Protection Schemes
745
Transformer Management Relay
Commission
ing
http://www.GEindustrial.com/multilin
7–28
GE Multilin
e) Slope
1. To measure the slope, connect current signals to the relay as shown in the fig-
ure above.
2. Inject the
I
1
current such that the ground differential pickup value divided by
the
I
1
current is less than the slope setting. Set
I
2
= 0 A. The element will
operate as since the current appears as ground differential.
3. The slope is calculated from the values of
I
ground differential
and
I
max
as shown
below:
(EQ 7.15)
where
I
max
represents the maximum phase current for the winding being
measured.
4. As
I
2
is increased, the element will reset when the percentage of slope drops
below the slope setting. Slowly increase
I
2
until the element operates again.
Calculate the slope at this point.
5. Decrease the slope setting to 0% then continue to increase the
I
2
current until
the element resets. Slowly increase
I
2
until the element operates again.
6. The reset level should be 97% of operate level. When the element resets, the
Trip and Message LEDs should remain on if the
W1 RESTD GND FAULT TARGET
was
selected as “Latched”. Otherwise only the Trip LED should remain on.
f) Winding 2 or 3 Elements
Since the second Restricted Ground Fault element can be set with completely
different parameters than the first element winding, it is necessary to repeat the full
set of tests described in this section for each winding.
To test the second element, disable all protection elements except for the Winding 2
(or Winding 3 as appropriate) Restricted Ground Fault element. Connect the ground
current signal to Terminals F12 and E12. Repeat all the tests described for the
Winding 1 element in this section.
The blocking from logic input, if enabled, can be tested as described in
earlier tests for other elements.
Negative Sequence
Time Overcurrent
a) Description
This procedure verifies that the Negative Sequence Time Overcurrent performance
matches the in-service settings. Since these elements 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 elements. The negative-sequence
element measures the derived negative-sequence component of the phase current
signals connected to the phase input CTs. Refer to
5–50 for additional information on timing curves.
If the relay elements are set for “Linear” reset characteristic when measuring the
operating times, ensure that there is sufficient time between test current injections
for the element to reset fully. Otherwise, erroneous timing measurements will be
obtained. Settings for these elements are found in the
S4 ELEMENTS
!"
NEG SEQ OC
!
W1 NEG SEQ TIME OC
settings menu:
b) Winding 1 Element
To ensure that only the Negative Sequence Time Overcurrent element operates the
trip relays (and any other output relays selected by the logic) disable all protection
features except Negative Sequence Time Overcurrent. Use the general test setup
shown in FIGURE 7–9: General Test Setup on page 7–18.
Connect the current supply to terminals X = H1 and Y = G1 to test the Winding 1
negative-sequence element. Monitor the appropriate output relays as per the relay
FlexLogic™ settings.
%slope
I
ground
differential
I
max
---------------------------------------------------
100%
×
=
NOTE
Summary of Contents for Multilin 745
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