Page 319 - Practical Power System and Protective Relays Commissioning

Protection Relays Settings Chapter | 19 313

P set
I set on Relay 5 p ffiffiffi
3V L :cos φ
3:33 3 10 3
5 p ffiffiffi
3 3 22 3 0:8
5 109:237 A
109:237
5
I set secondary
13000
5 8:4mA
t set 5 15 seconds
Action:

1. Trip HV CB 220 kV of T 1 ;
2. Generator excitation trip;
3. Incoming 6.6 kV of T 2 trip.

Subchapter 19.7

Switchgear (Busbar) Protection Settings

19.7.1 INTRODUCTION

The busbars in substations are a very important part of the system and should
have adequate protection, however this protection is very expensive in 11 kV
and 22 kV, and the faults in busbars are rare, therefore it is used in 66 kV
systems and above as essential protection.
The most commonly used scheme for busbar protection is high-
impedance differential protection.

19.7.2 WORKED EXAMPLES FOR BUSBAR PROTECTION
One hundred and thirty-two kiloVolts busbars have two sections and a bus
coupler CB, each busbar has one feeder and an incomer transformer (as
shown in Fig. 19.7.1).
CT ratios:
CT 1 ,CT 2 ,CT 3 ,CT 4 ,CT 7 ,CT 8 ,CT 9 ,CT 10 -1200/1 R CT 5 2.9 Ω
I mag 5 40 mA at V 5 130 V I mag 5 35 mA at V 5 125 V CT ratios:
CT 5 ,CT 6 -1500/1
R CT 5 3.1 Ω
I mag 5 45 mA at V 5 130 V
Lead resistances:
R 1 5 0.3 Ω R 4 5 0.32 Ω R 7 5 0.33 Ω