Capacitor banks are used in AC (alternating current) systems to improve power factor and reduce reactive power. To understand how they achieve this, let's break down the concepts of power factor, reactive power, and how capacitor banks work:
Power Factor (PF): Power factor is a measure of how efficiently electrical power is being used in an AC circuit. It's the ratio of real power (active power) to apparent power. A power factor of 1 (or 100%) indicates all the supplied power is being used for useful work, while a power factor less than 1 indicates a portion of the supplied power is being lost as reactive power.
Reactive Power: In AC systems, reactive power doesn't perform useful work like real power. It's needed to establish the magnetic fields in devices such as motors, transformers, and induction coils, but it doesn't contribute to actual work output. Reactive power causes inefficiencies, increases losses, and reduces the capacity of the power system to transmit real power.
Capacitor banks are utilized to address these issues:
Reactive Power Compensation: Capacitor banks are filled with capacitors, which store electrical energy in an electric field between their plates. When AC voltage is applied to them, they charge and discharge as the voltage alternates. When a circuit has inductive loads (like motors), it tends to draw reactive power from the power source. This reactive power is needed to create magnetic fields and support the functioning of inductive devices. However, this reactive power doesn't contribute to the actual work being done.
Phasor Diagrams: In an AC circuit, the voltage and current are not always in phase due to the reactive components. The phasor diagram illustrates the relationship between voltage, current, real power, and reactive power. When you introduce capacitor banks into the circuit, they provide capacitive reactance, which leads to a phase shift that compensates for the inductive reactance.
Improved Power Factor: By introducing capacitor banks strategically into the circuit, you can offset the inductive reactive power with capacitive reactive power. This results in a closer alignment of the current and voltage waveforms, improving the power factor. Capacitor banks effectively "cancel out" the excess reactive power, leading to a higher power factor closer to 1.
Reduced Losses and Increased Capacity: Improving the power factor through the use of capacitor banks reduces the amount of reactive power flowing through the system. This reduces losses due to reactive power and frees up capacity in transmission lines and transformers, allowing them to carry more real power. This optimization of the power system leads to more efficient utilization of resources.
In summary, capacitor banks improve power factor and reduce reactive power in AC systems by introducing capacitive reactance to counteract the inductive reactance of loads. This helps align the current and voltage waveforms, leading to a higher power factor and more efficient utilization of the electrical system's capacity.