HISTORY OF POWER CAPACITORS
A POWER CAPACITOR is a passive two-terminal electronic component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator.
The physical form and construction of practical POWER CAPACITORS vary widely and many capacitor types are in common use. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The non conducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, air, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy.
In electric power distribution, capacitors are used for POWER FACTOR CORRECTION. Such capacitors often come as three capacitors connected as a three phase load. Usually, the values of these capacitors are not given in farads but rather as a reactive power in volt-amperes reactive (var). The purpose is to counteract inductive loading from devices like electric motors and transmission lines to make the load appear to be mostly resistive. Individual motor or lamp loads may have capacitors for power factor correction, or larger sets of capacitors (usually with automatic switching devices) may be installed at a load center within a building or in a large utility substation.
Till late 1970 the POWER CAPACITORS main dielectric used was Paper which offers relatively high voltage performance. However, paper absorbs moisture due to which losses were very high and has been largely replaced by one layer of plastic and one layer of Paper which were popularly known as MIXED DIELECRTIC POWER CAPACITORS. These POWER CAPACITORS were impregnated with Chlorinated Diephynyl ( PCB), a harmful chemical which has been banned throughout the world.
Instead of one layer of Paper & one layer of Plastic Film a New innovative idea was introduced using both the layers of HAZY Polypropylene Film + Aluminium Foil with newly invented NON PCB Oil which is popularly known at present as ALL PP POWER CAPACITORS .Due the low loss charactrtic of PP Film the losses of these POWER CAPACITORS are low .
As the construction,design, manufacturing process ,and cost of material is very high for above POWER CAPACITORS, sometime in 1980 METALLISED POLYPROPYNE as dielectric was introduced for manufacturing of low Loss POWER CAPACITORS. Instead of plain hazy film+ aluminium foil a plain pp film with thin layer of metallization was introduced. These capacitors are comparatively cheaper than all PP Capacitors,having very low loss and self healing properties and called metalised polypropelene (MPP) capacitors.