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10.6 PROTECTION SCHEMES
12. Set the voltage to rated VT secondary value, the current to rated CT secondary, and the pre-trigger fre-
quency to the nominal frequency (60 or 50 Hz). If current sensing is not enabled, it is not necessary to con-
nect the current signal.
13. Set the post-trigger to 0.5 Hz below the setting for Underfrequency 1. Reset all targets and relays, if neces-
sary. Reset the timer.
14. Initiate the frequency step and timer start. The Interval Timer will record the operating time of element.
Compare this time to the setpoint value:
SETPOINT/S4 ELEMENTS/FREQUENCY/UNDERFREQUENCY 1 DELAY
15. Provided that the operate times are not scattered over a wide range, it may be desirable to repeat this test
several times and average the results. If there is a wide scatter, verify the test setup and ensure the signal
source behaves in a consistent manner.
c) CURRENT INPUT FUNCTION (VOLTAGE INPUT DISABLED)
If the Frequency elements are using the A-phase Winding 1 current signal as a source, verify the operation of
the element using the instructions below.
1. Using the variable-frequency current source connected to terminals H1 and G1 with no voltage connec-
tions, set the frequency to 60.00 Hz (or 50.00 Hz) and the amplitude to the rated CT secondary current.
Monitor the appropriate trip and auxiliary relays. Reset all alarms and indications. The display should
remain unchanged with no trip indications.
2. Slowly decrease the frequency until the output relay(s) operate. Check that the frequency at which opera-
tion took place is the selected frequency setting.
3. Slowly reduce the current. Note the current at which the output relay(s) reset. Check that this dropout cur-
rent is the minimum operating current selected in the settings.
If current sensing is not enabled, then the element will continue working all the way down
to a current level of 0.02 × CT A.
NOTE
4. Increase the current back to nominal. Verify that the relay(s) operate.
5. Check that the TRIP and PICKUP LEDs are on and the following trip message is displayed:
SS LATCHED (OPERATED):
SS Underfrequency 1
6. Slowly increase the frequency until the PICKUP indicator and output relays reset. Note the dropout level,
which should be the pickup plus 0.03 Hz. Check that the TRIP indicator is still on. The trip message
remains on if the TARGET setting is Latched ; if set to Self-resetting , the message resets when frequency is
above the setpoint.
7. For timing tests, the signal generator must be capable of triggering into step-wise changing of frequency or
ramping down to a pre-selected frequency in only a few milliseconds. Connect the Signal Source and
Timer Start triggers as shown in Figure 10–11: FREQUENCY ELEMENT TESTING on page 10–34.
8. Set the current to rated CT secondary value, no voltage connection, and the pre-trigger frequency to the
nominal frequency (60 or 50 Hz).
9. Set the post-trigger to 0.5 Hz below the Underfrequency 1 setting. If necessary, reset all targets and relays.
Reset the timer.
10. Initiate the frequency step and timer start. The Interval Timer will record the operating time of element.
10
Compare this time to setting under:
SETPOINT/S4 ELEMENTS/FREQUENCY/UNDERFREQUENCY 1 DELAY
10-36
745 Transformer Management Relay
10 COMMISSIONING
GE Power Management
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