Some one can help me for calculating the rated currrent of capacitor?

Question

A Power Factor correction capacitors is 100kvar 400vac. What is the formula for calculating its current?

Answer 1

The capacitor is seen differently by different frequencies. It is an open circuit to DC and a short circuit to very high frequencies. In the middle it's something like a resistor. If your capacitor is connected to the main line then the frequency is constant at 60Hz, so you can replace the capacitor in the circuit model by a resistor with a value of 1/(jwC) or 1/(377*jC) where C is the capacitance in Farads. Then you can calculate the current going through it by dividing the voltage across it by the equivalent resistance. As you can see, this will give an imaginary current since you're dividing by an imaginary resistance.....What does all this mean? It means that your capacitor does not consume any real power, you can think of it as a tank that charges half the time and discharges the other half.....

Answer 2

good question. It will be a time sensitive as well as voltage sensitive formula. Capacitors are not current rated as it is usually not an issue. Without a diagram I dont know but any circuit would have to assume the cap is a dead short, at some point in the cycle, plus any internal resistance which should be very low. The specs should give an internal resistance and along with the rated voltage that should give a max allowable current.

Answer 3

Goto the "HYPERPHISICS" web site for fantastic explainations

POWER FACTOR = WATT/(VOLTS*CURRENT)

or

Iinput=POWER/(VOLTS*PF)

Drew