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CHAPTER 4: SETPOINTS
NOTE:
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
TRIP CURVE
Range: Definite Time, Inverse Time
Default: Definite Time
Definite Time
When the curve is programmed as definite time, the trip element operates when the
operating quantity exceeds the pickup level for longer than the set time delay
(programmed as Trip Pickup Delay).
Inverse Time
The curve for the unbalance current is defined as:
2
T= TDM/[Unbal]
, where Unbal is defined by the preceding unbalance equation,
T= time in seconds when I
setpoints),
TDM= time dial multiplier
TRIP PICKUP DELAY
Range: 0.00 to 180.00 s in steps of 0.01 s (when TRIP CURVE = Definite Time)
Default: 1.00 s
The setting specifies a time delay for the trip function. This setting is only applicable
when Trip Curve is programmed as Definite 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. In order to prevent false operation of the element, it is strongly recommended to
set Trip Pickup Delay and Alarm Pickup Delay settings greater than two power cycles.
TRIP TDM
Range: 0.00 to 180.00 in steps of 0.01 (when TRIP CURVE = Inverse Time)
Default: 10.00
The setting provides a selection for Time Dial Multiplier which modifies the operating
times per the inverse curve. This setting is only applicable when Trip Curve is
programmed as Inverse Time.
TRIP MAX TIME
Range: 0.00 to 1000.00 s in steps of 0.01 s
Default: 1.00 s
The 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. This setting is only applicable when the Trip Curve is programmed as
Inverse Time.
TRIP MIN TIME
Range: 0.00 to 1000.00 s in steps of 0.01 s
Default: 0.25 s
Unbalance minimum time 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. This setting is only applicable when Trip Curve is
programmed as Inverse Time.
2
> pickup (minimum and maximum times are defined by
PROTECTION
4–135
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