CHAPTER 6: SETPOINTS
S3 PROTECTION
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
6–93
Ground timed
overcurrent
protection
The relay has two Ground Time Overcurrent elements per setpoint group. The settings of
the function are applied to the measured winding ground input current to produce pickup
and trip flags. The Ground TOC pickup flag is asserted, when the ground current is above
the PKP value. The Ground TOC trip 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 97-99% of the
pickup value, before the time for operation is reached. When Definite Time is selected, the
time for Ground TOC operation is defined only by the TDM setting. The Definite Time
selection has a default time of 0.1s.
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
NOTE
NOTE:
The settings from the menu for Sensitive Ground TOC, will appear only when the relay is
ordered with the sensitive ground CT. Otherwise, the relay displays the menu for Ground
TOC protection.
GND TOC1(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 TOC function. With the GND TOC function selected as
Alarm
, and GND TOC
operational, the “ALARM” LED will flash, and will self-reset, when the operating condition
clears. Until the reset command is initiated, if
Latched Alarm
is selected the “ALARM”
LED will flash during the TOC operating condition, and will stay “ON” after the condition
clears. If the
Trip
setting is selected, the TOC menu allows the user to select the
operation of either RLY1 TRIP W1 BKR”, “RLY2 TRIP W2 BKR”, or both trip output relays.
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 INPUT
S
Range: CT(W1), CT(W2)
Default: CT(W1)
The Ground Timed Over-Current menu provides for the selection for either ground CT of
winding 1 - CT(W1), or ground CT of winding 2 - CT(W2), input. If CT(W1) is selected, the
GND TOC 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 TOC1(2) PKP
Range: 0.04 to 20.00 x CT in steps of 0.01 x CT
Default: 1.00 x CT
SENS.GND TOC1(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 Time Overcurrent pickup level specified in times CT. For example, a
PKP setting of 0.9 x CT with 300:5 CT translates into 270A primary current. If the relay is
ordered with a Sensitive Ground CT, the range for this setting is 0.005 to 3.000 x CT, with
a step of 0.001xCT, and a default value of 1.000 x CT.
