EE 741 Voltage Regulators Spring 2014 Typical Voltage Profile from Substation to Customer Step-Voltage Regulator These devices are essentially auto-transformers with adjustable turns in the series winding. They usually have a maximum voltage regulation range of 10% of the incoming line voltage in 32 steps of 5/8% or 0.625%. 16 steps for buck, and 16 steps for boost.Voltage Regulation Relay Settings Set Voltage (desired output voltage) Bandwidth (difference between measured voltage and set voltage) typically between 0.75 V and 1.5 V. Time Delay (waiting time between when the voltage goes out of band and when the controller initiates the tap change)10-120 sec .75 -1.5 V 114-126 V Line Drop Compensator (LDC) The voltage can be regulated at a point downstream by adjustable resistance and reactance elements of the LDC located in the control panel. These settings are approximate (at best) when a load is tapped off the feeder between the regulator and the regulating point. Utility AVRs can be installed out on the feeders or at the substation bus. The voltage regulator units could either be single-phase or three-phase. However, on a three-phase feeder, it is more common in utility applications to use single-phase units. Voltage Regulator Placement Example LTC holds Vp constant at 1.035 pu (due to changes in sub-transmission voltage and voltage drop across transformer). Sub-transmission voltage varies between 1.05 pu and 1.00 pu. Feeder voltage criteria: not to go below 0.967 pu Example (cont.) A shunt capacitor or avoltage regulator is needed. Example (cont.) Desire regulation input at 1.01 pu s1 = 1.75 mi LDC disabled, and regulation output = 1.035 pu. Automation of Voltage Regulation Devices in The Smart Grid Era Voltage Fluctuations (Flicker Curve)