3171456 Power System Protection-I

© 2005. T.S. Sidhu

Course Instructor :Course Instructor : Prof. Tarlochan Singh Sidhu, Prof. Tarlochan Singh Sidhu, Ph.D., P.Eng., C.Eng.Ph.D., P.Eng., C.Eng.

Power System ProtectionPower System ProtectionECE 456ECE 456

© 2005. T.S. Sidhu

Protection Relay TechnologyProtection Relay Technology

© 2005. T.S. Sidhu

© 2005. T.S. Sidhu

Relay TechnologyRelay Technology

1. Functional block diagram

2. Relay technology evolution

3. Electromechanical relays

4. Solid state relays

5. Numerical relays

6. Impedance relay design using different

technologies

ContentsContents

© 2005. T.S. Sidhu






5. Numerical relays


technologies

ContentsContents

© 2005. T.S. Sidhu


Protection Relay Functional Block DiagramProtection Relay Functional Block Diagram

Input and Input and signal signal

conditioningconditioning

Decision Decision MakingMaking

Scheme logic Scheme logic and output and output

IIor/and

VV

Trip Trip and

AlarmAlarm

The voltage and/or current signal is first reduced to measurable quantities

and necessary conditioning done

The decision making stage does the actual protection as per the set value

The output stage implements the necessary logic before issuing trip and

alarm commands.

© 2005. T.S. Sidhu






5. Numerical relays


technologies

ContentsContents

© 2005. T.S. Sidhu

PROTECTION RELAY


Protection Relay Technology EvolutionProtection Relay Technology Evolution

© 2005. T.S. Sidhu

PROTECTION RELAY

Electromechanical Static



Electromechanical Electromechanical : A protection relay design which uses

magnetomotive force in its decision making stage and has

moving parts in it.

Static Static : A protection relay design which does not have any

moving part in the decision making stage

© 2005. T.S. Sidhu

PROTECTION RELAY


Rotational torque

Attractive force



© 2005. T.S. Sidhu

PROTECTION RELAY


Analog Electronic

Digital Electronic

Processor Based

Rotational torque

Attractive force



© 2005. T.S. Sidhu


PROTECTION RELAY


Analog Electronic

Digital Electronic

Processor Based

μPs

DSPs

Rotational torque

Attractive force


© 2005. T.S. Sidhu

PROTECTION RELAY


Analog Electronic

Digital Electronic

Processor Based

μPs

DSPs

hardware

software

Rotational torque

Attractive force



© 2005. T.S. Sidhu

Digital Signal Processor & User Interface

• Data acquisition• Digital Filtering• Protection Algorithm • Scheme logic• DR, ER, FR, etc.• Comm. & HMI

Communication Interface

DATA

BUS

Power Supply

Digital Input(Optos)

Digital Output(Relays)

VTAFiltering & Buffer

VTB

VTC

CTA

CTB

CTC

S/H

Filtering & Buffer

Filtering & Buffer

Filtering & Buffer

Filtering & Buffer

Filtering & Buffer

ADC

S/H

S/H

S/H

S/H

S/H

Crystal Clock

ADC

ADC

ADC

ADC

ADC

DIGITAL

MUX

fromVT

fromCT


Block diagram of a Modern Numerical relayBlock diagram of a Modern Numerical relay

© 2005. T.S. Sidhu






5. Numerical relays


technologies

ContentsContents

© 2005. T.S. Sidhu

Electromechanical RelaysElectromechanical Relays

Plunger-type relays

Balanced beam relays

Induction disc relays

Induction cup relays

ConstructionsConstructions

© 2005. T.S. Sidhu

Plunger Type RelaysPlunger Type Relays

A simple over voltage relay is shown

The coil impedance and turns decide the operating torque

The spring provides the restraining force

The relay operating value (setting) is thus controlled by both the coil and spring

© 2005. T.S. Sidhu

Balanced Beam RelaysBalanced Beam Relays

Beam is balanced for normal conditions

During fault, the operating torque exceeds the restraining torque causing

the beam to tilt and close the contacts

© 2005. T.S. Sidhu

Induction Disc RelaysInduction Disc Relays

Flux produced by both voltage and current coils. The interaction of these two

fluxes produces a rotational torque (like induction motors)

Disc rotates and closes contact during fault

© 2005. T.S. Sidhu

Induction Cup RelaysInduction Cup Relays

+

V-IZr2

+

φo

φ p

IZr1-V

Similar to disc, but the freedom of rotation is restricted.

Cannot provide additional time delay in operation..

© 2005. T.S. Sidhu






5. Numerical relays


technologies

ContentsContents

© 2005. T.S. Sidhu

Solid State Technology (Static)Solid State Technology (Static)

Common Solid State Circuits employed in Relays

Squaring circuits

Phase shifting circuits

Integrators

Coincidence circuits

Level Detection

‘AND’ing circuits

The above circuits are realised using transistors, Op-Amps, ICs etc.

A combination of the above circuits are used to implement a particular

protection in static technology

© 2005. T.S. Sidhu

Solid State Technology Solid State Technology

Squaring circuitsSquaring circuits

© 2005. T.S. Sidhu


Phase Shifting circuitPhase Shifting circuit

© 2005. T.S. Sidhu


IntegratorsIntegrators

© 2005. T.S. Sidhu


Coincidence circuitsCoincidence circuits

© 2005. T.S. Sidhu


Level DetectorsLevel Detectors

© 2005. T.S. Sidhu






5. Numerical relays


technologies

ContentsContents

© 2005. T.S. Sidhu

Numerical Relay Numerical Relay -- Data FlowData Flow

…..01470598096903780009

CTs & VTsPOWER SYSTEM

ADC

PROCESSOR

© 2005. T.S. Sidhu

Phasor Estimation Phasor Estimation -- ExampleExample

PROCESSOR0009

Inputs (3-Window Algorithm)

Current : 0009

Previous : -0500, -1230

Processing

1. Calculate Phasors

2. Apply logics (Algorithms)

3. Give Trip SignalTrip / No-Trip

Note:

All these processing should be done within T seconds (1 sampling interval), before the next sample arrives

ADC

© 2005. T.S. Sidhu

Data Flow Data Flow –– After T secondsAfter T seconds

PROCESSOR

0378Inputs (3-Window Algorithm)

Current : 0378

Previous : 0009, -0500

Processing




Note:


ADC

© 2005. T.S. Sidhu

Data Flow Data Flow –– After 2T secondsAfter 2T seconds

PROCESSOR


Current : 0969

Previous : 0378, 0009

Processing




Note:


ADC

© 2005. T.S. Sidhu

Data Flow Data Flow –– After 3T secondsAfter 3T seconds

PROCESSOR


Current : 0598

Previous : 0969, 0378

Processing




Note:


ADC

© 2005. T.S. Sidhu






5. Numerical relays


technologies

ContentsContents

© 2005. T.S. Sidhu

Implementation of a single phase impedance relay in different relay

technologies

Electrometrical

Static Analgue

Numerical

Input signals

Voltage

Current

Setting

Impedance setting


© 2005. T.S. Sidhu

Impedance Relay CharacteristicsImpedance Relay Characteristics

Impedance relay - circular characteristic with center at the origin

r1

r1 |Z||Z|zz ≤≤

oo 9090 +<<− ψ

Operate

Restrain

δ

Zr1

Zr2

Re

Im

C

Z

Operate

Restrain

Zr1

Zr2

Re

Im

C

Z

ψ

Zr1=Zr2 = Reach settingZ = Vf/If = Measured impedance (fault voltage/fault current)

© 2005. T.S. Sidhu

Impedance Relay Impedance Relay –– Electromechanical Electromechanical

The characteristic can be defined by

Multiplying both sides by I, we get

|Z||Z| r1≤

|IZ||IZ| r1≤

IZr1V

IZ is equal to V, the voltage at the relay location if Z is the impedance from the relay location to the fault

This can be implemented by comparing flux

|IZ||V| r1≤

Balanced Beam constructionBalanced Beam construction

Operate

Restrain

δ

Zr1

Zr2

Re

Im

C

Z

© 2005. T.S. Sidhu

Impedance Relay Impedance Relay –– Electromechanical Electromechanical

The characteristic can also defined by-90o < ψ < +90’o

where ψ is the angle between Z-Zr2and Zr1-ZMultiplying both terms by I, we get

IZ-IZr2 and IZr1-IZ.

+

V-IZr2

+

φo

φ p

IZr1-V

Induction Cup constructionInduction Cup constructionNow substituting IZ by V, we get

V-IZr2 and IZr1-V.The characteristic can now be defined by(V-IZr2)(IZr1-V) cos (ψ)>0

Operate

Restrain

Zr1

Zr2

Re

Im

C

Z

ψ

© 2005. T.S. Sidhu

Impedance Relay Impedance Relay –– Solid StateSolid State

The characteristic of an impedance relay is defined by

||||0 VIZr1 −≤

|IZ||V| r1≤

Impedance magnitude comparatorImpedance magnitude comparator

*Z r1 *(-1)

ADD

Level Detector>

I V

Trip

Convert to dcvoltage

Convert to dcvoltage

0

Operate

Restrain

δ

Zr1

Zr2

Re

Im

C

Z

© 2005. T.S. Sidhu


When ψ is greater than -90o and is less than +90o (the impedance is inside the characteristics), the coincidence between the positive parts of the waveforms is for more than one quarter of the period.

The coincidence logic, therefore, provides a means of providing a phase comparator.

Squaring circuit

V-IZr2

Squaring circuit

Coincidence

90o

Trip

Integrator

Level detector

IZr1-V

Impedance Phase comparatorImpedance Phase comparator

Operate

Restrain

Zr1

Zr2

Re

Im

C

Z

ψ

© 2005. T.S. Sidhu

Phase displacement ψ can also be checked using zero crossing detection technique.

Squaring circuit Phase shifting &Pulse circuits

AND

Trigger circuit

V-IZr2 IZr1-V

Trip

Squaring circuit

V-IZr2

Trip

IntegratedIZr1-V

Level detector

IZr1-V

Zero Crossing detector

Output of AND gate


© 2005. T.S. Sidhu

Single Phase Impedance relaySingle Phase Impedance relay

Impedance Relay Impedance Relay –– NumericalNumerical




DATA

BUS

Power Supply



VT Filtering & Buffer

CT

S/H

Filtering & Buffer

ADC

S/H

Crystal Clock

ADC

DIGITAL

MUX

fromVT

fromCT

To CB

FromPlant

© 2005. T.S. Sidhu




DATA

BUS

Power Supply



Filtering & Buffer S/H

Filtering & Buffer

ADC

S/H

Crystal Clock

ADC

DIGITAl

MUX

To CB

FromPlant

Input VT & CTInput VT & CT


VT

CT

fromVT

fromCT

The input current and voltage is reduced to electronics measurable range. Typical 1 to 5V full scale.

© 2005. T.S. Sidhu




DATA

BUS

Power Supply



S/H ADC

S/H

Crystal Clock

ADC

DIGITAl

MUX

To CB

FromPlant

VT

CT

fromVT

fromCT

Filtering & Buffer

Filtering & Buffer

Filtering & BufferingFiltering & Buffering


Analogue signal conditioning, to make is suitable for digitizing.

© 2005. T.S. Sidhu




DATA

BUS

Power Supply



ADC

Crystal Clock

ADC

DIGITAl

MUX

To CB

FromPlant

VT

CT

fromVT

fromCT

Filtering & Buffer

Filtering & Buffer

S/H

S/H

Sample & holdSample & hold


Sampling - Converting the continuous time analog signal to discrete time analog signal

Holds the signal at the sampled value for digitizing

© 2005. T.S. Sidhu




DATA

BUS

Power Supply



Crystal Clock

DIGITAl

MUX

To CB

FromPlant

VT

CT

fromVT

fromCT

Filtering & Buffer

Filtering & Buffer

S/H

S/H

ADC

ADC

Analog to Digital ConverterAnalog to Digital Converter


Converts the instantaneous current and voltage to equivalent digital value (0s and 1s)

No. of bits representing each value depends on resolution of ADC

© 2005. T.S. Sidhu




DATA

BUS

Power Supply



Crystal Clock

To CB

FromPlant

VT

CT

fromVT

fromCT

Filtering & Buffer

Filtering & Buffer

S/H

S/H

ADC

ADC

DIGITAL

MUX

MultiplexerMultiplexer


Sends digitized current and voltage in turns to the data bus.

Controlled from DSP

© 2005. T.S. Sidhu


DATA

BUS

Power Supply



Crystal Clock

To CB

FromPlant

VT

CT

fromVT

fromCT

Filtering & Buffer

Filtering & Buffer

S/H

S/H

ADC

ADC

DIGITAl

MUX



DSPDSP

Implements distance protection (magnitude, phase comparison, etc) – more in next lectureFind phasor from digital samples

Calculate Impedance

Compare with setting


© 2005. T.S. Sidhu

DATA

BUS

Power Supply

Crystal Clock

VT

CT

fromVT

fromCT

Filtering & Buffer

Filtering & Buffer

S/H

S/H

ADC

ADC

DIGITAl

MUX





Digital Output(Relays)To CB

FromPlant

Digital I/O and Digital I/O and CommunicatonCommunicaton

Digital I/O to issue trip/alarm commands and receive plant status

Communication for local and remote communication / SCADA, DCS


© 2005. T.S. Sidhu

DATA

BUS

VT

CT

fromVT

fromCT

Filtering & Buffer

Filtering & Buffer

S/H

S/H

ADC

ADC

DIGITAl

MUX





Digital Output(Relays)To CB

FromPlant

Power Supply

Crystal Clock

Power Supply & ClockPower Supply & Clock


DC/AC to DC converter to provide power to circuit comments at different rail voltage

Crystal to provide reference clock for digital processing

© 2005. T.S. Sidhu

Any protection can be implemented in all technology

Though technology has evolved from electromechanical to

numerical, each has its own strength

However the flexibility and series of extra features offered by

numerical relays combined with advancements in DSP and

communication has made numerical relays very popular in recent

times


Documents

3171456 Power System Protection-I