8-32
745 Transformer Management Relay
GE Multilin
8.5 PROTECTION SCHEMES
8 COMMISSIONING
8
3.
Slowly reduce the voltage. Note the voltage at which the output relay(s) reset. Check that this dropout voltage is equal
to the
S4 ELEMENTS
ÖØ
FREQUENCY
ÖØ
OVERFREQUENCY
ÖØ
MINIMUM OPERATING VOLTAGE
voltage level. 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.
4.
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.
5.
Slowly decrease the current until the element resets. Check that this dropout current level is equal to the
S4 ELEMENTS
ÖØ
FREQUENCY
ÖØ
OVERFREQUENCY
ÖØ
MINIMUM OPERATING CURRENT
setting. If current sensing has not been
enabled for this element, the element remains operated for current levels down to 0.00 A.
6.
Slowly increase the current and check that the element operates when the current reaches a value just above the set-
ting. Set the current to rated CT secondary.
7.
Check that the Trip and Pickup LEDs are on and one of the following trip messages is displayed:
8.
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
OVERFREQUENCY TAR-
GET
setting is "Latched"; if set to "Self-resetting", the message resets when frequency is below the setpoint.
9.
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 8–12: Frequency Element Testing on page 8–29.
10. Set the voltage to rated VT secondary value, the current to rated CT secondary, and the pre-trigger frequency to nom-
inal frequency (60 or 50 Hz). The current signal is not required if current sensing is not enabled for this element.
11. 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.
12. Initiate the frequency step and timer start. The Interval Timer records the operating time of element. Compare this time
to the
S4 ELEMENTS
ÖØ
FREQUENCY
ÖØ
OVERFREQUENCY DELAY
setting.
13. 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.
1.
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.
2.
Slowly increase the frequency until the output relay(s) operate. Check that the frequency at which operation took place
is the selected frequency setting.
3.
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 opera-
tion continues down to 0.00 A.
4.
Increase the current back to nominal. Check that the relay(s) operate.
5.
Check that the Trip and Pickup LEDs are on and one of the following trip messages is displayed:
6.
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
OVERFRE-
QUENCY TARGET
setting is "Latched"; if it is "Self-resetting", the message resets when frequency is below the setpoint.
LATCHED
Overfrequency
OPERATED
Overfrequency
LATCHED
Overfrequency
OPERATED
Overfrequency
