basic relaying

8/8/2019 Basic Relaying

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Florida Reliability Coordinating Council

Relay ClassRelay Class

John White

System Protection Manager

Ray Dawson

System Protection Technician

Introduction The reasons for protection

Safety of the public and employees.

Reliability of power supply to thecustomers.

Prevent damage to equipment.

What kind of equipment isprotected: generators, transformers,

transmission lines, breakers anddistribution lines.


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Types of faults

Three phase, three phase to ground,phase to phase, phase to phase to groundand single phase to ground.

Three phase faults have the highest faultcurrent.

Single phase faults have the lowest faultcurrent.

The fault current is determined by theimpedance of the fault path.

Fault paths closer to the source will have

less impedance. Faults caused by trees will have higherimpedance.

Equipment used CT current transformer

PT potential transformer

Transducers

Time overcurrent relay/51

Instantaneous Over current relay/50

Undervoltage relay/27

Recloser relay/79 Under frequency relay/81


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CT current transformer The secondary winding has a standard

rating of 5 amp. Its indicated as 400/200/5the 400 and 200 are the primary currentwhich gives us an 80 to 1 and 40 to 1 ratiorespectably.

It is important that CTs be accurate at faultlevels which may be 10 times normal loadcurrent. Standard classifications of CTsallow 10% error for current flow up to 20times rated value. They are marked ClassC ###. The higher the number the highercurrent that can flow though the CT and

still be 10% accurate. Never open a live CT circuit without firstshorting the secondary side. Without thesecondary side shorted very high voltagewill be seen on the secondary circuit.

Potential Transformers PTs The secondary voltage is usually

69V for relaying and 120V formetering.

There is no problem with errorreadings as during a fault thevoltage will drop.

At above 115KV coupling capacitorsare used. This is called CCVT. Theyare connected in series causing a

voltage drop across each cap. PTs should never be shorted.


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Transducers Measure voltages and currents and

converts them to a 0 to 1 milliamp dcoutput.

A scaling is used in SCADA(supervisory control and dataacquisition) to convert the milliampsignal to a numerical number.

Time Over current relay/51

Operate on the electromagnetic inductionprinciple. The protective relay isessentially a small AC motor. Usingshaded pole produce two fluxes that are atdifferent phase angles.

When current is passed through theelectromagnet coil,a magnetic field isproduced, which applies a torque to thedisc. When the magnetic field becomesstrong enough to overcome friction in the

damping magnet, bearing and tension inthe spiral spring, the disc rotates to movethe moving contact. Eventually the movingand fixed contacts close, completing thetrip coil circuit to the breaker.


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Time Over current relay/51 The disc rotates at a speed directly

proportional to the amount of fluxinduced into it by the electromagnet.

The time dial provides adjustment forhow long it takes the moving contact andstationary contact to make contact. Witha higher number on the time dial, thisincreases traveling distance and contacttime.

The spiral spring is use to set minimumpickup, resets the disc in normal

conditions or after a trip and provides atemporary path for the DC trip current.The spiral spring is not designed to carrythe trip current for very long. A seal-inbypass is used.


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Time Over current relay/51 The seal in coil is in series with the

contacts on the spiral spring. Theseal in coil contacts are in parallelwith the spiral spring contacts. Theseal in contacts shunt the currentaway from the spiral spring contacts.

The seal in coil also has a flag that

drops to indicate which relay had theovercurrent condition.


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Instantaneous Over current relays/50 Instantaneous relays have no time

delay. With a high level fault theinstantaneous unit will operatebefore time overcurrent relay.

Its a simple clapper relay with acore screw on top to adjust thepickup range.

The contacts are two moving contacton a bridge and two stationarycontacts. The contacts are directlyacross the trip circuit for thebreaker.

Undervoltage relays/27 The construction of a undervoltage relay

is very similar to an overcurrent relay. Themain different is the operating coil. Anovercurrent relays operating coil iswound with a few turns of heavy wire. Avoltage relays operating coil is woundwith many turns of fine wire.

The disc rotates in the counterclockwisedirection.

The contact closing torque for an

undervoltage relay is provided by thetension in the spiral spring. A time delay is the same as for an over

current relay.


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DEVICES USED AT OUC 21 Distance relay

25 Synchronizing-check device 27 Undervoltage relay 43 Manual transfer or selector device 50 Instantaneous overcurrent relay 51 Time overcurrent relay 52 AC circuit breaker 57 Grounding device 59 Overvoltage relay 63 Gas pressure relay 64 Ground protective relay 67 AC directional overcurrent relay 69 Permissive control device 74 Alarm relay 79 Reclosing relay 81 Frequency relay 86 Locking-out relay 87 Differential protective relay

The right man for the job

Mr. Bill Douglas


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OUC SYSTEM

OUC Protective Relay Statistics

60 Transmission Lines

4000 Protective Relays

36 Substations

14 Generators

400 Breakers 200 Transformers

200 Feeder Breakers


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OUC Protective Relaymain schemes

Protects Transmission Lines

Protects Distribution Lines

Protects Transformers

Protects Generators

Protects Busses Protects Reactors


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Stanton Substation


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S**t Happens


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FAULTCHARACTERISTICS

Two Phase to Ground

Three Phase to Ground

Phase to Phase

Phase to Phase to Phase

Single Phase to Ground

TYPES of FAULTS :

Test Question # 11

Impedance Diagram

Voltage= 22800 volts Load Z (one leg)= 70 ohms I= 300 amps

FAULT

Test Question # 12: 22800 volts / 3 ohms of fault impedance= 7600 amps.


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Ground current possibly damages generator before 50 G relay

operates.

Ground Fault Current circulates from the load to the generator

stator unimpeded.


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Resistance, Reactance, ImpedanceResistance, Reactance, Impedance

ResistanceResistance--(R)(R) The opposition to the flow ofThe opposition to the flow of

current in an electrical circuitcurrent in an electrical circuit..

ReactanceReactance--(X)(X) A measure of opposition to aA measure of opposition to asinusoidal current made up of Capacitance and inductancesinusoidal current made up of Capacitance and inductance

ImpedanceImpedance-- (Z)(Z)Combination of Resistance andCombination of Resistance andReactance that opposes flow of current.Reactance that opposes flow of current.

Test Question # 13Test Question # 13

Test Question #14: Reactor/Resistor limits fault currentto about 10 amps preventing damage to stator.


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Utility standard of Delta Wye configuration for GSU

transformer prevents fault current from circulating through

stator.

GSU boosts voltage for ease of transmission- 20kV to230kV.

During fault Voltage A-n collapses and Current A-n increases dramatically.

Voltages and Currents are 120 degrees between phases.


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Disturbance recording

File: J:\System Protection\Faults and oscillographys\SECA 6,20,03\SECA,6,20,03.

VA

VB

VC

IA

IB

IC

R1 Trip Brkr 757

R2 Trip Brkr 759

R3 SCADA RS1 Op

R6 757 RI N/A

R7 759 RI N/A

R9 757 BF Init

Part of System Protections

responsibilities is to analyze faultdata acquired from the

microprocessor based protective

relays such as the examplesshown.

Generator Protection

507

509

150,000 volt

Breaker

OUC uses high speed generator schemes that isolates the fault inthe Generator in approximately 2 cycles clearance (.033seconds).

150,000 volt

Breaker

FAULT

Generator GSU

Transformer

To OUC

system

Generator Relay


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GENERATORPROTECTION

Rotor Ground

Excitation Failure

Over-voltage/ Over-excitation

Turbine Trip

Motoring by loss of Prime Mover

TYPES of Generator Faults :

Test Question # 15

Stator Fault

87G- Generator

Differential

87T- GSU Transformer

Differential

87ST- Reserve

Auxiliary Differential.


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40- Loss of Field Relay

81- Under frequency

Relay59-Under Voltage

Relay.With loss of field condition, Generator cannot

produce VARS, lowering terminal voltage and

overheating of the stator.

Test Question #16:

VAR= Volt Ampere

Reactive

46- Negative Sequence

Relay


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59G- Generator GroundRelay

27G- Third harmonicsupervision Relay

Test Question #

17:

Third Harmonic is

at 180 HZ

TRANSFORMER

PROTECTION

Core Movement

Bushing Failure

Arrestor Failure

Through Fault

Winding to Ground Fault

Types of Transformer Faults :

Test Question # 18

Winding to Winding Fault


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Transformer Protection Relay Set 1 and 2 are high speed current differential schemes isolates

the faulted transformer. Approximately 2 cycle clearance (33milliseconds)

KBCH digital Current Differential relays for RS1.

T60 GE microprocessor Current Differential for RS2

Also uses Backup Overcurrent Protection in RS2

XFMR

FAULT

SWGR

Differential relay

10

507

509

Transformer Damage Curve

Test Question # 19:

Transformer damaged in 50seconds at 20,000 Amps


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Transformer Differential Relay

General Electric

T60 UR Differential

relay

Primary Current Flow

Normal Operation


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Fault Current Flow

Fault Condition

Transformer Protection

OUC uses a high speed current differentialscheme that isolates faulted substationtransformers in approximately 2 cyclesclearance (.033 seconds)

FAULT

Differential relay

10

507

509

150,000 volt

Breaker

13,000 volt

Breaker

150,000 volt

Breaker

To customersswitchgear

transformer


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TRANSMISSION LINE

PROTECTION

Arrestor Failure

Types of Transmission Line Faults :

Test Question # 22

Two Phase to Ground

Three Phase to Ground

Phase to Phase

Phase to Phase to Phase

Single Phase to Ground

Through Fault


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Transmission Line Protection

Relay Set 1 is high speed current differential schemes isolates

the faulted segment of a transmission line. Approximately 2 cycleclearance (33 milliseconds)

L90 digital Current Differential relays used by OUC.

Also uses Direct Transfer Trip for Breaker Failure

L90

FAULT

L90Fiber communication

501

503

507

509

Transmission Line Protection OUC uses high speed current differential

schemes that isolates the faulted segmentof a transmission line in approximately 2cycles clearance (.033 seconds).

FAULT

Fiber communication

501

503

507

509

The relays communicate over the OUC fiberOptic Network

Transmission BreakerTransmission Breaker

Transmission BreakerTransmission Breaker

Transmission Line

Protective Relay Protective Relay


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Transmission Line Protection Relay Set 2 is high speed directional impedance relay that isolates the

faulted segment of a transmission line using Permissive OvereachTransfer Trip

P442

FAULT

P442Zone 1 95 % of line

501

503

507

509

T1T1

Zone 2 125 % of line

Test Question # 23:

Zone 1 set at 95% of transmission line

Zone 2 set at 125% of transmission line

Directional distance relay

Substation

Remote Substation

Length of Line = 10. 7 miles

Line Impedance Positive sequence - .20 + j 1.11Zero sequence - 1.97 + j 3.55


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Under Load Conditions no Tripoutside of zone.

During fault, impedance moves into trip zone

For short transmission lines we use Reactance Relays that operate

at 90 degrees between voltage and current.


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Line Current Differential Relay

General Electric L90 UR Relay

Line Current Differential Relay


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Line Current Differential Relay Trip Conditions

Fault


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Description of Substation Automation

REMOTE TERMINALUNITS

RELAYS

ENERGYMANAGEMENT

SYSTEM

OUC

INTRANET

REMOTE TERMINALUNITS

RELAYS

PROGRAMMABLELOGIC

CONTROLLERS

MODEM

LINE

PERSHING OPERATION S CONTROL CENTER

CORPORATEUSER

OUC

CUSTOMER

INTERNET

Firewall

CORPORATE NETWORK

SUBSTATION

SUBSTATIONAUTOMATION

SYSTEM

REMOTE(EMERGENCY)

CONTROL ROOM

MODEMLINE

BACKUP ENERGYMANAGEMENT

SYSTEM

ENERGYMANAGEMENT

SYSTEM

FUTURESYSTEMS

Firewall

TRANSMISSION

SYSTEM

WIDE AREA NETWORK

(ALL SUBSTATIONS)

Comparison of Electro-Mechanical to Microprocessor-Based Protective

Relays


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Lower Cost

Easier to Test

Advantages of Electromechanical

Disadvantages of Electromechanical

Need three individual relays

Maintain more often

Moving Parts

Usually performs only one protective function

Slower operating than Micro-Processor Based

Test Question # 24:

Performs hundreds of protective functions

Only one relay needed for all phases

Advantages of Micro-Processor Based

Disadvantages Micro-Processor Based

Higher Cost

Complex training for testing

Faster operating than Electromechanical

Self-Monitoring

Takes up less space

Longer maintenance cycle

Test Question # 25:


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How a Micro-Processor Based Relay works.

It takes an analog signal from PTs and CTs and convertsit into digital data for analysis.

Test Question # 26:


Analog data under Sine Wave isconverted to digital data andanalyzed by the processor


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Analog dataConverted into Digital samples

The microprocessor in the relay analyzes millions of bitsof data per second and determines if the amplitude issufficient to trip. All in 18 milliseconds or less.

Customer Feeder Protection

FAULT

Main relay

1011

Feeder relay

501

503

13,000 volt

Breaker

150,000 volt

Breaker

150,000 volt

Breaker

13,000 volt

Breaker

transformer

switchgear

OUC uses a high speed microprocessor feederrelay that isolates faulted customer feeder inapproximately 3 cycles clearance (.050 seconds)

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