Overview of Protection Fundamentals-Trg School

8/4/2019 Overview of Protection Fundamentals-Trg School

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Overview Of ProtectionFundamentals


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Classification Of Relays

Protective relays

Monitoring Relays Programming relays

Regulating Relays

Auxiliary Relays


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Design Criteria

Reliability- the ability to act correctly when

needed (Dependability) & to avoid mal-operation (Security)

Speed min. fault time & damage

Selectivity max. service continuity

Economics max. protection at min. cost

Simplicity- min. equipment & circuitry.


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Protective Relaying Vs Station Operator

During abnormal conditions that developslowly, alert & skillful operator may be able toavoid unnecessary trips.

Protective Relaying should give only alarms.

Where quick & accurate action is required, it

is unwise to rely on operator. Also, under such conditions operator has so

many other things to do.


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Undesired Tripping Vs Failure to Trip

when Desired

When you are asked to choose between the

chance of undesired or unnecessary trippingand failure to trip when tripping is desired,which one do you choose?


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Undesired Tripping Vs Failure to Trip

when Desired

Best practice is to choose the former i.e the

chance of unnecessary tripping. Failure to trip has been the worst offender


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How do protective relays operate?

Relays operate by virtue of the current and/or

voltage supplied to them by current andvoltage transformers connected in variouscombinations to the system element that is tobe protected.


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Zones of Protection

The power system is divided into protective

zones for:Generators

Transformers

Buses

Transmission & distribution circuits

Motors


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Device Numbers

21 - Distance Relay

27

Under Voltage Relay32 Power Relay

37 Under Current or under Power Relay

40

Field Failure Relay49 Thermal Relay

50 Instantaneous Over Current


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Device Numbers

51 Time Over Current Relay

59

Over voltage relay60 Voltage or Current balance relay

64 Ground protective relay

78

Out of step protective relay81 Frequency relay

85 Carrier or pilot-wire receiver relay


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Device Numbers

86 Locking out relay

87

Differential protective relay94 Tripping or trip-free relay


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Applying Protective Relays

Information on the following areas needed:

- System Configuration

- Existing System protection and its difficulties

- Existing Operating procedure and practices

- Degrees of protection required

- Fault study

- Maximum load and current transformer ratios

- VT locations, connections & ratios

- Impedance of the lines and transformers


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Classification of Relays on

Technology

Electromechanical

Analogue

Numerical

Digital

Static

RELAYS


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Classification of Relays on Technology

Electromechanical Relays

- use magneto motive force

- have moving parts- hinged armature & disc

Static Relays

- no moving parts in the measuring element

- designed using electronics

- can have output elements with moving parts(miniature relays)


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Electromechanical Relays

- use magneto motive force

- have moving parts- hinged armature & disc

Static Relays

- no moving parts in the measuring element

- designed using electronics

- can have output elements with moving parts(miniature relays)


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Static RelaysDue to evolution in electronics static relaysare further divided into:

- Static Analogue

- Static Digital

- Static Numerical


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Static Analogue Relays

- Static relays designed using analogue electroniccomponents.

- The input signals fed to analogue measuringelements like comparators, operational amplifiers

etc.- compare input analogue signal with referencesignal & generate output signal


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Static Digital Relays

- Static relays designed using digital electroniccomponents.

- The input analogue signals converted into digitalsignals using A/D converters and fed to digital

comparators.- compare digital signal with reference signal &generate output signal


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Static Numerical Relays

- are also digital relays- The input analogue signals converted into digital signals usingA/D converters and fed to the microprocessor directly.

- Entire protection element realised using software programs.

- Application software stored in non-volatile memory.

- Input signals continuously sampled & stored in memory.


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Technology comparison for Protective Relays

Sl.No.

Subject Electro-mechanical

Static/Electronic Numerical

1. MeasuringElements/Hardware

Induction disc,Electromagnets,Induction cup,Balance beam

Discrete R, L, C,Transistors,Analogue ICs,Comparators

Microprocessors, Digital ICs,Digital SignalProcessors

2. Constructionsize

Bulky Modular, Compact Most compact

3. Parametersetting

Plug setting, Dialsetting

Thumb wheel,Potentiometers,Dual In Line

switches

Keypad forNumericalvalues


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Technology comparison for Protective Relays continued

Sl.No.


Static/Electronic

Numerical

4. CT Loading/burden

8-10 VA 1 VA < 0.5 VA

5. Self monitoring No Yes

.Hardware

partially

.Power supply

Yes

.Hardware

.Power supply

.Output relays

.Software

.CT, PT, Ckts


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Sl.No.



6. Calibration Frequentlyrequired assettings driftdue to ageing

Required assettings drift due toageing

Not required assettings are storedin memory in digitalformat

7. Electromagnet

ic/electrostatic/HFdisturbance

Immune Susceptible Immune

8. Multiplecharacteristics

Not possible Not possible Possible


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Sl.No.



9. Integratedprotectivefunctions



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Sl.No.


Static/Electronic

Numerical

15. Range of settings Limited Wide Wide16. Operational value

indicationNot possible Possible Possible

17. Fault disturbancerecording


18. Digitalcommunication port

Not possible Not available Available

19. Commissioningsupport from relay

No No Yes

Overview of Protection Fundamentals-Trg School

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