VOLTAGE STABILIZER

What is Voltage Stabilizers; Working of Voltage Stabilizers; Boost & Buck operations of Stabilizers; Types of Voltage Stabilizers; Selection of Voltage Stabilizers; FAQs on Voltage Stabilizers;

Definition – Voltage stabilizer is an electronic devise that regulates the output voltage or gives a constant output voltage irrespective of variation in input voltage.

Voltage stabilizer is an electric device that is required for an electrical/electronic apparatus /equipment such as fridge, AC etc. which are voltage sensitive because these apparatuses may be damaged on voltage fluctuation if voltage varies more than a specified percentage. Some apparatus may tolerate +/- 5% & some +/- 10%. But, voltage fluctuation may occur in electrical system due to many reasons such as electrical fault in transmission/distribution lines, major equipment etc.

For example, if a single phase AC is designed for 230V +/-10%, it means AC can work on from 207V to 253V without any problem, but if voltage variation is more than 10% then it may damage compressor /electronic part of AC.

Therefore, a voltage stabilizer is must for electrical apparatus/devices to protect from damage due to voltage variations in power supply which is fed to the equipment. Voltage stabilizers are available in VA or KVA rating.

Working of Voltage Stabilizer –

The main part of voltage stabilizer is a stepdown/auto transformer which controls the output voltage when input voltage is variable/fluctuating. This is done with the help of tapping on secondary side of the transformer. There is an electronic circuit which comprises of rectifier, amplifier & relays which senses input voltage difference (varying from desired output voltage). Details of each part is given below –

The function of rectifier is to convert AC power to DC power that is required for electronic circuit.

The function of amplifier is to sense different set voltage conditions such as lower & higher cut off voltage, boost or buck condition of voltage & normal operating voltage.

The function of relays is to regulate/operate the secondary side of the of the transformer so that load gets its desired/regulated/constant voltage.

Boost & Buck operations of stabilizer –

There are two operation conditions where voltage regulation is required for a load i.e. over voltage & under voltage. The function of stabilizer is to increase voltage from under voltage is called boost operation condition while when it decreases the voltage from over voltage, it is called buck operation. These are two main conditions which are performed by a stabilizer to provide constant voltage to the load. The boost condition is achieved by adding secondary voltage (through tapping) to the input voltage.

Example of boost operation –

if a single-phase load is designed to operate between 220V +/– 10%. It means safe working voltage of the load is 198V – 242V. If incoming voltage is low let’s say 180V then stabilizer will additional volage 40V by operating boost relays which further operates secondary winding of the transformer so that load gets its desired voltage.

Example of buck operation – Similarly, when incoming voltage is high i.e. 260V then stabilizer will reduce voltage by 40V by operating buck relays.

Types of voltage stabilizer –

Voltage stabilizers are of three types –

Relay Type
Servo controlled Type
Static Type

Relay type voltage stabilizer –

In this type, electromagnetic relays are used which are connected to tapping of transformer (secondary side). To maintain output voltage, they are activated one by one as per requirement. Accuracy in output voltage is not possible due to electromagnetic relays.

Servo controlled voltage stabilizer –

In this type, output tapping of transformer connected with servo motors which moves the tapping of transformer to maintain the output voltage. Servo controlled stabilizers are more accurate than relay type.

Static type voltage stabilizer –

In this type, microprocessor-based circuitry is used to control the output voltage. Therefore, static type servo stabilizers are more accurate than relay & servo type as there is no moving parts in it.

Single Phase Voltage Stabilizer & Three Phase Voltage Stabilizer-

Voltage stabilizers may be further classified according to type of load i.e. Single phase voltage stabilizer & Three phase voltage stabilizers.

Selection of voltage Stabilizer –

Selection of stabilizer depends on the type of load, use following steps (note- Stabilizers comes in VA or KVA rating) –

A) Single Phase Voltage Stabilizer –

Know rating/capacity/power of load/equipment such as Kw, VA or Amp
If load / equipment’s power is given in Watt then convert it into VA by considering 0.8 power factor. For example, if 500 Watt is the power of equipment, then convert it into VA by dividing 500 by 0.8 because VA (Apparent power) = Watt (active power) / power factor.
Once load is decided in VA then keep approx. 20-25% safety margin to select the stabilizer i.e. 500 W = 625VA + 20% = 750 VA.
Hence, we can say that for 500W equipment, we can buy 750VA voltage stabilizer.

Note-1 Voltage stabilizers are available in different-different range of input voltage variation so choose stabilizer according to the voltage fluctuation in your area.

Note-2 Accuracy plays an important role in the pricing of voltage stabilizer, so check the accuracy as per requirement.

B) Three Phase Voltage Stabilizer –

Case–1 (3 phase supply with single phase load)

Suppose you have a 3-ph DB installed at your home were incoming supply is 3-ph & load is divided in R,Y & B phase because you have single -ph load at your home (eg. AC, fridge, lights etc) If you want to put volage stabilizer for complete house, then you need to install it at incoming side. So, one 3 phase voltage stabilizer is required & calculation is given below –

Check load connected on each phase let’s say each phase is having one AC + some lights + some power points. All this load becomes 1500W or calculate load (W) according the current (I) drawn in each phase X 230V single phase supply to get values in VA.
Now convert Watt into VA (because stabilizers come in VA rating) by considering 0.8 power factor. So load (VA) on each phase will be 1500/0.8 = 1875VA
Consider 20% safety margin = 1875+20% = 2250VA.
Let’s say total load on each phase = 2500 VA (round off figure).
So, total capacity for stabilizer will be – 2500 * 3 = 7500VA = 7.5 KVA.

Case – 2 (3 phase supply with three phase load)

Know rating/capacity/power of load/equipment such as Kw, VA or Amp
If load / equipment’s power is given in Watts, then convert it into VA by considering 0.8 power factor. For example, if 2000W (or 2KW) is the power of equipment, then convert it into VA by dividing 2000 by 0.8 because VA (Apparent power) = Watt (active power) x power factor = 2500VA
Once load is decided in VA then keep approx. 20-25% safety margin to select the stabilizer i.e. 2500VA + 20% = 3000 VA.
Hence, we can say that for 2000W equipment, we can buy minimum 3000VA voltage stabilizer or 3KVA.

(Note- Safety factor 20% & 25% is OK for domestic load but for industrial load it should be between 1.5 times to 2 times).

Frequently Asked Questions (FAQs) on Voltage Stabilizer –

Q1) What is voltage fluctuation?

Ans) Voltage fluctuation means variation in incoming voltage value. Generally, single phase supply & three phase supply are provided by the local electricity distribution companies which may be a state electricity department or a private company (outsourced to third party by the state electricity dept) to consumers for lighting & equipment purpose. This power should be provided on a certain voltage e. g 230V supply is provided for single phase consumers & 415V supply is provided for three phase consumers. Normally, supplied power should have constant voltage but sometimes this incoming voltage varies & it is called voltage fluctuation. This variation is acceptable up to certain limits (depending on the type of equipment), after that this becomes dangerous to the equipment.

Q2) Why is voltage fluctuation harmful to the equipment?

Ans) As we know that each & every equipment is designed for certain voltage with some tolerance limit in incoming supply (voltage variation). Some equipment may run smoothly with 5% voltage variation while some may work up to 10% voltage variation. Normally, safe voltage fluctuation range is given on sophisticated equipment.

If, incoming voltage variation exceeds the safety limit of the equipment (either less or high from specified value), it can damage the equipment. In both the conditions, equipment may start heating up, speed of moving part may increase or decrease depending on high or low voltage, equipment may make noise, lights may be flickring/blown off etc.

Q3) What are the reasons of voltage fluctuation? Why does voltage fluctuation happen?

Ans) There are many reasons which can cause voltage fluctuation –

Loose / corroded connections, it may be at house end or in power lines.
Overloading of the power supply network can cause low voltage.
Due to lighting, power surges/spikes may occur
Switching on/off the lines due to which either sudden load is connected / disconnected from supply lines.
Domestic appliances drawing too much current (sometimes we have seen that when we switch on a heavy motor, a voltage dip is observed in electrical supply).
Loose neutral connection. This may damage lights because neutral provides zero reference point with respect to phase. In three 415 V system, phase is always at 415V but when we measure it with reference to neutral, the voltage becomes 230V which is provided to a light. But whenever neutral is missing or contacts are loose the voltage across load increases & damage the light.

Q4) What is protection from voltage fluctuation?

Ans) Generally, reasons which are given above are of temporary nature & for very small period. But, when any fault persist in the system then protection is required. Protection of the equipment can be done either with surge arresters or by installing voltage stabilizers of suitable rating.