GE 745 Instruction Manual page 287

CHAPTER 7: COMMISSIONING
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
 Compare this time to the
OVERFREQUENCY DELAY
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.
Current input function (voltage input disabled):
If the voltage input is disabled, the frequency elements use the winding 1 phase A current
signal as a source. Verify the operation of the element using the procedure below.
 Using the variable-frequency current source connected to terminals H1
and G1, no voltage connections, frequency at 60.00 Hz (or 50.00 Hz),
and the amplitude to rated CT secondary current.
 Monitor the appropriate trip and auxiliary relays.
 Reset all relay alarms and indications.
The relay display should remain unchanged with no trip indications.
 Slowly increase the frequency until the output relay(s) operate.
 Check that the frequency at which operation took place is the selected
frequency setting.
 Slowly reduce the current.
 Note the current at which the output relay(s) reset.
 Check that this dropout current is the minimum operating current
selected in the settings.
If current sensing has been disabled for this element, then operation
continues down to 0.00 A.
 Increase the current back to nominal.
 Check that the relay(s) operate.
 Check that the Trip and Pickup LEDs are on and one of the following
trip messages is displayed:
LATCHED: Overfrequency or OPERATED: Overfrequency
 Slowly decrease the frequency until the Pickup LED turns on and output
relays reset.
 Note the dropout level, which should be the pickup minus 0.03 Hz.
 Check that the Trip LED is still on.
The trip message stays on if the
Latched; if it is Self-resetting, the message resets when frequency is
below the setpoint.
 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
7–12: Frequency element testing on page 7–44.
PROTECTION SCHEMES
S4 ELEMENTS FREQUENCY

setting.
OVERFREQUENCY TARGET

setting is
7–49