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TCC Number 691-9-U1February 16, 2009 S&C Electric
Company
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.5
.02
.01
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910
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.5 .6 .7 .8 .9 1 2 3 87654 400
9 600
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.5 .6 .7 .8 .9 1 2 3 87654 9400
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CURRENT, MULTIPLES OF PICKUP SETTING
CURRENT, MULTIPLES OF PICKUP SETTING
TIMEINSECONDS TIM
EINSECONDS
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.02
.01
.4
.2
.04
.03
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910
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15.00
12.00
10.00
8.00
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2.00
1.00
0.50
BASISThe average tripping time-current characteristic
curvesshown above are applicable to both 50-Hz and 60-Hz systems.
Inaddition, these curves are applicable over the entire S&C
VistaUnderground Distribution Switchgear operating temperature
rangeof -40C to +40C. No adjustments need to be made to these
curvesfor ambient temperatures within this temperature range.
TOLERANCESCurves are plotted to average test points.
Time-overcurrent tolerance, expressed in terms of current, is 5
amperesplus 5% of the selected pickup setting. Tolerance, expressed
interms of time, is 1.5 cycles plus 10% of the time indicated on
theselected curve at a specied value of current between 2 and
30multiples of the pickup setting.
Instantaneous pickup current tolerance is -0% to +10% of
theselected instantaneous pickup current level.
Denite-time response tolerance is -0 to 8 milliseconds.
I2t SECuRITy ChARACTERISTICTo protect the relay from
exceedingits thermal limits, for faults above 14.5 kA up to the
maximum sens-ing current of 25 kA, the I 2t security characteristic
may implement adenite-time tripping characteristic of 0.25 second
for any currentmagnitude above 14.5 kA, depending on the time-dial
set ting andthe minimum-pickup current selected. Refer to
Instruction Sheet681-515, Appendix D, Coordination.
APPLICATIONThe maximum continuous current-carrying capabil-ity
of S&C Vista Underground Distribution Switchgear is
1200amperes. The overcurrent control is capable of sensing currents
inthe range of 50 to 25,000 amperes RMS.
Since the tripping time-current characteristics are
electronicallyderived, they are not subject to change due to aging,
transient over-currents, or fault currents. It is, therefore, only
necessary to resetthe fault interrupters following a fault-clearing
operation.
CONTROL SETTINGSCurves are set using a laptop computer.
AVERAGE TRIPPING TImE-cuRRENT chARAcTERIsTIc cuRVEs
VISTA OVERCURRENT CONTROL U.S. mOdERATELy INVERSE (U1)
