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CHAPTER 6: SETPOINTS
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
UNBAL TRIP FUNC
Range: Disabled, Enabled
Default: Disabled
For details see
Common
UNBAL TRIP PKP
Range: 4.00% to 40.00% in steps of 0.01%
Default: 30.00%
This setting specifies a pickup threshold for the current unbalance trip stage. This setting
should be greater than the corresponding setting for the alarm stage.
UNBAL TRIP TDM
Range: 0.00 to 100.00 in steps of 0.01
Default: 10.00
This setting provides a Time Dial Multiplier which modifies the operating times per the
inverse curve. When the curve is set to "Definite Time", T(s) = TD multiplier. For example,
setting the TD multiplier to 2 results a time delay of 2 seconds to operate when
operating quantity is above the pickup level setting.
UNBAL TRIP CURVE
Range: Definite Time, Inverse Time
Default: Definite Time
For the definite time curve, T(s) = TD multiplier. For example, setting the TD multiplier to 2
results a time delay of 2 seconds to operate when operating quantity is above the
pickup level setting. Instantaneous operation can be obtained the same way by setting
the TD multiplier to "0".
For the Inverse Time curve setting, the curve for the unbalance current is defined as:
where:
T = time in seconds when Unbal > pickup (minimum and maximum times are defined by
setpoints)
TDM= time dial multiplier
UNBAL TRIP MAX TIME
Range: 0.00 to 1000.00 s in steps of 0.01 s
Default: 1.00 s
Unbalance maximum time defines the maximum time that any value of negative
sequence current in excess of the pickup value will be allowed to persist before a trip is
issued. This setting can be applied to limit the maximum tripping time for low level
unbalances.
UNBAL TRIP MIN TIME
Range: 0.00 to 1000.00 s in steps of 0.01 s
Default: 0.25 s
This setting defines the minimum time setting that can be applied to limit the minimum
tripping time. Small power system transients or switching device operation can
generate spurious negative sequence current that can result in the false operation of the
Current Unbalance element. Unbalance minimum time must be set in order to prevent
false operation of the element
setpoints.
S3 PROTECTION
6–57
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