Electronic Tap Switching Voltage Regulator
The typical electronic tap switching voltage regulator works very much like the mechanical tap switching regulator – except that it replaces mechanical servo drives and brushes with solid-state semiconductor switches. Rather than using a motor to move brushes connected to the regulator output, the electronic voltage regulator will have taps on the secondary side of the transformer controlled (on or off) by semiconductor switches (like the silicon controlled rectifier – “SCR”).
Within the classification of electronic tap switching voltage regulator there are two distinct types: the full power semiconductor type, and the series transformer type.
The full power semiconductor (FPS) type of electronic tap switching voltage regulator is most analogous to the servo tap switcher and is the most common type of electronic voltage regulator. In operation, all of the SCR switches, except one, will be “off” so current flows only through the desired tap. When the controller senses the need for a tap change, it turns “off” the SCR switch on one tap and then turns “on” the SCR for the appropriate tap. With no mechanical components to be moved and ultrafast and non-sequential SCR tap switching, the electronic tap voltage regulator can correct voltage levels much faster than its mechanical counterpart. The speed and simplicity of the electronic tap switching voltage regulator does come at a price: in contrast with mechanical voltage regulators, the SCRs are easily damaged by high currents such as inrush, overload or short circuit currents.
The series transformer (ST) type of electronic tap switching voltage regulator uses SCRs connected to taps in a fashion similar to the FPS design, however the ST design uses additional transformer components to isolate the SCRs from the load current path. This isolation provides the ST type of electronic tap switching voltage regulator with the speed and simplicity of the FPS type EVR and the high tolerance to excessive currents of the mechanical voltage regulator.