Power in an Alternating Current Circuit

In AC circuits, power is defined as the quantity of energy delivered by a circuit per unit of time. There is a lot of importance of power in an ac circuit. It’s used to calculate how much total energy is required to run a load. 

A power factor in an AC circuit is described as the ratio of the real power (P) to the apparent power (S).

Power Factor=True power (P)/Apparent power (S) 

A power factor could be expressed as a percentage or a decimal. 

What is an alternating current?

An alternating current is a current whose amplitude and polarity change at regular intervals.

It can alternatively be defined as an electrical current that periodically alternates between flowing in one direction and flowing in the other direction.

The power factor in an AC circuit

Electric power is the rate at which electric energy is dissipated or consumed in an electric circuit. All electrical and electronic equipment and gadgets have a limit on how much electrical power they can safely manage. 

The quantity of power is calculated using the formula P=VI.

Where P refers to power, V stands for voltage, and I is the current.

So power is only present inside an electrical circuit when both voltage and current are present, i.e., when there are no open-circuit nor closed-circuit circumstances.

An AC circuit’s electrical power

Since the sinusoidal waveform (a smooth repeated oscillation is described by a sinusoidal wave, which is a curve) is not connected to a source, the voltages and DC circuit currents are generally constant. In an AC circuit, on the other hand, the amounts of current, voltage, and power change and are influenced by the source.

So, even if we don’t calculate power in AC circuits the same way we do in DC circuits, we can still state that power (p) = voltage multiplied by amperes (i). 

Another crucial element to remember would be that AC circuits include reactance, which means that the magnetic or electric fields formed by the components have a power component. As a result, unlike a simple resistive component, the power is saved and then restored to the supply after 1 complete periodic cycle of the sinusoidal waveform. 

As a result, the average power consumed by a circuit is similar to the aggregate of the power saved and returned throughout one entire cycle. As a result, the average power absorption of a circuit will equal the average of instantaneous power beyond one complete cycle, with instantaneous power, p, defined as the product of an instantaneous voltage, v, and instantaneous current.

The average power delivered throughout will be the same as that of the average power granted over a single cycle since the sine function is periodic and continuous. 

Power factor

The ratio of the genuine power running across the circuit to an apparent power existing in the circuit is known as the power factor of the alternating current.

Power Factor=True power (P)/Apparent power (S) 

Also, cosΦ = R/Z

Here R represents resistance, Z represents impedance, and CosΦ is the power factor

Importance of power in an ac circuit

A power factor is critical because it indicates the amount of current that is consumed by the circuit and, as a result, the wire size that must be used. Low power factors cause higher heating losses in transmission lines

This factor has an impact on the voltage and current waveforms.

Power equation

In a pure resistor, electrical power is P = VI. Here P is the power, V is the voltage and I is the current.

The voltage and current waveforms are in phase, meaning they both achieve their peak values and flow through 0 at the same moment. 

The magnitude of power depends on only VI. 

As a result, the volt-ampere product can be used to calculate the power at any given time by multiplying the two waveforms. This is known as “Real Power,” which is measured in watts, kilowatts (kW), megawatts (MW), and other such units.

In a pure inductor, Real power is p = 0.

A pure inductor could not use any real power, but because we have both voltage and current, we can no longer utilise cos(θ) in the formula: P = VICos.

Where Cosθ is power factor, The ratio of the genuine power running across the circuit to an apparent power existing in the circuit is known as the power factor of the alternating current.

In this scenario, the product of current and voltage is imaginary power, also known as “Reactive Power,” which is measured in volt-amperes reactive, kilo-volt-amperes reactive, and other units. 

In a pure inductor, Reactive power (Q) is the power consumed in an AC circuit that does not perform any useful work but has a big effect on the phase shift between the voltage and current waveforms. Reactive power is linked to the reactance produced by inductors and capacitors and counteracts the effects of real power. Reactive power does not exist in DC circuits.

As a result, it is the multiplication of the voltage and the element portion of the current that’s 90 degrees out of phase with the voltage.

Reactive Power (sometimes referred to as imaginary power) and is expressed in a unit called “volt-amperes reactive”, symbol Q and is given by the equation: VI.sinΦ. Reactive power, is not really power at all but represents the product of volts and amperes that are out-of-phase with each other. Reactive power is the portion of electricity that helps establish and sustain the electric and magnetic fields required by alternating current equipment. The amount of reactive power present in an AC circuit will depend upon the phase shift or phase angle between the voltage and the current and just like active power, reactive power is positive when it is “supplied” and negative when it is “consumed”.

Conclusion

An alternating current is a current whose amplitude and polarity change at regular intervals. We have seen how in AC circuits, both voltage and current flowing in a passive circuit are usually out of phase, and hence they cannot be used to do any real work. We have already seen that electrical power in the direct current circuit is equivalent to the voltage products of the current, that is, P = V*I. However, we cannot calculate it in the same way we do in an AC circuit since we need to account for phase differences.