{"id":528,"date":"2013-10-04T13:57:32","date_gmt":"2013-10-04T18:57:32","guid":{"rendered":"http:\/\/www.kele.com\/keleblog\/?p=528"},"modified":"2013-10-04T13:57:32","modified_gmt":"2013-10-04T18:57:32","slug":"what-are-power-system-vars","status":"publish","type":"post","link":"https:\/\/www.kele.com\/content\/blog\/2013\/10\/04\/what-are-power-system-vars","title":{"rendered":"What Are Power System VARs?"},"content":{"rendered":"

Most people involved in building automation are familiar with kW, which is the rate at which a building is consuming energy from the power company. But there is another power system parameter known as VAR\/kVAR which is less well understood. In this article we will attempt to dispel some of the VAR mystery.<\/p>\n

The term \u201cVAR\u201d stands for \u201cVolt-Amperes Reactive.\u201d Guess we\u2019re done here, right? What\u2019s that? You were hoping for a little more explanation. OK, let\u2019s dig a little deeper.<\/p>\n

First, for any readers that are complete newbies to power monitoring, let\u2019s explain the \u2018k\u2019 prefix frequently found on power system readings. \u201ck\u201d simply means \u201ctimes 1000.\u201d So three kV is three thousand volts, two kW is two thousand watts, one kVAR is one thousand VARs, etc…<\/p>\n

What is a VAR?<\/strong><\/p>\n

Let\u2019s begin our VAR discussion by saying that some of the electrical loads in a building (motors, transformers, classic style fluorescent lighting ballasts) use rising and falling magnetic fields to perform their intended functions. We call these \u201cinductive\u201d loads. When an inductive load is drawing power from the power company, some of this power is used to build up the load\u2019s magnetic field during one part of the power cycle. The magnetic field stores part of the energy being delivered to the load.<\/p>\n

Here is the interesting part \u2013 at a later point in the power cycle, the magnetic field which was built up earlier collapses. When that happens, the energy that was stored in the magnetic field is converted back into power which is returned to the power company! So with inductive loads, extra power is \u201cborrowed\u201d from the power company temporarily but is later \u201creturned\u201d to the power company. The extra power needed by inductive loads essentially bounces back and forth between the power company generator and the loads. This power is called reactive power and given the name VAR (Volt-Amperes Reactive) power.<\/p>\n

VAR power does not show up on a conventional kW-only power meter. The kW meter only shows power that is actually consumed by the load. However, many modern electronic power meters such as Kele\u2019s endicator<\/a> will display both kW and kVAR power being drawn by a load.<\/p>\n

Are VARs a problem?<\/strong><\/p>\n

So\u2026 if VAR power is not actually consumed by the load, but is returned to the power company, then there is no problem, right? Wrong. The extra VAR power, even though it\u2019s not consumed by the load, causes larger currents to flow through the power company\u2019s generators and power distribution system. So the power company has to install beefier generators and distribution equipment to handle that extra current flowing. Therefore they are not happy when a customer\u2019s load is drawing high VARs.<\/p>\n

To discourage customers from presenting high-VAR loads to the power system, the power company will sometimes install a VAR meter on a commercial or industrial building and tack a penalty on to the power bill if the VAR reading goes over a certain limit. This is normally not done for residential customers (good news for your home power bill).<\/p>\n

How can I compensate for a high-VAR inductive load?<\/strong><\/p>\n

The good news is that there is a way to compensate for a high-VAR inductive load. There is an electrical component called a \u201ccapacitor\u201d which also draws reactive power but stores the energy in an electric field instead of a magnetic field. Now, here\u2019s the cool part \u2013 the capacitor stores and releases its reactive energy at the opposite times of an inductive load. That is, just as the inductive load needs extra energy to build up its magnetic field the capacitor is ready to give up the extra energy stored in its electric field, and vice-versa.<\/p>\n

So by installing the correct amount of capacitance in parallel with an inductive load, the extra reactive power needed just cycles back and forth between the capacitor and the inductive loads, and the power company does not ever see the reactive power on their system.<\/p>\n

Note we said the \u201ccorrect amount\u201d of capacitance. The value of the capacitance must match the value of the load inductance for complete cancellation of the reactive power seen by the power company. Of course, in the real world they won\u2019t be perfectly matched; but still, the reactive power seen by the power company can be reduced to a low level.<\/p>\n

If your building has a relatively constant inductive VAR load, then a fixed bank of capacitors can be installed for \u201cnominal\u201d reactive power cancellation. If your building has inductive loads that are dynamically cycled so that the inductive VARs fluctuate a lot, there are \u201csmart\u201d controllers that can measure the instantaneous inductive VARs and switch different values of capacitance in or out of the system to maintain on-the-fly dynamic cancellation of the inductive VARs.<\/p>\n

Conclusion<\/strong><\/p>\n

The inductive VAR load presented by a building to the power company is always undesirable. You may or may not be penalized by the power company for a high-VAR load, depending on your situation. Capacitor banks can be added to a load to cancel the inductive VARs seen by the power company. Capacitor banks can be provided as fixed-value or dynamically-adjusted devices depending on whether your inductive VARs are steady or fluctuate widely. Kele\u2019s endicator\u00a0power monitor will give your building automation system the information it needs \u2013 both kW and kVAR, to control capacitor banks and minimize those utility penalties if they are causing you a pain in the wallet. Call Kele today to find out how!<\/p>\n","protected":false},"excerpt":{"rendered":"

Most people involved in building automation are familiar with kW, which is the rate at which a building is consuming energy from the power company. But there is another power system parameter known as VAR\/kVAR which is less well understood. In this article we will attempt to dispel some of the VAR mystery. The term […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[4,7,12],"tags":[52,103],"class_list":["post-528","post","type-post","status-publish","format-standard","hentry","category-industry-happenings","category-kele-makes-it-easy","category-technical-reference","tag-endicator","tag-power-monitoring"],"yoast_head":"\r\nWhat Are Power System VARs? - kele.com<\/title>\r\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\r\n<link rel=\"canonical\" href=\"https:\/\/www.kele.com\/content\/blog\/2013\/10\/04\/what-are-power-system-vars\" \/>\r\n<meta property=\"og:locale\" content=\"en_US\" \/>\r\n<meta property=\"og:type\" content=\"article\" \/>\r\n<meta property=\"og:title\" content=\"What Are Power System VARs? - kele.com\" \/>\r\n<meta property=\"og:description\" content=\"Most people involved in building automation are familiar with kW, which is the rate at which a building is consuming energy from the power company. 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