Reactive Power & Compansation
May be the most important one is the reactive power component that needs to be supplied along with active power. Depending on the current and voltage waveforms, reactive power can be leading or lagging (one of the waveforms leads or lags the other). Active power contributes to the energy consumed, or transmitted, meanwhile reactive power does not contribute to the energy. Reactive power is an inherent part of the ‘‘total power.’’ that is created because of the current – voltage seperation in the circuit.
Reactive power is either generated or consumed in almost every component of the system including generation, transmission, and distribution and of course by the loads. The impedance of a branch is very important while defining the reactive and active power. A circuit in an AC system (not ideal) consists of two components, resistance (active power) and reactance (reactive power).
Reactance can be either inductive or capacitive, which contribute to reactive power in the circuit.Most of the loads are inductive (the ones that do mechanical work), and must be supplied with lagging reactive power. It is economical to supply if this reactive power is supplied to the load nearby in the distribution system. Hence we have the term, reactive power compensation.
Reactive power compensation in power systems can be either shunt or series. Shunt compansation is the most common one.
Shunt Reactive Power Compensation
Since most loads are inductive and consume lagging reactive power (voltage leads current) the compensation required is usually supplied by leading reactive power (capacitors). Shunt compensation of reactive power can be employed either at load level (prefered), substation level, or at transmission level.
Compansation can be capacitive (leading) or inductive (lagging) reactive power, although in most cases capacitive compansation is employed. The most common form of leading reactive power compensation is by connecting a series of shunt capacitors to the line, but since the reactive power of the load changes, these capacitors (banks) should be controlled in a sequence.
Shunt capacitors have great effects while distributing energy, most common ones are:
Shunt capacitors increases voltage at around %5. The main reason that shunt capacitors are installed at substations is to control the voltage within required levels. Load varies over the day, with very low load during midnight and peak values occurring in the evening. Shape of the load curve also varies from day to day, with weekend load typically low.
As the load varies, voltage at the substation bus and at the load bus varies. Since the load power factor is most of the time lagging, a shunt connected capacitor bank at the substation can raise voltage when the load is high. The shunt capacitor banks can be permanently connected to the bus (fixed capacitor bank) or can be switched when needed.
2.Reducing power losses
Compensating the load lagging power factor with the bus connected shunt capacitor bank improves the power factor and reduces current flow through the distribution lines, transformers, generators, etc. This will reduce power losses (I2R losses) in these equipments.
3.Increased utilization of equipment
Shunt compensation with capacitor banks reduces kVA loading of lines, transformers, and generators, which means with compensation they can be used for delivering more power with high efficiency and without overloading the equipment.