What is Electric Power? Definition, Formula and Types

What is Electric Power? Definition, Formula and Types

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What is electric power? Before explaining what electric power definition let us try to review the Voltage and current. Is the electric power definition related to Voltage and electric current? see below.

Voltage and current are two basic parameters of an electric circuit. But, only voltage and current are not sufficient to express the behaviour an electric circuit element. We essentially need to know, how much electric power, a circuit element can handle. All of us have seen that a 60 watts electric lamp gives less light than a 100 watts electric lamp.

What is Electric Power? Definition, Formula and Types

When we pay electric bill for electricity consumption, we are actually paying the charges for electric power for a specified period of time. Thus electric power calculation is quite essential for analyzing an electric circuit or network.

Power is the rate of energy supplied or consumed by an electric element with respect to time.

Electric Power Formula

Suppose, an element supplies or consumes an energy of dw joules for a time of dt second, then power of the element can be represented as,

This equation can also be rewritten as,

Hence, from the as the expression of voltage and current in the equation are instantaneous, the power is also instantaneous. The expressed power is time-varying.

So, the power of a circuit element is the product of voltage across the element and current through it.

As we have already told that a circuit element can either absorb or deliver power. We represent the absorption of power by putting a positive sign (+) in the expression of power. Likewise, we put a negative sign (-) when we represent the power delivered by the circuit element.

Passive Sign Convention

There is a simple relationship between the direction of current, polarity of voltage and sign of the power of a circuit element. We call this simple relationship as passive sign convention.

When a current enters in an element through its terminal of positive voltage polarity, we put a positive sign (+) before the product of the voltage and current.

This implies that the element absorbs or consumes power from the electric circuit. On the other hand, when the current through the element leaves its terminal of positive voltage polarity, we put a negative sign (-) before the product of the voltage and current. This implies that the element delivers or supplies power to the electric circuit.

Let us take a resistor connected across two circuit terminals. Although, the rest of the circuit is not shown here in the figure. The polarity of the voltage drop across the resistor and the direction of current through the resistor are shown in the figure below.

The resistor is consuming a power of vi watts as current i ampere enters in the resistor though its positive side of the dropped voltage v volt, as shown.

resistor

Let us take a battery connected across two circuit terminals. Although, the rest of the circuit is not shown here in the figure. The polarity of the voltage drop across the battery and the direction of current through the battery are shown in the figure below. The battery is delivering a power of vi watts as current i ampere enters in the battery of v volt through its positive polarity terminal as shown.

battery

Types of Electrical Power

The electrical power is mainly classified into two types. They are the DC power and the AC power.

1. DC Power

The DC power is defined as the product of the voltage and current. It is produced by the fuel cell, battery and generator.

electrical-circuit

Where P – Power in watt.
V – voltage in volts.
I – current in amps.

2. AC Power

The AC power is mainly classified into three types. They are the apparent power, active power and real power.

1. Apparent Power – The apparent power is the useless power or idle power. It is represented by the symbol S, and their SI unit is volt-amp.

electrical-power-equation-3

Where S – apparent power
Vrms – RMS voltage = Vpeak√2 in volt.
Irms – RMS current = Ipeak√2 in the amp.

2. Active Power – The active power (P) is the real power which is dissipated in the circuit resistance.

apparent-power-equation-1

Where, P – the real power in watts.
Vrms – RMS voltage = Vpeak√2 in volts.
Irms – RMS current = Ipeak√2 in the amp.
Φ – impedance phase angle between voltage and current.

3. Reactive Power – The power developed in the circuit reactance is called reactive power (Q). It is measured in volt-ampere reactive.

electric-power-equation-2

Where, Q – the reactive power in watts.
Vrms – RMS voltage = Vpeak√2 in volt.
Irms – RMS current = Ipeak√2 in the amp.
Φ – impedance phase angle between voltage and current.

The relation between the apparent, active and reactive power is shown below.

electrical-power-equation-4

The ratio of the real to the apparent power is called power factor, and their value lies between 0 and 1.

Electric Power Definition, Formula and Types

After going through the above portion of electric power formula we can now establish a Electric definition definition. I hope you enjoy when reading this article, thank you.