ELECTRONIC VOLTAGE REGULATOR (EVR) FOR LOW VOLTAGE POWER QUALITY APPLICATIONS

Wednesday, April 27, 2011

Electronic Voltage Regulator (EVR) is a type of automatic voltage regulator that is typically used in low voltage power quality applications. It is a single-phase power quality device that functions to protect equipment from overvoltage and undervoltage. The electronic voltage regulator’s performance and speed make it appropriate for commercial and industrial power quality applications than the mechanical voltage regulator. In addition, EVRs come in two types: Tap Switching and Double Conversion.
Electronic Voltage Regulator (EVR)
Electronic Voltage Regulator (EVR)
Electronic Tap Switching Voltage Regulator

An electronic tap switching voltage regulator operates in the same principle as the mechanical tap changing regulator (i.e. step-voltage regulator). However, this type of electronic voltage regulator utilizes solid-state semiconductor switches such as the silicon controlled rectifier (SCR) and the triac for tap-changing, rather than the mechanical servo drives and brushes. The use of semiconductor switches makes the EVR regulate voltage much faster than the mechanical AVR. Also, electronic tap switching voltage regulators are either full power semiconductor (FPS) or the series transformer (ST) type.

Full power semiconductor type of electronic tap switching voltage regulator is the most common type of electronic voltage regulator. Generally, all but one of the SCR or triac switches are OFF. This design guides the current to flow only through the desired tap. If the embedded controller detects the need for a tap change, it will deactivate the semiconductor switch on one tap and turns ON the triac or SCR for the required tap. However, in this setup the solid-state switches are prone to damage caused by overload, inrush, or short circuit currents.
Electronic Voltage Regulator - Full Power Semiconductor
Electronic Voltage Regulator - Full Power Semiconductor
On the other hand, the series transformer type of electronic tap switching voltage regulator eliminates the weakness of the solid-state semiconductor switch against high currents. Its design employs additional transformer components to isolate the triacs or SCRs from the path of the load current. Consequently, this provides the electronic voltage regulator with the simplicity and speed of the FPS type and the high tolerance to excessive currents of the mechanical voltage regulator.
Electronic Voltage Regulator - Series Transformer Type
Electronic Voltage Regulator - Series Transformer Type

Double Conversion Electronic Voltage Regulator

Unlike the tap switching EVR, the double conversion electronic voltage regulator uses a rectifier to convert AC power to DC and then uses an inverter to convert the DC power back to AC - hence, the name double conversion.

In this type, there are two ways to regulate the output voltage:

1.    Regulating the DC voltage output from the rectifier
Ø     Least cost of components

2.    Supplying a constant DC voltage to the inverter
Ø     This includes adjusting the voltage level during the conversion back to AC in the inverter. Also, this is the usual method used by an uninterruptible power supply (UPS).

Reference:
Utility Systems Technologies, Inc. (2009). AC Automatic Voltage Regulators

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I am an Electrical Engineer with a Masters Degree in Business Administration. My interest is in Power Quality, Diagnostic Testing and Protective Relaying. I have been working in an electric distribution utility for more than a decade. I handle PQ studies, power system analysis, diagnostic testing, protective relaying and capital budgeting for company projects.