Voltage Stabilizers

Power supply is erratic at most places in India, with voltage fluctuating in both directions (up and down) at many places frequently. These voltage fluctuations can damage appliances, there by causing them to end much before their normal useful life. When voltage goes down, electric current in the appliance increase, which can result in burning of the appliance. Voltage Stabilizers have thus found place in many homes and offices in India. In this article we will talk about voltage stabilizers: what they do, how much power do they consume and how to select one for your setup.

Principle of a voltage stabilizer:

A voltage stabilizer is an electrical appliance used to feed constant voltage current to electrical gadgets like ACs and computers, and protects them from damage due to voltage fluctuations. It works on the principle of a transformer, where the input current is connected to primary windings and output is received from secondary windings. When there is a drop in incoming voltage, it activates electromagnetic relays which add to more number of turns in the secondary winding, thus giving higher voltage which compensates for loss in output voltage. When there is rise in the incoming voltage, the reverse happens, and, thus, the voltage at the output side remains almost unchanged.

What are voltage stabilizers and how do they work?

As the name suggests, voltage stabilizers stabilize the voltage, which means if the supply voltage fluctuates or varies, it brings it to the desired range. It does so by using electromagnetic regulators that use tap changers with autotransformer’s. If the output voltage is not in range a mechanism switches the tap, to change the transformer to move the voltage in acceptable range. It does not give a constant voltage output, but operates the system in a safe voltage range.

How to choose a right sized stabilizer?

Sizing of a stabilizer is very similar to sizing of a UPS or Inverter (power backup). The most important thing is to know the load connected to the stabilizer. First you must note down the power (or watts) for all the appliances that will be connected to a stabilizer. The sum total of the power consumption (or watts) will give you the load on stabilizer in watts. But most stabilizer sizes are in VA (Volt Ampere) or kVA (kilo Volt Ampere which is equal to 1000 Volt Ampere). Although to get to actual VA (or Volt Ampere) from Watts (W) you will have to do some measurements, but to give a rough approximation, you can increase the Watts value by 20% to get the approximate VA size that you may need.

So for e.g. if sum of watts connected to your stabilizer is 1000 then you can take a 1200 VA or 1.2 kVA stabilizer. (Please note that 20% is suitable for residential systems and may not work in industries if your power factor is bad).

Are there different single-phase and three-phase voltage stabilizers?

Yes they are. But a three-phase voltage stabilizer is required only if voltage stabilization is needed for a three phase motor or for stabilizing voltage for a full three-phase setup.

All appliances that are used at homes can work on single-phase voltage stabilizer, and a three-phase voltage stabilizer may not be required for residential use unless one is trying to stabilize the voltage of complete house on a three-phase connection.

It is not recommended to put a stabilizer for the complete house because voltage stabilizers also consume electricity, and thus using it for the whole house will result in electricity consumption for all 24 hours. Instead if it is used for individual appliance, then it can be switched off when the appliance is switched off.

How much electricity do voltage stabilizers consume?

Electricity consumption of voltage stabilizers depends on the efficiency of the stabilizer. Typically they are 95-98% efficient. Which means, they consume about 2-5% of the maximum load. So if you have a 1 kVA (or 1000 VA) stabilizer, it would consume about 50 Watts (on peak load). Which means if a 1kVA stabilizer is left on for 10 hours, it would consume about 0.5 unit of electricity. Thus leaving it on for 24 hours can lead to a lot of electricity consumption.

Do modern refrigerators/air conditioners come with in-built voltage stabilization?

Modern appliances (mostly refrigerators and air conditioners) do come with a bigger voltage range for operation, i.e. if in past refrigerators worked well only between 200-240V, now they have a bigger range of 170-290V. But they do not come with in-built voltage stabilizers. Using voltage stabilizer with such appliances may not be necessary unless voltage in your area shoots up or down much above or below the limit in which the appliance can operate.


Always choose a right sized voltage stabilizer and also try to get them for individual appliances rather than for the whole electricity connection. Leaving them on for longer duration can result in higher electricity bills.

What are differences between Static Voltage Stabilizer and Servo Stabilizer?

There are many major differences between new age Static voltage Stabilizer (SVS) and tradition Servo stabilizer. In this post we will discuss every difference in detail.  This differences are in terms of construction, operation, reliability and features of both servo voltage stabilizer and static voltage stabilizer. Lets see differences one by one:

Static Voltage Stabilizer vs Servo regulator.

Static Voltage Stabilizer Vs Servo type stabilizer

1) Voltage Correction speed:

It does not contains any moving part. Static voltage stabilizer has pure electronic circuit to achieve correction in voltages. Hence static stabilizer has exceptionally high voltage correction speed than servo voltage stabilizer. Voltage correction  speed to SVS can be in range of 360 to 500 V/sec. On other hand Servo stabilizer has moving servo motor with help of which it achieves correction in voltage. Servo stabilizer is electromechanical device hence its voltage correction speed is slower than static voltage stabilizer.

2) Correction Time:

Due to high voltage correction speed static voltage stabilizer has low correction time of 20 to 30 millisecond as compared to servo stabilizer correction time of 50 milliseconds to 5 Seconds.

3) Maintenance:

Since Servo stabilizer has moving servo motor hence it has regular wear and tear which needs maintenance. Due to static nature of Static voltage regulator it don’t need maintenance.

4) Reliability:

In servo voltage stabilizer correction in voltage achieve by increasing or decreasing no of winding in autotransformer with help of shaft of servo motor. This increases or decreases voltage across primary of buck boost transformer in turn secondary of buck boost transformer and hence correcting output voltage.  Hence reliability of servo voltage regulator is mainly depend on reliability of servo motor. Similarly reliability of  static voltage stabilizer depends on reliability of IGBT power stage. In General static IGBT power stage is more reliable than electromechanical servo motor hence SVS are more reliable than servo regulator.

5) Auto Bypass facility:

In static voltage stabilizer providing auto bypass is very easy. And due to fast electronic nature, SVS can transfer to bypass automatically and without break in output voltage (zero transition time) in case of even of fault. In servo voltage stabilizer it is complicated to provide auto bypass mechanism and even it provided it becomes very costly proposition and transition to bypass ill be with break in output voltage (needs transition time).

6) Protection from over current fault due to short circuit:

In static voltage stabilizer, DSP control board continuously senses input voltage, output voltage, IGBT current and load current as part of working principle. In event of short circuit at output of static voltage stabilizer, load current increases exponentially high which automatically get sense by DSP controller and it  cuts output &  switches of IGBT power stage instantaneously to clear over current fault. Hence over current fault get clear in SVS very quickly and without adding  any extra hardware. In case of servo voltage stabilizer, over current  protection can be achieve with help of extra hardware (MCCB, CB etc.) and that of clearing of fault is not instantaneous.

Other Differences between Static type Voltage stabilizer and Servo voltage Stabilizer:

Specifications Static Voltage Stabilizer Servo Voltage Stabilizer
EMI/RMI Filter As standard with no extra cost Optional at extra cost.
Size Very Compact Compact
Weight Very low weight High weight
Input Voltage Window Wider as 170-290VAC less wider 185-260VAC
Voltage Stability 1% 2%
Working Principle PWM method, IGBT based Servo motor controlled.
Sound Silent operation High sound over age.
Output waveform Distortion Not distortion Distortion
Overload cutoff standard optional