Capacitor current Formula, calculation, Example

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Capacitor current Formula, calculation, Example:

Capacitor current I(A) in amps is equal to the capacitance C(F) in farad times of the derivative of the applied voltage V(V) in volts. The formula for calculating capacitor current will be

I(A) = C(F) x dV(V) / dt

Look at the above formula, the capacitor only allows the current in the time-varying voltage. When the voltage across the capacitor is constant, the capacitor current will be zero. I.e. the voltage is alternating with respect to time, the capacitor allows the current through it.

In an alternating current system, the current flow through the capacitor I(A) is equal to the ratio between reactive power Q(VAR) to the applied voltage V(V).

I(A) = Q(VAR) / V(V)

The above formula is applicable for a single-phase AC power system.

For a three-phase AC power system, the current is equal to 0.577 times the reactive power divided by the voltage.

 I(A) = 0.577 x Q(VAR) / V(V)

Also, the capacitor current we can calculate if you know the capacitive reactance. Here the capacitor current I(A) in Amps is equal to the voltage across the capacitor terminal V(V) in volts divided by the capacitive reactance Xc in ohms. The formula,

Icapacitor = V(V) / Xc

Here Xc = 1 / 6.28 x f x C

Icapacitor = V(V) / (1/6.28*f*C) = 6.28 x V(V) x f x C

Here f is the frequency in Hz and C is the capacitance value in Farad

Example 1:

Let us calculate the current flow through the capacitor of 100 microfarads and the potential difference between the capacitor is 10sin100t.

Apply our formula,

The capacitor current I(A) = 100 x 10-6 x 10 sin 100t

 = 1 x 10-3 x sin 100t

 = sin 100t mA.

Example 2:

Calculate the reactive current flow through the 25kVAR capacitor bank, the voltage across the capacitor is 440V.

The capacitor current = 25000 / 440

= 56.818 Amps.

Significance of capacitor current:

  • Capacitor creates an infinite resistance to the direct current circuit. Here the capacitive reactance will be infinite.
  • In AC circuits, the capacitor is used to complement the reactive current generated by the Load. It used to improve the power factor.
  • The current is supplied by a capacitor is called a reactive current.

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