In the actual production of many enterprises, often find some motor for a period of time is not used, again enabled when the motor winding insulation resistance decreased, especially in the rainy season, the air humidity is big, the insulation value even reduced to zero, this time should be dry, so that the insulation resistance and absorption ratio the specified value, if hastily put into operation, it is possible to make the motor coil insulation breakdown, causing the accident.
1. External heat source heating method
For the damp motor, it will be disassembled and inspected. Then, the high-power incandescent bulb will be placed inside the motor to bake it, or the motor will be put into the drying room for drying. This method is easy to operate, safe and reliable, but is only suitable for small motor with easy dismantling. For large or medium sized or not easily inspecting motors, the amount of work is larger and the feasibility is reduced. It should be noted that when the method is operated, the bulb or the heat source should not be too close to the coil, so as to prevent burnout of the coil.
2. Drying method of electric welding machine
2.1, AC welder before drying operation will damp winding 6 wiring head series, chassis grounding, so that it can be of three groups of windings for heating and drying, current monitoring changes in the drying process, can be strung into a current meter, observe whether its current reaches the rated motor current to 60% 70%. With the drying of the motor motor AC welder without dismantling the motor at the same time, reduce the workload, in the case of electricity by its heat resistance, the coil is evenly heated, the drying effect is better, but this method is only applicable to the motor below 100kW, and cannot be used for a long time, because the current AC welder when working with in the transformer on electric welding machine is large, can not be used for a long time, or it may burn the electric welder.
2.2. The drying method of the direct current welding machine is similar to the connection and communication. The series of ammeter should be a DC ammeter. It is convenient to use the DC electric welding machine to dry the dampness motor. At the same time, the large and medium motor and the high voltage motor can be dried for a long time. Because now we use the DC inverter welding machine, which adopts 380V three-phase AC voltage by three-phase bridge rectifier, filter feeding frequency conversion processing with new IGBT inverter power switch, the intermediate frequency step-down transformer, then rectified output for power source welding required, a logic control circuit through the integrated circuit the feedback of voltage and current signals are processed to achieve the closed-loop control, pulse width modulation control technology using PWM as the core, so as to obtain the constant current characteristics of fast pulse width modulation, and the cooling fan for cooling. In this way, when the welder works for a long time or at a high current, its internal components will not be damaged due to the long time high current operation, so it can be used for large and medium motors for a long time. It is worth noticing that when all two methods are used for drying, all contact points must be well contacted and fastened. The wire for the welder must be dedicated, and the size of the section shall meet the current carrying capacity of the electric welder. Pay attention to the cooling of the electric welding machine's own transformer, and ensure that the insulation resistance of the motor can not be less than 0.1M Omega. We should pay close attention to the temperature of the motor winding and adjust the voltage and current in time.
Summary: three-phase asynchronous motor with dry, no matter what method should be dry, in order to ensure personnel and motor safety, which requires in the process must always pay attention to motor winding and core temperature and insulation resistance, the temperature does not exceed the allowable value and record. When using infrared thermometer, class a insulation shall not exceed 70 degrees C, E and B shall not exceed 90 degrees. When using resistance method, a level shall not exceed 90 degrees, E and B shall not exceed 110 degrees. When dry, the insulation resistance of motor windings increases initially, then goes down, then rises again, so reciprocating, when the insulation resistance is stable, the drying can be finished.