GE 845, Instruction Manual

Page: 289 / 552

CHAPTER 4: SETPOINTS PROTECTION
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 4–161
Phase Time
Overcurrent
Protection (51P)
The 845 relay TOC element can be configured with any of the IEEE, ANSI, IEC, and IAC
standard inverse curves, any of the four FlexCurves, or set to definite time. The selection of
Time Dial Multiplier (TDM) and minimum PKP, helps the user to fine tune the protection for
accurate upstream/downstream coordination and during certain conditions, such as
manual closing and Maintenance.
The settings of this function are applied to each of the three phases to produce Pickup and
Trip flags per phase. There is no intentional “dead band” when the current is above the
Pickup level. However the Pickup accuracy is guaranteed within the current input
accuracy of 1.5% above the set PKP value. The TOC Pickup flag is asserted, when the
current on any phase is above the PKP value. The 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 measured current
drops below 97 to 98% of the Pickup value before the time for operation is reached. When
Definite Time is selected, the time for TOC operation is defined only by the TDM setting.
The selection of TDM when in Definite Time mode sets the time to operate in seconds.
Path :
Setpoints > Protection > Group 1(6) > Current > Phase TOC 1(X)
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
INPUT
Range: Phasor, RMS
Default: Phasor
PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 1.000 x CT
CURVE
Range: IEEE Extremely / Very / Moderately Inverse; ANSI Extremely / Very / Normally /
Moderately Inverse; Definite time IEC A / B / C and Short Inverse; IAC Extremely / Very /
Inverse / Short Inverse; FlexCurve A / B / C / D, I2t, I4t
Default: IEEE Moderately Inverse
TDM
Range: 0.05 to 600.00 in steps of 0.01
Default: 1.00
The setting provides a selection for Time Dial Multiplier which modifies the operating
times per the selected inverse curve. For example, if an IEEE Extremely Inverse curve is
selected with TDM = 2, and the fault current is 5 times bigger than the PKP level, the
operation of the element will not occur before 2.59 s have elapsed after Pickup.
RESET
Range: Instantaneous, Timed
Default: Instantaneous
Selection of an Instantaneous or a Timed reset time is provided using this setting. If
Instantaneous reset is selected, the Phase TOC element will reset instantaneously
providing the current drops below 97-98% of the Phase TOC PKP level. If Timed reset is
selected, the time to reset is calculated based on the reset equation for the selected
inverse curve.
DIRECTION
Range: Disabled, Forward (Ph Dir OC 1 FWD), Reverse (Ph Dir OC 1 REV)
Default: Disabled