Connecting 30 motors to one source help


by richardv24
Tags: breaker, motors, pcb, surge
richardv24
richardv24 is offline
#1
Mar21-13, 01:30 PM
P: 3
Hi guys. I am having some issue and would love any help.

I have a project that requires 30 motors to be hooked up to a single power source. The problem is, the surge voltage that happens the moment the motor turns on causes the buildings circuit breaker to trip. The only way to bypass this is to have each motor turn on at different times. note that each motor is 460 volts 3phase.

I don't know much about this topic so sorry if i sound dumb.

I was wondering. Is it possible to do something with a PCB so that it takes in the supply power and distributes it to 30 devices that will output the supplied power but at, lets say, 1 second intervals.

Is there another solution to this problem that you might have in mind?

Thanks for any help.
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Windadct
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#2
Mar21-13, 02:54 PM
P: 534
Hello Rich-

I am assuming these are not too small being 480V/3Ph - and yes starting all 30 I am sure creates a problem. ( What HP or KW are they?)

Is each motor connected directly to a circuit breaker ( makes this difficult) or does each motor have a starter ( usually a contactor with some thermal overload and possibly a fuse)? - this would be easier.

If each one is on it's own circuit breaker, or even multiple ones on one breaker - I can not think of a simple way to stage their starts.

also - just curious, what do these 30 motors do?
richardv24
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#3
Mar21-13, 03:03 PM
P: 3
Thanks for the fast reply.

To get the easier questions out of the way, each motor is somewhere around 5 HP. They will be going into a Huge air conditioning unit meant to be used for a hospital. This purpose eliminates one or two LARGE fans with many smaller fans.

As the motors are being installed into my air conditioning unit, I can wire them pretty much any way that I would want. These motors are EC motors that elminate VFD's to power them up. It pretty much has overload protections and starters built into it. It just requires a 0-10 volt dc signal to adjust speed. However, powering the internal capacitor is where we get this in-rush current. I still protect each motor with fuses. The thought of time-delay fuses has come up before, but some projects would cause 100's of fan and doing a time-delay system on those would not be recommended.

Thanks for your response.

jim hardy
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#4
Mar21-13, 06:09 PM
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Connecting 30 motors to one source help


5hp is a huge fan. 30 of them is really huge.
Are you sure 5hp is the fan and not the compressor?

Search on "Inrush Current Limiter. It's a negative temperature coefficient resistor that limits inrush to hungry electronic power supplies for just the problem you describe.
I had a manufacturer add them to some supplies for our plant. We used "Keystone Carbon Company" thermistors but I can no longer find them. They were a good ol' Pennsylvania company.
Here's a similar product line:
http://www.ge-mcs.com/en/temperature...t-limiter.html

If instead your overcurrent is from trying to start 30 compressor motors all at once - I think you'll have to stagger their starts.
Windadct
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#5
Mar22-13, 02:16 PM
P: 534
So there is still a speed controller - so really you are trying to energize 30 motor controllers, If Jim's inrush current limiters are not a possibility, it would be possible to do an AC Pre-charge circuit - You will need a smaller contactor on 2 legs of the AC with a current limiting resistor, then a main contactor ( for 30 x 5 HP this really should be a few contactors * )
Once the Pre-charge Contactor pulls in, it feeds the 480 via limiting resistor to the drives, the Drives Capacitors will come up to full voltage after a few sec, then the main contactor can pull in ( delayed by a timer relay - which is energized by the PC Relay).
The main contact needs to self-energize ( via appropriate safety loop(s) of course).

The controllers for the fan motor may (should) have single phase protection, and/or AC Under Voltage - these fault may need to be reset once the main contactor pulls in.

I am not finding data on 5HP EC motors - can you post a link to a DS?


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