Motors with Starting power factor of 0.8 or better

[RRaghunath]

This is all about 6.6kV class motors.

One of the clients stipulated in the project specifications that 'all the motors supplied shall be with starting power factor of 0.8 or better'.

We asked for clarification whether the stipualtion of 0.8 is motor running power factor and is there error in the specification (may be typographical). The client insisted that the specification is correct and shall be adhered to.

I am only familiar with motors that have starting power factor of 0.2 to 0.3 and running power factor of about 0.8. Could some one explain this to me.

Thanks in anticipation.

 

[Skogsgurra]

You could get that kind of PF with a wound rotor and starting resistor. All other cases (except using a VFD as a starter) will make PF much lower. A 6 kV VFD will be very expensive...

 

[rbulsara]

May be its time to ask the client the reason behind his/her specs. Ultimately it should be related to reducing the starting current demand..and if you can find and explain him/her the ways it can be achieved, like different starting method stated above, the client may understand.

I know, its difficult to educate some clients.

 

[jraef]

"I know, its difficult to educate some clients."

Ain't it the truth!

I find that specifications such as this are often remnants of specifications from some older system. It may have indeed been a wound rotor motor originally, but on this new project the new engineer failed to notice that difference and ended up specifying something that does not exist! Either that or they took a performance exerpt from a drive / motor system and applied it to the motor alone. I have seen some older specifications for motor and soft starter packages where they asked for this, but the "soft starter" was in fact an LCI drive that was bypassed at full speed.

Bottom line is that if they specified a Sqirrel Cage Induction Motor with this specification, they are asking for something that does not exist and as far as I know cannot exist (in this universe anyway) without another device such as an LCI or PWM drive.

"Venditori de oleum-vipera non vigere excordis populi"

 

[busbar]

 
Aside: Playing devil’s advocate — Some facilities have capital-project procurement groups that go to great extremes in review of purchase-order verbiage. One has to be careful in differentiating ‘doesn’t exist,’ ‘nobody does that’ and ‘not so mainstream.’

Skirting by a specification may mean a month of inconvenience for a vendor, but also may mean 30 years of special handling over the facility life by the buyer’s organization. Ii may be that the spec was overlooked until it was ‘tossed back’ to the buyer’s organization after bid award. It works both ways from the pay now or pay later perspective.