Reactive loads such as inductors and capacitors dissipate zero power, yet the fact that they drop voltage (Links to an external site.)Links to an external site. and draw current gives the deceptive impression that they actually do dissipate power. This “phantom power” is called reactive power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather than watts. The actual amount of power being used, or dissipated, in a circuit is called true power. The combination of reactive power and true power is called apparent power, and it is the product of a circuit’s voltage and current, without reference to phase angle (fig. 1). Although it is considered unused power, reactive power is necessary for the stability and reliability of electrical systems.
Power system components are designed to operate within ±5% of the nominal voltages. Fluctuations in voltage levels lead to malfunctioning of the various appliances. High voltage damages the insulation of windings where as low voltage causes poor performance of the various equipment like low illumination of blubs and overheating of induction motors.
If the power demand is more than that supplied by transmitting lines, current drawn from supply lines increases to a higher level, which may cause voltage to decrease drastically at the receiving end. If this low voltage is decreased further, it leads to the tripping of generator units, overheating of motors, and possibly other equipment failures.
To overcome this, reactive power should be supplied to the load by putting reactive inductors or reactors in transmission lines. Capacity of these reactors depends on amount of apparent power to be supplied.
Transformers, motors, generators and other electrical devices require reactive power to produce magnetic flux. This is because generation of magnetic flux is necessary for these devices to do useful work. Reactive power (fig. 2), indicated by red color, helps to create magnetic field in motors but it leads to decrease in the power factor. This is why a capacitor is placed to compensate the inductive reactive power by supplying capacitive reactive power.
Most of the equipment connected to the electric supply systems consume or produce apparent power but not all these control the voltage levels. Power plant generators produces both active and reactive power whereas capacitors inserts the reactive power to maintain the voltage levels.
Figure 1.
Figure 2.
Hawaiian Electric Company (HECO) uses power substations (fig.3) through transformers and voltage regulators. From what I understand these banks of installed capacitors and inductors control reactive power compensation to provide desirable reactive power consumption and generation levels at the high voltage winding buses of the transformers. Although I recognized the existence of these power substations prior to this course I was unaware of their actual duty in the power distribution process.
Figure 3.
Reference
All About Circuits, (n.d.). True, Reactive, and Apparent Power. Retrieved from https://www.allaboutcircuits.com/textbook/alternating-current/chpt-11/true-reactive-and-apparent-power/
El-Sharkawi, M. A., (2013). Electric energy: An introduction. Boca Raton: CRC Press, Taylor & Francis Group
Hawaiian Electric, (2004). Harmonics Part 2. Retrieved from https://www.hawaiianelectric.com/Documents/for_business/power_quality/advanced_topics.pdf
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