- Shunt Capacitor Definition: A shunt capacitor is defined as a device used to improve power factor by providing capacitive reactance to counteract inductive reactance in electrical power systems.
- Power Factor Compensation: Shunt capacitors help improve the power factor, which reduces line losses and improves voltage regulation in power systems.
- Capacitor Bank: A capacitor bank is a group of capacitors used together to provide the necessary reactive power compensation, commonly connected in shunt configuration.
- Connection Methods: Shunt capacitor banks can be connected in star or delta configurations, with grounded star connections offering advantages like reduced recovery voltage and better surge protection.
- Location Considerations: For maximum effectiveness, capacitor banks should be located near reactive loads, although practical and economic factors often influence the final placement.
What is a Shunt Capacitor?
A capacitor bank is very essential equipment of an electrical power system. The power required to run all the electrical appliances is the load as useful power is active power. The active power is expressed in kW or MW. The maximum load connected to the electrical power system is mainly inductive in nature such as electrical transformer, induction motors, synchronous motor, electric furnaces, fluorescent lighting are all inductive in nature.
In addition to these, inductance of different lines also contributes inductance to the system.
Inductive loads cause the system current to lag behind the voltage. As this lag increases, the electrical power factor decreases. Lower power factor means the system draws more current for the same active power, leading to higher line losses.
Poor electrical power factor causes poor voltage regulation. So to avoid these difficulties, the electrical power factor of the system to be improved. As a capacitor causes current to lead the voltage, capacitive reactance can be used to cancel the inductive reactance of the system.
The capacitor reactance can be used to cancel the inductive reactance of the system.
The capacitor reactance is generally applied to the system by using static capacitor in shut or series with system. Instead of using a single unit of capacitor per phase of the system, it is quite effective to use a bank of capacitor units, in the view of maintenance and erection. This group or bank of capacitor units is known as capacitor bank.
There are mainly two categories of capacitor bank according to their connection arrangements.
- Shunt capacitor.
- Series capacitor.
The Shunt capacitor is very commonly used.
How to determine Rating of Required Capacitor Bank
The size of the Capacitor bank can be determined by the following formula :
Where,
Q is required KVAR.
P is active power in KW.
cosθ is power factor before compensation.
cosθ’ power factor after compensation.
Location of Capacitor Bank
Ideally, a capacitor bank should be placed near reactive loads to minimize reactive power transmission across the network. When a capacitor and load are connected together, they disconnect simultaneously, preventing overcompensation. However, it’s not practical or economical to connect a capacitor to each individual load due to varying load sizes and availability of capacitors. Additionally, not all loads are connected continuously, so the capacitors may not be fully utilized.
Hence, capacitor, is not installed at small load but for medium and large loads, capacitor bank can be installed at consumer own premises. Although the inductive loads of medium and large bulk consumers are compensated, but still there would be considerable amount of VAR demand originated from different uncompensated small loads connected to the system. In addition to that, inductance of line and transformer also contribute VAR to the system. On viewing of these difficulties, instead of connecting capacitor to each load, large capacitor bank is installed at main distribution sub-station or secondary grid sub-station.
Connection of Shunt Capacitor Bank
The capacitor bank can be connected to the system either in delta or in star. In star connection, the neutral point may be grounded or not depending upon protection scheme for capacitor bank adopted. In some cases the capacitor bank is formed by double star formation.
Generally large capacitor bank in electrical substation is connected in star.
The grounded star connected bank has some specific advantages, such as,
- Reduced recovery voltage on circuit breaker for normal repetitive capacitor switching delay.
- Better surge protection.
- Comparatively reduced over voltage phenomenon.
- Lesser cost of installation.
- In a solidly grounded system, the voltage of all three phases of a capacitor bank remains fixed, even during two-phase operation.
