Sequence control of AC voltage controllers is employed for the improvement of system power factor.

Power Factor
Power factor is a measure of how effectively electrical power is being used in a system. It is the ratio of the real power (kW) to the apparent power (kVA) in an AC circuit. Power factor can be either leading or lagging, depending on the phase relationship between the voltage and current waveforms.

Importance of Power Factor
A low power factor can result in several issues, including increased power loss, reduced system efficiency, and higher energy costs. Low power factor also puts additional stress on electrical equipment, leading to decreased lifespan and increased maintenance requirements.

AC Voltage Controllers
AC voltage controllers, also known as AC phase controllers or AC regulators, are devices that control the amplitude of the AC voltage supplied to a load. They use thyristors or other semiconductor devices to regulate the output voltage by controlling the firing angle of the thyristors.

Sequence Control
Sequence control of AC voltage controllers involves controlling the firing angle of multiple voltage controllers in a specific sequence. By adjusting the firing angle of the voltage controllers, the power factor of the system can be improved.

Improvement of Power Factor
The power factor can be improved by adjusting the firing angle of the voltage controllers to achieve a leading power factor. This can be done by introducing a controlled delay in the firing angle of the thyristors, which leads to a phase shift between the voltage and current waveforms.

By implementing sequence control of AC voltage controllers, the power factor of the system can be increased towards unity (1.0) or even made leading, depending on the requirements. This leads to a more efficient utilization of electrical power, reduced power losses, and lower energy costs.

Advantages of Improved Power Factor
- Increased system efficiency: A higher power factor means that more of the supplied power is being effectively used by the load, resulting in improved overall system efficiency.
- Reduced power losses: A higher power factor reduces the reactive power component in the system, which in turn reduces power losses in the transmission and distribution lines.
- Lower energy costs: By improving the power factor, the apparent power demand is reduced, resulting in lower energy costs for the consumer.
- Extended equipment lifespan: Improved power factor reduces stress on electrical equipment, leading to longer lifespan and reduced maintenance requirements.

In conclusion, the sequence control of AC voltage controllers is employed to improve the system power factor, resulting in increased efficiency, reduced power losses, and lower energy costs.