GE 745 Instruction Manual page 271

CHAPTER 7: COMMISSIONING
7.5.10.2 Winding 1 Element
7.5.10.3 Pickup Level
7.5.10.4 Operating Time
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
elements in service at the same time.
If the relay elements are set for the "Linear" reset characteristic when measuring the
operating times, ensure there is sufficient time between test current injections for the
element to reset fully. Otherwise, erroneous timing measurements will be obtained. The
settings for these elements will be found under the
setpoints menu.
GND TIME OC
To ensure that only the ground time overcurrent element operates the trip relays (and any
other output relays) selected by the logic,
 Disable all protection features except ground time overcurrent.
Use the general 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 ground 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 slowly
increase its magnitude until the trip relay (and all the selected auxiliary
relays) operate.
If the relay has a very inverse time characteristic, it is easier and more accurate to increase
the current far above the pickup level until the trip relay operates and then reduce the
current to just above the operate level. Then slowly reduce the current below the operate
level and observe for a reset action on the trip relay. This reset level for the current should
be approximately 98% of the pickup level. Once the relay drops out, slowly increase the
current until the trip contact closes. The operate level should correspond to the
ELEMENTS GROUND OC

 When the element operates, check that the Trip, Ground, and Pickup
LEDs are on and one of the following messages is displayed:
LATCHED a: W1 Gnd Time OC or OPERATED a: W1 Gnd Time
OC
 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
TIME OC TARGET
LED should remain on.
 Reset indicators and clear messages.
Using a table like the one shown blow,
 Select three (3) or four (4) values of current multiples at which the
timing is to be measured.
S4 ELEMENTS
W1 GND TIME OC W1 GROUND TIME OC PICKUP
 
was selected as Latched. Otherwise, only the Trip
PROTECTION SCHEMES
GROUND OC W1
 
S4
setpoint.
W1 GROUND
7–33