Method and apparatus for testing of induction motor overload protection device

Apparatus for testing the operability of an overload protection device incorporated in an AC induction motor having motor input terminals and motor windings adapted for energization by a power signal applied to the input terminals, which device has contacts operative to disconnect the motor windings from the motor input terminals when the device temperature exceeds a predetermined temperature limit, said apparatus comprising:

• means for converting an AC input power signal to an unfiltered full wave rectified output power signal and applying said output power signal to the input terminals of the motor under test to rapidly raise the overload device temperature above the predetermined temperature limit;
• timing means for periodically interrupting said output power signal for relatively brief interrupt periods of sufficient duration to extinguish such arcing as may be occasioned by the opening of the overload device contacts, the period between successive interrupt periods being short enough to extinguish such arcing before the contacts are damaged;
• means for detecting the opening of the overload device contacts;
• means for determining if the contacts open within a predetermined time period;
• and
• means for generating a signal if the contacts fail to open within said predetermined period indicating that the overload device failed to operate properly.