we have two 20/25 MVA, 11/33 KV power transformers for 35 MW power plant. And we have the protection relay for transformer (brand: schneider electric, SEPAM 20&80 series). Now we need the parameter setting like over current, over voltage (ANSI code: 50/51, 50N/51N, 50BF, 46, 49RMS, 27, 59, 59N, 81H, 81L, etc.).

what should be the perfect setting of above factor? for example what should be the current of 50/51 at 33KV side? 437A or? please give me the details setting of above.

 

The starting point for any relay setting is the Short Circuit Level (Fault Level) of the bus where your installation battery limit ends. If you are connected to a substation owned by a 400 KV network, get the fault level figures from concerned authority and also relay setting details at their end. Then by using impedance diagram of your own network you can find out short circuit level at each point inside your network. This will give you an idea of PSM (Plug setting multiplier ) to be set on O/C & E/F relays. Also you have to follow time coordination by setting a suitable TMS (Time Multiplier setting)on O/C & E/F relays. This is necessary to ensure that in case of any fault in your network the breaker at your end will act fast to isolate it from outside network and there will not be any nuisance tripping of other network breakers.