Force Failure Dielectric Test Design For Stators Of Inverter Compressors

(PMAC) Electric motor is used at Variable Speed Refrigeration Compressors. Stator is the stationary part of a PMAC motor and stator wires directly carry the current, which energizes the motor and runs the refrigerator compressors. These wires are wound on stator stack which is made of electrical steel. The windings can be also close to other metal parts of the compressor. Stator stack is connected to compressor metal parts by metal screws. So, if a leakage current occurs through the stator stack, it is directly conveyed to compressor housing and then to refrigerator which can cause electric shock on the customer. That’s why, not only the quality but also the reliability of insulation between stator wires and metal parts is so critical. Standard dielectric strength tests are applied to both stators and compressors during production in order to check the insulation quality for product safety in the field. But it is not possible to detect the weakness and aging in this way. Most insulaton faults arise in time by repetitive voltage increase, thermal, mechanical, environmental and electrical stresses. This study explains the test which is carried out to detect potential electrical safety, leakage current and compressor failure problems which can occur on inverter stators in process of time. The development of Forced Failure Dielectric Test for the stators aims to uncover the insulation weakness which cannot be find out by Quality Tests and which can cause functional and safety problems in the field

Restart Test Design For Inverter Compressors

When a short power cut or electricity failure occurs on an electric supply system, which the household refrigerator is connected to, the suction and discharge pressures of the system become unbalanced, and the compressor exposes to higher loads than rated conditions. If the power recovers very quickly before the pressures get balanced, the compressor may not overcome the load and fails to start up. If the inverter control of the compressor has Class B protection software instead of mechanical overload protector; the inverter software forms a fault signal, cuts the energy through the compressor and waits for a while that provides pressure balancing before the next compressor start up trial. Provided that the compressor starts up, or the inverter control cuts energy by a fault signal, the compressor periodically tries running in an infinite loop. This situation prevents compressor running and cooling of the refrigerator. In order to prevent this, the inverter board and the control software should be controlled at every load condition if it works properly or not. Generally, a standard restart test is done to refrigerators by cutting the electricity off and energizing after a few seconds in order to check if the compressor starts up or a fault signal occurs. This test only checks one load condition and every different suction-discharge pressure value after power cut cannot be simulated that can occur in the field. Simulation of all loads on the refrigerator is a hard situation because providing variable suction-discharge pressure values on the refrigerator system is impossible and waiting for pressure balancing takes a long time for every load condition. For this paper; a compressor restart test is studied without a refrigerator and an array of suction-discharge pressures that can occur against the compressor is determined in case of a short power off-on situation in order to check all load conditions of the refrigerator. The test is carried out by compressor-electronic control pairs on a cooling system simulator. The compressor test results are verified by testing the same compressors on the refrigerator