Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
9.20
SYNCH CHECK UNIT
The synch check unit in GARD 8000 is used with the recloser and/or manual closing commands to
determine if the two sides of the circuit breaker are synchronous with each other. Closing a circuit
breaker out of synchronism may cause damage to the breaker or result in out of step conditions.
The synch check function has two parts:
•
Synchronism check by comparing voltages on both sides of the breaker with regards to
magnitude, frequency and/or angle.
•
Energizing check by confirming that the voltage is low on one side (dead) and high on the other
(live). Settings for which direction this is allowed are available; D BUS/D LINE, H BUS/D
LINE, D BUS/H LINE, H BUS/H LINE. To have the synch check function enabled, the H
BUS/H LINE setting should be enabled in addition to the other type of energizing check
selected.
Phase A line voltage is always used for the comparison. The bus voltage can be selected to be phase A,
B or C. The voltage selected has to be entered in the settings so that the appropriate phase shift can be
taken into account.
Note that the “line voltage” refers to the side where the three phase VT used for the distance protection
is located. In some applications this may be on the bus, while a single phase VT used for synch check
is located on the line side.
The angular compensation used is shown in the Table below.
Table 9-18. Angular Compensation
Line side
Bus side
ABC phase rotation
V
A
V
A
0º
V
A
V
B
120º
B
V
A
V
C
240º
9.20.1
VOLTAGE DIFFERENCE UNIT
The voltage difference unit asserts when the difference between the bus and the line voltage is below
the set threshold for this function. It resets at 105% of set value.
9.20.2
PHASE DIFFERENCE UNIT
The phase difference unit asserts when the phase angle difference between the two voltages is below
the set threshold. It resets at 105% of set value, or set value + 2 degrees, whichever is greater.
9.20.3
FREQUENCY DIFFERENCE UNIT
The frequency difference unit asserts when the frequency difference between the two voltages is below
the set threshold. It resets at set value + 0.01 Hz.
August 1, 2009
9-72
973.334.3100
