PFC panel Connection

[maddog]

At work in the main switch room, we have a PFC panel, connected by the 3 phases, each 300mm CSA SWA and an earth.

I expected to see a power in and a power out. But there is only one set of cables, and nobody I have asked seems to know why.

How does this work? I know what the PFC does and why. But does it just need to be connected to the power supply in order to negate the inductance created from all the motors and disharge lighting with it's capacitors?

Any explanation you can give will help.

Thanks

 

[paulr57]

Hi there maddog. You've given the answer yourself. Indeed, inductive loads such as motors and fluorescent lighting introduce an inductive reactance into the circuit, causing the circuit current to 'lag' the voltage in phase. By using phasor diagrams, we can see that this introduces an 'apparent power' which is greater than the actual power being used. To remedy this, we use a capacitance in the circuit in order to cancel out this inductance and bring the power factor as close as possible to 1.0, though 0.98 is typical.

The capacitances are connected between each phase, hence only one set of three cables and an earth.

Hope this helps.

 

[Marvo]

A LV pfc panel doesn't have power running through it as such, the capacitors are just connected between the phases.

Edit
Beaten to the post

 

[Knobhead]

I’m shocked that none of you colleagues can explain it. If you take a motor as an analogy it only has one cable but it does useful work.

As an experiment switch the PFC unit off and watch the effect on the switch room incoming ammeter. There needs to be load on the board for you to see the effect. ONLY do this under supervision, PFC units can be dangerous.
This is a little experiment I would go through with all our 3[SUP]rd[/SUP] year apprentices. It was always funny to see their expression when the ammeter did the unexpected.

Click HERE

 

[paulr57]

Just Google PFC CORRECTION and get the facts.

 

[Knobhead]

Just Google PFC CORRECTION and get the facts.

Just for you're benifit I edited my last post.

 

[maddog]

Thanks guys. The video I watched helped a lot. I understood the inductance, the current lagging, the PFC panel using capacitors to get a better power factor. I knew that the reason for doing this was because of wasted energy (although untill I watched the video, I didn't realise how much was wasted), so I wasnt suprised by the effects on the ammeter, or in the case of the video I watched, the power change. I remembered all this from college, but the fact that The PFC is in parralel and the capacitors are between the phases is where I got lost. For some reason, I expected it to be in series. This is the first time I have installed a PFC panel, so still learning.
Thanks for clearing it all up though, and going into the detail that you did to make it understandable.

I do google for solutions. But the fact is, the guys on this site are better sources of information.
Thanks guys. Aprecitate it

 

[Knobhead]

You do occasionally come across PF units with loop in loop out on motor feeds. The feed will first go to the isolator and then loop in to the PF unit and out to the motor. The nearer the PF is to the motor the better as it helps reduce cable losses. I’ve only come across them on large HV motors.