The purpose of this article is to consider some ways of compensating reactive power. The Russian Federation is known to have a highly-developed industry. So, electric power is consumed by a large number of electrical machines used in the manufacturing process such as induction motor, transformers, arc welding units, induction furnaces, and so on. The fact is that the magnetic flow is dependent on the windings in electrical machines. When alternating current flows through the coil, it induces reactive electromotive force which causes a phase shift between voltage and current. This process is characterised by consumption of both active and reactive power.
The problem is that reactive power in the power grid not only adversely affects its performance but also leads to greater losses in grids and bigger voltage drop. In addition to this, fuel consumption in power plants increases when generators are loaded with reactive currents. Reactive current brings additional load to power lines, making it necessary to increase the cross-sections of wires. That is why all companies need to compensate reactive power in order to improve energy efficiency. In view of this, on November 23, 2009 the State Duma of the Russian Federation enacted Federal Law №261 «On energy saving and improving energy efficiency», which implies enhancing energy efficiency of all kinds of consumers.
In practice different devices are used for reactive power compensation. These include: capacitor installation, synchronous compensators, compensating reactor, harmonic filters, static VAR compensators.
Capacitor installations give reactive power to the system. Since the power flows decrease in the network, this leads to a reduction of active energy losses and decline in voltage losses. As a result the load on transmission lines and transformers declines as well.
Synchronous compensator is a synchronous motor of lightweight construction designed to operate at idle mode. When operating in overexcitation mode it generates reactive power.
Compensating reactor consume reactive power. They compensate for the excess reactive power, reduce its flow while decreasing the current in the lines and transformers and bringing down the active losses.
Harmonic filters are devices designed to reduce harmonic distortion of voltage and to compensate reactive power of consumers loads in electric networks.
Static VAR compensators both give and consume reactive power. They allow you to quickly and smoothly adjust reactive power. Static VAR compensators in electric networks are designed to increase the capacity and sustainability of power lines, to ensure voltage stabilization in the load centers reducing electricity losses and improving its quality.
When choosing a reactive power compensation device we should take into account the complexity of the repair and maintenance, their cost effectiveness. For example, static VAR compensators have a complex structure and high cost. Synchronous compensators should be installed as closely as possible to the consumer for their efficient operation without loading the network with reactive currents. Filter compensation devices are costly, and can rationally be used only for stationary loads. The disadvantage of compensating reactors is the fact that they cause voltage drop of the network.
Capacitor installations have been found to be the most simple in design and economical devices. They have a long life and can be directly connected to the bus bars of both low and high voltage and guarantee low active power losses. Capacitor installations are easy to use, simple to install, allow both internal and external installation.
The structure of capacitor installation consists of a bank of capacitors, current limiting reactor, switching cabinet and capacitor banks protection with measuring current transformers. The main element of the static capacitor battery is single-phase cosine capacitors. The design of the capacitor battery is an assembly of the blocks of high-power capacitors, arranged in the welded metal frames, which are interconnected in series and in parallel. Blocks of condensers are mounted vertically in a few levels to support insulators. Three-phase battery usually consists of three monophase structures, including static capacitors, current limiting reactors and current transformers, which are connected to form a star or a triangle, depending on the mode of neutral.
Current transformers (one for each phase) are connected by means of a primary winding in the gap between two parallel groups and are intended to supply a signal to the relay protection device to disconnect the switch head in the case of unbalance. The function of current limiting reactors is to limit starting current when the capacitor bank is turned on. Capacitor banks can be produced with the power of 5 to 200 MVar, voltage — 6, 10, 35, 110, 220 kV.
To conclude, reactive power compensation can best be achieved at industrial enterprises with almost constant electrical load by means of static capacitors, since the main electrical load is carried by asynchronous motor. This will increase the power factor up to 0.7-0.75 0,93-0,99 and significantly improve the power efficiency of the enterprise.