GE 745 - 7.5.14 Restricted Ground Fault Element Test; 7.5.14.1 Description; 7.5.14.2 Winding 1 Element

CHAPTER 7: COMMISSIONING PROTECTION SCHEMES
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 7–37
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
NOTE
Note
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, .
7.5.14 Restricted Ground Fault Element Test
7.5.14.1 Description
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
o
) current is calculated from
the vector sum of the three phase currents. Injecting current into one phase automatically
produces a neutral current (i.e. 3I
o
= I
A
). Settings for these elements are found in the S4
ELEMENTS
 RESTRICTED GROUND  W1(3) RESTD GND FAULT setpoints menu.
7.5.14.2 Winding 1 Element
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
1
current source to
terminals H1 and G1 for the winding 1 phase current element and I
2
to terminals G10 and
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
3I
0
I
g
–=