GE 745 Instruction Manual page 284

PROTECTION SCHEMES
Note
NOTE
7–46
 Using the variable-frequency current source connected to terminals H1
and G1 with no voltage connections, 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.
 Slowly decrease 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 is not enabled, then the element will continue working all the way
down to a current level of 0.02 × CT A.
 Increase the current back to nominal. Verify that the relay(s) operate.
 Check that the Trip and Pickup LEDs are on and one of the following
trip messages is displayed:
LATCHED: Underfrequency 1 or OPERATED: Underfrequency 1
 Slowly increase the frequency until the Pickup LED and output relays
reset.
 Note the dropout level, which should be the pickup plus 0.03 Hz.
 Check that the Trip LED is still on.
The trip message remains on if the
setting is Latched; if set to "Self-Resetting", the message resets when
frequency is above 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.
 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 below the underfrequency 1 setting.
If necessary, reset all targets and relays.
 Reset the timer.
 Initiate the frequency step and timer start.
The Interval Timer will record the operating time of element.
 Compare this time to the
UNDERFREQUENCY 1
CHAPTER 7: COMMISSIONING
UNDERFREQUENCY 1 TARGET
S4 ELEMENTS

UNDERFREQUENCY 1 DELAY

745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
FREQUENCY

setting.