The attached picture shows the use of unit protection where differential relays areprotecting...

Question

The attached picture shows the use of unit protection where differential relays are protecting
transformers. For each of the circuit
eaker configurations:(i) CB A open and CB B closed(ii)
CB A closed and CB B open(all other CBs closed)(a) To a base of 10 MVA determine initially
the fault levels at the 11 kV and 3.3 kV bus bars for a fault at the transformer, T1, output as
shown.(b) Determine the cu
ent settings and TMSs for the relays shown if the operating time of
the directional over cu
ent relays on the 3.3 kV side of the transformers is 0.5 s. (Use a 0.4 s
discrimination...

David · Accepted Answer

The attached picture shows the use of unit protection where differential relays are protecting 
transformers. For each of the circuit breaker configurations:(i) CB A open and CB B closed(ii) 
CB A closed and CB B open(all other CBs closed)(a) To a base of 10 MVA determine initially 
the fault levels at the 11 kV and 3.3 kV bus bars for a fault at the transformer, T1, output as 
shown.(b) Determine the current settings and TMSs for the relays shown if the operating time of 
the directional over current relays on the 3.3 kV side of the transformers is 0.5 s. (Use a 0.

The attached picture shows the use of unit protection where differential relays areprotecting transformers. For each of the circuit breaker configurations:(i) CB A open and CB B closed(ii) CB A closed...

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