EE 741
Voltage Regulators
Spring 2014
Typical Voltage Profile from Substation to Customer
Step-Voltage Regulator
• These devices are essentially autotransformers 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
114-126 V
.75 -1.5 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.
Voltage Regulator Placement
• Utility AVRs can be installed out on the feeders or at the
substation bus.
• The voltage regulator units could either be single-phase or threephase. However, on a three-phase feeder, it is more common in
utility applications to use single-phase units.
Example
• LTC holds Vp constant at 1.035 pu (due to changes in subtransmission 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 a
voltage 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)