Most of our readers were stumped on this one, just like we were. We gave partial credit to some answers, but no one included the fact that several power factor correction capacitors are added to help with air conditioners turning on and off, altering the type of power that flows into buildings. Because this was such an interesting question and answer, we had one of our engineers, Andrew Errato, research the issue even further and he came up with this excellent explanation:

"As we all know, fans and air conditioners are used in the summer months as well as in areas that experience warm weather year round.  These devices can be from the size of a small desk fan to industrial size HVAC units which can cool thousands of square feet. In the case of Las Vegas which falls into Nevada’s Energy arena, every casino, hotel and buildings all require air conditioning to cool their facilities to keep their customers and residents comfortable.  In fact, the summertime load swing between day and night ranges from 3,000 MW to 6,000 MW in Nevada mostly due to the demand from Las Vegas.  All the HVAC units contain motors, compressors and capacitors to cool the incoming air and disperse it throughout a facility.

In the power world, these loads are considered inductive and capacitive, meaning unlike a pure resistive load (like a light bulb) which dissipates energy, inductive and capacitive loads are considered reactive.  These devices tend to store energy and are typically referred to in units of kVAR (Volt-Amperes Reactive). 

How does this effect power transmission?  As more and more AC units are turned on, a greater kVAR rating is created which alters the basic three-phase power triangle.  More reactance will cause the angle between kW and KVA to alter.  This angle is calculated into what is known as your power factor.  Power factor is essentially the overall efficiency of a power system.  An average Power Factor of a given system is 0.8.  The addition of all these AC units lowers your Power Factor leading to a less efficient power system.  This includes voltage fluctuations.

What power transmission or utility companies do to compensate for the drop in Power Factor and control reactive power flow is to add large capacitor banks and other components (such as phase-shifting transformers and static VAR compensators) throughout their distribution system.  This aides in the reduction of loss and hels in the stabilization of system voltage."

There is no Trivia Question for June, but check back next month for your chance to test your industry knowledge and win Lex T-shirts, mugs, and more!