What are the advantages of proper reactive power control?
Earlier this week I attended the CIGRE conference in Paris. Walking around at the exhibition I noticed that underground cables, monitoring and diagnostics, substation automation and power flow and voltage control received a lot of attention—which inspired today’s blog post about what can be gained from proper reactive power control.
Reactive power (Q measured in VAR) is needed for a proper functioning AC power system—to keep the voltage up—and is related to the active power (P measured in W) and apparent power (S measured in VA) through the power triangle. For a reliable and stable operation of the power system, an active power balance must be present at all times, and the reactive power has to be balanced as well. Unlike active power, reactive power cannot be transmitted over long distances; it has to be generated locally.
If we take a look at power system from a broad perspective, we observe that the amount of reactive power compared to the amount of active power in the transmission grid is much bigger than in the distribution grid. For transmission a typical value is 70%, while for distribution values around 50% are common. The two contributors of reactive power are the grid itself—overhead lines and cables have to be energized—and the loads placed at the customer locations. For high voltage the biggest contributor to reactive power is the grid itself, and for low voltage the loads.
In Table 1 it is clear what actions can be taken to reduce the amount of reactive power in the grid, and thus reduce losses and decrease electricity supply needs while increasing transmission capacity and defer capacity upgrades. Furthermore, reactive power control enables more operating flexibility and increased reliability. Transmission companies should focus on reduction of reactive power needs from the grid itself, this can be done, e.g., with local reactive power compensation. Distribution companies should also focus on controlling the reactive power needs of the customer loads. As the amount and fluctuations of the power flows will increase in the future, we can achieve more from installing proper reactive power control.