power factor

[io748]

The disadvantage to that, in addition to difficulty of switching correction as loads change, is that your internal wiring system still has to carry the reactive power as well as the real power.

If your correction is near the load(s), the supply system only needs to carry real power. Your system would benefit the same way the POCO's system does with service-located correction.

Larry, can you help me understand something on this subject? Our POCO has installed PF correction at their transformer. By doing that, they have reduced the reactive power they deliver to us, and also increased the current carrying capacity of their distribution system, correct? If they are not delivering the reactive power to me because of the power factor correction, how is it that I still have reactive power in my distribution system?

 

[markstg]

Larry, can you help me understand something on this subject? Our POCO has installed PF correction at their transformer. By doing that, they have reduced the reactive power they deliver to us, and also increased the current carrying capacity of their distribution system, correct? If they are not delivering the reactive power to me because of the power factor correction, how is it that I still have reactive power in my distribution system?

Not to step on Larry's answer, but the POCO has not reduced the reactive power they deliver to the us (if us means the transformer downstream electrical loads). They have changed the source for the reactive power the electrical loads require from the POCO generator to the capacitors. Adding Caps doesn't change the need for reactive power by electrical loads only the source of it.

They have increased the current carrying capacity of their distribution system upstream of the transformer since it no longer carries the reactive current (power) the the caps are now providing.

 

[jghrist]

anything other than residential gets charged per VA and not KW

The majority of US utilities charge per kW, not per kVA or VA. Power factor correction only will save money from the reduction in losses unless there is a power factor penalty. The reduction in losses only occurs in parts of the system ahead of the capacitors.

 

[io748]

Not to step on Larry's answer, but the POCO has not reduced the reactive power they deliver to the us (if us means the transformer downstream electrical loads). They have changed the source for the reactive power the electrical loads require from the POCO generator to the capacitors. Adding Caps doesn't change the need for reactive power by electrical loads only the source of it.

They have increased the current carrying capacity of their distribution system upstream of the transformer since it no longer carries the reactive current (power) the the caps are now providing.

OK, so the caps are providing the reactive power instead of the POCO's generator. So regarding a large bank of capacitors at your main switchgear: It will help with your utility bill (if you are penalized for poor PF), but it won't help lessen the load of the plant distribution system. Is that correct?

 

[markstg]

OK, so the caps are providing the reactive power instead of the POCO's generator. So regarding a large bank of capacitors at your main switchgear: It will help with your utility bill (if you are penalized for poor PF), but it won't help lessen the load of the plant distribution system. Is that correct?

That is correct.

Motors, Heaters, Lights, etc., all take the same Real and Reactive Power as they did before the capacitors are added.

When pf correction caps are added to a motor feeder if the caps area added before the overloads (between the contactor and the overloads) no correction for current is needed. But if they are added after the overloads, then the current through the overloads is changed and the currrent through the overloads must be calculated to acount for the reduced current through the overloads and this corrected current used to size the overloads.

 

[Besoeker]

Larry, can you help me understand something on this subject? Our POCO has installed PF correction at their transformer. By doing that, they have reduced the reactive power they deliver to us, and also increased the current carrying capacity of their distribution system, correct? If they are not delivering the reactive power to me because of the power factor correction, how is it that I still have reactive power in my distribution system?

Not actually correct. The reactive power you take is determined by your load.
PFC works for the upstream supply, not the downstream load.
If the PoCo install PFC on the secondary side of their transformer, it may reduce the current that their transformer has to supply.

 

[Wes G]

Let me see if I can take a stab at this that will be helpful. When working at an industrial plant a few years ago, I noticed that the amount of amperage drawn on the line side of the load appeared to be significantly less than that of the load side of the caps.

I would interpret this to say that the same voltage is able to cause a greater flow of electrons when in phase, or more nearly in phase, with the amperage.

Of course, as you no doubt know, you can over correct and have reduced efficiency because of more capacitive reactance than inductive reactance

 

[markstg]

Let me see if I can take a stab at this that will be helpful. When working at an industrial plant a few years ago, I noticed that the amount of amperage drawn on the line side of the load appeared to be significantly less than that of the load side of the caps.

I would interpret this to say that the same voltage is able to cause a greater flow of electrons when in phase, or more nearly in phase, with the amperage.

Of course, as you no doubt know, you can over correct and have reduced efficiency because of more capacitive reactance than inductive reactance

From the Source's (Line) point of view less flow of electrons (less current) is required to be provided, as you state the current angle decreases relative to the voltage. From the Load point of view, nothing changes, the load draws the same current at the same voltage and power factor.

Adding to much capacitive reactance.....increasing the pf to be leading.... once all the inductive reactive loads are satisified, the only thing that can change is the voltage and it will increase...Not a good thing. I don't think efficency has anything to do with this.

 

[LarryFine]

Local PF correction acts as sort a 'shunt' to reactive power. There is always reactive power between the load and the upstream correction (if there is any) or the power generation itself (if there isn't.)

Correction indirectly 'increases' the system ampacity by relieving the upstream-of-the-correction portion of the supply system of the burden of reactive power, leaving more capacity for real power.

The closer the correction is to the offending load, the less of the supply system that has to be sized for it. Correction doesn't make anything more efficient, per se, it acts more like a shunt filter.

 

[Besoeker]

Local PF correction acts as sort a 'shunt' to reactive power. There is always reactive power between the load and the upstream correction (if there is any) or the power generation itself (if there isn't.)

Correction indirectly 'increases' the system ampacity by relieving the upstream-of-the-correction portion of the supply system of the burden of reactive power, leaving more capacity for real power.

The closer the correction is to the offending load, the less of the supply system that has to be sized for it. Correction doesn't make anything more efficient, per se, it acts more like a shunt filter.

Nicely put, Larry.