3-phase vs SGL phase starting torque 1

[tjmurf]

The Application / Problem:
5 hp 230 volt single phase motor driving a constant torque load, which is a gear pump. The process is an asphalt emulsion and, at times thick slugs of this stuff will load down the motor to near locked rotor conditions. Before the overload protection trips, the start caps cut in and blow. This has occurred 3 times over the last 6 months of operation.

My Recommendation to my Boss:
Since 3 phase is not available, I would like to install a VFD and a three phase motor. The drive will provide the 3-phase power, better monitoring of the motor and, speed regulation of the pump which is also needed. My electrical supplier is offering me a good deal on the drive, because of the voltage. It is a flux vectored constant torque drive rated for 10 hp. Will it work?

Thanks!!

 

[SteveKW]

Sounds like your overloads are not sized for the job if the caps blow!

Is the voltage good at THE motor while she is loaded?

Considered the cost of a 7.5 HP motor versus the fancy electronics? (Which will probably just end up being very expensive overloads for when the motor stalls again!)

 

[DanDel]

I agree with SteveKW. Sounds like the perfect application for a larger motor. Maybe even 10HP.

 

[busbar]

I’ll side with the two other responders—I don’t think a same-HP 3ø motor and a VFD will buy you much extra in short-term overload handling, for curing reduced RPM closing a centrifugal start switch. [Is the particular 10HP drive published as positively operable on a 1ø source?] Agreed it is far less technically interesting, but a larger 1ø motor is likely a better investment.

 

[Marke]

One thing to consider, It sounds like you are struggling to get enough torque with the existing motor. If you use a variable speed drive and similar motor, you wil end up with even less torque unless you upsize both the motor and inverter. Small motors can produce upwards of 250% torque under high slip conditions. You would need to ensure that the new motor and inverter can produce a similar or better level of torque.
Best regards,


Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion to tjmurf (Specifier/Regul) Apr 25, 2003 marked ///\\My Recommendation to my Boss:
Since 3 phase is not available, I would like to install a VFD and a three phase motor.
///Please, elaborate on this. Do you mean a phase converter, e.g. electronic phase converter, three phase VFD and three phase motor, or single phase VFD input, and three phase VFD output and three phase motor?\\ The drive will provide the 3-phase power, better monitoring of the motor and, speed regulation of the pump which is also needed.
///Good intend, including smoothly started electrical motor by three phase input power supply.\\ My electrical supplier is offering me a good deal on the drive, because of the voltage. It is a flux vectored constant torque drive rated for 10 hp.
///10HP may be ok since the present 5HP motor is slowed down to locked rotor condition at some point.\\\
Will it work?
///Yes, based on the input that was provided. If there are some hitches, then it would be better to post them, sooner the better.\\\