10-44 745 Transformer Management Relay GE Power Management
10.7 AUXILIARY PROTECTION/MONITORING FUNCTIONS 10 COMMISSIONING
10
10.7.2 HARMONIC DERATING FUNCTION
Testing of the Harmonic Derating Function requires that accurate transformer parameters such as
Load Losses at Rated Load and Winding Resistance be entered. This feature makes use of the Har-
monic Derating Factor (HDF) computed by the relay, using the harmonic content of the current sig-
nals and the transformer data (refer to IEEE C57.110-1986 for the computation method). Once the
derating factor falls below a set value, the 745 can trip and/or alarm.
The harmonic derating settings are under:
SETPOINTS/S4 ELEMENTS/HARMONICS/W1 (2) HARM DERATING/...
a) OPERATING LEVEL
1. To verify the correct operation of this element, a current signal containing harmonics must be introduced
into one phase of the relay. The test setup of Figure 10–1: TEST SETUP on page 10–3 is to accomplish
this. Set the fundamental component at rated CT secondary into phase A Winding #1. Gradually increase
the second harmonic component (and the rest of the even harmonics) while displaying the harmonic derat-
ing factor under:
ACTUAL VALUES/A2 METERING/HARMONIC CONTENT/HARMONIC DERATING/HARMONIC DERATING FACTOR
The element should operate when the displayed HDF equals the element setting.
2. Check that the TRIP, PICKUP (and ALARM if selected) LEDs are on, and the following trip message is dis-
played:
3. Lower the DC component until the element resets. The reset value should be approximately 2% larger
than the operate value. Verify that the Pickup and Alarm LEDs reset if the target function is set to
Self-reset-
ting
. The trip LED should remain latched.
b) OPERATING TIME
To measure the basic operating time of this element, preset a fundamental and DC component composite cur-
rent signal to cause the element to operate. Using the setup of Figure 10–1: TEST SETUP on page 10–3,
apply the current suddenly, at the same time the timer is triggered. The measured operating time should corre-
spond to the time delay setting for the element.
yy LATCHED (OPERATED):
yy
NOTE
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