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CHAPTER 6: SETPOINTS
Neutral
instantaneous
overcurrent
protection
NOTE:
NOTE
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
The relay has two Instantaneous Overcurrent elements per setpoint group. The settings of
this function are applied to the calculated neutral current to produce pickup and trip flags.
The Neutral IOC pickup flag is asserted when the neutral current is above the PKP value.
The Neutral IOC operate flag is asserted if the element stays picked up for the time defined
by the Neutral IOC 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 neutral current drops below 97-99% 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 > S3 SETPOINT GROUP 1 (2) > S3 NEUTRAL IOC1(2)
NTRL IOC1(2) FUNCTION
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
The selection of the Alarm, Latched Alarm or Trip setting enables the Neutral IOC
function. With the NTRL IOC function selected as Alarm , and NTRL IOC 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 IOC operation, 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.
NTRL CT INPUTS
Range: CT(W1), CT(W2)
Default: CT(W1)
The Neutral Overcurrent menu provides selection for either CT (W1), or CT(W2) phase
inputs. If CT(W1) is selected, the NTRL IOC element will use the neutral current computed
by the relay based on Winding 1 phase currents and the Winding 1 CT ratings. If CT(W2)
setting is selected, the relay will use the computed neutral current based on Winding 2
phase currents and Winding 2 CT ratings.
NTRL IOC1(2) PKP
Range: 0.05 to 20.00 x CT in steps of 0.01 x CT
Default: 1.00 x CT
This setting sets the neutral instantaneous overcurrent pickup level specified in times CT.
NTRL IOC1(2) DELAY
Range: 0.00 to 300.00 sec in steps of 0.01 sec
Default: 0.00 sec
This setting provides for selection of the pickup time delay used to delay the operation of
the protection.
RLY1 TRIP W1 BKR and RLY2 TRIP W2 BKR
Range: Do Not Operate, Operate
Default: Do Not Operate
The menu for the two trip output relays - RLY1 TRIP W1 BKR and RLY2 TRIP W2 BKR - is
available only if the Trip setting is selected as a function for the Neutral IOC element.
One or both trip output relays can be selected to operate upon Neutral IOC operation.
The "RLY1 TRIP W1 BKR" and "RLY2 TRIP W2 BKR" setpoints will be displayed on the OC
menu regardless of the selected OC function. These output relays will not operate if
either Alarm or Latched Alarm is selected as an OC function, regardless of the Operate/
Do Not Operate value selected. The output relays are operational only if the OC function
is selected as Trip.
S3 PROTECTION
6–103
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