BENSHAW RediStart MX3 Series, User Manual

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The following diagram illustrates how the current and the Motor Overload Hot/Cold Ratio (PFN31) parameter determine the steady state
overload content. It assumes there is no current imbalance.
At time T0, the motor current is 100%FLA and the OL H© Ratio is set at 30%. It is assumed that the motor has been running for some
time and the motor overload content has reached a steady state value of 30% (30% H/C Ratio x 100% FLA = 30%).
At time T1, the motor current drops to 50%FLA. The motor overload content exponentially cools to a new steady state value of 15%
(30% H/C Ratio x 50% FLA = 15%).
At time T2, the OL H© Ratio is set to 80%. The motor overload content exponentially rises to a new steady state value of 40% (80%
H/C Ratio x 50% FLA = 40%).
At time T3 the motor current rises back up to 100%FLA. The motor overload content exponentially rises to a new steady state value of
80% (80% H/C Ratio x 100% FLA= 80%).
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7 - THEORY OF OPERATION
Motor
Current
OL H/C
Ratio
Motor
Overload
Content
100%FLA
0%FLA
50%FLA
0 %
80 %
30 %
T0 T1 T2 T3
0 %
30 %
15 %
40 %
80 %
Figure 36: Motor Overload H/C Ratio Example