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# Starting Power Factor

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## Starting Power Factor

(OP)
Dear everybody,
Do you know about Starting Power Factor?
How to know it?
What is the formula?
Thank you for your attention.
Regards

### RE: Starting Power Factor

Regarding induction motors, the tipical Starting Power Factor is about 0.2. If you consider the equivalent circuit of an induction motor, at the starting moment the motor coul be considered simply as an inductor with a very low resistance.

### RE: Starting Power Factor

Agreed.
The power factor at start is initially between 0.1 and 0.2 and increases as the rotor speeds up reaching a maximum whinch is motor design dependant just before full load speed. The power factor of an unloaded motor then drops down again between the speed of maximum torque and synchronous speed.

Best regards

Mark Empson
http://www.lmphotonics.com

### RE: Starting Power Factor

Suggestion: Visit
http://www.tornatech.com/contenu/ulfm_wye_delta_open_transition_ang.cfm
where the starting power factor = 0.4
http://www.nts.no/norsok/e/E00104.pdf
where the typical starting power factor = 0.2
and
IEEE Std 141-1993 Red Book "IEEE Recommended Practice for Electric Power Distribution for Industrial Plants,"
Figure 8-11 Motor Characteristics for Typical Medium-Sized and Medium-Speed Induction Motor
where the starting power factor = 0.2

### RE: Starting Power Factor

(OP)
Thank you everybody for your attention.
by the way, how to calculate the starting power factor..?

### RE: Starting Power Factor

The power factor could be estimated from motor equivalent circuit parameters, with proper attention to skin effect for large rotors.  The parameters can be estimated in various ways depending on what info you have available about this motor.

For some applications it is sufficient to assume a value such as 0.2, or sometimes use arithmetic vs vector calcs. It will depend on your specific application and what you are trying to accomplish and how accurate you need to be.

### RE: Starting Power Factor

Suggestion: Neglecting the parallel branch (magnetizing branch), since there is flowing a relatively small current, the starting power factor can be expressed as:
PF=Rr'/[(Rr')**2 + (ws x Llr')**2]**0.5, in per unit

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