Power Factor For The Electric Motor

Why?

http://energy.gov/sites/prod/files/2014/04/f15/amo_motors_handbook_web.pdf

• Systems have power factors. Power factor correction equipment is used to approach unity. Investment is based upon the return to be gained from lower heat losses and smaller cables on the basis of the tariff charged.
• The minimum power factor of anything is zero. An energised, unloaded cable could be said to have a power factor approaching zero.

But OP was asking about motors, and whether a minimum power factor is required by various standards. I don't know, but it seems a reasonable question.

my concern is on the power factor for the electric motor, if there are minimum requirement based on international standard (IEC, ANSI and etc..)..I just received an electric motor which mentioned in the datasheet that the power factor for this electric motor is 0.74 which is quite low for me, it cause the electric motor has high rated current.

For efficiency, there are min efficiency that the manufacturer have to follow as mentioned in IEC 60034-30-1. Whichever electric motor has the efficiency below the standard, it may say that its not comply with the international standard.

....and the reason for the concern is what, please?

I'm not familiar with the standard, but if a minimum efficiency is specified it would have to be related to motor rating, as efficiency varies quite a bit with size - bigger ones have higher efficiency. Same goes for power factor.

Typically, motors with rated speed 1500 rpm or above have higher power factor such as 0.8/0.85 for LV and 0.85/0.9 for HV. Low rpm motors have low power factor and this is due to limitation in the principle of induction motors.

It may be good idea to go for Synchronous motor if the requirement is for low speed motor and high power factor is required.

This applies even if the kW rating happens to be a couple of thousands. in return for the additional expenditure, the benefits would be high power factor and efficiency.

It's like this. The power factor for an ideal inductor (or capacitor) is zero.

Since motors are made from loops of wire, it means by definition that they are in fact a version of the ideal inductor with the exception that the interaction between inductor fields causes motion, thereby making them useful for converting electrical energy into mechanical energy.

So, power factor really is an indicator of how much deviation there is between the perfect inductor and something that effectively converts electricity into mechanical energy. If you are concerned about the current, you can try to optimize the power factor (to 1.0000000000000000000000000000) or you can do something useful with your time.

If your motor is not stamped "Conforms to XYZ Standard #123..." then there is no need for it to conform to any particular standard, it just has to perform to the information listed on the nameplate. You bought a motor on price alone, it was inexpensive because it has less iron and less copper than a high efficiency, better rated one of identical physical size that clearly states which standards it conforms to.

You got what you paid for, and as a bonus you will continue paying extra for it every hour that the motor is in service.

It would be difficult to formulate a meaningful minimum standard for power factor. Partly loaded motors tend to have low power factor, so that a standard would have to allow for that, or maybe prohibit partly loaded motors, which would be ridiculous.

Power factor and efficiency are often confused, though quite distinct.

The "minimum" is going to be dictated by the utility servicing you, because they are the only ones who will really care. The reactive current represented by the low PF value has to be supplied by the utility, but is not registered on a WH meter, because by definition, Watts are a measurement INCLUSIVE of the PF; A x V x PF. But the utility is going to need to supply the kVA, ie A x V, so their distribution transformers and other lines and equipment must be over sized to accommodate that reactive current, even though they don't get paid for it.

That's why utilities will PENALIZE a user (not usually residential) for having a low PF, and most of then will base that on the PF being lower than .95. You will not find an AC induction motor that has a .95 PF however, it is up to the USER to correct the poor power factor if necessary.

Also, PF is a cumulative effect so if your total load has a lot of high PF loads, like resistive heating, such as 750kW, and only one inductive load like a 3kW motor with a .74PF, then the ratio of that total load represented by that one motor is really small and the fact that is it, stand-alone, at a .74PF, might be completely irrelevant. But if you are the other way around, with 3 x 250kW motors and 3kW of heating, you are going to need to correct the PF of those motors to avoid penalties.