CHAPTER 6: SETPOINTS S3 PROTECTION
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL 6–81
Neutral
instantaneous
overcurrent
protection
The relay has two Instantaneous Overcurrent protection elements per setpoint group. The
settings of this function are applied to the calculated neutral current for 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 before
the time for operation is reached.
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 > PROTECTION > SETPOINT GROUP 1 (2) > NEUTRAL IOC1(2)
NTRL IOC1(2) FUNCTION
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
The selection of the Latched Alarm, Alarm, or Trip setting enables the Neutral IOC
function. The output relay #1 “Trip” will operate if the Neutral IOC function is selected as
Trip, and the neutral current calculated by the relay satisfies the operating condition set
by the settings. The “ALARM” LED will not turn on if the neutral IOC operates when set to
function Trip. The “ALARM” LED will flash upon Neutral IOC operation with the IOC
function selected as Alarm and will self-reset when this operation clears. If Latched
Alarm is selected as an IOC function, the “ALARM” LED will flash during IOC operation and
will stay “ON” after the operating condition clears, until the reset command is initiated.
The output relay #1 “Trip” will not operate if the Latched Alarm or Alarm setting is
selected. Any or all of the output relays 3 to 6 can be selected to operate when the
Neutral IOC function - Latched Alarm, Alarm, or Trip - is selected.
NTRL IOC PKP
Range: 0.05 to 20 x CT in steps of 0.01 x CT
Default: 1.00 x CT
This setting sets the neutral instantaneous overcurrent pickup level.
NTRL IOC DELAY
Range: 0.00 to 300 sec in steps of 0.01 sec
Default: 0.00 sec
This setting sets the neutral instantaneous overcurrent delay.
NTRL IOC DIRECTION
Range: Disabled, Forward, Reverse
Default: Disabled
This setting provides control to the Neutral IOC1(2) function in terms of permitting
operation upon fault conditions in the selected current flow direction, and blocking it
when faults occur in the opposite direction.
OUTPUT RELAY 3 to 6
Range: Do Not Operate, Operate
Default: Do Not Operate
Any or all of the output relays 3 to 6 can be selected to operate upon a Neutral IOC
condition. Relay outputs operation is available no matter whether the Latched Alarm,
Alarm, or Trip function is selected.
Courtesy of NationalSwitchgear.com
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