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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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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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Classification of Relays on Technology
Static RelaysDue to evolution in electronics static relaysare further divided into:
- Static Analogue
- Static Digital
- Static Numerical
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Classification of Relays on Technology
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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Classification of Relays on Technology
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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Classification of Relays on Technology
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.
Subject Electro-mechanical
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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Technology comparison for Protective Relays continued
Sl.No.
Subject Electro-mechanical
Static/Electronic Numerical
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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Technology comparison for Protective Relays continued
Sl.No.
Subject Electro-mechanical
Static/Electronic Numerical
9. Integratedprotectivefunctions
Not possible Not possible Possible
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Technology comparison for Protective Relays continued
Sl.No.
Subject Electro-mechanical
Static/Electronic
Numerical
15. Range of settings Limited Wide Wide16. Operational value
indicationNot possible Possible Possible
17. Fault disturbancerecording
Not possible Not possible Possible
18. Digitalcommunication port
Not possible Not available Available
19. Commissioningsupport from relay
No No Yes