Over View of Transformer Relay Protection in 132/25 or 66/25 KV railway

INK PLAYLIST : Railway Traction Substation
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About speaker: Atanu Biswas , Master of Engineering specialization in Power Electronics from IIEST Shibpur, Senior Section Engineeer Electrical ,Railway Electrification (RE)
Differential Protection by Differentia Relay:
Relay shall be of high speed type and operates in less than 0.04 s or 40ms
Relay shall not operate at max through current fault
and due to charging magnetization current
Current setting 20% to 80%
Adjustable bias setting at minimum operating current 20%,30% or 40%
Depending upon tap changer
This is connected through Inter tripping relay
Earth leakage protection by Restricted Earth fault Relay :
This is backup protection for internal earth fault
It is very sensitive ,high speed realy
It is provided separately on primary and secondary side
Relay connected to separately mounted current transformer
Relay is adjustable between 20-40% of 5Amp in eual step of 5%
Of T10 Class , Operating time not exceeding 10ms
This is connected through Inter tripping relay
It is also a single pole non directional over current relay
It works on IDMT(Inverse definite time lag) characteristics
Primary and secondary side have separate Overcurrent IDMT relay
There is a separate Instantaneous over current relay of T10 class
Other protective devices
Low oil level alarm
Buchholz relay with alarm and trip contact
Oil temperature indicator with alarm and trip contact
Winding temp. indicator with alarm trip contact

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Thank you so much