Neutral Time Overcurrent - GE TRANSFORMER MANAGEMENT RELAY 745 Instruction Manual

8.5 PROTECTION SCHEMES
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 above for each winding.
b) PHASE IOC 2
The Phase IOC 2 elements are identical to the Phase IOC 1 elements. As such, the same test procedure can be used to
verify their correct operation. Disable all protection features except the Phase IOC 2 elements and follow the steps in Sec-
tion 8.5.5: Phase Instantaneous Overcurrent on page 8–19, making the appropriate changes for the display indications and
output relays which are operated by the Phase IOC 2 elements.
The blocking from logic input, if enabled, can be tested as described in earlier tests for other elements.
NOTE
This procedure verifies that the Neutral Time Overcurrent performance matches the in-service settings. Since these ele-
ments can have any one of a multitude of timing curves, a table of expected operating times versus applied current should
be prepared prior to testing. The neutral element measures the derived zero-sequence current signal as an input. Refer to
Time Overcurrent Curves on page 5–49 for information on timing curves.
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 are found under the
only be one or two Neutral Time Overcurrent elements in service at the same time.
WINDING 1 ELEMENT:
To ensure that only the Neutral Time Overcurrent element under test operates the trip relays (and any other output relays)
selected by the logic, disable all protection features except Neutral 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 = H1 and Y = G1 to test the Winding 1 neutral element. Monitor the appropriate
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 under test 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, then reduce the current to just above the expected operate level.
Slowly reduce the current below the operate level and observe for a reset action on the trip relay. This current reset
level should be approximately 98% of the pickup level setting. Once the relay drops out, slowly increase the current
until the trip contact closes. The operate level should correspond to the
OC W1 NEUTRAL TIME OC PICKUP
8
signal is equal to the 3I
3. When the element operates, check that the Trip, Pickup, and Phase LEDs are on and one of the following messages is
displayed:
LATCHED
W1 Ntrl Time OC
4. 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 remains on.
5. Reset indicators and clear messages.
8-20
Courtesy of NationalSwitchgear.com
S4 ELEMENTS
setpoint: Since current is being introduced into one phase only, the input current
signal used by the element.
o
OPERATED
W1 Ntrl Time OC
745 Transformer Management Relay

8.5.6 NEUTRAL TIME OVERCURRENT

setpoints menu. Note that there can
NEUTRAL OC
S4 ELEMENTS NEUTRAL OC
W1 NEUTRAL TIME OC TARGET
8 COMMISSIONING
W1 NTRL TIME
was selected as "Latched".
GE Multilin