Abt 3-phase

[shermaine]

Is it good to have a capacitor bank to a 3-phase supply?
What's the usage of a capacitor bank?
Please advise.
Thanks.

 

[Sebi]

Only resistor load give cos-fi=1.
When the load is inductive, the cos-fi go to inductive direction, and increasing the VAr. If need, You can compensate it with appropriate capacitor.

 

[Nigel Goodwin]

Yes, we discussed this at college briefly - across the road was a large Trebor factory - making lot's of sweets!. Our lecturer told us they had a large room full of capcitors with a man responsible for switching them in and out of circuit.

It's called 'power factor correction', and by keeping it as balanced as possible it produces significant savings on your electricity bill - at least for a large factory!.

 

[Styx]

It's mostly used for power-factor correcton cap but also EMC filter caps.

Most industry have inductive load and it will cause the current being drawn to lag the supply voltage (and thus the useful power is less) - very bad for the network as a whole. Unlike home's where we are charge by the KWh, industry are charged by VA.

hence you can see if you draw crappy laggy power you are punished with higher utility bill. Caps try to counter teh lagging effect of inductive loads by providing a leading term to the current.



If a company is drawing really shitty current waveforms (ie not sinusoidal) due to non-linear loads - thyristor choppers, 3ph inverters or alot of computers hanging off the 3ph it will distort the supply voltage waveform.

This distortion is seen by all at the point of common coupling and will mess everyone else hanging off that distribution point. The national grid fine very heavily for excessive distortion of the supply voltage (since it messes everyone else at the PCC plus causes generators to experience higher order current harmonics and increase eady loss in the rotor/stator of their generators). By providing caps to Neutral you can filter out some of the harmonic content. You will be charged for higher VA being drawn but small price to pay if you do draw crappy harmonics since the alterniative is a nice big fine