Relay & Protection

1. RELAY & PROTECTION

2. NATURE AND CAUSES OF FAULT IN 11 KV OR 33 KV LINE
• Conductors clashing in the wind
• Breakdown of Conductor
• Tree branches falling on overhead conductors
• Aanimals or birds getting curious
• Careless motor vehicle drivers
• Lightning strikes
• Insulator Crack
•
• Operating error : leaving earths connected etc
• Some are more permanent:

3. Effects of faults
1. Heavy Short circuit current may cause Damage of
equipment
2. Fire Hazards
3. Loss of system stability , Individual generator in power
system may lose synchronism, resulting in a complete
shutdown of power system ( BLACK OUT)
4. Interruption of supply consumer, thereby causing a loss
of revenue

4. PROTECTIVE RELAY
 A automatic Device which detects an abnormal
condition in an electrical circuit and causes a circuit
breaker to isolate the faulty elements of the system
and may gives alarm to alert operator.
Line CT Relay Trip coil
Circuit
Breaker

5.  MCGG 52/82
MiCOM
 P121/122
 CDG
OVER CURRENT AND EARTH FAULT RELAY USED
IN WZPDCL AREA

6. CIRCUIT DETAILS OF 3 O/C AND 1 E/F RELAY( MICOM
(P121/122)

7. CIRCUIT DETAILS OF 3 O/C AND 1 E/F RELAY
(MICOM MCGG 52

9. PROTECTION RELAYS – SETTINGS
Pick up setting Low set
High set
Time delay setting Definite time
Inverse time
% of CT
Rating
TMS
Setting

12. PROTECTION OF FEEDER AND SUBSTATION
S.No. Voltage Protection Scheme
1. 33 KV lines 3 or 2 phase Over current and 1 earth fault relays.
2. 11 KV lines 3 or 2 phase Over current and 1 earth fault relays.
Voltage ratio & capacity HV Side LV Side Common relays
1 33/11KV upto 8 MVA 3 O/C relays + 1 E/F
relay
3/2 O/C relays + 1 E/F
relay
Buchholz, OLTC
Buchholz, OT, WT
2 33/11KV above 8 MVA and
below 31.5 MVA
3 O/C relays + 1 dir. E/F
relay
3 O/C relays + 1 E/L
relay
Differential,
Buchholz, OLTC
Buchholz, OT, WT

13. RELAY SETTING BASIC
Feeder Load
3 MW
CT ratio 300/5

14. CAUSES OF DIFFERENTIAL FAULT
Winding to winding fault
Winding to Core fault
Relay loose it selectivity
CT problem
Necessary Action after Differential Fault:
Insulation test ( by 5KV Magger )
Open Circuit Test
Short Circuit test
Winding DC resistance test