Capacitors for PFC and for reducing starting current of induction motors

[sinnadurai sripadmanaban]

Will someone give the ratings (kVAr)of power capacitors needed for a)correcting power factor of individual induction motors(kW/rpm) and b)reduce starting current of various sizes of (kW/rpm) started by across the line or star-delta starters

 

[tallgirl]

They have to be sized to the individual motor itself.

Have you asked the motor manufacturer for the information?

 

[sinnadurai sripadmanaban]

Capacitors for IM for starting and pfc

Capacitors for IM for starting and pfc

Thanks.I thought if you know the kW,rpm and design code from tables provided by NEC
one can select the size of capacitor. If you know any link please provide

 

[jim dungar]

Thanks.I thought if you know the kW,rpm and design code from tables provided by NEC
one can select the size of capacitor. If you know any link please provide

Any manufacturer of power factor correction capacitors can help you select one.
Their websites should have the table you are looking for.

 

[bob]

julie
How tall do you have to be in order to be called Tall Girl?

 

[sinnadurai sripadmanaban]

Capacitors for IM for starting and pfc

Capacitors for IM for starting and pfc

Any manufacturer of power factor correction capacitors can help you select one.
Their websites should have the table you are looking for.

I tried and I didn't get any results.Could someone give a link please?.

 

[weressl]

Will someone give the ratings (kVAr)of power capacitors needed for a)correcting power factor of individual induction motors(kW/rpm) and b)reduce starting current of various sizes of (kW/rpm) started by across the line or star-delta starters

Without specific motor data this can not be given. The power factor correction capacitor would dependent on the desired power factor and there is an economy model to calculate the proper sizing. You also need to take into consideration the actual load on the motor, not to over-correct. Wide and indiscriminate use of capacitors can create harmonic problems. Capacitors for starting current reduction need even more precise calculations and usually applied to large MV motors only.

 

[sinnadurai sripadmanaban]

Size of power capacitor for PFC and reducing starting current of induction motors

Size of power capacitor for PFC and reducing starting current of induction motors

Without specific motor data this can not be given. The power factor correction capacitor would dependent on the desired power factor and there is an economy model to calculate the proper sizing. You also need to take into consideration the actual load on the motor, not to over-correct. Wide and indiscriminate use of capacitors can create harmonic problems. Capacitors for starting current reduction need even more precise calculations and usually applied to large MV motors only.

One softstart manufacturer has given a rule of thumb for PFC as sq root of 3xVx0.8xno load current .Similarly is there any rule of thumb for starting across the line/star delta?.

 

[jim dungar]

I tried and I didn't get any results.Could someone give a link please?.

Try harder.

This is the sixth link provided by a Google search for "power factor capacitor sizing".
http://www1.eatonelectrical.com/calculators/PowerFactorROI/index.html.

As others have said, you need specifics on the moter.

 

[weressl]

One softstart manufacturer has given a rule of thumb for PFC as sq root of 3xVx0.8xno load current .Similarly is there any rule of thumb for starting across the line/star delta?.

So which part of 'specific data' do you have difficulty comprehending?

'Soft start' usually refers to Solid State Reduced Voltage starters and those manufacturers routinely warn you AGAINST using PFC's in conjunction with their drives. SO I am curious who gave you this 'rule of thumb' which I have never heard of. As I said capacitors are sized based on motor data AND the desired power factor. Larger capacitors and multiple units eventually need to be incorpoprated intot he harmonic (system) study to see what constrains may need to be put on those or what corrective actions/hardware they may require.

 

[Jraef]

One softstart manufacturer has given a rule of thumb for PFC as sq root of 3xVx0.8xno load current .Similarly is there any rule of thumb for starting across the line/star delta?.

You are mixing issues here.
PFC capacitor sizing can be estimated, but that is for all intents and purposes a SWAG* without specifics of the motor. As mentioned, many (if not most) capacitor manufacturers will provide a chart by which you can estimate the PFC capacitor sizes, but the charts make assumptions from generalizations about the motors. This however has nothing to do with starting.

Using capacitors for trying to reduce starting current is required to be even more specifically engineered for each specific application and something highly discouraged by most responsible engineers. The only advantage it offers over more conventional and legitimate forms of starting current reduction is cheapness, and that is rarely a valid engineering concern, especially when there are very significant risks to this method. The biggest problem with it, and one often ignored by proponents, is that the timing for switching out the capacitors is CRITICAL because the amount of capacitance is huge and if left in after the motor reaches roughly 80% speed, runs a severe risk of over correcting and creating voltage spikes, torque shock, all kinds of potentially damaging consequences. Just for you do do more effective searching, it is referred to as "Capacitor Assisted Starting".

*SWAG, if you are unfamiliar with the term, is short for Scientific Wild Ass Guess