GE 745 Instruction Manual page 273

CHAPTER 7: COMMISSIONING
7.5.11 Ground Instantaneous Overcurrent 1
7.5.11.1 Description
7.5.11.2 Winding 1 Element
7.5.11.3 Pickup Level
7.5.11.4 Operating Time
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
This procedure verifies that the ground instantaneous overcurrent performance matches
the in-service settings. Settings for these elements are found under the
GROUND OC W1 GND INST OC 1

test at current multiples of several times the rated CT secondary value do not leave the
current signal on for more than a few seconds.
To ensure only the ground instantaneous overcurrent 1 element operates the trip relays
(and any other output relays) selected by the logic, disable all protection features except
ground instantaneous overcurrent 1. Use the test setup shown in FIGURE 7–9: General test
setup on page 7–25.
Connect the current supply to terminals X = H10 and Y = G10 to test the winding 1
element. Monitor the appropriate output relays as per the relay FlexLogic™ settings or
assigned relay settings.
 With the interval timer disabled, apply the current signal and increase its
magnitude until the trip relay (and all the selected auxiliary relays)
operate.
 Compare the measured operating level against the
GROUND OC
setpoint.
 When the element operates, check that the Trip and Message LEDs are
flashing and one of the following messages is displayed:
LATCHED a: W1 Gnd Inst OC 1 or OPERATED a: W1 Gnd Inst OC
1
 Reduce the current until the element resets.
The reset level should be 97% of the operate level. When the element
resets the Trip, Ground, and Message LEDs should remain on if the
GND INST OC 1 TARGET
Trip LED should stay on.
 Reset indicators and clear messages.
Using the setup shown in FIGURE 7–9: General test setup on page 7–25 with the Interval
Timer enabled,
 Set the current level to 1.5 times the element operate level and apply
suddenly by closing the double-pole switch.
 Record the operate time and compare to the
OC

setpoints menu. If your relay settings require you to
W1 GND INST OC 1

was selected as "Latched". Otherwise, only the
W1 GND INST OC 1 W1 GND INST OC 1 DELAY

PROTECTION SCHEMES
S4 ELEMENTS
S4 ELEMENTS

W1 GND INST OC 1 PICKUP

S4 ELEMENTS GROUND

value.

W1
7–35