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Construction Of Automatic Voltage Regulator

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1. Introduction

Automatic voltage regulation is a process of converting the alternating voltage into a steady voltage. The device that is used to perform this process is known as an automatic voltage regulator(UST,2007,p1). An automatic voltage regulator is an electronic equipment that is used and designed to maintain the constant voltage level. This device prevent malfunctioning and damaging of the electrical equipment . Automatic voltage regulator uses electromechanical and electronic components of various types and designs. Automatic voltage regulator may include negative feedback control loops. The feedback voltage regulator operates by making comparison between the output voltage and input voltage.Electromechanical mechanism or electronic components are used in automatic voltage regulations. It can be used to regulate one or more AC (alternating current ) to DC voltage (direct current ).There are vast varieties of automatic voltage regulators depending on their types and size.

2. Construction of automatic voltage regulator

The electronic voltage regulator is made in two different combinations i.e shunt and series regulator. In the shunt regulator, resistor is attached in parallel. In series regulator, resistance is attached in series. The diagrams below illustrate examples of series and shunt regulators.

2.1. Shunt Regulator

It is not highly used for various applications. The current is drawn through the series resistor in order to maintain the constant level of voltage.Some current is passed through the load while the remaining current is passed through the shunt voltage regulator. These regulators are inefficient and are not widely used (Radio electronics,n.d,p1).

2.2. Series regulator

The series regulators operate by using a variable element in series with the load. Due to this mechanism, the series voltage regulator provides an extremely efficient form of voltage regulation with the linear power supply (Radio electronics,n.d,p1).

3. Device which use Automatic Voltage Regulator

Automatic voltage regulator is mostly used in computer power supplies in which DC voltage is stabilized. It is also used in automobile alternators and in central power station generation plants where automatic voltage regulators controls the output of the plant .In case of electric power distribution systems voltage regulators are installed at substations or along distribution lines so that all the users can receive constant and steady voltage . These regulators are also used in kitchens and in refrigerators(Meiji,n.d,p1).

4. Types of regulation

The regulation is commonly calculated as constant. However, the regulation has been specified by two measurements (Robinson,2012,p1).

4.1. Load regulation:

Load regulation is defined as the change in output voltage of a voltage regulator for a given change in the load current.

4.2. Line Regulation

Line regulation is the degree or amount to which an output voltage which changes with an input voltage.

5. Working of Automatic Voltage regulators

5.1. Basics

An automatic voltage regulator is a device that is housed inside an electronic device. It is primarily used to maintain a consistent voltage level. It can regulate alternating as well as direct current.

5.2. How it works

It works by estimating the output level of the voltage of the devices against the reference voltage inside the device. They normally take a specific range of the voltage levels and produce an output voltage of a narrow range. (ehow,2012,p1). The diagram below clearly illustrates this phenomenon. It shows a voltage regulator that takes an input voltage ranging from +10% to -25% and converts it into the regulated range of +3% to -3%.

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Figure :( Voltage Regulator)

6. Operations of Automatic Voltage Regulators

Automatic voltage regulator is designed for both single and three phase alternating current applications. The phase and phase regulation has been classified into two types .The single phase voltage regulation is the best method as it provides balance phase to phase voltage level .In case of three phase regulation, large difference in voltage level causes failure of electronic and electric devices due to overheating and vibration.

6.1. Single Phase regulation

The single phase regulators are used in units pole that are mounted outdoors .Single phase voltage regulators are combined together and they provide voltage regulation for three phase .The below mention figure is an example of single phase regulation.

6.2. Three Phase regulation

Three phase regulator can regulate all three phases at once or it may regulate all the three phases independently .In three phase power, it has not been observed that one phase has very high voltage while other has low voltage .The below figure is an example of three phase regulation.

7. Different types of Automatic Voltage Regulator

On the basis of size and design the automatic voltage regulator exists in different varieties some are mention below:

The Ferroresonant Transformer (Type) Voltage Regulator

The Mechanical (Type) Voltage Regulator

The Electronic (Type) Voltage Regulator

8. The Ferro resonant Transformer (Type) Voltage Regulator

This type of voltage regulator has been invented by Joseph Sola in the year of 1983.The change in design of ferroresonant is very minor .This type of regulators are extremely reliable in use. Presently, they are being replaced with the voltage regulators.

8.1 Operation of Ferro resonant transformer

It operates on the principle of ferroresonance. It is based on the operation of transformer in the region of magnetic saturation. During this stage, high changes in the winding current leads to minor changes in magnetic flux. The winding current is proportional to the input voltage and magnetic flux is proportional to output voltage(UST,2007,p1). This shows that the purpose of automatic voltage regulator is being fulfilled by this method. The graph below exhibits the respective pattern.

8.1. Different types of Ferro resonant transformer

The Ferro transformer voltage regulator is also known by various names. These names are Constant voltage transformer, Constant voltage regulator, Ferro resonant voltage regulator,Ferro resonant transformer,Ferro and CVT.

8.2. Properties of Ferro resonant Transformer (Type) Voltage Regulator

Their sizes range from 30VA to 25KA. The input voltage in these regulators range from +10% to -20%. The voltage regulation in the output ranges from +1% to 3%. It has a single phase application only. It has the tendency of stepping up and down the level of voltage. The cooling media of such regulators is air. It is mostly located indoors and has as efficiency of almost 92%.

8.3. Discussion

This type of regulator provides complete isolation of load equipment from line noise and surges. The output voltage regulation is very smooth .This type of regulators are very efficient and durable .The design of this type of regulator limits the amount of current to the load end. The electronic devices can be easily protected if ferroresonant voltage regulator is used in these devices.

9. The Mechanical (Type) Voltage Regulator

The mechanical type voltage regulator has been used in the market since 50 years .This type of voltage regulator exits in different variety of design .The electronic devices which use this type of regulator have an outstanding ability of correcting voltage drop in distribution lines. Mechanical type voltage regulator uses two methods of operation. The first one is changing turns ratio and the second method is by changing the magnetic induction between primary and secondary coils of the transformer.

9.1 Operations of Mechanical Voltage Regulator

There are various operations that occur inside mechanical voltage regulators. These processes include

9.2. Tap Changing Voltage Regulator Operation

Tap changing is a process in which a transformer has equal number of the winding turns on the primary as well as the secondary side .The voltage at input side is equal to the voltage at output side. The changing of number of turns on the secondary side can result in changing the voltage. The ratio of the turns can be easily altered by changing the location of the physical connection as well (UST,2007,p1). The mechanical tap changing voltage regulator uses some kinds of motorized drive system to change the taps on the output of transformer .

9.3.Magnetic Induction Voltage Regulator Operation

The output voltage in a transformer can be changed by making the physical change of primary turn and secondary turns relative to each other .The primary side of transformer generates a magnetic flux which induces current to flow in the secondary windings(UST,2007,p1) . Physically rearrangement of the turn of secondary within the flux field can change the amount of current induced and output voltage.

This type of voltage regulator changes the orientation of the transformer secondary side with respect to the magnetic filed .The magnetic induction voltage regulator is similar to the motor which have the primary windings in a cylindrical stationary configuration just like stator and the output windings which are called as rotor .

9.4. Different names of mechanical voltage regulator

The various names of mechanical voltage regulator are Mechanical tap changing regulator,Tap changer, Motorized variable transformer, Motor-driven variable autotransformer, Auto-boost regulator, Electromechanical voltage stabilizer, Step voltage regulator,On load tap changer, Motorized variac and Line drop compensator.

9.5. Mechanical Voltage Regulator Characteristics

The power quality automatic voltage regulators are of tap switch or magnetic induction types. Their size varies from 1 to 1500 KVA. The nominal voltages are less than 600 volts. The input voltage range varies from +20% to _20%. The regulated output voltage is between 1% to 3%. It has single phase as well as three phase applications. They possess the ability of stepping up and down the voltage. They require air as the cooling media. They are located indoors as well as outdoors. Their efficiency is greater than 95%.

The utility automatic voltage regulators are of tap switch type. Their size varies from 500 to 3500 KVA. They have nominal voltages up to 34.5 KV. The input voltage range is between +10% to _10%. The regulated output voltage is between the range of 0.6% to 2.5%. It can operate on single as well as three phases. They require oil as the cooling media. They are located outdoors. Their efficiency is greater than 95%.

9.6. Discussion

It provides very accurate output voltage regulation. It provides wide choice of kVA rating, voltage and configuration. It can be easily applicable to outdoor applications. It has high tolerance to system faults and overload. It has high tolerance to power factor and frequency deviations. It has good line isolation. It is relatively inexpensive. The mechanical drive components, brushes and contactors needs regular maintenance and replacement (UST,2007,p1).The overloads can damage brushes. The speed of voltage correction might be not fast enough for electronic loads.

10. The Electronic (Type) Voltage Regulator

Electronic voltage regulator has been used in industries and for various commercial applications because of its speed and extraordinary performance. The demand of electronic voltage regulator is greater as compare to mechanical voltage regulator.

10.1 Operations of electronic voltage regulator

The operations of electronic voltage regulator are based on the principle of double conversion electronic voltage.

10.2. Double Conversion Electronic Voltage Regulator Operation

The double conversion electronic voltage converts AC power supply to DC with the help of rectifier .The voltage regulation is done in two ways. The first method is to regulate DC voltage output from the rectifier. It is an economical method .The second method is to supply inverter with constant DC voltage and set the voltage level during converting back to alternating current in the inverter(UST,2007,p1) .The double conversion voltage regulators have a low tolerance to high load currents mostly above than normal rating of the unit.

10.3. Electronic Voltage Regulator Characteristics

Electronic voltage regulators are basically design for indoor, low voltage applications .

10.4. Double Conversion Electronic Voltage Regulators

Their sizes range from 3KVA to 400 KVA. The input voltage ranges from +10% to _25 % for the tap switchers and +10% to _15 % for UPS. The regulated output voltage is between the range of +/-1% to +/-5%. It can operate on single and three phase as well. It can easily regulate voltage up and down. The cooling media required for double conversion electronic voltage regulators is air. They are generally located indoors and have efficiency up to 95 percent.

Size (kVA):

3 VA up to400 kVA

Nominal Voltages:

Common AC voltages - 120, 208, 240 & 480 at 60 Hz

Input Voltage Range:

+10% to -25% for tap switchers and+10% to -15% for UPS (varies by manufacturer)

Output Regulation:

+/-1% to +/-5%


Single and three phase

Voltage Step Up/Down:


Cooling Media:





Up to 95

10.4. Discussion

The output voltage regulation is very good. It possesses ultrafast voltage correction speed. It offers no restrictions on the number of correction cycles. It gives versatility in kVA rating, voltage and configuration. It needs very low or no regular maintenance. It has good line isolation. It has poor current overload capacity. It is more expensive than mechanical voltage regulators.

11. Conclusion

The automatic voltage regulators are becoming of increase significance due to variety of reasons. They are extremely essential for maintaining the utility level of the voltage. They can drop the voltage due to their ability of voltage regulation. They are highly sensitive to voltage levels and they prevent any kind of fluctuations , thus help in ensuring that equipments do not suffer any kind of damage. The use of voltage regulators avoids and reduces the risks of overheating of equipments as well. The use of voltage regulators is constantly increasing with the passage of time.

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