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CHAPTER 6: SETPOINTS
Ground instantaneous
overcurrent
protection
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
The relay has two Ground/Sensitive Ground Instantaneous Overcurrent protections per
setpoint group. The settings of these functions are applied to the measured ground, or
sensitive ground current for producing pickup and trip flags. The Ground IOC pickup flag is
asserted when the ground current is above the PKP value. The Ground IOC operate flag is
asserted if the element stays picked up for the time defined by the Ground IOC PKP Delay
setting. If the pickup time delay is set to 0.00 seconds, the pickup and operate flags will be
asserted at the same time. The element drops from pickup without operation if the ground
current drops below 97 to 99% of the pickup value.
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 IOC1(2)
GND IOC1(2) FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm
Default: Disabled
The selection of the Alarm, Latched Alarm or Trip setting enables the Ground/Sensitive
Ground IOC function. With the GND IOC function selected as Alarm , and GND IOC
operational, the "ALARM" LED will flash, and will self-reset, when the operating condition
clears. Until a reset command is initiated, if Latched Alarm is selected, the "ALARM" LED
will flash during the IOC operating condition, and will stay "ON" after the condition clears.
If the Trip setting is selected, the IOC menu allows the user to select the operation of
either one of the two trip output relays "RLY1 TRIP W1 BKR", "RLY2 TRIP W2 BKR", or both.
Any or all of the output relays 3 to 6 can be selected to operate no matter whether the
Alarm, Latched Alarm or Trip setting is selected.
GND CT INPUTS
Range: CT(W1), CT(W2)
Default: CT(W1)
The Ground Instantaneous Overcurrent menu provides for selection of either the ground
CT of Winding 1-CT(W1), or the ground CT of Winding 2- CT(W2) input. If CT(W1) is
selected, the GND IOC element will use the ground CT rating of Winding 1 entered on the
relay under SYSTEM SETUP/S2 CURRENT SENSING. If CT(W2) setting is selected, the relay
will use the ground CT rating associated with transformer Winding 2.
GND IOC1(2) PKP
Range: 0.05 to 20.00 x CT in steps of 0.01 x CT
Default: 1.00 x CT
SENS.GND IOC1(2) PKP
Range: 0.005 to 3.000 x CT in steps of 0.001 x CT
Default: 1.000 x CT
This setting sets the ground overcurrent pickup level specified as times CT. For example,
a PKP setting of 0.9 x CT with 300:5 CT translates into 270A primary current. For Sens.
Ground CT, the range of the setting is from 0.005 to 3.000 x CT, with a step of 0.001 x CT,
and a default value of 1.000 x CT.
GND IOC1(2) DELAY
Range: 0.00 to 300.00 sec in steps of 0.01 sec
Default: 0.00 sec
This setting provides the selection of the pickup time delay used to delay operation of
the protection.
S3 PROTECTION
6–97
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