Relays for Transformer protection

Voltage Ratio andCapacity of Transformer

Relays on HV Side Relays on LV Side CommonRelays

1 11/132 KVGenerator Transformer

3 nos Non-Directional O/L Relay1 no Non-Directional E/L Relayand/or standby E/F + REF Relay

– - Differential Relay orOverall differential RelayOverflux RelayBuchholz RelayOLTC Buchholz RelayPRV RelayOTTrip RelayWT Trip Relay

2 13.8/220 KV

15.75/220 KV

18/400 KV

21/400 KV

Generator Transformer

3 nos Non-Directional O/L Relay1 no Non-Directional E/L Relayand/or standby E/F + REF Relay

– - Differential Relay orOverall differential RelayOverflux RelayBuchholz RelayOLTC Buchholz RelayPRV Relay

OTTrip RelayWT Trip Relay

3 220 /6.6KVStation Transformer

3 nos Non-Directional O/L Relay1 no Non-Directional E/L Relayand/or standby E/F + REF Relay

3 nos Non-Directional O/L Relay

Differential RelayOverflux RelayBuchholz RelayOLTC Buchholz RelayPRV RelayOT Trip RelayWT Trip Relay

4 Gen-volt/6.6KV UAT 3 nos Non-Directional O/L Relay

3 nos Non-Directional O/L Relay

Differential RelayOverflux RelayBuchholz RelayOLTC Buchholz RelayPRV RelayOT Trip RelayWT Trip Relay

5 132/33/11KV upto 8 MVA

3 nos O/L Relay1 no E/L Relay

2 nos O/L Relays1 no E/L Relay

Buchholz RelayOLTC Buchholz RelayPRV RelayOT Trip RelayWT Trip Relay

6 132/33/11KV above 8 MVA &below 31.5 MVA

3 nos O/L Relay1 no Directional E/L Relay

3 nos O/L Relay1 no E/L Relay

Differential RelayBuchholz RelayOLTC Buchholz RelayPRV RelayOT Trip RelayWT Trip Relay

7 132/33KV, 31.5 MVA & above

3 nos O/L Relay1 no Directional E/L Relay

3 nos O/L Relay1 no E/L Relay

Differential RelayOverflux RelayBuchholz RelayOLTC Buchholz RelayPRV RelayOT Trip RelayWT Trip Relay

8 220/33 KV, 31.5MVA &50MVA 220/132KV, 100 MVA

3 nos O/L Relay1 no Directional E/L Relay

3 nos O/L Relay1 no Directional E/L Relay

Differential RelayOverflux RelayBuchholz RelayOLTC Buchholz RelayPRV RelayOT Trip RelayWT Trip Relay

9 400/220KV 315MVA 3 nos Directional O/L Relay

3 nos Directional O/L Relay

Differential RelayOverflux Relay

(with dir.highset)1 no Directional E/L relay.Restricted E/F relay3 nos Directional O/L Relay foraction

(with dir.highset)1 no Directional E/L relay.Restricted E/F relay

Buchholz RelayOLTC Buchholz RelayPRV RelayOT Trip RelayWT Trip Relay

Over Load