An electric measurement unit of power called a volt ampere is equal to the product of 1 volt and 1 ampere. This is equivalent to 1 watt for a direct current system, and a unit of apparent power is separated into real and reactive power. Real power is the work-producing part of apparent power that measures the rate of supply of energy and is denoted as kilowatts (kW). Reactive power is the portion of apparent power that does no work and is referred to as kilovars; this type of power must be supplied to most types of magnetic equipment, such as motors, and is supplied by generator or by electrostatic equipment. Volt amperes are usually divided by 1,000 and called kilovolt amperes (kVA). Energy is denoted by the product of real power and the length of time utilized; this product is expressed as kilowatt hours.