Improving the reliability of feeder protection using digital relays

By

Improving the Reliability of Feeder protection using

Digital relays

Sudarshan ReddyElectrical Engineer InternMill Electric Bagdad

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Protective Relaying is one of several features of the power system design that is concerned with minimizing damage to equipment and interruptions to service when electrical, mechanical, or natural failures occur.

Functional characteristics of Protective relaying Types of Protective relays

Definition of Protective Relaying

Electro-mechanical relay Solid-state relay Digital relay

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Natural causes

Why do we need protective relaying

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Who’s Minding the Store?

If the Controllers and State Estimators are the Watchdogs of our Electric System and

the Breakers are the Muscle –

Protective Relaying is the Brain of our System

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Protective relays – Personal safety

Arc-FlashReasons for Arc-FlashArc Flash- HazardsMethods to reduce Arc-Flash

Hazardi. Enable instantaneous settingsii. Arc-Flash detectioniii. Fast bus trip scheme

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CT saturation can be minimized One digital relay can replace a bank of analog devices Self monitoring and time stamped event recording Communication using Modbus Custom functions can be programed Improved performance

Do we need Digital relays?

Solid-state relayDigital relay

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Feeder protection

50 51 50 50 5051 51 51

5150

GE MULTILIN 850 GE MULTILIN 850 GE MULTILIN 850 GE MULTILIN 850

GE MULTILIN 850

B1

B2 B3 B4 B5

115Kv

12.47Kv

12.47Kv

Reclaim System Conveyor systemPIT loop SX and PIT area

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Factors to be considered in Feeder protection

Fault current CT ratio Protective relay characteristics Cable Ampacity Load current Protective device ratings Coordination

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Coordination

100 1000 10000 1000000.01

0.1

1

10

100

1000

Current(A)

Tim

e in

sec

Fuse melting curve

ANSI very in-verse curve

ANSI very in-verse curve

B1

B3

50 51

50 51

utility

XFMR115/12.47Kv

CT 2000:5

Fuse

Breaker

=2,000A

B1

B3

Solid state Relays Cost of each Relay = $2,500 Total cost of relays for each

feeder = 2,500*3= $7,500

Wiring cost = $500 Cost of Maintenance = $ 1000 Takes more time to Install Total Cost of protection of

each feeder= $9,000

Digital Relays Cost of each Relay = $6,300 Total cost of relays for each feeder = 6,300*1=

$6,300 Wiring cost = $400 Cost of Maintenance = $

800 Takes less time to Install Total Cost of protection of

each feeder= $7,500

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Cost benefits

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Mining Industry – Electricity Reliability Safety is Increased

Conclusion

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