GE 745 Instruction Manual page 288

PROTECTION SCHEMES
Note
NOTE
7.5.17.5 Frequency Decay Rate
Note
NOTE
7–50
 Set the current to rated CT secondary value, no voltage connection, and
the pre-trigger frequency to the nominal frequency (60 or 50 Hz).
 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.
 Initiate the frequency step and timer start.
The Interval Timer records the element operating time.
 Compare this time to the
OVERFREQUENCY
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.
A high-quality programmable function generator is required to verify this element. Since
the frequency 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 Multilin that some commercial dedicated relay test
equipment with built-in frequency ramping functions 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 in the
FREQUENCY
The following procedures are for the frequency decay rate 1 element. They can be applied
to the frequency decay rate 2, 3, and 4 elements as well, making the necessary changes
where appropriate.
Voltage input function (voltage input enabled):
 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 is disabled for this element, the current signal is not required for
the tests).
 Monitor the appropriate trip and auxiliary relays.
CHAPTER 7: COMMISSIONING
S4 ELEMENTS
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OVERFREQUENCY DELAY

FREQUENCY DECAY setpoints menu.

745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
FREQUENCY

setting:
S4 ELEMENTS
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