Ground/Sensitive Ground Timed Overcurrent Protection (51G/Sg) - GE 350-A9 Instruction Manual

S3 PROTECTION

Ground/Sensitive Ground timed overcurrent protection (51G/SG)

NOTE:
NOTE
6–48
The relay has one Ground Time Overcurrent protection per setpoint group. The settings of
this function are applied to the ground input current to produce trip or pickup flags. The
Ground TOC pickup flag is asserted, when the ground current is above the PKP value. The
Ground TOC operate flag is asserted if the element stays picked up for the time defined by
the selected inverse curve, and the magnitude of the current. The element drops from
pickup without operation if the measured current drops below 97 to 98% of the pickup
value, before the time to operate is reached. The selection of Definite Time has a base time
delay of 0.1 s, multiplied by the selected TD multiplier. For example the operating time for
TOC set to Definite Time and a TDM set to 5 will result in 5*0.1 = 0.5 s.
The following path is available using the keypad. For instructions on how to use the
keypad, please refer to Chapter 3 - Working with the Keypad.
PATH:
SETPOINTS > S3 PROTECTION > SETPOINT GROUP 1(2) > GROUND TOC
The settings from the menu for Sensitive Ground TOC, appears only upon selection of the
Sensitive Ground CT when ordering the relay. Otherwise, the relay displays the menu for
Ground TOC protection.
Sensitive ground CTs are used in cases where the fault current is limited by a grounding
resistor.
GND TOC FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm
Default: Disabled
For details see Common
GND TOC PKP
Range: 0.05 to 20.00 x CT in steps of 0.01 x CT
Default: 1.00 x CT
SENS.GND TOC PKP
Range: 0.005 to 3.00 x CT in steps of 0.001 x CT
Default: 1.00 x CT
This setting sets the time overcurrent pickup level. For example, a PKP setting of 0.9 x CT
with 300:5 CT translates into 270A primary current.
GND TOC CURVE
Range: ANSI Extremely/Very/Moderately/Normally Inverse, Definite Time, IEC Curve A/B/C
and Short Inverse, IAC Extremely/Very/Inverse/Short, User Curve, FlexCurve A, FlexCurve
B
Default: Extremely Inverse
This setting sets the shape of the selected over-current inverse curve. If none of the
standard curve shapes is appropriate, a custom User curve, or FlexCurve can be
created. Refer to the User curve and the FlexCurve setup for more detail on their
configurations and usage.
GND TOC TDM
Range: 0.05 to 50.00 in steps of 0.01
Default: 1.0
This setting provides selection for Time Dial Multiplier by which the times from the
inverse curve are modified. For example if an ANSI Extremely Inverse curve is selected
with TDM = 2, and the fault current was 5 times bigger than the PKP level, the operation
of the element will not occur before an elapsed time from pickup, of 495 ms.
setpoints.
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS