Synchronous Motor Capability per PF 1

[Laplacian]

For example a large synchronous motor rated 14,000HP @ 0.85 leading PF.

What would be a good way to approximate maximum HP output at say 1.0 PF and 0.85 lagging PF?

 

[RRaghunath]

Synchronous motors and lagging power factor? Some thing amiss!

 

[electricpete]

Power factor can be adjusted on a sync machine by varying field excitaiton.

As a rough approximation, the power output limit is set by stator current heating (although there are other sources of heat that change with excitation as well and also other limits in the highly overexcited and underexcited regions).

In the case that stator current limit determines max power, the power output limit at 0.85 pf would be 85% of power output at 1.0 pf.

For sync generators, the supplier provides a capability curve.

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[ScottyUK]

On such a large machine the mechanical limitations of the machine at least need to be considered. 15% increase in output power is substantial.

Further to ePete's post, the heavily over-excited condition will probably be limited by the rotor reaching its thermal limit. In the severely under-excited condition, the stability limit of the machine will be reached. The stability limit will depend upon shaft loading. It is quite improbable that a motor would be operated at either of these extremes, so the limits are largely theoretical rather than likely to be encountered in operation.

There are a lot of similarities in the capability curves of synchronous motors and synchronous generators. Discussion of generator curves seems to be more common.



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