The most frequent cause of electrical power quality events is voltage sags. The voltage drops below its normal rated value for a short period typically ½ a cycle (8 milliseconds) up to one second. If the voltage value drops below a threshold value, typically 80%-85% of nominal value, then unplanned production stoppages can occur. Many customers may believe they have lost power but voltage sags have been proven by independent studies to occur much more frequently than actual power loss.
In many parts of North America electrical utilities user reclosers on medium voltage supply to isolate faults caused by such events as lightning strikes, tree branches across lines or animals making contact with live wires. The result of a recloser operation is a momentary power outage, lasting for up to a few seconds. This creates an unplanned production stoppage which can be very costly for some industries.
Omniverter Automatic Voltage Regulator (AVR) solutions are used to correct voltage variations that cause problems for electrical equipment. In many parts of the world the quality of electrical power is poor or inconsistent. Voltages can vary significantly from nominal values, typically +15%/-20% or more at 380V or 400V, sometimes for several hours at a time. This causes problems for electrical equipment. Omniverter has Automatic Voltage Regulator (AVR) solutions to correct such voltage variations based on two different technologies Digit@L AVR which is based on a mechanical system and EY-AVR which uses multi-tap transformers and power electronic tap switching
As the price of electricity form utilities has increased over recent years, customers have started to concentrate on energy reduction programs to save costs. While utility metering at the service entrance gives a measure of overall usage it does not allow for examination of individual production lines or even individual machines such as compressors, air conditioners etc. Digital meters have become the standard for detailed measurement of many types of electrical load and with appropriate software can provide much information for management.
The switching of large electric loads in one location can create power quality problems on the electrical utility supply to customers in other locations. These may occur as voltage sags, a rapid fluctuation in voltage or an extended drop in voltage for a second or two commonly known as electrical flicker. Loads such as electric furnaces, starting of large electric motors or where there are frequent repetitive processes such as a saw mills , gravel dredges, rock crushers and car shredders can all cause problems. In some cases production lines using large numbers of robots may experience widely fluctuating loads. These conditions can cause premature failure of electrical equipment and increase energy bills due to poor power factor. Loads such a data centres can experience leading power factor which is a major issue when they need to run on backup generators
Many utility customers suffer from unplanned production stoppages and frequently they believe that these events are due to loss of power, or service interruption from the utility. Sometimes they are correct but most of such unplanned events are due to voltage sags. In order to provide the correct solution to these stoppages, it is important to diagnose the real causes and the primary tool to do this is the installation of a power quality analyzers. These devices measure and record events such as voltage sags and swells, detect and measure harmonic voltages and currents, flicker and energy parameters.
Some industries require their suppliers of electrical equipment to demonstrate that it has voltage sag withstand capability in accordance with published Standards e.g. SEMI F47, IEC61000-4-34, IEE1668. In order to evaluate voltage sag withstand capability it is necessary to have a means of creating voltage sags of predetermined variable depth (e.g.70% ), variable duration and the means of recording results of such tests.