Frequency Decay Rate 1 - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

10 COMMISSIONING
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 above the setting of the Overfrequency element. Reset all targets and relays,
if necessary. Reset the timer.
10. Initiate the frequency step and timer start. The Interval Timer records the element operating time. Compare
this time to the setting:
SETPOINT/S4 ELEMENTS/FREQUENCY/OVERFREQUENCY DELAY
11. 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.
The blocking from logic input, if enabled, can be tested as described in earlier tests for other
elements.
NOTE
a) PRELIMINARIES
A high-quality programmable function generator is required to verify this element. Since the fre-
quency rates of change are measured over a narrow range, the test instrumentation must accurately
simulate frequency decay rates without any significant jitter. It is the experience of GE Power Man-
NOTE
agement that some commercial dedicated relay test equipment with built-in frequency ramping func-
tions is not accurate enough to verify the 745 performance.
Disable all protection functions except the Frequency Decay function. Verify that settings match in-service
requirements. The settings are entered and modified under:
SETPOINTS/S4 ELEMENTS/FREQUENCY/FREQUENCY DECAY/...
b) VOLTAGE INPUT FUNCTION (VOLTAGE INPUT ENABLED)
1. Use a frequency-ramping programmable voltage/current source connected to terminals C11 and C12, for
the voltage signal and H1 and G1 for the current signal. Set the frequency to 60.00 Hz (or 50.00 Hz) and
the voltage amplitude to the rated VT secondary voltage. Set the current amplitude to rated CT secondary.
( Note: If current sensing has been disabled for this element, the current signal is not required for the tests.)
Monitor the appropriate trip and auxiliary relays. Reset all alarms and indications on the relay. The relay
display should remain unchanged with no trip indications.
2. Program the function generator to simulate a frequency rate-of-change just above Rate 1. The start fre-
quency should be the nominal frequency of the relay; the end frequency must be below the Frequency
Decay Threshold if the relay is to operate. Note that operation occurs if the rate criterion is satisfied and
the frequency is below the threshold.
3. Initiate ramping action and verify element operation once the frequency drops below the threshold.
4. Check that the TRIP and PICKUP LEDs are on and the following trip message is displayed:
SS LATCHED (OPERATED):
SS Free Decay Rate 1
If the target was selected as Latched , the trip LED and the message remain on.
5. Reduce the voltage to below the voltage supervision level set under:
GE Power Management 745 Transformer Management Relay
10.6 PROTECTION SCHEMES

10.6.20 FREQUENCY DECAY RATE 1

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