Transformer Protection Overview
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Transcript of Transformer Protection Overview
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Transformer Protection Overview
Ahmed Ibraheem
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Transformers Main Faults
Overloads
Short Circuit
Frame Fault
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Overload
Resulted from:
Increase in the number of loads being fedsimultaneously.
increase in the power absorbed by one or
more loads.
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Overload
Effect:
It results in an overcurrrent of long durationcausing a rise in temperature that isdetrimental to the preservation of insulationand to the service life of the transformer.
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Overload
Protection:
The secondary circuit breaker (B) LV Side should trip at time tb.
In case of malfunction of circuit
breaker (B), circuit breaker (A)should trip at time ta=tb+t.
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Short Circuit
Resulted from:
Internal Short Circuit
External Short Circuit
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Short Circuit
Internal Short Circuit:
Faults occurring between winding conductors
with different phases.
Faults in the same winding
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Short Circuit
Effect:
Winding damage and then fire.
The arc causes the emission of decompositiongas in oil transformers.
That can destroy the winding and also the tankframe by the spread of burning oil.
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Short Circuit
External Short Circuit:
Faults occurring in the downstream
connections:
Phase to phase fault
Phase to ground fault
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Short Circuit
Effect:
Produces electrodynamic forces In the
transformer that are liable to affect thewindings mechanically and then develop inthe form of internal faults.
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Short Circuit
Protection:
a Buchholz relay, DGPT or DMCR that are sensitive
to gas release or oil movement is used.
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Short Circuit
Protection:
Differential transformer
protection ensures rapidprotection against phase-to-phase faults. It is sensitiveto fault currents in therange of 0.5 In and is usedfor important transformers.
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Short Circuit
Protection:
An instantaneous overcurrent
protection device located at thetransformer primary is used.
Discrimination between upstream& downstream protection relaysshould be considered
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Short Circuit
Protection:
for low power transformers, a fuse is used for
overcurrent protection.
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Tank frame faults
Resulted from:
Between the winding and the tank frame.
Between the winding and the magnetic core.
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Tank frame faults
Effect:
Causes gas emission in oil transformers. Like
internal short circuits, it can causetransformer damage and fire.
The amplitude of the fault current dependson the grounding systems, and also on theposition of the fault within the winding.
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Tank frame faults
Delta Connection the frame current
varies between 50and 100% of themaximum valuedepending onwhether the faultis in the middle or
at the end of thewinding.
Star Connection The frame
current variesbetween 0 andthe maximumvalue dependingon whether thefault is at theneutral or phaseend of thewinding.
Effect:
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Tank frame faults
Protection:
Using an instantaneous
overcurrent protectiondevice installed on theframe earthingconnection.
The transformer tank hasto be isolated from theground.
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Tank frame faults
Protection:
Earth protection located on the upstreamsystem for frame faults affecting thetransformer primary.
Earth fault protection located on the incomingline, if the neutral of the downstream systemis earthed on the busbars.
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Tank frame faults
Protection:
They are only sensitive to phase-to-earthfaults located in the transformer or on theupstream and downstream connections.
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Tank frame faults
Protection:
Restricted earth protection if the neutral of
the downstream system is earthed at thetransformer.
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Tank frame faults
Protection:
This is a high impedance differential
protection system which detects thedifference in residual currents measured atthe grounding point and at the three phasetransformer outlet.
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Tank frame faults
Protection:
Neutral earth
protection if thedownstream systemis earthed at thetransformer
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Protection Summary
MV/LV Transformers
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Protection Summary
MV/MV Transformers