1. Faults on 11kV or 33kV power lines can be caused by conductors clashing in wind, breakdown of conductors, tree branches falling, animals or birds, careless drivers, lightning strikes, insulator cracks, or operating errors. 2. Faults can result in damage to equipment from short circuits, fire hazards, loss of system stability and blackouts, and interruption of power to consumers causing revenue loss. 3. Protective relays automatically detect faults and cause circuit breakers to isolate faulty elements to protect the system and may alert operators. Common relays used include overcurrent, earth fault, and differential relays.

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