Electric power:

Electric power can be defined as the rate at which the electrical energy is transferred by an electric circuit. The SI unit of power is watt. The electric power in watts associated with the complete electric circuit or a circuit component represents the rate at which the energy is converted from the electrical energy of the moving charges to some other form, for example heat, mechanical energy, or energy stored in electric fields or magnetic fields. For a resistor in a D C Circuit the power can be given by the product of applied voltage and the electric current:

P = VI

 Electrical power is transmitted with the overhead Lines. For the underground transmission see the high voltage cables. When electric current flows in the circuit, it can transfer energy to do mechanical work. Devices convert electrical energy into a number of useful forms, such as heat (electric heaters)

, motion (electric motors), light (light bulbs), sound (loudspeaker) or chemical changes. Electricity can be produced mechanically by generation, or by chemicals, or by direct conversion from light in photovoltaic cells, also it can be stored chemically in batteries.

Electric power transmission or "high voltage electric transmission" is bulk transfer of electrical energy, from generating power plants to substations located near the population centers. This is distinct from the local wiring among high voltage substations and customers, which is referred to as electricity distribution.

Electric power, like mechanical power, can be represented by the letter P in the electrical equations. The term wattage is used colloquially to mean "electric power in watts."Electric power is usually measured in Watts, kilowatts, and megawatts. The amount of electrical energy used by an appliance can be found by multiplying its consumed power by the length of time of operation. The units of electrical energy are usually watt-hours, watt-seconds (joules), or kilowatt-hours. For the commercial purposes the kilowatt-hour is the unit of choice.

P=VI where P is electric power, V potential difference, and I electric current.

In alternating current circuits, energy storage elements like inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC waveform, results in the net transfer of energy in one direction is called as real power (also referred to as active power). That portion of power flow because of stored energy that returns to the source in each cycle is known as reactive power.