Wednesday, September 18, 2013

Different protective relays



 Different protective relays are used for different power system equipment protection
Now let’s have a look on which different protective relays are used in different power system equipment protection schemes
Relays for Transmission & Distribution Lines protection
SL
Lines to be protected
Relays to be used
1
400 KV
Transmission Line
Main-I: Non switched or Numerical Distance Scheme

Main-II: Non switched or Numerical Distance Scheme
2
220 KV
Transmission Line
Main-I: Non switched distance scheme (Fed from Bus PTs)

Main-II: Switched distance scheme (Fed from line CVTs)

With a changeover facility from bus PT to line CVT and vice-versa.
3
132 KV
Transmission Line
Main Protection: Switched distance scheme (fed from bus PT)

Backup Protection: 3 Nos. directional IDMT O/L Relays and
1 No. Directional IDMT E/L relay.
4
33 KV lines
Non-directional IDMT 3 O/L and 1 E/L relays.
5
11 KV lines
Non-directional IDMT 2 O/L and 1 E/L relays.
Relays for Transformer protection
SL
Voltage Ratio and
Capacity of Transformer
Relays on HV Side
Relays on LV Side
Common
Relays
1
11/132 KV
Generator Transformer
3 nos Non-Directional O/L Relay
1 no Non-Directional E/L Relay
and/or standby E/F + REF Relay
– -
Differential Relay or
Overall differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT
Trip Relay
WT 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 Relay
1 no Non-Directional E/L Relay
and/or standby E/F + REF Relay
– -
Differential Relay or
Overall differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT
Trip Relay
WT Trip Relay
3
220 /6.6KV
Station Transformer
3 nos Non-Directional O/L Relay
1 no Non-Directional E/L Relay
and/or standby E/F + REF Relay
3 nos Non-Directional O/L Relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
4
Gen-volt/6.6KV UAT
3 nos Non-Directional O/L Relay
3 nos Non-Directional O/L Relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
5
132/33/11KV upto 8 MVA
3 nos O/L Relay
1 no E/L Relay
2 nos O/L Relays
1 no E/L Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
6
132/33/11KV above 8 MVA &
below 31.5 MVA
3 nos O/L Relay
1 no Directional E/L Relay
3 nos O/L Relay
1 no E/L Relay
Differential Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
7
132/33KV, 31.5 MVA & above
3 nos O/L Relay
1 no Directional E/L Relay
3 nos O/L Relay
1 no E/L Relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
8
220/33 KV, 31.5MVA &
50MVA 220/132KV, 100 MVA
3 nos O/L Relay
1 no Directional E/L Relay
3 nos O/L Relay
1 no Directional E/L Relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
9
400/220KV 315MVA
3 nos Directional O/L Relay
(with dir.highset)
1 no Directional E/L relay.
Restricted E/F relay
3 nos Directional O/L Relay for
action
3 nos Directional O/L Relay
(with dir.highset)
1 no Directional E/L relay.
Restricted E/F relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay

Over Load (Alarm) Relay
Points to be remembered in respect of protection of transformers
i. No Buchholz relay for transformers below 500 KVA capacity

ii. Transformers up to 1500 KVA shall have only Horn gap protection

iii. Transformers above 1500 KVA and upto 8000 KVA of 33/11KV ratio shall have one group control breaker on HV side and individual LV breakers if there is more than one transformer.

iv. Transformers above 8000 KVA shall have individual HV and LV circuit breakers.

v. The relays indicate above shall be provided on HV and LV

vi. LAs to be provided on HV & LV for transformers of all capacities and voltage class.

vii. OLTC out of step protection is to be provided where Master follower scheme is in operation

viii. Fans failure and pumps failure alarms to be connected.

ix. Alarms for O.T., W.T., Buchholz (Main tank & OLTC) should be connected.