Jump to content


Photo

Emx3 With 2 Parallel Motors

emx3 parallel

  • Please log in to reply
8 replies to this topic

#1 MB123

MB123

    Intermediate Member

  • Full Member
  • PipPipPip
  • 11 posts

Posted 28 March 2017 - 05:53 PM

Hi Mark and All,

 

We have a mixing machine with two motors coupled to the one shaft. Motors are identical. I would like to use one EMX3 soft starter, as I have done with other vendors, but I cant find anything addressing multiple parallel motors in Aucom's documentation

 

If I do this with their starter will they say that it was against their advice/warranty?

 

Thanks Michael



#2 mariomaggi

mariomaggi

    Senior Member

  • Full Member
  • PipPipPipPipPip
  • 230 posts
  • Gender:Male
  • Location:Milan, Italy
  • Interests:electric vehicles http://www.evlist.it , 3-phase AC sources to test PV inverters, high-power AC/DC power supplies up to 1500 VDC to test photovoltaic inverters, bidirectional AC/DC power supplies to test and simulate big batteries, infrared windows for thermography, renewable energies, special electric motors, special inverters, energy savings, power quality

Posted 28 March 2017 - 06:52 PM

MB123, 

you can use without problems your configuration. 

Best regards, 

Mario 


Mario Maggi - Italy - http://www.evlist.ithttps://www.axu.it


#3 marke

marke

    Posting Freak

  • Moderator
  • PipPipPipPipPipPip
  • 2,601 posts
  • Gender:Male
  • Location:Christchurch, New Zealand

Posted 28 March 2017 - 07:50 PM

I agree with Mario, there will not be a problem other than the motor protection will not discriminate between motors and will look at the combined current.

 

With two motors on the same shaft, the loading must be identical as the slip will be identical, so it will be effectively one motor with two stator windings. If you wanted to protect each winding, you could add individual overload relays to each winding.

 

Best regards,

Mark.



#4 MB123

MB123

    Intermediate Member

  • Full Member
  • PipPipPip
  • 11 posts

Posted 29 March 2017 - 06:17 AM

Thanks all for your quick and valuable responses

 

So the conclusion is that I should not be spooked by the fact that Aucom do not have application guidance for running two motors in parallel?

 

And, Mark, with respect to your comments regarding the slip being the same - are you saying that technically it would not be required to protect the two motors individually? This would make sense as any overload caused either by the process or a mechanical i.e. gearbox issue would present an overload on both motors equally.

 

We will probably still provide individual overloads though

 

Thanks again guys!



#5 marke

marke

    Posting Freak

  • Moderator
  • PipPipPipPipPipPip
  • 2,601 posts
  • Gender:Male
  • Location:Christchurch, New Zealand

Posted 29 March 2017 - 07:17 AM

Hello  MB123

 

Given that the two motors are identical, and the speed is identical, and the supply voltage is identical, the  torque produced by each motor will be close to identical, so there is no way for one motor to overload relative to the other. The only "individual" issue is a stator insulation breakdown.

 

Best regards,

Mark



#6 Shozza

Shozza

    Junior Member

  • Full Member
  • PipPip
  • 7 posts
  • Gender:Male
  • Location:Melbourne - Australia

Posted 20 April 2017 - 03:43 AM

Hello All,

 

Wouldn't AS/NZS 3000:2007 clause 4.13.2 dictate that "each" motor must be protected with a means of protection against overload?

I interpret this as an overload would be required for each motor to achieve compliance with the wiring rules.

I'd be interested to hear how others interpret this?

 

Best regards,

Shaun



#7 marke

marke

    Posting Freak

  • Moderator
  • PipPipPipPipPipPip
  • 2,601 posts
  • Gender:Male
  • Location:Christchurch, New Zealand

Posted 20 April 2017 - 04:53 AM

Absolutely, in order to be fully compliant, I would agree, but functionally, identical motors with a hardcoupled shaft, must be running at the same slip and voltage, so would load share well and you would not compromise the reliability by treating them as a single motor with two stator windings.

 

Best regards,

Mark



#8 MB123

MB123

    Intermediate Member

  • Full Member
  • PipPipPip
  • 11 posts

Posted 07 June 2017 - 02:23 AM

Hi All

 

Thanks for your response

 

Hey Shozza, thanks for the wiring rules reference. We would always have a thermal overload relay for each motor to ensure they are protected individually.

 

I have another question though on this topic. Another engineer has made the decision in this case to use two EMX3 starters in lieu of one larger one. Hence the two motors, on the same shaft, will each have their own starters.

 

Assuming the two starters are identical, and their settings are identical, can anyone see an issue with this? I.e. when starting I would not expect the voltage/torque produced by both motors to be exactly the same if they are connected to two different starters. How much difference could this be? Over time this may break the machine I would imagine.

 

Or even when it comes to commanding a start, would two EMX3s, each being commanded at the same moment, both start the motor at the same time or would there be a difference?



#9 marke

marke

    Posting Freak

  • Moderator
  • PipPipPipPipPipPip
  • 2,601 posts
  • Gender:Male
  • Location:Christchurch, New Zealand

Posted 07 June 2017 - 06:17 AM

Absolutely no problem with using two separate soft starters on the motors. I have done this many times.

 

If you set both starters up equally, then the start current on each will be similar, but if there is plenty of thermal capacity in the rotors of the motors, I would suggest looking at starting one motor only with a higher start current and then start the second when the machine is up to speed.

 

If starts are relatively frequent, you could add some logic and alternate the starts between the two motors.

 

The torque reduces by the square of the current reduction. If you start both motors at as 400% start current with a LRC of 900% and an LRT of 180%, then the start current is more than halved and the start torque is less than a quarter. 4/9 x 4/9 = 16/81 = 19.75% of the total start torque.

 

If we start one motor only at the same torque, the start current would be SQRT(19.75/90) x 900 = 596%

So this is 596% of one motor as opposed to 400% of two motors which is a much lower current.

 

Best regards,

Mark







Also tagged with one or more of these keywords: emx3, parallel

1 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users


    Google (1)