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marke

Member Since 24 Apr 2002
Offline Last Active Today, 08:51 AM
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Topics I've Started

Reducing Vfd Stray Voltage Problems In Dairy Sheds (Parlours)

08 August 2020 - 11:58 PM

VFD induced stray voltages can cause major issues in cow shed (dairy palours).

Typical symptoms are :

  • Interference with ear tag readers
  • High Somatic Cell Count in the milk
  • Agitated Cows - reluctance to enter the milking bales
  • Extended milking times due to poor milk let down
  • Excessive defecation while in the bails
  • High Mastitis incidence.

 

There are some basic fundimental issues when using VFDs in dairy sheds that must be adhered to when using PWM VFDs :

 

  1. The connection between the VFD output and the motor MUST be using a screened cable with the screen continuous the whole way.
     
  2. The screen must be terminated in the output of the VFD by a circular clamp around the screen to the chassis of the VFD, or, if there are conatcors on the output of the VFD, the screen must be bonded to the metal gear tray the the VFD is mounted on by a circular clamp or saddle clamp.
     
  3. If there is an isolator on the output of the VFD, (typically mounted near the motor), the screen of the cable going to the VFD and the screen of the cable going to the motor must be bonded together by a circular clamp(s). This can be via a flat metal plate, or bonded together.
     
  4. The screen of the cable must be bonded to the motor. This can be by means of an EMC gland into the motor terminal box (assuming metal box) or via a clamp onto the frame of the motor.
     
  5. The EMC filter in the VFD must be enabled, or an external EMC must be fitted.

     

Where these steps have been correctly taken, and a problem still exists, there are a number of steps that can be taken, but there must be a continuous screen path between the VFD chassis and the motor for these additional steps to work properly.

Potential improvements :

  1. Add low frequency common mode chokes to the output cores going to the motor. This usually entails one or more turns of all the three phase conductors through one or more common cores. (NOTE: output conductors only, not the earth conductor). High inductance EMC ferrite cores can be used but the best results are from specialised cores designed for this purpose. - consult your VFD supplier.
     
  2. External EMC filter on the input.
     
  3. dv/dt filter on the output of the VFD
     
  4. Sinewave Filter on the output of the VFD. (use sinewave or dv/dt, but not both.)

 


Posting To The Forum

03 August 2020 - 09:52 AM

Recent updates to web browsers and security issues have made posting to this forum difficult.

Microsoft explorer, Mozilla Firefox and Google Chrome do not save new posts reliably, but Opera still seems to work.

 

I am working on determining the cause of this so that it can be rectified.

Replies to existing posts still seems to work OK.

 

Best regards,

Mark.


Webinars

03 August 2020 - 09:43 AM

Horner have been running very good webinars on CScape and the Horner OCS units during May, June and July 2020.
At present, these webinars can be viewed from the Horner website.
See www.hornerautomation.com/webinars/
The next is on August 12 2020 on the topic of Ethernet IP Communications.

Xle Updated

03 August 2020 - 09:18 AM

The XLe has gone through two stages of update.

The first update, was to include a mini USB programming port.

This requires CScape 9.8 or later to connect. Earlier versions of CScape will not find this processor.

 

The second update, is to enhance the processor performance and include an Ethernet port.

This unit is known as the XLEe and will commonly be specified as an XLe 1E2 where the 'E' refers to the Ethernet port.


Emx4I

03 August 2020 - 09:01 AM

The EMX4i range is being expanded to cover larger models.

More information coming.