Inverter: Peripheral circuit diagram is also important

It is connected to something outside, and it fails. In many cases, it is not necessarily caused by itself. It is necessary to find the inverter manual and the electrical schematic diagram of the on-site circuit according to the brand specifications, and sort out the overall start-stop logic of the inverter according to the drawings. This situation is very important for the situation where there is no alarm after the inverter stops.

Once, we helped a customer repair a medium-voltage inverter and tested the installation with an electrical cabinet. The programmable controller is controlled by the touch screen to start the inverter. As a result, when the PLC controls the intermediate contactor to supply power to the inverter, the switch of the entire cabinet trips. In this case, it can be immediately judged that there is a short circuit or poor insulation in the periphery. Later, the main circuit was checked one by one. diangon.com found that there is a large transformer at the front end of the inverter, which increases the three-phase voltage from 380 volts to 690 volts to power the inverter. The transformer is insulated from the ground.

The inverter has start and stop signals. If there is a problem with the external interlock I/O, the start-stop signal cannot be switched normally, the inverter will definitely not start and stop normally, and there will be no fault indication, because the inverter is normal.

Similarly, if the potentiometer is broken or the wires are connected incorrectly, it will also cause the inverter to not adjust the speed normally.

There is a customer's machine, after the inverter is started, it has been running at the same speed. They thought the inverter was broken and changed another one. Still the same. No way. Please come over. At first I felt very strange. Always keep the speed, but not too fast, and the external speed given by the potentiometer is also normal and good. Later, I checked the drawing and found that the start signal was connected to the jog mode. In this way, once started, the inverter will work in the jog state. The jog speed is usually 5% of the factory value, so it will run at a low speed. If it is changed back, it is normal.