6–78 350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
S3 PROTECTION CHAPTER 6: SETPOINTS
Neutral timed
overcurrent
protection
The relay has one Neutral Time Overcurrent protection element 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 operate 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 neutral current drops below 97-99% of
the pickup value, before the time for operation is reached. The selection of Definite Time
has a base time delay of 0.1 s, multiplied by the selected TD multiplier. For example the
operating time for TOC set to Definite Time and a TDM set to 5 will result in 5*0.1 = 0.5 s.
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) > NEUTRAL TOC
NTRL TOC FUNCTION
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
The selection of the Latched Alarm, Alarm, or Trip setting enables the Neutral TOC
function. The output relay #1 “Trip” will operate if the Neutral TOC 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 TOC operates when set to
function Trip. The “ALARM” LED will flash upon Neutral TOC operating condition with the
TOC function selected as Alarm, and will self-reset when the operating condition clears.
If Latched Alarm is selected as a TOC function, the “ALARM” LED will flash during TOC
operation, and will stay “ON” after the operation clears, until a reset command is
initiated. The output relay #1 “Trip” will not operate if 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 TOC function is selected as Latched Alarm, Alarm, or Trip.
NTRL TOC 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 time overcurrent pickup level. For example, a PKP setting of 0.9 x CT
with 300:5 CT translates into 270A neutral current.
NTRL TOC CURVE
Range: ANSI Extremely/Very/Moderately/Normally Inverse, Definite Time, IEC Curve A/B/C
and Short Inverse, IAC Extremely/Very/Inverse/Short, User Curve, FlexCurve A, FlexCurve B
Default: Extremely Inverse
This setting sets the shape of the selected over-current inverse curve. If none of the
standard curve shapes is appropriate, a custom User curve, or FlexCurve can be
created. Refer to the User curve and the FlexCurve setup for more detail on their
configurations and usage.
NTRL TOC TDM
Range: 0.50 to 20.00 in steps of 0.01
Default: 1.00
This setting provides selection for 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 an elapse of 495 ms from pickup.
Courtesy of NationalSwitchgear.com
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