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Anonymous Poster #1

variable frequency drive starter

08/04/2011 12:01 PM

Kindly note that I need to specifu a Variable frequency drive starter for a motor and the distance between the starter and the motor is around 200 meters. Can this be done? If it's the case, what other equipments are to be specified and what are the constrainsts?

Waiting for your reply,

Thank you.

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#1

Re: variable frequency drive starter

08/04/2011 1:51 PM

You're very vague about your equipment and application, so here's a general paper about the things you need to know when developing a VFD applicaton.

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#2
In reply to #1

Re: variable frequency drive starter

08/04/2011 3:45 PM

An interesting read...

I wonder why the graphic on page 3 shows spiking as a result of long lead length, but the text of the article does not touch on it specifically. I guess that's the part where noise is referred to as a concern and shielding is recommended, or insulation breakdown and improvement is necessary.

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#3
In reply to #2

Re: variable frequency drive starter

08/04/2011 5:14 PM

I wonder why the graphic on page 3 shows spiking as a result of long lead length, but the text of the article does not touch on it specifically.

That's probably because that issue warrants white papers all by itself, it's a fairly involved issue. A "reader's digest" version is that capacitive coupling occurrs between the motor lead conductors as a result of the high speed DC switching that makes up the PWM signal going from the VFD to the motor. The capacitive coupling is additive over distance, so the longer the distance the higher the voltage peak of the "standing wave" that is generated, so much so that after a certain amount, it exceeds the insulation breakdown voltage of the motor winding insulation and destroys the motor. If you do a web search for "standing wave generation in VFDs" you will find plenty of articles and papers that will go into it more.

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#4

Re: variable frequency drive starter

08/05/2011 3:57 AM

Of course it can be done. And there are no special constraints if the drive is CE-marked. Just follow British Standard 7671 in selecting the correct cable.

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#5

Re: variable frequency drive starter

08/05/2011 4:18 AM

Yes, of course it can be done, you can discuss any installation considerations with any decent supplier e.g.

  • Type of motor cable - normally shielded or armoured for VFDs
  • Power rating - some smaller drives may need a motor choke for this cable length (capacitance)
  • Motor approval - peak voltage is regarded as a maximum of 2x so about 1200V on a 400V system, any decent motor insulation is rated higher than this. Is it a standard motor?
  • Any other cables e.g. encoder will need consideration as this distance may then need optical fibre or 'repeaters'
  • Inverter settings re the PWM or v/f or vector taking motor cable (+ choke?) into account

Generally, if the application is pretty standard, it's not too much of a problem but if you need specific advice, please supply more details re your application details and other installation / environmental conditions to get a more measured specific response.

I've just been installing pumps with 1200m motor cable at 5.5kW, for example.

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