GE 745 Instruction Manual page 286

PROTECTION SCHEMES
7–48
 Check that this dropout voltage is equal to the
FREQUENCY
VOLTAGE
Note that this level can be set down to 0.00 A, in which case the element
remains operated to a voltage level of approximately 2% of nominal.
 Slowly increase the voltage and check that the element operates when
the voltage reaches 2% above the set level.
 Return the voltage to nominal value.
 Slowly decrease the current until the element resets.
 Check that this dropout current level is equal to the
FREQUENCY
CURRENT
If current sensing has not been enabled for this element, the element
remains operated for current levels down to 0.00 A.
 Slowly increase the current and check that the element operates when
the current reaches a value just above the setting.
 Set the current to rated CT secondary.
 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 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 remains on if the
"Latched"; if set to "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.
 Set the voltage to rated VT secondary value, the current to rated CT
secondary, and the pre-trigger frequency to nominal frequency (60 or 50
Hz).
The current signal is not required if current sensing is not enabled for
this element.
 Set the post-trigger to 0.5 Hz above the setting of the overfrequency
element. If necessary, reset all targets and relays.
 Reset the timer.
 Initiate the frequency step and timer start.
The interval timer records the operating time of element.
OVERFREQUENCY
 
voltage level.
OVERFREQUENCY
 
setting.
OVERFREQUENCY TARGET
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: COMMISSIONING
S4 ELEMENTS

MINIMUM OPERATING
S4 ELEMENTS

MINIMUM OPERATING
setting is