GE P741, Technical Manual

Page: 374 / 560

Commissioning P74x/EN CM/Na7
MiCOM P741, P742, P743 (CM) 10-21
CM
5. COMMISSIONING TEST MENU
5.1 Test mode
5.1.1 Test mode for PU
This cell is used to allow secondary injection testing to be performed on the relay, without
operation of the trip relays, or commissioning of other relays in the same bay as the PU,
without mal-operation of the breaker failure protection. It also enables the user to directly test
the output contacts and the effect of plant position via the application of controlled tests
signals.
Two test modes are available:
−
In the ‘CB Failure Protection (50BF) disabled’ mode, all tripping information from
external relay are not taken into account. The topology algorithm forwards the feeder
positions to the central unit as normal. As the peripheral unit continues to monitor the
analogue values the central unit will maintain a balanced condition with the remainder
of the system still in normal operation. However, the CB failure backtrip information
will not be sent to the Central Unit. The local protections (Dead Zone, Overcurrent,
Earth Fault) are still enabled and the PU is able to retrip the breaker. However, the
Peripheral Unit is able to react to a fault condition by creating a CB fail condition and
back tripping the zone(s) if the CU sends a trip order (87BB or 50BF backtrip), to clear
a genuine fault).
−
In the ‘Overhaul’ mode, the feeder is totally disconnected from the system because all
the isolators are open but all information is passed back to the central unit for inclusion
in zone calculations and hence the protection scheme. Hence the central unit can
keep the zone elements in service as the contribution of this feeder will be zero. (The
CT is still used by the Check Zone element)
Whilst in this mode the peripheral unit can be tested locally for example secondary
injections tests can be carried out (The system is stable because during the current
injection there is a differential current in the CZ but not in the Zone).
When a test mode is select, the relay is out of service causing an alarm condition to be
recorded and the yellow ‘Out of Service’ LED to illuminate (see § 4.2.3.1 for particular
conditions). Once testing is complete the cell must be set back to ‘Disabled’ to restore the
relay back to service.
5.1.2 Test mode for CU
This cell is used to allow commissioning of busbar and general breaker failure protection. It
also enables a facility to directly test the output contacts by applying menu controlled tests
signals. During the test mode, opto inputs and outputs contacts remain in last known state
before the test mode is selected.
To select test mode this cell should be set to ‘Enabled’ which takes the relay out of service
causing an alarm condition to be recorded and the yellow ‘Out of Service’ LED to illuminate
(see § 4.2.3.1 for particular conditions). Once testing is complete the cell must be set back
to ‘Disabled’ to restore the relay back to service.
W
HEN THE
‘T
EST
M
ODE
’
CELL IS SET TO
‘E
NABLED
’,
THE RELAY SCHEME LOGIC DOES NOT DRIVE
THE OUTPUT RELAYS AND HENCE THE
CU
WILL NOT TRIP THE ASSOCIATED CIRCUIT BREAKER IF A
BUSBAR FAULT OCCURS
(
COMMISSIONING MODE
1
AND
2).
H
OWEVER
,
THE COMMUNICATIONS CHANNELS WITH REMOTE RELAYS REMAIN ACTIVE
,
WHICH
,
IF
SUITABLE PRECAUTIONS ARE NOT TAKEN
,
COULD LEAD TO THE REMOTE ENDS TRIPPING WHEN
CURRENT TRANSFORMERS ARE ISOLATED OR INJECTION TESTS ARE PERFORMED
.