wiki/Digital_protective_relay

http://en.wikipedia.org/wiki/Relay

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