# Power factor correction (capacitor in parallel with inductive load)

1. Nov 22, 2016

### FionaZJ

Why we must install capacitor in parallel to inductive load? Why not install it in series?

2. Nov 22, 2016

### Baluncore

The real and reactive currents of a partially inductive load are not in series, they are in parallel. The real component of current is load dependent. The inductive component, or magnetising current is usually independent of load.
A parallel capacitor will operate at the supply voltage and needs to compensate most of the fixed inductive current. It can be quite a small capacitor.

If a series capacitor was used it would be necessary for the real current also to flow through the correction capacitor. It would need to be a big capacitor and the value would have to be changed with load.

3. Nov 22, 2016

### FionaZJ

Is it capacitor will draw all the voltage source in parallel?

4. Nov 22, 2016

### cnh1995

Voltages across the inductive load and the capacitor will be equal since they are in parallel. But the capacitor voltage may not be equal to the source voltage as there can be some resistance in between the source and the inductor.

5. Nov 22, 2016

### FionaZJ

Oh.okay. All of you Thank you!

6. Nov 23, 2016

### jaus tail

I guess if you add capacitor in series to load, then you're introducing an additional 'current-dependent voltage drop' element across line.

V load = V source - V capacitor.

So if load changes, then load current changes, so the voltage drop across capacitor will also change as it depends in Load current times the Xc, so the voltage available for load will also change. Not sure we want that.
At low voltage motor torque will reduce, and bulbs will go dim.

7. Nov 23, 2016

### FionaZJ

So if we install capacitor in parallel, there will be full voltage supplied available?

8. Nov 23, 2016

### jaus tail

Not really. The transmission line will have inherent inductance, resistance, and capacitance which depend on:
length of line
proximity to other conductors
whether ac or dc voltage

So voltage across load is source voltage minus the transmission line voltage drop.

Not sure if I am right with the below part:
Capacitors are put in series in lines to improve over all voltage regulation. This is done at source end. The series capacitor will nullify the line inductance to some extent so the line impedance reduces.

While at the generating end we have capacitors in parallel or tap changing transformers to keep voltage constant.

Likewise even inductors are installed in series and parallel. A series reactor is useful to limit short circuit current and starting current.
A shunt reactor is useful during light loads. At light loads the system is highly capacitive due to the C banks. This causes high voltage. So the shunt reactor absorbs this VAR.

9. Nov 23, 2016

### FionaZJ

Too hard to understand

10. Nov 23, 2016

### Svein

11. Nov 23, 2016

### Baluncore

Yes. The inductive magnetising current will be stable when running. The power factor correction capacitor will have the full supply voltage across it so it will cancel most of the inductive component. The real load will have the full supply voltage across it.

I think jaus tail is writing about neutralisation of regional transmission lines while I am writing about neutralisation of local electric motors.