GE Multilin 850, Instruction Manual

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CHAPTER 6: PROTECTION SETPOINTS CURRENT ELEMENTS
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL 6–11
DEFINITE TIME CURVES
The Definite Time curve shape operates as soon as the Pickup level is exceeded for a
specified period of time. The base Definite Time curve delay is in seconds. The curve
multiplier of 0.05 to 600 makes this delay adjustable from 50 to 600000 milliseconds.
Where:
T = operate time (in seconds)
TDM = Multiplier setting
I = input current
I
pickup
= Pickup Current setting
T
RESET
= reset time in seconds (assuming energy capacity is 100% and RESET is
“Timed”)
Percent of Load-To-Trip
The Percent of Load-to-Trip is calculated from the phase with the highest current reading.
It is the ratio of this current to the lowest pickup setting among the phase time and the
instantaneous overcurrent elements. If all of these elements are disabled, the value
displayed is “0”.
Phase Time Overcurrent Protection (51P)
The 850 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 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 > Phase TOC 1(X)
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
SIGNAL INPUT
Range: Dependant upon the order code
Default: CT Bank 1-J1
This setting provides the selection for the current input bank. The default bank names
can be changed in: Setpoints > System > Current Sensing > [Name] > CT Bank Name.
INPUT
Range: Phasor, RMS
Default: Phasor