Jump to content

Common Mode Noise From Vsd


Recommended Posts

We have 4 ABB make ACS 550 series drives (30kw) in a dairy facility.

 

There are few computers on the same location which constantly have harddisk failures...we measured the common mode noise and found 5 volts.(output of UPS)

 

The online (APC make) UPS does filter some of the noise but still some noise is seen at its output.

 

I propose,

 

1.Replacing the existing unarmoured cable (VSD to motor) into armoured cable and the armour grounded at both sides.

 

2. Putting isolation transformer at the output of the UPS.

 

3. Putting line chokes for the VSD.

 

Are there any other known culprits which cause common mode noise... ( I have used Fluke 435 and found THDVN going as high 233% range 50-233%)

 

Are there any other things which can be done to protect the computers.

 

 

Any ideas appreciated.

Link to comment
Share on other sites

Hello Chaterpilar

VFDs do create a lot of switching noise and this noise is capacitively coupled inot the frame of the motor.

It is important to get the switching noise from the frame of the motor back to the frame of the VFD.

The best way to do this, is to use a proper EMC type screened cable with the screen connected to the motor frame via a screened gland, and connected to the frame of the motor using a screened gland or clamp.

 

The high frequency noise travels on the surface of the earth return, typically penetrating around 0.2mm inot the cable, so the important issue is maximum conductor surface area.

 

The addition of an EMC filter on the input of the VFD will improve the problem further, but will not work until the output is connected to the motor via a screened cable.

 

Best regards,

Mark.

Link to comment
Share on other sites

A screened cable is not necessary on the input unless you are using an input EMC fiter, in which case use a screened cable between the VFD and the filter unless it is installed very close to the VFD.

 

An isolation transformer may assist, but I expect that due to the high capacitance between the primary and secondary, it will have reduced affect.

 

Best regards,

Mark.

Link to comment
Share on other sites

A screened cable is not necessary on the input unless you are using an input EMC fiter, in which case use a screened cable between the VFD and the filter unless it is installed very close to the VFD.

 

An isolation transformer may assist, but I expect that due to the high capacitance between the primary and secondary, it will have reduced affect.

 

Best regards,

Mark.

 

 

Thanks Marke.

 

 

 

Link to comment
Share on other sites

  • 2 months later...

Hello Chaterpillar

 

NEVER NEVER use pigtails on motor screened cables!!!

 

You can fit an isolator in a metal box and gland the cable into and out of the box with screened glands.

As a compromise, put a metal plate across the bottom of a plastic box and gland into and out of the box via the metal plate.

 

If this is still not possible, clamp the screens together by overlapping the cables and putting a single hose clip around both cables.

 

Using a pigtail, is like a water pipe system using 6 inch pipe with a step down to 1/4 inch pipe and back up again. The smal pipe dictates the flow or hydraulic impedance.

 

Best regards,

Mark.

Link to comment
Share on other sites

  • 4 weeks later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...