Technical information

5 – PARAMETER DESCRIPTIONS
67
P37 Motor Overload Hot/Cold Ratio PFN 15
LCD Display
PFN:OL H/C Ratio
15 60 %
Range 0 – 99% (Default 60%)
Description The Motor Overload Hot/Cold Ratio parameter defines the steady state overload content (OL
ss
) that is
reached when the motor is running with a current less than full load current (FLA) * Service Factor
(SF). This provides for accurate motor overload protection during a “warm” start.
The steady state overload content is calculated by the following formula.
Facto
r
Derate ImbalanceCurrent
1
FLA
Current
Ratio H/C OLOLss ××=
The rise or fall time for the overload to reach this steady state is defined by the Motor Overload
Cooling Time parameter.
The default value of 60% for Motor Overload Hot/Cold Ratio parameter is typical for most motors.
A more accurate value can be derived from the hot and cold locked rotor times that are available from
most motor manufacturers using the following formula.
100% x
TimeRotor Locked ColdMax
TimeRotor LockedHot Max
1Ratio H/C OL
⎟
⎠
⎞
⎜
⎝
⎛
−=
NOTE: Consult motor manufacturer data to determine the correct motor overload settings.
See Also Motor Overload Cooling Time parameter on page 68
Independent Starting/Running Overload parameter on page 65
Motor Running Overload Class parameter on page 42
Motor Starting Overload Class parameter on page 66
Relay Output Configuration parameters on page 70
Theory of Operation section 8.1.6, Hot / Cold Motor Overload Compensation, on page 113
Theory of Operation section 8.1.4, Current Imbalance / Negative Sequence Current Compensation,
on page 112