Why capacitor is connected in parallel not in series for Power Factor improvement?

What is Power Factor improvement?

In simple language, power factor improvement is the process of keeping the power factor unity or almost near unity.

Always remember that if the power factor is unity or nearly unity then it is good. When a load is connected with an AC supply then it draws current from the source. If the load is inductive then the current drawn by the load will lag behind the voltage but if the load is capacitive then the current drawn by the load will lead behind the voltage.

So both lagging or leading currents can create power loss. So we need to keep the power factor near unity.

How we can improve the Power Factor?

Suppose an inductive load is connected to a source. So it draws the lagging current. In this case, we can compensate for the lagging current by flowing the leading current. So we have to connect any device or load which can draw a leading current such as the capacitor, or synchronous motor.

If a capacitive load is connected to a source then it draws a leading current. In this case, we can compensate for the leading current by flowing the lagging current. So we have to connect any device or which can draw a lagging current such as an inductor.

Why we connect Capacitor in parallel, not in series?

Reason 1: Current Flow

We know that in a series connection, the Current is constant and voltage is varying but in a parallel connection, the voltage is constant and the current is varying. 

So we need to keep constant the voltage across the load. If we connect a capacitor in parallel it will be drawn a leading current according to its rated value. But if we connect a capacitor in series then the flow of current through the capacitor will depend on the load.

Reason 2: Rating

As in the case of a series connection of capacitor current fully depends upon the load so we need a capacitor of high value which can deliver the full load current.

Reason 3: Voltage Drop

If we connect a capacitor in series with the load for power factor improvement then a voltage will be dropped by the capacitor. Even if the Capacitors are connected in series, it can create resonance issues with the inductance of the load that may lead to unwanted voltage spikes and waveform distortion. 

Reason 4: Damaging

If we connect the capacitor in series with the load then if a short circuit fault occurs in the load then the total voltage will be applied to the capacitor which may blow them. Additionally, the resonance frequency of the LC circuit formed by the series capacitor and the inductance of the load could coincide with the operating frequency, causing instability and possible damage to the circuit.

Reason 5: New addition

In the case of a series connection, if we want to connect additional capacitors then we need to open the whole circuit. But in the case of parallel connection, we can easily connect an additional capacitor in parallel with the existing capacitor.

Reason 6: Recovery Voltage

If we connect the capacitor in series with the load for power factor improvement then the recovery voltage across the contacts of the switchgear shall be high.

Reason 7: Reactive Power Compensation

The power factor improvement method is used to reduce the reactive power in the circuit to bring it closer to unity (power factor of 1). Reactive power is the power that flows back and forth between the inductive elements (e.g., motors, transformers, coils) in the circuit. Capacitors are reactive elements that produce reactive power opposite in nature to the inductive elements. By connecting capacitors in parallel, they provide reactive power in the same line as the inductive loads, so it can effectively compensate for the reactive power and improve the overall power factor.

Read Also:

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• Why Current, Voltage changes But Power, Frequency constant in Transformer?
• Can DC Motor run on AC supply and Vice-Versa?

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