GE 745 - 7.5.16 Negative-sequence Instantaneous Overcurrent; 7.5.16.1 Description; 7.5.16.2 Winding 1 element

7–42 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION SCHEMES CHAPTER 7: COMMISSIONING
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.
NOTE
Note
The blocking from logic input, if enabled, can be tested as described in earlier tests for
other elements.
7.5.16 Negative-sequence Instantaneous Overcurrent
7.5.16.1 Description
This procedure verifies that the negative-sequence instantaneous overcurrent
performance matches the in-service settings. These elements are found under the
S4
ELEMENTS
 NEG SEQ OC  W1 NEG SEQ INST OC settings menu. If the relay settings
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.
7.5.16.2 Winding 1 element
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.
7.5.16.3 Pickup Level
 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
S4 ELEMENTS 
NEG SEQ OC
 W1 NEG SEQ INST OC  W1 NEG SEQ INST OC
PICKUP
relay settings.
NOTE
Note
With current applied to a single phase, the negative sequence current component is
calculated from:
(EQ 7.13)
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:
I
neg seq
1
3
---
I
phase
×=