The role of shunt capacitors in power systems

Shunt capacitor concept

6. Shunt capacitor, shunt capacitor, formerly referred to as shunt capacitor.It is mainly used to compensate the reactive power of inductive load in power system to improve power factor, improve voltage quality and reduce line loss.Single-phase shunt capacitors are mainly composed of cores, shells and outgoing structures.A capacitor core is formed by pressing a number of components, insulators and fasteners and impregnated with insulating oil.The lead wire of the capacitor electrode plate is connected to the outgoing connector at the lower end of the outgoing porcelain bushing through series and parallel connection.The metal case of the capacitor is filled with dielectric oil.

Installing shunt capacitors in substations is an effective measure to improve voltage quality and reduce power loss.Most of the power loads in the power grid, such as motors and transformers, are inductive loads. In the operation process, corresponding reactive power should be provided to these devices.Installation of shunt capacitor in the power grid, reactive power compensation equipment, can provide reactive power consumed by a perceptual load, reduce the power grid power supply provided to the perceptual load, by reactive power line transmission, due to reduce the reactive power flow in the grid, so can reduce the lines and transformers caused by transmission of reactive power loss of electric power.

Connection method for shunt capacitors

The connection of shunt capacitor is usually made by triangle and star, among which star is the most widely used.

1. Triangles

The connected capacitor directly bears the voltage between the lines. When any capacitor is broken down due to fault, a two-phase short circuit will be formed. The fault current is very large.

Therefore, this kind of wiring has been rarely used in 10kV system, only a small number of use in 380V distribution system.

2, star

Wye - connected capacitor Banks are widely used in high voltage power network.The inter-electrode voltage of wye capacitor is the phase voltage of power grid, and the insulation voltage is lower, so the manufacturing design of capacitor can choose the lower working field strength.

When one capacitor in the capacitor bank breaks down due to fault, the fault current will be reduced to a certain range due to the impedance limit of the other two sound phases, and the fault effect will be reduced.

The role of shunt capacitors in power systems

Voltage is an important index to measure power quality.Electrical equipment in a power system has the best technical and economic performance only when the voltage is rated.However, in the normal operation of the power system, the power load and the system operation mode are often changing, which causes the voltage change, inevitably voltage deviation.

And the operation of the power system voltage level depends on the balance of reactive power, all kinds of reactive power in the system reactive power output should be able to meet the system load and network loss in the demand for reactive power measurement under the rated voltage, otherwise it will deviate from the rating, the lower the power quality, ultimately affect the normal operation of the equipment in the power system.Therefore, it is a practical and economical method to install shunt capacitor Banks for reactive power compensation in 110kv and below power grids.Reactive power compensation can reduce the design capacity.Reduce investment;Increase the transmission ratio of active power in the power grid, reduce line loss, improve voltage quality, and stabilize equipment operation;It can improve the power factor of low-voltage network and electrical equipment, reduce the power loss and energy saving.

In the power system, motor and other equipment with many of the coil, such devices in addition to the part from line current work, but also from the line inductance current consumption part of not doing any work, this makes the circuit current will increase some additional, the power factor is used to measure this part of the current of not doing any work, when the inductor current is zero, the power factor is equal to 1, when the demand is gradually increasing proportion of inductor current, power factor gradually decline, obviously, the lower the power factor, line the extra burden, the greater the additional burden of generator, electric transformer and distribution equipment is bigger also,In addition to reducing the utilization rate of the line and power equipment, it will also increase the power loss on the line, increase the voltage loss, and reduce the supply quality.Therefore, the power factor should be increased.

The most convenient way to improve the power factor is the shunt capacitor:

A shunt capacitor produces a capacitive current that offsets an inductive current, reducing the so-called reactive current that does no work to a certain extent.Reactive power supply, like active power supply, is an indispensable part to ensure the quality of power, should maintain reactive power balance in the power system, otherwise, will make the system voltage reduction, equipment damage, power factor decline, serious, will cause voltage collapse, system cracking, causing a large area of power failure.