Why out put current increase in transformer with capacitance load?

Answer 1

ferranti effect...

B.*If we use capacitive load the stator MMF aid the rotor MMF. It means that in times

of capacitive load rotor flux and main field flux are additive. So the alternator voltage increase with capacitance loading.

[By Akhtaruzzaman08]

Answer 2

For alternator electrical circuit

input voltage = output voltage + ( current * alternator_impedance )

alternator internal developed voltage ( in the above equation it is referred as input voltage ) is constant, since the speed of rotation and field is constant throughout the operation.

alternator impedance is constant, but current is not constant. current varies as the load impedance varies.

The output voltage is less than the input voltage for inductance loading while for capacitance loading output voltage might be more if resistive voltage drop is less.

Let us take resistance is negligible ( R = 0 ) then for inductance load Current lags input voltage by 90 deg, then the voltage drop in the alternator impedance is exactly 180 deg in phase with input voltage so the output voltage is lower than input voltage. In the same way for capacitance load current leads input voltage by 90 deg and voltage drop in capacitance is in phase with the input voltage so output voltage is more than the input voltage or internally developed voltage. so as the capacitance load increases i.e current increases the voltage drop across the alternator impedance increase, which is exactly in phase with the input voltage, so output voltage increases as capacitance load increases.

All the above explanation is true in terms of phase angles only if alternator resistance is zero and also load resistance is zero. In practice it is not possible.

So the current leads the input voltage by an angle for capacitance load. If we take the voltage drop in the alternator impedance, it can be divided in to two parts

1: Alternator internal Resistive drop

2: Alternator internal Inductance drop

The resistance drop always subtracts the input voltage, but inductance drop adds the input voltage for leading current, so output voltage increases, that's why there is some minimum capacitance load required to make the output voltage = input voltage. As the capacitance load increases current increases as well as the leading P.f angle increases so output voltage increases.

Answer 3

A capacitive load on a transformer produces a tuned circuit, which has a resonant frequency given by 1/2.pi.sqrt(LC) where L and C are the inductance and capacitance in the tuned circuit.

If the circuit happens to resonate at the supply frequency, a dangerously large voltage could be generated.

Tuned transfomers are used extensively in radio systems for signal processing to select a wanted signal and reject signals on unwanted freqencies.

Answer 4

voltage will be in lagging and current will be in leading position