Ground Time Overcurrent - GE TRANSFORMER MANAGEMENT RELAY 745 Instruction Manual

8.5 PROTECTION SCHEMES
2. Check that, when the element operates, the Trip and Pickup LEDs are on and one of the following messages is dis-
played:
LATCHED
W1 Ntrl Inst OC 1
3. 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
Otherwise only the Trip LED should stay on.
4. Reset indicators and clear messages.
OPERATING TIME:
With the setup shown in Figure 8–9: General Test Setup on page 8–18 and 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
S4 ELEMENTS
WINDING 2 AND 3 ELEMENTS:
Because the Winding 2 and 3 elements can be set with completely different parameters than the Winding 1 elements, it is
necessary to repeat the full set of tests described in this section for each winding.
Only two Neutral Instantaneous Overcurrent 1 elements can be in service simultaneously.
NOTE
The blocking from logic input, if enabled, can be tested as described in earlier tests for other elements.
NOTE
b) NEUTRAL IOC 2
The Neutral IOC 2 elements are identical to the Neutral IOC 1 elements. Consequently, the same test procedure can be
used to verify their correct operation. Disable all protection features except Neutral IOC 2 and follow the steps in the previ-
ous section, making the appropriate changes for the LEDs and output relays operated by the Neutral IOC 2 elements.
This procedure verifies that the Ground Time Overcurrent performance matches the in-service settings. Since these ele-
ments can be assigned a multitude of timing curves, a table of expected operating times versus applied current should be
prepared prior to testing. The ground element measures the current signal connected to the ground current input CT, H10
and G10 or F12 and E12. Refer to Time Overcurrent Curves on page 5–49 for information on timing curves. There can only
be one or two Ground Time Overcurrent 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 suffi-
cient 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
points menu.
WINDING 1 ELEMENT:
8
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 8–9:
General Test Setup on page 8–18.
Connect the current supply to terminals X = H10 and Y = G10 to test the Winding 1 ground element. Monitor the appropri-
ate output relays as per the relay FlexLogic™ settings.
PICKUP LEVEL:
1. 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.
2. 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 cur-
rent should be approximately 98% of the pickup level. Once the relay drops out, slowly increase the current until the
8-22
Courtesy of NationalSwitchgear.com
OPERATED
W1 Ntrl Inst OC 1
W1 NEUTRAL INST OC 1 TARGET
NEUTRAL OC W1 NTRL INST OC 1
745 Transformer Management Relay
was selected as "Latched".
W1 NEUTRAL INST OC 1 DELAY

8.5.8 GROUND TIME OVERCURRENT

S4 ELEMENTS GROUND OC
8 COMMISSIONING
value.
set-
W1 GND TIME OC
GE Multilin