What is the difference between Relay Type Voltage Stabilizer & Servo Voltage Stabilizer?

Today, Voltage stabilizers have become mandatory for electrical equipment of home, offices & industries. It helps to protect electrical equipment and machine from over & under voltage and other voltage surges. Voltage stabilizer delivers a constant voltage at its output terminals regardless of changes in the input or incoming voltage. In the starting, manually operated voltage stabilizers used to boost or buck the voltage. These manually stabilizers ware built with electromechanical relays to give an output voltage within a desired range.
Later on, additional electronic circuitry came in to the force and became tap changer automatic voltage regulators. At present the latest technology of voltage stabilizer is servo stabilizer in which voltage correction is carried continuously. That can protect your appliances more effectively. Before we point out the differences between relay type and servo voltage stabilizer, let’s have a look on type of technology used in voltage stabilizers. Through this we can clearly notify you about features & components difference between both types of voltage stabilizer.


1. Relay Type of Voltage Stabilizers:


In this type of stabilizer, electronic circuit and set of relays besides the transformer, comprises rectifier circuit, controller unit and other tiny components. The electronic circuit compares the output voltage with a reference value provided by built-in reference voltage source. Whenever the voltage rises or falls, the control circuit switches the corresponding relay to connect a desired tapping to the output voltage. Relay types of voltage stabilizers usually change the output voltage accuracy of ±10 %. It is used for low rating appliances in homes, offices and industries. Many electrical equipment & machines are suffering with several limitations such as unaspected performance, less durability, interruption to power path etc. Therefore it helps to provide reliable voltage for protecting much equipment. At the same time researcher has developed a latest technology called servo controlled system to stabilize the voltage fluctuation rate very quickly. Let’s know the second and most popular technology used for stabilizing the voltage.


2. Servo Voltage Stabilizers:

Servo-StabilizerIn this stabilizer, a phase of buck boost transformer primary is connected to the fixed tap of the auto transformer and other one connects with moving arm which is controlled by the servo motor. Apart from it the buck boost transformer primary of servo stabilizer gets connected in the series of incoming voltage. These stabilizers called servo stabilizer because it uses a servo motor to enable the voltage correction. It is mainly used for high output voltage accuracy. Usually, ±1 % with input voltage changes up to ± 50 %. It is most popular for low high rating appliances used in homes, offices and industries to provide correct voltage rate for protecting equipment and their desired performance. Demand

These stabilizers can be single-phase, three-phase Oil cooled and Air cooled balanced unit type or three-phase unbalanced. In a single phase servo stabilizer, motor coupled to the variable transformer to achieve voltage correction. Meanwhile, in three-phase balanced type, a servo motor is coupled with three auto transformers such that stabilized output is provided during fluctuations by adjusting the output of the transformers. Whereas in unbalanced servo stabilizers, there are three independent servo motors coupled with three auto transformers.

If we compare servo stabilizers with relay type stabilizers we can find various advantages of servo voltage stabilizer such as higher correction speed, high precision of stabilized output, capable to withstand inrush currents and most importantly the high reliability. We can highlight the different between both types of voltage stabilizer are as follows:


Differences between a relay type of voltage stabilizer and servo voltage stabilizer can easily find under given table:


Features Relay type of voltage stabilizer Servo voltage stabilizer
Voltage Accuracy output of ±10 % Output Voltage ±1 % input voltage change up to ± 50 %.
Technology Relay Type Controlled by Servo Motor
Voltage correction Correcton in steps of of 20Volt Stepless correction. 25Volt/second
Models Only Air Cool Model Available Available in both, Air & oil cool models, depend on capacity also
Load Capacity Up to 10 KVA only Up to 5000KVA and above as per the demand
Functioning criteria Set of relays connected besides the transformer Buck-Boost transformer connected with a fixed tap
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