What is Voltage Stabilizer – Why we need it, How it works, Types and Applications

Applications of Voltage Stabilizers have became a need for every home. Different types of Voltage stabilizers are available now with different functionality and works. The latest advancements in technology like Microprocessor chips and Power Electronic Devices have changed the way we see a Voltage Stabilizer. They are now fully automatic, intelligent and packed with a lot of additional functions. They also have an ultra fast response to voltage fluctuations and allow their users to adjust the voltage requirements remotely including start/ stop function for the output.

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What is a Voltage Stabilizer?

A Voltage Stabilizer is an electrical device which is used to provide a constant voltage output to a load at its output terminals irrespective of any change/ fluctuation in the input i.e. incoming supply.

The basic purpose of a Voltage Stabilizer is to protect the electrical/ electronic gadgets (for example – Air conditioning Unit, Refrigerator, TV, etc.) from the probable damage due to Voltage Surge/ fluctuations, Over Voltage and Under Voltage conditions.

Fig.1 – Different types of Voltage Stabilizers

Voltage Stabilizer is also known as AVR (Automatic Voltage Regulator). The use of Voltage Stabilizer is not only limited to house/ office equipment which are being fed power supply from outside. Even the ships, who have their own internal power supply arrangement in form of Diesel Alternators, are heavily dependent on these AVRs for safety of their equipment.

We can see different types of Voltage Stabilizers available in the market. Both analog and digital automatic Voltage Stabilizers are available from so many manufactures. Thanks to the rising competition and increasing awareness for the safety devices. These Voltage Stabilizers may be single phase (Output of 220-230 volt) or three phase (Output of 380/400 volt) as required by the type of application. The regulation of desired stabilized output is done by buck and boost method as performed by its internal circuitry. Three phase Voltage stabilizers are available in two different models i.e. Balanced load models and Unbalanced load models.

They are available in different KVA rating and ranges too. A normal range Voltage Stabilizer can ensure a stabilized output voltage of 200-240 volt with 20-35 volt boost-buck from an input voltage feed ranging from 180 volt to 270 volt. Whereas, A wide range Voltage Stabilizer can ensure a stabilized out voltage of 190-240 volt with a 50-55 volt boost buck from an input voltage ranging from 140 volt to 300 volt.

They are also available for wide variety of applications such as dedicated voltage stabilizer for small units like TV, Refrigerator, Microwave ovens to a single huge unit for an entire house hold appliances.

In addition to its basic stabilizing function, Present Voltage Stabilizers come with many useful additional features such as overload protection, zero voltage switching, frequency variation protection, voltage cut off display, output start and stop facility, manual/ auto start, voltage cutoff, etc.

The Voltage Stabilizers are very high energy efficient devices ( with an efficiency of 95-98%). They consume very less power which is usually 2 to 5% of maximum load.

Why do we need Voltage Stabilizers? – Its Importance

All electrical/ electronic devices are designed and manufactured to operate at maximum efficiency with a typical voltage supply which is known as the nominal operating voltage. Depending on the designed safe operating limit, the working range (with optimum efficiency) of an electrical/ electronic device may be limited to ± 5%, ±10% or more.

Owing to many issues, the input voltage supply which we get always tends to fluctuate resulting to a constantly varying input voltage supply. This varying voltage is a major contributing factor for reduction of a device’s efficiency as well increase in its failure rate.

Fig. 2 – Problems Due to Voltage Fluctuations

Remember, Nothing is more important for an electrical/ electronic device than a filtered, protected and stable power supply feed. A correct and stabilized voltage supply is very much required for the device to perform its intended function in the most optimized way. It is the Voltage stabilizer which ensures that the device get the desired and stabilized voltage no matter how much the fluctuation is. Therefore, Voltage stabilizer is a very efficient solution for anyone who desire to get an optimum performance and protect their devices against these unpredictable voltage fluctuations, surge and noise present in the supply.

Like UPS, voltage stabilizers are also an asset to the protection of electrical and electronic equipment. The voltage fluctuations are very common irrespective of where ever you live. There may be various reasons for the voltage fluctuation such as electrical faults, faulty wiring, lightning, short circuits, etc. These fluctuations may be in the form of Over voltage or Under voltage.

Effects of Continuous/ Recurring Over Voltage to Home Appliances

• It may cause permanent damage to the connected device.
• It may cause damage to the winding insulation.
• It may lead to unnecessary disruption in the load
• It may lead to over-heating of the cable or device.

• It may degrade useful life of the device

Effects of Continuous/ Recurring Under Voltage to Home Appliances

• It may lead to equipment’s malfunction.
• It may result in low efficiency of the device.
• The device in some cases can take extra hours to perform the same function.
• It may degrade performance of the device.
• It may lead the device to draw large currents, that may further cause over-heating

How a Voltage Stabilizer Works? – Working Principle of Buck and Boost Operation

The basic work of a Voltage Stabilizer is to carry out two necessary functions i.e. Buck and Boost function. Buck and Boost function is nothing but the regulation of a constant voltage from over voltage and under voltage circumstances. This Buck and Boost function may be carried out manually with the help of selector switches or automatically with the help of additional electronic circuits.

Fig. 3 – Basic Function of Voltage Stabilizer

During Over voltage circumstances, Buck function does the necessary reduction of voltage intensity. Similarly, during Under voltage circumstances Boost function increases the voltage intensity. The idea of the both the functions as a whole is to maintain the same voltage output.

Voltage stabilization involves addition or subtraction of voltage from the primary voltage supply. To perform this function, Voltage Stabilizers use a transformer that is connected to switching relays in various required configurations. Few of the Voltage Stabilizers use a transformer having various taps on its winding for providing various voltage corrections while few Voltage Stabilizers (such as Servo Voltage Stabilizer) contain auto transformer for providing the desired range of correction.

How Buck and Boost function works in a Voltage Stabilizer

For a better appreciation of both the concepts, we will divide it into separate functions.

Buck Function in a Voltage Stabilizer

Fig. 4 – Circuit Diagram of Buck Function in Voltage Stabilizer

The above figure depicts the connection of a transformer in ‘Buck’ function. In Buck function, the polarity of transformer’s secondary coil is connected in such a way that the applied voltage to the load is resultant of Subtraction of Primary and secondary coil’s voltage.

Fig. 5 – Voltage Subtracts in Buck Function of Voltage Stabilizer

There’s switching circuit in the Voltage Stabilizer. Whenever it detects Over Voltage in the Primary Supply, the connection of the Load is manually/ automatically shifted to the ‘Buck’ mode configuration with the help of Switches/ Relays.

Boost Function in a Voltage Stabilizer

Fig. 6 – Circuit Diagram of Boost Function in Voltage Stabilizer

The above figure depicts the connection of a transformer in ‘Boost’ function. In Boost function, the polarity of transformer’s secondary coil is connected in such a way that the applied voltage to the load is resultant of Addition of Primary and secondary coil’s voltage.

Fig. 7 – Voltage Adds in Boost Function of Voltage Stabilizer

How Buck and Boost configuration works automatically?

Here is an example of 02 Stage Voltage Stabilizer. This Voltage Stabilizer uses 02 relays (Relay 1 and Relay 2) for providing stabilized AC power supply to the Load during Over Voltage and Under Voltage circumstances.

Fig. 8 – Circuit Diagram for Automatic Buck & Boost Function in Voltage Stabilizer

In the Circuit diagram of 02 stage Voltage Stabilizer (depicted above), Relay 1 and Relay 2 are used to provide Buck and Boost configurations during the different Voltage fluctuation circumstances i.e. Over Voltage and Under Voltage. For example – Suppose the ac input is 230 volt AC and output required is also constant 230 volt AC. Now if you have +/- 25 Volt Buck & Boost stabilization, that it means that your Voltage Stabilizer can provide you constant desired voltage (230 volt) in between 205 volt (Under Voltage) and 255 Volt (Over Voltage) of input AC supply.

In Voltage Stabilizers that use tapped Transformers, the tap points are selected on the basis of required amount of voltage to be Bucked or Boosted. In this case, we have different voltage ranges to select for. Whereas, in Voltage Stabilizers that use auto transformers, Servo motors along with sliding contacts are used for obtaining required amount of voltage to be Bucked or Boosted. Sliding contact is necessary as auto transformers have only a single winding.

Different Types of Voltage Stabilizers

Initially manually operated/ selector switch operated Voltage Stabilizers came in the market. These type of stabilizers used electro-mechanical relays for selection of desired voltage. With advancement of technology, added electronic circuits came into existence and the Voltage Stabilizers became automatic. Then came the Servo based Voltage Stabilizer which is capable of stabilizing the voltage continuously, without any manual intervention. Now, IC/ Micro controller based Voltage Stabilizers are also available which can perform additional functions too.

The Voltage Stabilizers can be broadly categorized into three types. They are:

• Relay Type Voltage Stabilizers
• Servo based Voltage Stabilizers
• Static Voltage Stabilizers

Relay Type Voltage Stabilizers

In Relay type Voltage Stabilizers, the voltage is regulated by switching relays. The relays are used to connect the secondary transformer(s) in different configurations to achieve Buck & Boost function.

How a Relay type Voltage Stabilizer works?

Fig. 9 – Inner View of Relay Type Voltage Stabilizer

The figure above indicates how a Relay type Voltage Stabilizer looks from inside. It has a transformer with tappings, relays and an electronic circuit board. The Circuit board contains rectifier circuit, amplifier, micro-controller unit and other supporting components.

The electronic circuit board carries out the comparison of the Output Voltage with the reference voltage source. As soon as it detects any rise or fall in the input supply beyond the reference value, it switches the related relay to connect the required tapping for Buck/ Boost function.

The Relay type Voltage Stabilizers normally stabilize the input fluctuations of ±15% with an output accuracy between ±5% to ±10%.

Uses/ Advantages of Relay type Voltage Stabilizers

This stabilizer is mostly used for low power rating appliances/ equipment in Residential/Commercial/Industrial use.

• They cost less.
• They are compact in size.

Limitations of Relay type Voltage Stabilizers

• Their response to voltage fluctuation is a bit slow if compared to other type of Voltage Stabilizers

• They are less durable
• They are less reliable
• They are not able to withstand high voltage surges as their fluctuation tolerance limit is less.
• While stabilization of voltage, transition of power supply path may provide minor interruption in power supply.

Servo based Voltage Stabilizers

In Servo based Voltage Stabilizers, the voltage regulation is done with the help of servo motor. They are also known as Servo Stabilizers. They are close loop systems.

How a Servo based Voltage Stabilizer works?

In a Close loop system, a negative feedback (also known as error feed) is warranted from the output so that the system can ensure that the desired output has been achieved. This is done by comparing Output and Input signals. If in case the desired output is over/under the required value, then an error signal (Output value- Input Value) will be received by the input source regulator. This regulator will then again generate a signal (positive of negative depending on the achieved output value) and feed it to the actuators to bring the output to the exact value.

Due to its Close loop property, Servo based Voltage Stabilizers used for appliances/ equipment which are very sensitive and need accurate input power supply (±01%) for performing intended functions.

Fig. 10 – Inner View of Servo Based Voltage Stabilizer

The above figure indicates how a Servo based Voltage Stabilizer looks from inside. It has a Servo Motor, Auto-transformer, ‘Buck & Boost’ (tapped) transformer, a motor, an electronic circuit board and other supporting components.

In Servo based Voltage Stabilizer, one end of the primary coil of ‘Buck & Boost’ (tapped) transformer is connected to the fixed tapping of the auto-transformer, and the other end of the primary coil is connected with the moving arm which is controlled by the servo motor. One end of the Secondary coil of the ‘Buck & Boost’ transformer is connected to the input supply and the other end is connected to the output of Voltage Stabilizer.

Fig. 11- Circuit Diagram of Servo Based Voltage Stabilizer

The electronic circuit board carries out the comparison of the Output Voltage with the reference voltage source. As soon as it detects any rise or fall in the input supply beyond the reference value, it starts operating the motor which further moves the arm on the auto-transformer.

As the arm on the auto-transformer moves, the input voltage to the primary coil of ‘Buck & Boost’ transformer will change to the required Voltage Output. The servo motor will keep rotating till the difference between the Reference Voltage value and Stabilizer output becomes zero. This complete process happens in milliseconds. Today’s Servo based Voltage stabilizers comes with Microcontroller/ Microprocessor based control circuitry to provide intelligent control to users.

Different Types of Servo Based Voltage Stabilizers

The different types of Servo based Voltage Stabilizers are: –

Single Phase Servo Based Voltage Stabilizers

In Single Phase Servo Based Voltage Stabilizers, Voltage stabilization is achieved with the help of a servo motor connected to a variable transformer.

Three Phase Balanced type Servo Based Voltage Stabilizers

In Three Phase Balanced type Servo Based Voltage Stabilizers, Voltage stabilization is achieved with the help of a servo motor connected to 03 auto-transformers and a common control circuit. The output of auto-transformers are varied to achieve the stabilization.

Three Phase Unbalanced type Servo Based Voltage Stabilizers

In Three Phase Unbalanced type Servo Based Voltage Stabilizers, Voltage stabilization is achieved with the help of a servo motor connected to 03 auto-transformers and 03 independent control circuits (one for each auto-transformer).

Fig. 12 – Inner View of Three Phase Unbalanced type Servo Based Voltage Stabilizers

Uses/ Advantages of Servo Based Voltage Stabilizer

• They have fast response to voltage fluctuations.
• They have high Voltage Stabilization accuracy.
• They are very reliable
• They can withstand high voltage surges.

Limitations of Servo Based Voltage Stabilizer

• They need periodic maintenance.
• To nullify error, servo motor needs to be aligned. Alignment of Servo motor needs skilled hands.

Static Voltage Stabilizers

Fig. 13 – Static Voltage Stabilizers

A Static Voltage Rectifier has no moving parts as in case of Servo based Voltage Stabilizers. It uses a Power Electronic Converter Circuit to stabilize the voltage. These Static Voltage Stabilizers have very high accuracy and the voltage stabilization is within ±1%.

A Static Voltage Stabilizer contains ‘Buck & Boost’ transformer, Insulated Gate Bipolar Transistor (IGBT) power converter, Microcontroller, Microprocessor and other essential components.

Fig. 14 – Inner View of Static Voltage Stabilizer

How a Static Voltage Stabilizer works?

Microcontroller/ Microprocessor controls IGBT power converter to generate the required voltage level using ‘Pulse Width Modulation’ technique. In ‘Pulse Width Modulation’ technique, Switch mode Power Converters uses a power semiconductor switch (such as MOSFET) to drive the transformer for the desired output voltage. This generated voltage is then applied to the primary coil of the ‘Buck & Boost’ transformer. The IGBT power converter also controls the phase of the voltage. It can generate a voltage that may be in phase or 180 degree out of phase to the input supply, which in turn enables it to control whether the voltage has to be added or subtracted depending on the rise or fall of the input power supply level.

Fig. 15 – Circuit Diagram of Static Voltage Stabilizer

As soon as the microprocessor senses the fall in voltage level, it send the Pulse Width Modulation signal to the IGBT power converter. The IGBT power converter accordingly generates a voltage which is similar to the voltage difference by which the input power supply has reduced. This generated voltage is in phase to the input power supply. Then this voltage is fed to the primary coil of the ‘Buck & Boost’ transformer. Since the secondary coil of ‘Buck & Boost’ transformer is connected to the input power supply, the voltage that has been induced in the secondary coil will be added to the input power supply. And so the stabilized increased voltage will then be provided to the load.

Likewise, as soon as the microprocessor senses the rise in voltage level, it send the Pulse Width Modulation signal to the IGBT power converter. The IGBT power converter accordingly generates a voltage which is similar to the voltage difference by which the input power supply has reduced. But this time, the generated voltage will be 180 degree out of phase to the input power supply. Then this voltage is fed to the primary coil of the ‘Buck & Boost’ transformer. Since the secondary coil of ‘Buck & Boost’ transformer is connected to the input power supply, the voltage that has been induced in the secondary coil will now be subtracted from the input power supply. And so the stabilized decreased voltage will then be provided to the load.

Uses/ Advantages of Static Voltage Stabilizers

• They are very compact in size.
• They have extremely fast response to the voltage fluctuation.
• They have very high accuracy of voltage stabilization.
• As there is no moving part, it is almost maintenance free.
• They are very reliable.
• Their efficiency is very high.

Limitations of Static Voltage Stabilizer

They are costly as compared to their counterparts

What is Difference between Voltage Stabilizer and Voltage Regulator?

Well.. both sound same. They both carry out the same function of stabilizing the voltage too. However, the way they do it brings the difference. The main functional difference between voltage stabilizer and voltage regulator is:

Voltage Stabilizer is a device which delivers constant voltage to the output without any changes in incoming voltage. Whereas,

Voltage Regulator is a device which delivers constant voltage to the output without any changes in load current.

How to select best Voltage Stabilizer for your Home? A buying Guide

You need to consider various factors while purchasing a Voltage Stabilizer. Otherwise, you may land up with a Voltage Stabilizer that may underperform or over perform. Over performing will not harm, but it will cost you extra bucks. So why not choose such a Voltage Stabilizer which can fulfill your requirements and save your pocket too.

Various factors which plays important role in selecting a Voltage Stabilizer

The Various factors that plays a vital role and needs consideration before selecting a Voltage Stabilizer are: –

• Wattage requirement of the appliance (or a group of appliances)
• Type of Appliance
• Voltage fluctuation level in your area
• Type of Voltage Stabilizer
• Working range of Voltage Stabilizer which you need
• Over Voltage/ Under Voltage cutoff
• Type of Stabilization/ Control circuit
• Type of Mounting for your Voltage Stabilizer

Step by Step Selection/ Buying Guide for Voltage Stabilizer for your Home

These are the essential steps which you must follow to select best Voltage rectifier for your home: –

• Check the appliance power rating for which you need Voltage Stabilizer. The power rating is available on the back of appliance in the form of a sticker or nameplate. It will be in Kilowatt (KW). Generally, the Voltage Stabilizer power rating is in KVA. Convert it into Kilo watt (KW).

(KW = KVA x Power Factor)

• Consider keeping an add-on margin of 25-30 % of the Stabilizer’s power rating. This will give you extra option to add any appliance in future.
• Check the Voltage fluctuation tolerance limit. If it suits your need, you are set to go ahead.
• Check the mounting requirement and size which you need.
• You can ask and compare extra features within same price range of different makes and models.

A Practical Example for Better Understanding

Suppose you need a Voltage Stabilizer for your TV. Let’s assume that your TV has a power rating of 1 KVA. Add-on margin of 30% for 1KVA is 300 watts. Adding both, You may consider to purchase a 1.3 KW (1300 watts) Voltage Stabilizer for your TV.

Hope, the article has been informative. Keep on learning.
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