GE SR345 Instruction Manual page 188

S3 PROTECTION
IG
6–76
Courtesy of NationalSwitchgear.com
maximum measured line current (Imax) to produce a percent slope value. The slope setting
allows the user to determine the sensitivity of the element based on the class and quality
of the CTs used.
The figure below shows the typical wiring between the winding CTs and the 345 CT
terminals to assure the correct performance of the protection. The restricted earth fault
protection is also available for delta windings with in-zone grounding transformer, or for
Delta corner grounded windings.
Transformer Winding
Rg
Ig
The 345 RGF protection includes ground current supervision mechanism o provide more
security during external non-ground faults associated with CT saturation, that may result
into spurious neutral current, and may jeopardize the security of the RGF protection. When
the GND CURRENT SUPERVISION setting is selected as "Enabled", the algorithm checks if
the ground current measured by the relay satisfies the selected GND CURRENT
SUPERVISION LEVEL, before making operation decision. The ground current supervision is
not active if the GND CURRENT SUPERVISION is selected as "Disabled". The RGF protection
works without the supervision as well.
PATH:
SETPOINTS > S3 PROTECTION > S3 PROTECTION GROUP 1(2) > RESTRICTED GROUND
FAULT 1(2)
RGF FUNCTION
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
The selection of Latched Alarm, Alarm, or Trip setting enables the Restricted Ground
Fault function. Output relays #1 "R1 TRIP" and #2 "R2 TRIP" will operate, only when the
Trip setting is selected, and the Restricted Ground Fault protection is operational. In this
mode the "ALARM" LED does not turn on. When the Alarm setting is selected as a
function, and the RGF protection is operational, the "ALARM" LED will flash and turn off
after the condition clears. If Latched Alarm is selected as a function, the "ALARM" LED
will flash during the operating condition, and will stay "ON" after the condition clears,
until a Reset command is initiated. Output relays #1 "R1 TRIP" and #2 "R2 TRIP" do not
operate if the Latched Alarm or Alarm setting is selected.
CT INPUTS
Range: CT (W1), CT(W2)
Default:CT (W1)
This setting defines the winding three-phase and ground currents used by the RGF
function.
IA
IB
IC
E5 D5 E6 D6 E7 D7 E8 D8
Ia Ib Ic Ig
Winding 1 Current Inputs - CT (W1)
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS
E9 D9 E10 D10 E11 D11 E12 D12
Ia Ib Ic Ig
Winding 2 Current Inputs - CT (W2)