×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Motor with centrifcal pump runing at 385-393 volts 3ph incomming.

Motor with centrifcal pump runing at 385-393 volts 3ph incomming.

Motor with centrifcal pump runing at 385-393 volts 3ph incomming.

(OP)
We have motor rated at 460 3ph .5hp with centrifical pump 60hz. There are two machining centers from France and They have large step down transformers from 480 down to 400 volts, each have one of these .5hp pumps.  The incoming voltage to one is 388-393 volts the other is 385-390 volts the amp reading are .8 amps and 1.3 amps repectively. we have been burning out the one with higher amps.  
    One thing more the outlet dia. of the problem pump has been down sized. will this also cause higher current? Also should look to see if the taps on transformer can be changed?

RE: Motor with centrifcal pump runing at 385-393 volts 3ph incomming.

The smaller outlet would not normally increase the load but would actually decrease it. So that is not the issue.

If the those motors are really 460V and you are ultimately feeding them with 390V that is your problem.  You would need to fix that. Soon!

These are 60Hz rated motors correct?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor with centrifcal pump runing at 385-393 volts 3ph incomming.

400/480=50/60. Looks like the transformers were selected to allow the 60Hz motors to run on the French 50Hz system. If they are now installed on a 60Hz system, bypass the transformers.

RE: Motor with centrifcal pump runing at 385-393 volts 3ph incomming.

I think it is possible the pump is an Axial Flow Pump.
The usually encountered pump is the Radial Flow Pump, indeed. If one will reduce the outlet orifice he will increase the head and reduce the flow and so will reduce the bhp also. If the pump is a Mixed Flow Pump no change in bhp will occur with outlet change. But if it is an Axial Flow Pump, by reducing the outlet the head will increase so much that the bhp will increase too even the flow will decrease.
If it is an Axial Flow Pump and the outlet is so reduced that the flow will be only 30% of the rated the bhp will be 1.5*bhp rated.
 

RE: Motor with centrifcal pump runing at 385-393 volts 3ph incomming.

Hello EETechs

If the motor is rated at 460 volts, then I would expect that this rating is at 60Hz. As you are operating at 60Hz, you should run the pumps at 460 volts.
As suggested by stevenal, the transformers are probably fitted to allow the pumps to run at 50Hz, and operation at 60Hz will have two results.
1. The pump is running faster and so the load on the motor is greatly increased relative to 50Hz. If the wet end (pump) has been selected to fully load the pump at 50 Hz, then you have a problem and the impeller will need to be reduced to reduce the load within ratings.
2. If a 460V 60Hz motor is operated at 400V 60 Hz, then the maximum torque capacity is reduced and the current draw under load will increase. Provided that the torque is within the rating of the motor and the motor is rated at 460V 60Hz, increasing the voltage will reduce the work component of the current. A small motor like 0.5hp will have a high magnetising current and this will increase with an increased voltage so the current reduction may not be as great as you would expect.

My suggestion is first establish that the motor is rated at 460V 60Hz and if that is the case, increase the voltage on the motor. If the motor is still overloading, check the pump curves at 60Hz speed and see if it is able to run at that speed without overloading the motor.

restricting the flow of a single stage centrifical will usually increase the head and reduce the power consumed by the pump but this does depend on the pump curves.

Best regards,

Mark Empson
L M Photonics Ltd

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources