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S3 PROTECTION
Neutral timed
overcurrent
protection
6–100
Courtesy of NationalSwitchgear.com
The relay has two Neutral Time 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 TOC pickup flag is asserted when the neutral current is above the PKP value.
The Neutral 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 operating if the neutral current drops below 97-99% of the pickup value,
before the time for operation is reached. When Definite Time is selected, the time for
Neutral TOC operation is defined only by the TDM setting.
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 TOC1(2)
NTRL TOC1(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 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 Alarm,
Latched Alarm or Trip setting is selected.
NTRL CT INPUTS
Range: CT(W1), CT(W2)
Default: CT(W1)
The menu of the Neutral Time OverCurrent element provides for selection of either CT
(W1), or CT(W2) input currents. If CT(W1) is selected, the NTRL TOC 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 NTRL TOC element will use the
computed neutral current from Winding 2 phase currents and Winding 2 CT ratings.
NTRL TOC1(2) PKP
Range: 0.04 to 20.00 x CT in steps of 0.01 x CT
Default: 1.00 x CT
This setting sets the time overcurrent pickup level specified as times CT. For example, a
PKP setting of 0.9 x CT(W1) with CT(W1) rating of 300:5 translates into 270A primary
current.
NTRL TOC1(2) CURVE
Range: ANSI Extremely/Very/Moderately/Normally Inverse Definite Time IEC Curve A/B/C
and Short Inverse IAC Extremely/Very/Inverse/Short
Default: Extremely Inverse
This setting sets the shape of the selected overcurrent inverse curve.
NTRL TOC1(2) TDM
Range: 0.05 to 20.00 in steps of 0.01
Default: 1.00
This setting provides for selection of the Time Dial Multiplier by which the times from the
selected 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,
operation of the element will not occur before 2.59s have elapsed from pickup.
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS
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