How does a capacitor work in an electromagnetic heater AC circuit?

What happens when alternating current (AC) is applied to a capacitor? A capacitor behaves differently than a resistor - in a resistor, the flow of electrons is proportional to the voltage drop; in a capacitor, when charging or discharging it to a new voltage level, It resists changes in voltage by absorbing or releasing current.

When the electromagnetic heater operates by supplying direct current (DC) to the capacitor, as long as the supply voltage is present, it is charged to the value of the applied voltage like a temporary accumulator, and then maintains or maintains this charge indefinitely. If there is any change in voltage, a charging current flows into the capacitor to resist the change at a rate equal to the rate of change of the charge on the capacitor plate.

As shown in Figure 1, the following studies only circuits with capacitors and AC power. It turns out that there is a 90° phase difference between the current and the voltage, with the current reaching its peak 90° (1/4 cycle) ahead of the voltage reaching its peak. An AC power source produces an oscillating voltage, and the larger the capacitance, the more charge must flow in order to establish a specific voltage on the plates, and therefore the greater the current. The higher the voltage frequency, the less time is available to change the voltage, so the current must be higher. Therefore, the current increases with capacitance and frequency.

                      Figure 1. A circuit with only capacitors and AC power and how it works.

Capacitive AC Circuit

A purely capacitive AC circuit is a circuit that contains an AC source and a capacitor, as shown in Figure 2. The capacitor is directly connected across the two ends of the AC power supply voltage. As the power supply voltage increases and decreases, the capacitor will be charged and discharged accordingly. Current will first flow through the circuit in one direction and then in the other direction, however, no current actually flows through the capacitor. Electrons build up on one plate and are then expelled from one plate in rapid succession, giving the impression that current flows through the insulator separating the plates.


                                                   Figure 2 Pure capacitive AC circuit.

capacitive reactance

The current flowing in the capacitor is proportional to the rate of change of the voltage across the capacitor. The capacitive reactance in a purely capacitive circuit hinders the current flow in an AC circuit. Since, like resistance, reactance is measured in ohms, in order to distinguish it from pure resistance values, reactance is represented by the symbol X. Since the capacitive reactance depends on the value of the capacitor (in farads), and the frequency of the AC waveform, it can be expressed by the following formula.

This formula shows that if the frequency or capacitance value is increased, the total capacitive reactance decreases. Similar to an ideal conductor, the capacitive reactance of a capacitor will decrease to zero as the frequency approaches infinity.