Igbt Card Failures

[munkey]

Hi,

 

Wonder if anyone can shed any light for me on a problem i face with some ABB ACS800 drives.

 

Background;

 

A 160Kw 4 pole motor driven through an ACS800 0260 drive.

The motor is turning the bowl of a centrifuge approx weight 8 tonnes at a max speed of 1200 rpm, through a pulley ratio of 1.35 so max motor speed of 1620rpm.

 

Very slow ramp up time of 600 seconds. The control mode is DTC.

 

Beacause of the weight of the centrifuge a very slow controlled ramp down time of 800-1200 seconds is used.

 

There are multiple machines set up the same way and a few have now had the same problem. Short circuit fault down to faulty IGBT cards. This is a costly repair and should not normally be needed when the drive has only run a motor for less than 3000 hrs!!!!

 

Could this be caused by the generative power/heat during ramp down??

 

Is there any other way of stopping this apart from using a braking resistor??

 

Would running the drive in SCALAR be of any use??

 

Any help or advice would be greatly appreciated.

[AB2005]

Hi,

 

Could this be caused by the generative power/heat during ramp down??

 

Is there any other way of stopping this apart from using a braking resistor??

 

Would running the drive in SCALAR be of any use??

 

Any help or advice would be greatly appreciated.

 

I am sure this happened due to regenerative power during ramp down.

 

I am surprised that in such a case you did not use braking resistor. For me there should be a high wattage resistor connected with inverter whether you set a very slow ramp down. May be it happened that some time synchronous speed < then rooter speed (during ramp down) which then caused by regenerative voltage to drive.

 

I think using the drive in SCALAR mode is not a problem in such case, problem is that how you treat with regenerative power.

 

 

Best Regards

[marke]

Hello Munkey

 

It sounds as though you are controlling a high inertia load and once the load is at full speed, there is a lot of energy stored in the load. When you stop the machine, you have to take all that energy out of the load and move it elsewhere.

When you use the VFD to slow the load down, it will draw energy out of the load and this will cause the DC bus voltage to rise. If the DC bus voltage rises too much, the drive would normally trip out on over voltage but in same cases, the drive could fail in the manner that you describe.

Braking resistors can be used to dissipate the energy from the load, but the resistors must be large enough (power rating) to absorb the full speed kinetic energy of the load.

Sized correctly, the brake resistors will prevent the DC bus voltage from rising excessively.

Another issue to be careful of, is to ensure that there is no way that the VFD can start while the load is still spinning. If this occurs, there can be major problems as the VFD will be at a very low speed and the load at a much higher speed. There is usually a function on the drive called spin start or similar. I would recommend that this is turned ON. At start, the drive will scan through the speed range and determine the speed of the load before applying voltage to the motor. This preents problems but does introduce a start delay of a few seconds.

Another suggestion is to selct the stop mode to coast to stop so that the VFD does not try to slow the load down. If you select cost to stop, you must also selct spin start.

 

Best regards,

Mark.

[munkey]

Hi,

 

Thanks for your comments, i have some more questions though,

 

Do you think using flux braking on the motor would help? If more energy was was taken from the DC Bus in the form of heat in the motor then this could reduce the chance of the IGBT's being damaged. Then maybe fitting a forced vent unit to cool the motor?

 

I dont think i mentioned this in my earlier post but from the DC Link on the large drive is fed another VSD. This powers another motor @ 55kw so as the large 160kw motor ramps down the generated power or part of is being consumed by this other motor.

 

I have never had to use a braking resistor before but i believe thay can be rather large and expensive.

 

Munkey