2-phase loading in 3-phase circuit

[peterwork]

Dear Friend,

We have conducted an energy audit to a 2-phase loading which was supplied by a 3-phase circuit (Phase R & B). We found that the power factor with both the leading and lagging signs for the phases. Why?

Since we're not often work with the 2-phase loading, so would the expert here can give me some advise on how's the 2-phase loading works ? i.e. power factor, current

Thanks,

HK

 

[waross]

It depends.
What is the nature of your loads, single phase, two phase and three phase? Do you have automatic power factor correction?
It is easy to improperly connect a Power Factor Meter.
yours

 

[cuky2000]

Peterwork

Your question is unclear.

Are you confusing 2 wires with 2 phase?

Please clarify

 

[jghrist]

If you are measuring power by connecting phase-neutral voltages and line currents, and your 2-phase loads are connected phase-phase, then you will get odd readings. If the R phase voltage is at 0 deg and B is at 120 deg, then the voltage between R&B phases will be 150 deg. A resistive load will have a current 150 deg leading the R phase voltage and 30 deg leading B phase voltage.

 

[peterwork]

Dear all,

It is a 380V 3-phase 4 wire system. A two-phase loading was connected to the system (Ph-R & B). Also, a 3-phase fixed type capacitor was connected to the system (Ph-R, Y & B) as well.

Since we made the power analyser in "3-phase 4 wire" mode as usual for the measurement, may it cause the problem ?

Thanks and regards,

HK

 

[waross]

I assume that the KVARs used by the load are more than 2/3 of the KVARs supplied by the capacitor bank.
This would show your load running at a lagging power factor The third phase with a capacitor connected but no load would show a leading power factor.
On the other hand if the load is a large resistive load and the system power factor is close to unity you may be reading leading on the single phase load and lagging on the rest of the system.

There are several things you can do.
1> Ignore the issue.
2> Determine the power factor on each phase and correct individually. I don't recommend this.
3> Check your revenue meter or your power invoice to see if Your power factor is within limits. If you are not paying a power factor penalty then see suggestion #1>.
4> If you are paying a power factor penalty, we need more information in order to suggest a course of action for you.
For instance in some areas of India you will lose a 1% rebate if your PF is 99%. In a lot of other areas you can go down to 90% PF with no penalty. The number of hours a week and the number of hours a month your facility operates are important. Is your load steady during working hours or do you have high peak loading during working hours? What type of loads do you have? What are the utility's policies and tariffs for power factor. These are some of the issues that I address in the course of a power factor study.

Are we going to correct to 90%, or 100%
Do we need a Power Factor controller? Can we add capacitors to existing motors? Do we need contactors for the capacitors? Can we permanently connect the capacitors with a switch? Do we really care about the power factor or do we just want the penalties to end?
yours