Part Winding Starter

[manuel bonilla]

I am doing the inspection of an electrical fire pump system that I had specified. I asked for a part winding start to reduce start current because the motor is a 40HP, 120/208V motor.

When I did the starting test the motor would not rotate during the first part of the starting sequence an would then rotate once the second contactor was connected.

In my opinion, when I connect the second contactor I am seeing a current inrush similar to that of an accross the line starter (locked rotor of the first coil + locked rotor of the second one). Therefore I am not seeing any inrush current reduction.

The manufacturer says it is normal for a part winding not to rotate on the first coil (actually Nema MG-1 does accept this, but is this logical on a low inertia, low friction load like a centrifugal pump?)

Should I accept this system?

Reegards,

Manuel Bonilla
San Jose, Costa Rica

 

[templdl]

Re: Part Winding Starter

Manuel, I don't know if the followint will be of some help but:
Part-winding start is a low cost method of reduced-inrush starting. But, low starting torque of only 40-48% is a problem and starting current run 60-80% of the full low current which is not of that great of a benifit.
However, even with the low starting torque one would think that if the Wr2 of the centrifugal pump was not an issue that the motor would turn pump. It is common for centrifugal pumps not to start to load until they reach about 70% if the RPM.One word of caution is that heating of the first part windings can be a serious problem.
One of my referrences is Power Feb. 1981, vol.2, by John Reason.

 

[ron]

Re: Part Winding Starter

Part winding starters can only be used with part winding motors. During a part winding start, only one winding is energized, which reduces the inrush current to 60-70% (depending on the motor design) and starting torque to 50% of normal starting values with both windings energized. Most (but not all) dual voltage 230/460 volt motors are suitable for part winding starts at 230 volts.
See this web site for reduced voltage starter info.
http://ecatalog.squared.com/catalog/pdf/8600CT9601.pdf

 

[bennie]

Re: Part Winding Starter

The 208 may be the downfall. Is the motor rated for 200 volts? There is no 120/208 motor.
Change to 480 volts and start this motor across the line.

[ June 27, 2003, 10:51 PM: Message edited by: bennie ]

 

[templdl]

Re: Part Winding Starter

I overlooked the fact in my previous post that with a part winding motor start the total current drawn may approach that of line voltage starting if the motor doesn't excellerate to practically full speed on one winding. This appears to be describing your problem.

 

[manuel bonilla]

Re: Part Winding Starter

This motor is marked as suitable for part winding and is installed with a FM approved fire system.

I can?t change the voltage.

What really concerns me is that with 40% torque the motor shoul be able to start the pump and acquire some speed. But it doesn?t.

Thanks all for yoour input.

 

[bennie]

Re: Part Winding Starter

Manuel: You will either have to boost the voltage or change the motor.

 

[ronaldrc]

Re: Part Winding Starter

I wonder if this was a true part winding motor with two separate windings or a wye start and delta run motor?

And either way the motor should turn on the first half of your windings or motor winding make up.

Maybe you need to hold the load off of the motor during start up.

And if you don't have a large voltage drop the way it is maybe your part winding started wasn't needed to start with.

Ronald

[ July 17, 2003, 11:16 PM: Message edited by: ronaldrc ]