The active energy is transformed into work and heat from electrical devices. Devices such as incandescent light bulbs absorb only active energy. It is measured in kWh (kilowatt hours).
Reactive energy is the amount of energy that instead of being consumed immediately by the user is stored for a fraction of a second and dropped into the power grid. Reactive energy use affects the equipment to work need a magnetic field, such as electric motors, fluorescent (neon), electronic equipment (tv, computer, etc.). The unit of measurement of reactive energy is the varh (Volt Amperes Reactive hours). This energy is not marketed, so moderate consumption of reactive energy is to consider as physiological. Shall be a maximum amount of consumption of reactive energy, in italy currently valid only for supply of electric energy above 16.5 kW, beyond which take a penalty.
The parameter which normally is taken into account to see if the electrical plant has a high consumption of reactive energy is the power factor or cosφ. This parameter evaluates the relationship between active and reactive energy and ideally, only with resistive load and therefore without reactive energy consumed, worth 1. In case there is a reactive energy consumption, the parameter values are less than 1 and on the basis of how much it deviates from the ideal value you may incur a penalty. The consumption of reactive energy is considered normal until electrical user has a power factor (cosφ) greater than 0.9. Values less than this limit indicate problems at the electrical plant and the simultaneous request for penalties by the distributor of electrical energy with which we have concluded the contract.
The reactive energy consumption may be limited or even undone by some simple technological devices that are installed on the electrical equipment of the customer, in this case we speak about power factor correction of the electrical plant.