What is a shunt capacitor in a substation?
Shunt capacitors are connected in parallel with the load to improve the power factor. The power factor is defined as the ratio of the real power to the apparent power of an AC circuit. In AC circuits, some amount of energy is lost due to the reactive power that is required to establish the electric and magnetic fields in the inductors and capacitors in the circuit. Shunt capacitors help to reduce the reactive power and improve the power factor.
When the load is inductive, the current lags the voltage, resulting in a low power factor. By adding shunt capacitors to the circuit, the reactive power component can be reduced, which increases the power factor. The capacitors store energy during one part of the AC cycle and release it during the other part, which cancels out the reactive power component.
Under no-load or light-load conditions, medium and long transmission lines may operate at a leading power factor due to the capacitance effect. The capacitance effect results from the inherent capacitance of the transmission line, which causes the line to act as a capacitor. When there is no load or a light load on the transmission line, the line's capacitance dominates, and the line appears capacitive.
As a result, the current leads the voltage in phase, and the power factor becomes leading. The leading power factor causes the receiving end voltage to become higher than the sending end voltage, which can lead to voltage stability issues and damage to the equipment connected to the transmission line.
To address this issue, shunt reactors are used. Shunt reactors are electrical devices that are connected in parallel with the transmission line. Shunt reactors provide reactive power to the system, which compensates for the effect of capacitance and reduces the leading power factor.
By reducing the leading power factor, the shunt reactor brings the receiving end voltage down to a safe and acceptable level. In addition, shunt reactors can also change the leading power factor to a lagging power factor. This is done by overcompensating for the capacitance effect, which causes the system to become inductive, and the power factor to become lagging.
Why shunt capacitor used in substations?
Shunt capacitors are used in substations to improve the power factor of the network. Power factor is a measure of how efficiently the electrical power is being used in a system. A low power factor indicates that a significant portion of the electrical energy is being lost as reactive power, which is not useful for doing any work. Shunt capacitor banks are installed near reactive loads to compensate for the reactive power generated by the load.
When a shunt capacitor bank is installed near the reactive load, it reduces the reactive power demand from the network. This is because the shunt capacitors provide the reactive power required by the load, reducing the reactive power flow in the network. By reducing the reactive power demand, the shunt capacitors improve the power factor of the network and reduce line losses.
Shunt capacitors operate at a leading power factor, similar to the no-load over-excited synchronous motors. This means that they consume leading VARs by delivering lagging VARs to the system. The shunt capacitors store energy during one part of the AC cycle and release it during the other part, which cancels out the reactive power component. This results in a power factor that is close to unity, which is desirable for efficient power transmission and utilization.
It is important to note that the location of the shunt capacitor bank plays a critical role in their effectiveness. It is always desirable to commission a capacitor bank near the reactive load, as this removes the transmission of reactive kVARS from a greater part of the network. This reduces the losses in the network and improves the overall efficiency of the system.
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