High-Inertia Load Applications

The voltage dependent overload curve feature in Thermal Model is

tailored to protect motors which are used in high inertia load applications.

Voltage is continually monitored when the motor is started and during

acceleration. The thermal limit curve is then adjusted accordingly. This

enables the Multilin 869 to distinguish between a locked rotor condition,

an accelerating condition and a running condition.

This feature acts as an additional check of the amortisseur, or squirrel

cage winding rotor heating. This feature uses estimated speed-dependent

thermal capacity used (actual value ‘’ and compares this value to the

Thermal Capacity Used calculated by the current-based and RTD Bias

(when Enabled) methods. The larger of the three values is used from that

point onward.