Electric power: formula, units

Every modern appliance has electrical power. Its digital value is indicated by the manufacturer on the case of the dryer or electric kettle, on the lid of the food processor.

electric power


The calculation of electrical power allows you to determine the cost of electrical energy consumed by different devices for a certain period of time. Excessive watts and kilowatts lead to wire failure, contact deformation.

electric power formula

Dependence between electric current and power consumed by devices

Electrical power is the work that takes place over a period of time. A plugged in appliance does work measured in watts (W). The case indicates the amount of energy that will be consumed by the device over a certain period of time, that is, the consumed electrical power is given.

Power consumption

It is expended on the movement of electrons in the conductor. In the case of a single electron with a single charge, it is comparable to the magnitude of the voltage network. The total energy that is needed to move all electrons will be defined as the product of voltage and the number of electrons in a circuit when an electrical device is operating. Below is the formula for electrical power:

P = (U * Q) / t.

Given that the number of electrons flowing over a period of time through a cross section of a conductor, is an electric current, we can represent it in the expression for the desired quantity. The formula of electric power will look like:

P = I * U.

In reality, it is necessary to calculate not the power itself, but the magnitude of the current, knowing the mains voltage and the rated power. By determining the current that is consumed by a particular device, you can correlate the value of the outlet and the circuit breaker.

electric power calculation

Calculation examples

For a kettle, the electrical power of which is designed for two kilowatts, the current consumption is determined by the formula:

I = P / U = (2 * 1000) / 220 = 9A

To connect such a device in a conventional electrical network, the connector, designed for 6 amps, is clearly not suitable.

The dependences between power and electric current given above are relevant only if the phase coincides with the values ​​of voltage and current. Practically for all household electric devices the formula of electric power approaches.

Exceptional situations

In the event that a large capacitance or inductance is present in the circuit, the formulas used will be unreliable, they cannot be used for mathematical calculations. For example, the electrical power for an AC motor will be determined as follows:

P = I * U * cosφ.

cosφ is the power factor, which for electric motors is 0.6-0.8 units.

Determining the parameters of the device in a three-phase network with a voltage of 380 V, it is necessary to sum up the power of the individual values ​​for each phase.

consumed electric power

Calculation example

For example, in the case of a three-phase boiler designed for a power of 3 kW, 1 kW is consumed in each phase. Calculate the magnitude of the phase current by the formula:

I = P / U_f = (1 * 1000) / 220 = 4.5A.

For the modern man is characterized by constant use in the workplace and in the life of electricity. It uses devices that consume electrical current, uses such devices that produce it.Working with such sources, it is important to take into account the maximum possibilities that are assumed in the technical specifications.

Such a physical quantity, such as electrical power, is one of the main indicators of any device that functions when electrons flow through it. For transportation or transmission of electrical power in a large volume, required in industrial conditions, high-voltage electrical transmission lines are used.

Energy conversion is performed at high-power transformer substations. Three-phase conversion is typical for industrial and household appliances for various applications. For example, thanks to this transformation, incandescent lamps of different denominations function.

In theoretical electrical engineering, there is such a thing as instantaneous electrical power. Such a value is associated with the flow through a certain surface over a small time interval of a single elementary charge. The work is performed by this charge, which is associated with the concept of instantaneous power.

By performing simple mathematical calculations, you can determine the amount of power. Knowing this value, it is possible to select the voltage for the full functioning of a variety of household and industrial appliances. In this case, you can avoid the risks associated with burnout of expensive electrical appliances, as well as the need to periodically change electrical wiring in the apartment or office.

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