Short Answer:

Reactive power is the part of electrical power that does not perform any useful work, but is essential to maintain electric and magnetic fields in inductive and capacitive equipment. It is measured in kVAR (kilovolt-ampere reactive) and flows back and forth between the source and load.

Reactive power affects the power system by causing voltage drops, increasing line losses, and reducing overall efficiency. While it does not produce mechanical output, it is necessary for the proper functioning of motors, transformers, and other AC equipment.

Detailed Explanation:

Reactive power and its effect on the power system

In AC (alternating current) electrical systems, the total power supplied is made up of two components: real power (kW) and reactive power (kVAR). Real power is the useful power that performs actual work like lighting, heating, or running motors. Reactive power, on the other hand, is the power that alternates between the source and the load, used to establish and maintain magnetic and electric fields in equipment such as motors, transformers, and capacitors.

Reactive power is vital for the operation of AC power systems, especially for inductive loads, which are very common in industrial and commercial setups. However, too much reactive power can cause problems like overloading, voltage instability, and increased losses.

Definition and Nature of Reactive Power:

Reactive power arises due to the phase difference between current and voltage.
In purely resistive loads, voltage and current are in phase, so no reactive power is needed.
In inductive loads (like motors, coils), current lags behind voltage.
In capacitive loads, current leads the voltage.
Reactive power flows back and forth, meaning it is not consumed like real power but is exchanged between source and load.

How Reactive Power Affects the Power System:

Voltage Regulation Issues:
Reactive power affects voltage levels in the system. If reactive power demand is too high and not supplied locally, voltage can drop, leading to poor equipment performance and possible malfunction.
Increased Transmission Losses:
Low power factor caused by excessive reactive power increases current flow, resulting in higher I²R (resistive) losses in cables and transformers.
Reduced System Capacity:
Since apparent power (kVA) includes both real and reactive components, more reactive power means less capacity for useful (real) power. This limits the system’s ability to carry additional loads.
Higher Energy Costs:
Utilities may charge for low power factor, which is often the result of excessive reactive power. Maintaining a good power factor reduces these charges.
Unstable Grid Operation:
Reactive power imbalances can cause voltage fluctuations and system instability, especially in long-distance transmission networks and during load variations.

Importance of Managing Reactive Power:

Improves Voltage Stability: Proper reactive power management ensures voltage remains within safe limits.
Enhances System Efficiency: Reduces current, losses, and overheating of cables and equipment.
Supports Reliable Operation: Maintains smooth operation during varying load conditions and helps during faults.
Enables Renewable Integration: Helps manage voltage levels in systems with solar or wind energy sources.

Common Devices for Reactive Power Control:

Capacitor Banks: Provide leading reactive power to offset lagging loads.
Synchronous Condensers: Synchronous machines that generate or absorb reactive power as needed.
Static VAR Compensators (SVCs): Power electronic systems for fast reactive power control.
Reactors and Filters: Used for controlling capacitive effects or harmonics in the network.

Conclusion:

Reactive power is essential for the operation of inductive equipment and the overall AC power system, even though it does not contribute to real work. If not managed properly, it leads to voltage drops, system inefficiencies, and higher costs. Controlling reactive power using proper correction devices helps ensure a stable, efficient, and reliable power supply in all electrical networks.