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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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