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5.6 S5 PROTECTION
5.6S5 PROTECTION
a) DESCRIPTION
The relay has a total of six phase, two neutral, one ground, one sensitive ground, and one negative sequence time overcur-
rent elements. The programming of the time-current characteristics of these elements is identical in all cases and will only
be covered in this section. The required curve is established by programming a Pickup Current, Curve Shape, Curve Multi-
plier, and Reset Time. The Curve Shape can be either a standard shape or a user-defined shape programmed with the
FlexCurve™ feature.
Accurate coordination may require changing the time overcurrent characteristics of particular elements under different con-
ditions. For manual closing or picking up a cold load, a different time-current characteristic can be produced by increasing
the pickup current value. In the 760, the pickup current can also be raised between autoreclose shots. The following set-
points are used to program the time-current characteristics.
•
<ElementName> PICKUP: The pickup current is the threshold current at which the time overcurrent element starts
timing. There is no intentional 'dead band' when the current is above the pickup level. However, accuracy is only guar-
anteed above a 1.03 per unit pickup level. The dropout threshold is 98% of the pickup threshold. Enter the pickup cur-
rent corresponding to 1 per unit on the time overcurrent curves as a multiple of the source CT. For example, if 100: 5
CTs are used and a pickup of 90 amps is required for the time overcurrent element, enter "0.9 x CT".
•
<ElementName> CURVE: Select the desired curve shape. If none of the standard curve shapes is appropriate, a cus-
tom FlexCurve™ can be created by entering the trip times at 80 different current values. See
. Curve formulas are given for use with computer based coordination programs. Calculated trip time val-
FLEXCURVE A
ues are only valid for I / I
curve with the protection requirements. The available curves are shown in the table below.
Table 5–4: TOC CURVE SELECTIONS
5
ANSI
Extremely Inverse
Very Inverse
Normally Inverse
Moderately Inverse
•
<ElementName> MULTIPLIER: A multiplier setpoint allows shifting of the selected base curve in the vertical time
direction. Unlike the electromechanical time dial equivalent, trip times are directly proportional to the value of the time
multiplier setpoint. For example, all trip times for a multiplier of 10 are 10 times the multiplier 1 or base curve values.
Setting the multiplier to zero results in an instantaneous response to all current levels above pickup.
•
<ElementName> RESET: Time overcurrent tripping time calculations are made with an internal 'energy capacity'
memory variable. When this variable indicates that the energy capacity has reached 100%, a time overcurrent trip is
generated. If less than 100% is accumulated in this variable and the current falls below the dropout threshold of 97 to
98% of the pickup value, the variable must be reduced. Two methods of this resetting operation are available, Instanta-
neous and Linear. The Instantaneous selection is intended for applications with other relays, such as most static units,
which set the energy capacity directly to zero when the current falls below the reset threshold. The Linear selection can
be used where the relay must coordinate with electromechanical units. With this setpoint, the energy capacity variable
is decremented according to the following equation.
where: T
= reset time in seconds; E = energy capacity reached (per unit); M = curve multiplier
RESET
C
= characteristic constant (5 for ANSI, IAC, Definite Time, and FlexCurves™; 8 for IEC)
R
Graphs of standard time-current curves on 11" × 17" log-log graph paper are available upon request. Requests may
be placed with our literature department.
NOTE
b) TOC CURVE CHARACTERISTICS
DEFINITE TIME CURVE:
Definite Time curves trip as soon as the pickup level is exceeded for a specified period of time. The base Definite Time
curve has a delay of 0.1 seconds. The curve multiplier adjusts this delay from 0.00 to 10.00 seconds in steps of 0.01.
5-32
Courtesy of NationalSwitchgear.com
> 1. Select the appropriate curve shape and multiplier, thus matching the appropriate
pu
GE TYPE IAC
IEC
Extremely Inverse
Curve A (BS142)
Very Inverse
Curve B (BS142)
Inverse
Curve C (BS142)
Short Inverse
IEC Short Inverse
T
=
RESET
750/760 Feeder Management Relay
OTHER
Definite Time
FlexCurve™ A
FlexCurve™ B
×
×
E M C
R
5 SETPOINTS
5.6.1 OVERVIEW
S2 SYSTEM SETUP
(EQ 5.1)
GE Multilin
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