GE Power Management DGP Digital Generator Protection System 5-
7
5 PERIODIC TESTS 5.3 MEASURING UNIT TESTS
5
5.3.4 T7: CURRENT UNBALANCE TRIP 46T
1. Record the following Settings:
46T
(403)
PICKUP
(
I
2
) = ______ A rms
(404)
K2
(Time Factor) = ______ sec.
2. Current Unbalance Trip is calculated with the following equation:
(equation 5–3)
I
2
is equal to the negative-sequence current,
K2
is equal to the time factor, and
I
rated
is equal to the rated
current (Setting 115:
RATEDCUR
). The unit should pick up when
I
2
>
PICKUP
. If the unit has been picked
up for a time equal to the Trip Time, the test trip relay will operate.
3. Connect relay as shown in Figure 4–7: CURRENT UNBALANCE TEST CONNECTIONS on page 4–21.
4. Set up relay in test mode for the 46T function;
46T ON
will be displayed on the MMI.
5. Set the negative-sequence current to
PICKUP
+ 0.1 (0.02) =______ A rms and apply to the relay. The test
pickup relay should operate and the test trip relay should operate after the Trip Time has expired.
6. Lower the negative-sequence current to
PICKUP
– 0.1 (0.02) =______ A rms and the test pickup and test
trip relays should not operate.
If this test is repeated, the operate time of the trip contact will change according to how soon
the test is repeated. The trip time can be calculated according to the following equation:
where
T
= the time between successive tests and Original Trip Time = the time to trip the relay
when the test was first run. If the time between successive trips is greater than 230 seconds,
the relay will trip in the original trip time.
Trip Time
K2
I
2
I
rated
⁄()
2
-----------------------------
=
NOTE
New Trip Time
T
230
----------
Original Trip Time
×
=
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