GE 745 Instruction Manual page 275

CHAPTER 7: COMMISSIONING
Note
NOTE
7.5.14 Restricted Ground Fault Element Test
7.5.14.1 Description
7.5.14.2 Winding 1 Element
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
The procedure for this test is shown below:
 Select the D/Y30° transformer type into the relay and set the same CT
ratio for both phase and ground winding inputs.
The selected transformer type assures the G1/2 ground input is
associated to winding 2 (wye).
 Enable the restricted ground fault protection only and monitor the
ground differential current under the relay actual values.
 Connect the single current source to inject current into G10 of the
ground G1/2 terminal and to the connected in-series winding 2 phase A
terminals as shown on the figure above.
 Verify the ground current and phase A current are in phase
 Verify the ground differential current is zero
The polarities and wirings of the CTs for the restricted ground fault protection are correct if
the external phase-to-ground fault current is seen on both relay terminals (phase and
ground) in the same direction. The response of the restricted ground fault protection is
based on the magnitude of the ground differential current resulting from the vector
difference of the neutral and ground currents; that is,
This procedure verifies that the restricted ground fault performance matches the in-
service settings. The ground element measures the current signal connected to the ground
current input CT, H10 and G10 or F12 and E12. The neutral (3I
the vector sum of the three phase currents. Injecting current into one phase automatically
produces a neutral current (i.e. 3I
ELEMENTS RESTRICTED GROUND

To ensure that only the restricted ground fault element operates the trip relays (and any
other output relays selected by the logic) disable all protection features except restricted
ground fault.
Using a current supply as shown in the figure below, connect the I
terminals H1 and G1 for the winding 1 phase current element and I
H10 as shown for the ground current element. Monitor the appropriate output relays as
per the relay FlexLogic™ settings or assigned relay settings.
I
=
gd
= I ). Settings for these elements are found in the
o A
W1(3) RESTD GND FAULT

PROTECTION SCHEMES
3I I .
–
0 g
) current is calculated from
o
S4
setpoints menu.
current source to
1
to terminals G10 and
2
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