GE Multilin M60 Motor Protection System 5-147
5 SETTINGS 5.6 GROUPED ELEMENTS
5
• IEC CURVE TIME CONSTANT: This setting specifies thermal time constant for IEC motor curves in the above equa-
tions per the IEC 255-8 standard. When the IEC motor curves are selected, the M60 calculates the time to trip using
the IEC255-8 cold curve and IEC255-8 hot curve equations and increases thermal capacity used as defined by the
thermal capacity used equation above. If the overload disappears or the motor is tripped (stopped), then the thermal
capacity used decreases as per the following equations to simulate motor cooling, depending on the motor status and
the values programmed for the
COOL TIME CONSTANT RUNNING and COOL TIME CONSTANT STOPPED settings.
If the IEC curve is selected, then the following applies:
1. For two-speed motor applications, the IEC CURVE K FACTOR and IEC CURVE TIME CONSTANT settings are used at
both speeds.
2. Voltage dependent overload curves are not applicable.
3. The motor status is evaluated using motor FLA (I
b
) and the IEC CURVE K FACTOR setting.
• THERMAL MODEL TD MULTIPLIER: This multiplier is used to shift the overload curve on the time axis to create a
family of the different curves. The TD multiplier value is used to select the curve that best matches the thermal charac-
teristics of the protected motor.
If thermal model curve is selected as “Motor”, then the THERMAL MODEL TD MULTIPLIER can be specified
between “1.00” and “15.00” as indicated in the Standard motor curves diagram below.
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