In the air compressor starter box, the motor start and stop is completed by the contact of the intermediate relay in the instrument control cabinet, and the air compressor is automatically started and stopped by the system pressure control, that is, when the system pressure reaches the set upper limit of 0.75 MPa, the unit unloading operation The running time reaches the set time and the system pressure has not dropped below the system setting pressure lower limit of 0.4 MPa, and the unit automatically unloads and stops.
If the gas consumption is large, the unit will stop without unloading, load and run until unloading operation, and repeat. These controls are completed by the pressure relay, time relay and intermediate relay in the instrument control cabinet. The air compressor unit is running in the automatic control state. The operation personnel are in the unsupervised state except for the inspection twice per shift.
The cause of the auto-coupling transformer heating is that the main contactor does not pull in during the starting process, the motor can not run at full pressure, and the autotransformer is operated, causing it to heat up and ignite. There are two reasons why the intermediate relay does not pick up:
First, since the air compressor motor is 138 kW, the main contactor uses an AC contactor, and its armature is heavier. When the air compressor starts, it vibrates greatly. Over time, its own coil lead is vibrated or the armature is buckled. In normal operation, the normally open contact of the intermediate relay and the normally closed contact of the autotransformer star point contactor make the relay pull in and can not be sucked. The motor runs with the autotransformer, and the autotransformer becomes Reactor, the coil heats up and causes an accident;
Second, the time relay in the control loop is damaged, so that the motor is always decompressed by the autotransformer, and the autotransformer heats up and burns out.
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