starting HV induction motor PF 2

[sberbece]

Hi!

I have to calculate the voltage drop in case of DOL starting a 6.6 kV induction motor (squirrel cage).
I used starting PF=0.3.
My boss said that PF=0.3 is too low for a MV motor.
I recall a calculation example from an IEEE book, that use for a LV motor, the starting PF=0.2. Therefore, I believe that PF=0.3 is quite generous, since there is no big constructive difference between a MV & a LV induction motor.
Obvious, using a low starting PF, will result an unacceptable voltage drop and consequently I have to consider an alternative starting method, such as: Y-D, autotransformer, series resistors or a capacitor bank.

Can anyone please advice me where I can find (a standard, paper or book) an advice on MV-HV induction motor’s, starting PF?

Thank you for your time.

 

[dpc]

I would contact a motor manufacturer. I typically use 0.2 for starting analysis.

I don't see why MV motors would behave much differently at locked rotor than LV motors, in terms of power factor.

 

[jraef]

It doesn't matter if it is MV or LV, the math is the same. But dpc is right, you are best to start with a motor manufacturer. MV motors are built to order: you can ask for pretty much anything you need but there are design limits and tradeoffs. I have worked on several MV motor projects doing TMS analysis where the motors were not yet selected, and every time a vendor came to us with a different motor, the numbers were always different and no two of the studies came out the same. I saw MV motors with as little as .15 and as high as .25 power factor at startup, but for a blind study I also always use a .20 pf.

Good paper on the subject from one of our members, Marke:

http://www.lmphotonics.com/m_control.htm

Word to the wise however: stay away from Y-Delta starting on MV motors. Transition spikes can damage other nearby electrical equipment and/or the torque spike can snap shafts on power train components. Primary resistors are nasty as well (think of the heat). Stick to Autotransformer, reactor or solid state starting.