GE 745 Instruction Manual page 280

PROTECTION SCHEMES
Note
NOTE
7.5.16 Negative-sequence Instantaneous Overcurrent
7.5.16.1 Description
7.5.16.2 Winding 1 element
7.5.16.3 Pickup Level
Note
NOTE
7–42
To test these elements, disable all protection elements except for winding 2 negative-
sequence time overcurrent. Connect the current signal to X = H4 and Y = G4. Repeat all the
tests described for the winding 1 element in this section. For winding 3, connect the
current signal to X = H7 and Y = G7.
The blocking from logic input, if enabled, can be tested as described in earlier tests for
other elements.
This procedure verifies that the negative-sequence instantaneous overcurrent
performance matches the in-service settings. These elements are found under the
ELEMENTS NEG SEQ OC

require testing at current multiples of several times the rated CT secondary value, do not
leave the current signal on for more than a few seconds.
To ensure that only the Negative Sequence Instantaneous Overcurrent element operates
the trip relays (and any other output relays selected by the logic),
 Disable all protection features except Negative Sequence Instantaneous
Overcurrent.
 Use the general test setup in FIGURE 7–9: General test setup on page
7–25.
 Connect the current supply to terminals X = H1 and Y = G1 to test the
Winding 1 element.
 Monitor the appropriate output relays as per the relay FlexLogic™
settings.
 With the interval timer disabled, apply the current signal and increase its
magnitude until the trip relay and all selected auxiliary relays operate.
 Compare the measured operating level against the
NEG SEQ OC
PICKUP
With current applied to a single phase, the negative sequence current component is
calculated from:
Hence, the phase current will be three times the pickup setting.
 When the element operates, check that the Trip and Pickup LEDs are on
and one of the following is displayed:
settings menu. If the relay settings
W1 NEG SEQ INST OC

W1 NEG SEQ INST OC

relay settings.
1
-- -
I × I
=
neg seq phase
3
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: COMMISSIONING
S4
S4 ELEMENTS

W1 NEG SEQ INST OC

(EQ 7.13)