Vsd Failure

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

Welding Set

Dear All,

I have an application Welding Set, on which I have to install a VFD. Welding Set is 200kva 415V, 2 phase input. Power Supply is from Generator which has a 3 phase output. Presently without a VFD, the Welding Set creates unbalance load at the Generator. I think that if VFD is installed in between, the problem of unbalance load can be solved. My worry is that since only 2 phase output of VFD will be used, will the VFD trip on motor cable open at output?

Has anyone installed a VFD in such application?

Regards,
Anurag

Centrifuge

Dear All,

I have been trying to start a Horizontal Centrifuge for last 2-3 days without any success. Traditionally the Centrifuge has been started either with VFD or with Slip Ring motor and starter. We tried to install a Softstarter on a 37kw 415V 1485rpm motor driving a Horizontal Centrifuge through a V Belt in between. The centrifuge was been started in unloaded condition ie the basket was empty. I tried possibly all the settings possible by Softstarter in both Voltage Ramp and Torque Ramp, but faced majorly one issue which was not getting solved.

Both in Voltage and Torque ramp, just when the motor was getting to reach full speed, high amount of slip started at motor shaft between shaft and belt. The sound suddenly increased to high levels, with high amount of friction between motor and belt, smoke starts coming out and current suddenly jumps for 2-3 seconds and then come back to low but since the friction is so high, I have to stop the SS.

In torque ramp, I started with 60 sec ramp, start torque of 15% and end torque of 100%. Increased it upto 90sec ramp, end torque 70% and then increased upto 120sec ramp, end torque 60%. But just when the motor seems to be coming up at full speed at the end of ramp up time, slip starts happening.

In voltage ramp, I started with 30 sec ramp, start voltage 30%. Then increased it to 60 sec ramp, start voltage 45%. But same slip at around full speed.

We started the same motor with Star Delta starter, and it went to full speed in 120 sec without any slip problems.

Any suggestions why this is happening. If Im unable to start an empty basket, how will I start fully loaded centrifuge.

Regards,
Anurag

Regenerative Application

Dear All,

I have a test bench application on which I want to install a drive which does not have an Active Front End rectifier. The drive rating is of 600hp/700hp/800hp. As the application is regenerative, AFE is mandatory. Im looking for a manufacturer who makes AFE rectifier on which any make drives can be hoooked up. Can anyone pls suggest if they have done such kind of application and company where I can get such rectifiers.

Regards,
Anurag

Ht Softstarter

Dear All,

Is it possible to install 690V softstarter on a 3.3kv 400kw motor for wood chipper application. For VFD, we used to install a step down transformer at the input of VFD, then at the output there was a sine wave filter and a step up tranformer afterwards. Is it possible to do the same way for a softstarter? Has anyone of you done this before?

Regards,
Anurag