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S3 PROTECTION
6–46
THERMAL O/L CURVE
Range: Standard, FlexCurve
Default: Standard
When FlexCurve is selected, the 339 relay used motor speed indication to apply
FlexCurve A or FlexCurve B. Flex curve A is active when the motor is running at low
speed. Flex curve B is active when the motor is running at high speed. If two-speed
function is not deployed, only FlexCurve A is active.
CURVE MULTIPLIER
Range: 1 to 15 in steps of 1
Default: 4
Fits the Standard Overload Curve to the thermal characteristics of the protected motor.
THERMAL O/L PKP
Range: 1.01 to 1.25xFLA in steps of 0.01xFLA
Default: 1.01xFLA
The Thermal Overload Pickup setting defines the current level at which the motor is
considered to be overloaded. The Overload Curve is cut off at current values below this
pickup value. Normally, the Thermal Overload Pickup Setting is set slightly above the
motor Service Factor, to account for inherent load measuring errors (CTs and limited
relay accuracy). The typical total inaccuracy factor is 8 to 10%; as such, for motors with
a thermal capability at rated service factor of 1 or 1.15, the Thermal Overload Pickup
level should be set as 1.10 or 1.25, respectively.
The Thermal Capacity Used value decreases exponentially when the motor equivalent
current (I
) is less than the Thermal Overload Pickup setting.
eq
UNBALANCE K FACTOR
Range: 0 to 19 in steps of 1
Default: 0
Sets the degree of unbalance biasing used by the Thermal Overload Curve. Zero disables
the unbalance bias.
COOL TIME RUNNING
Range: 1 to 1000 min in steps of 1 min
Default: 15 min
Sets the Cooling Time Constant used by the Thermal Overload Curve when the motor is
in service. Enter the time in minutes for the motor to cool by 63% of the difference
between the initial and ambient temperature when the motor is running at rated speed.
COOL TIME STOPPED
Range: 1 to 1000 min in steps of 1 min
Default: 30 min
Sets the Cooling Time Constant used by the Thermal Overload Curve when the motor is
not in service. Enter the time in minutes for the motor to cool by 63% of the difference
between the initial and ambient temperature when the motor is stopped.
HOT/COLD RATIO
Range: 0.01 to 1.00 in steps of 0.01
Default: 0.85
This setpoint controls the Hot/Cold Bias and RTD Bias features. If the safe stall time hot/
cold cannot be determined from the motor specification, a typical value of 0.85 is
suggested. If a HCR value of 1 is programmed, Hot/Cold Biasing is defeated.
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS
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