anu_rags Posted August 19, 2008 Report Share Posted August 19, 2008 Dear All, We had installed a VFD for a rack and pinion hoist (passenger and material elevator in construction industry). The drive had inbuilt brake chopper and brake resistor was connected to it. Brake resistor had been mounted on top of the elevator. The drive was operating satisfactory for 2 days and on the 3rd day there was some smoke coming out from the resistor and the main breaker tripped. Once the supply was regiven customer tried to start drive twice but it didnt started. Later the drive was completely broken and there was no display. These events have been described by customer, so Im not sure if the drive was broken the first time itself when breaker tripped or it broke later when they tried to restart it. The opened the resistor and found nothing burnt inside. They also checked the resistance and found OK. Im not sure if they properly did the continuity test. Later it was replaced by new spare VSD by the customer and as soon as they connected the brake resistor cable to the VSD, the main breaker tripped. That confirmed to them, that there is something wrong in resistor only. Later when our service engineer reached the site and opened the resistor, he found that one of the cable sleeve inside the resistor panel was cut and the cable was touching the body. Resistor manufacturer is explaining that the cable had not come with cut when delivered as the VSD has run without any problems for 2 days. Since there is vibration in the elevator, the inside panel acted like knife and cut the cable. When new VSD was connected, the main breaker was tripping on earth fault as it was detecting cable touching with the body. During running when the cable touched body, the breaker tripped. Why did the 1st VFD got broken? It should have tripped on overcurrent or earth fault. Regards, Anurag Link to comment Share on other sites More sharing options...
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