GE 745 Instruction Manual page 274

PROTECTION SCHEMES
7.5.11.5 Winding 2 or 3 Element
Note
NOTE
Note
NOTE
7.5.12 Ground Instantaneous Overcurrent 2
7.5.13 Restricted Ground Fault Polarity Test
7–36
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 ground instantaneous overcurrent 1 elements can be in service
simultaneously.
The blocking from logic input, if enabled, can be tested as described in earlier tests for
other elements.
The ground instantaneous overcurrent 2 elements are identical to the ground
instantaneous overcurrent 1 elements. Consequently, the same test procedure may be
used to verify their correct operation. Disable all protection features except ground
instantaneous overcurrent 2. Make the appropriate changes for the display indications
and output relays operated by the ground instantaneous overcurrent 2 elements.
This procedure verifies the correct wiring of field CTs (phase and ground) to the
corresponding phase and ground CT terminals on the relay for the purposes of the
restricted ground fault protection. The correct wiring is determined by the distribution of
fault current during external phase A to ground faults on wye-connected windings with
grounded neutral.
From the figure below, the I
and can be simulated by injecting a single current into the phase A (W2) and G1/2
terminals.
Phase A CT(W2)
I1
G4 H4 *
H10 *
G10
*
Ig
*
I2
Ground CT
FIGURE 7–10: Fault current distribution due to an external phase-to-ground fault on winding 2
fault current travels through the wye-grounded neutral as I
f
RGF polarity wiring test
If
If = I1
AC source
50/60 Hz signal
Ig = I2
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: COMMISSIONING
745 relay
Phase A (W2)
Ig
H4 *
G4
3I0
G1/2 input
H10 *
G10
If = Ig = I1 = I2
I 3Io – Ig I = 0
g