GE 745 Instruction Manual page 276

PROTECTION SCHEMES
7.5.14.3 Pickup Level
7.5.14.4 Operating Time
7.5.14.5 Slope
7–38
FIGURE 7–11: Restricted ground test setup
 With the interval timer disabled, apply the current signal feeding the
phase current element and increase its magnitude slowly until the trip
relay, and all the selected auxiliary relays, operate.
The operate level should correspond to the
RESTRICTED GROUND

FAULT PICKUP setting.
 When the element operates, check that the Trip, Ground, and Pickup
LEDs are on and that one of the following messages is displayed:
LATCHED a: W1 Restd Gnd Fault or OPERATED a: W1 Restd
Gnd Fault
 Reduce the current until the element resets.
The reset level should be 97% of the operate level. When the element
resets, the Trip and Message LEDs should remain on if the
GND FAULT TARGET was selected as Latched. Otherwise, only the Trip
LED should remain on.
 Reset indicators and clear messages.
 Select three (3) or four (4) delay times at which the timing is to be
measured.
 With the interval timer enabled, set the current level to the desired value
and apply suddenly by closing the double-pole switch.
 Record the operate time and compare to the expected value.
 Repeat for the all the desired values of current.
 To measure the slope, connect current signals to the relay as shown in
the figure above.
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: COMMISSIONING
S4 ELEMENTS
W1 RESTD GND FAULT


W1 RESTD GND
W1 RESTD