GE Power Management 745 Transformer Management Relay 10-45
10 COMMISSIONING 10.7 AUXILIARY PROTECTION/MONITORING FUNCTIONS
10
10.7.3 TRANSFORMER OVERLOAD
The transformer overload element uses the A-phase current of each winding to compute a trans-
former loading. The computation assumes a rated voltage on the wInding, hence the loading is effec-
tively a percent of rated load current.
The transformer overload settings are under:
SETPOINTS / S4 SETPOINTS/XFORMER OVERLOAD/...
a) OPERATING LEVEL
1. Inject a fundamental-frequency current into phase A of winding #1. Increase the current signal to a value
just above the Transformer Overload Pickup setting (take into account the CT ratio and the rated-MVA
phase current to set the current correctly). The element should operate after its set time delay.
2. Check that the TRIP and PICKUP (and ALARM if selected) LEDs are on, and the following trip message is
displayed:
3. Lower the current until the element resets. The reset value should be approximately 97% of the operate
value. Verify that the Pickup and Alarm LEDs reset if the target function is set to
Self-resetting
. The trip
LED should remain latched.
b) OPERATING TIME
Using the setup in Figure 10–11: FREQUENCY ELEMENT TESTING on page 10–34 with the Interval Timer
enabled, set the current level to 1.5 times the operate level of the element and apply suddenly by closing the
double pole switch. Record the operate time and compare to the setting under:
SETPOINTS/S4 ELEMENTS/XFORMER OVERLOAD/TRANSFORMER OVERLOAD DELAY.
The blocking from logic input, if enabled, can be tested as described in earlier tests for other
elements.
yy LATCHED (OPERATED):
yy Xformer Overload
NOTE
NOTE
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