What is a Shunt Capacitor & Its Working

In electric power systems, the different loads can use real power as well as reactive power. These loads can be placed at long distances of plants; so real power can be generated whereas reactive power can be generated either during heavy load stages otherwise absorbed when light load stages. Not like real power, the reactive power generation at plants as well as its transmission toward loads over long distances cannot possible economically. A shunt capacitor is extensively used to transmit reactive power to loads in the main distribution. These capacitors supply an economical reactive power to meet up reactive power necessities for different loads. The transmission, as well as distribution lines, operates at lagging PF (power factor) to reduce line losses & enhance voltage regulation.


What is a Shunt Capacitor?

A capacitor that is connected to a supply point or a ĺoad in parallel is known as a shunt capacitor. The function of this capacitor mainly changes based on the application. Throughout power transmission, there will be many troubles such as power factor, poor voltage regulation, poor efficiency & low-reliability shunt capacitive reimbursement is a technique to keep away from these issues.

This technique is used to get enhanced power factor. In most power systems, an inductive load can be loaded. To recompense this load, the shunt capacitor is used by connecting to the load. This kind of compensation could be done toward the transmission level or substation level.

HV Shunt Capacitor
HV Shunt Capacitor

To enhance the reliability as well as security of a distribution system, the possible power supply should transmit through a particular transmission line. So this can be attained with the help of shunt capacitors like compensators to enhance the capacity of load carrying for the transmission line by controlling the flow of reactive power.

Generally, these capacitors are called power factor correction capacitors which serve different functions by providing several advantages like these are used at all voltage levels. When these capacitors are used at the location of the customer for PF correction otherwise for controlling the voltage at the distribution system,

Shunt capacitors, either at the customer location for power factor correction or on the distribution system for voltage control, significantly change the impedance variation in the system through frequency. These capacitors do not make harmonics, however, sometimes severe harmonic distortion can be credited to their occurrence.

How to Determine Rating of Required Capacitor Bank

The rating of capacitor bank can be implemented through the following formula

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Q = P(tanϴ – tanϴ’)

From the above equation,

‘Q’ is the required amount of KVAR

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‘P’ is the required active power calculated kilowatts

‘cosϴ’ is the PF before the compensation


cosϴ’ is the PF after the compensation is done

By using this formula, we can determine the rating of the necessary capacitor bank.

Connection of Shunt Capacitor Bank

The shunt capacitor can be connected in two formats either in delta connection or star connection. In the star connection, the connection of the neutral point can be done to the GND terminal otherwise depending on the bank’s protection arrangement.

In few settings, the capacitor bank connection is in the form of a double star. Generally, capacitor banks are mainly utilized in electrical substations are in the form of star arrangement. This kind of arrangement gives several benefits such as

  • Less installation cost
  • Improved surge protection
  • Minimal recovery voltage in the case of circuit breakers for general recurring capacitor switching interruptions
  • The voltage level in rigid grounded systems will be for the entire 3-phases is stable within the capacitor bank & it will be the same for a two-phase functioning stage

Location of Shunt Capacitor

The shunt capacitor can be connected at different locations of the system bus, at the load & distribution point itself. In specific loads in industries, the whole load can be operated based on the requirement. So in that situation, it is suggested to connect a capacitor bank using the feeder which provides the entire of this particular load that is called as branch capacitor bank method. When the capacitor bank is connected directly to the branch otherwise feeder, then it does not assist to decrease losses within the main system from wherever the branch comes out.

Location of Capacitor
Location of Capacitor

In this system, the separate capacitor bank which is connected with a separate load feeder can be turned ON & OFF independently using the load feeder. Therefore the system provides enhanced control above reactive power however the system is expensive.

Even though connecting a shunt capacitor bank at each load point will compensate reactive power independently for every load. Thus, it gives better development for voltage profile, improved reduction within separate load losses & energy bill reduction for each customer however still it is not feasible because it makes the system difficult and costly.

The major reasons for system complexity are, various sizes, as well as capacities of the capacitor bank, are necessary to be connected based on the necessity of separate load. To overcome this, a bulk capacitor bank is used in a bus system as an alternative to a small capacitor bank at every load point.

Even though the system control over reactive power is compromised a little bit however it is still a practical approach within the cost as well as a view of complexity. So when the capacitor bank is used at load or primary systems then they have their advantages.

Based on the system demand, these two methods are used. These are applicable in different systems like high voltage, HV, feeders & separate distribution systems.

Advantages

The advantages of shunt capacitor include the following.

  • When the reactive power is decreased then the loss of transmission power can be decreased by reducing reactive current
  • The power factor for the source of the generator can be increased
  • High capacity is accessible to supply the power toward the load.
  • There will be reduced pressure for the excitation system of the generator
  • Improved regulation because of low voltage drop
  • It could attain peak load demand
  • Because of low loading, the power system life can be increased

Applications

The applications of shunt capacitors include the following.

  • These capacitors are used in the electric power systems
  • These are used like reactive power sources by connecting them in line-to-neutral.
  • These capacitors are also connected to electric utilities in series through long lines to decrease their impedance. So this is mainly common within the transmission level, wherever the length of lines is hundreds of kilometers.
  • These capacitors are used by utilities at distribution by using voltages for providing reactive power by the inductive loads. This decreases the whole flow of current on the feeder of distribution to improve the voltage & decrease losses.
  • The transformers in the substation will experience fewer loadings once utilities set up enough capacitors on the distribution system. These loadings not only develop emergency switching options but also enhance the life of the equipment.
  • These capacitors enhance the capability of power transfer for a transmission system without using big conductor’s otherwise new lines.
  • The shunt capacitors with high voltage support the voltage of the transmission system, which is frequently required whenever the transmission grid is moved. Since these capacitors generate reactive power, generators no longer require generating as much, allowing them to work at high PFs & generate more real power.
  • Shunt capacitors also increase the operating voltages of transmission bus. When the transmission voltage raises, then a low current is required to supply a load, so again the transmission losses will reduce.

Thus, this is all about an overview of a shunt capacitor. These capacitors are used in electronic devices, where the capacitors are connected in parallel with inductance or resistance for various purposes. But these components are not particularly known as shunt capacitors. Here is a question for you, what are the disadvantages of shunt capacitors?

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