Page 360 - Practical Power System and Protective Relays Commissioning

Protective Relays Testing and Commissioning Chapter | 20 355

The tests in Sections 20.6.1 and 20.6.2 are repeated for the check
zone if a separate CT is provided for this check zone.
5. CT supervision test
This unit is overcurrent relay and is set to monitor the differential circuit
for each phase and to give an alarm after a time delay of about 3 seconds
when one CT secondary circuit is detected as open and to switch off that
zone of the busbar protection. This can be tested by injecting a current
greater than the required setting for 3 seconds then checking the operation of
the relay to SC the buswires which this CT is connected to and putting this
faulty zone of the CT out of service.

Subchapter 20.7

Synchronizing Relay Testing and

Commissioning

20.7.1 INTRODUCTION

When there are two parts of a power system network, each has a separate
generation to be connected together. This connection should avoid any
damage to the power system components or shock loads.
The voltage, phase angle, and frequency difference between the two
connected systems should be within the acceptable limits. There are two
methods for synchronizing:
1. Check synchronizing
When the two systems are tied by an open breaker then the two
frequencies will be different and the phase angle difference will increase
(slow slip).
2. System synchronizing

When the two systems are asynchronous, as two generation islands, the
rate of slip between the two frequencies will be high. Then the system
synchronizing limits are applied. In this case, the phase angle limit will be
narrow and closure of the CB will be allowed when the phase angle differ-
ence decreases.
Refer to Fig. 20.7.1 to check the synchronizing and system check
operation.
Check synchronizing limits:
ΔF 5 50 mHz
ɸ 5 35-60 degrees