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One case of fault handling of motor soft start control cabinet

2019-09-26

Soft start control cabinet troubleshooting:

One SSI)-320 soft start control cabinet controls two 280 kW units to supply water to the water purification plant by one-to-two connection. During one start-up operation, the operator closes the automatic switch QF, QF3, QF4 according to the procedure. Then press the "Start" button, the SSD-320 panel status indication "ON/EXIERNAL FAULT" is on, the KM3 action is closed, the motor does not rotate, the test is retried after reset, the fault remains, and the power cannot be turned on. The electrical wiring of the soft starter is shown in Figure 1. Show.

When analyzing this fault, first consider whether it is the soft start control cabinet itself or the external fault. Using the universal meter 5 v file to detect that the soft starter output vvw has no voltage, the contactor KM3 can be reliably closed, and the panel indicator 2HY1 is on, so the fault is likely to be in the soft starter itself. According to the panel status indication "ON x TERNAL FAULT" is on, it should be searched from the following three aspects, that is, whether the soft starter is overheated, whether the external fault input OE is open, and whether the microprocessor is faulty. Through analysis, we believe that there is no overheating when the motor is turned on, and it is important to check whether the external input OE () H 9-11 end point) is open. This point is a thermal relay normally closed contact that is overload-protected by the current transformer for the operation of the motor. It is used to prevent the soft starter from continuing to work when overloaded, resulting in protective measures for equipment failure. Since the motor has not been rotated, the thermal relay should not be operated. Check with a multimeter. The resistance between the 9·11 terminals of the KH is zero (normal). After the manual reset, the test is repeated. Although the fault is not solved, in many operations, it is occasionally successful. Once, it indicates that there is a bad contact at a certain point. According to the panel status indication °CN/EXTERNAL FAULT, focus on the OE input circuit, use the partial short-circuit measurement method, and short the OE ends with wires to try again, troubleshoot, replace with new ones. After the thermal relay is used normally, this is a special electrical circuit fault. The contact of the removed thermal relay is measured, and the resistance is zero (normal). The cause of the fault is due to the poor manufacturing quality of the components. The control cabinet is subjected to the strong vibration force of the AC contactor during the startup process, causing the thermal relay to instantaneously break, giving the soft starter a computer a command signal, causing the soft starter to stop.

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