What is voltage stabilizer and how it works?

What is voltage stabilizer?

A voltage stabilizer, also known as an automatic voltage regulator (AVR), is an electrical device that maintains a consistent voltage at its output terminals, irrespective of fluctuations in the input voltage. Its primary function is to safeguard electrical equipment and machinery from the adverse effects of high or low voltage variations and other voltage irregularities.

Voltage stabilizers are essential for protecting sensitive and costly electrical equipment, such as air conditioning units, offset printing machines, laboratory apparatus, industrial machinery, and medical devices, from the potentially harmful impacts of voltage fluctuations.

Voltage stabilizers work by regulating input voltage fluctuations before they can harm the connected load or equipment. These devices adjust the output voltage to fall within a specific range, typically 230 volts for single-phase systems and 400 volts for three-phase systems, and these adjustments are achieved through internal circuitry using buck and boost mechanisms.

There is a diverse range of automatic voltage regulators available in the market, classified based on their application and capacity, which can be either single-phase or three-phase. Within the realm of three-phase stabilizers, there are balanced load models and unbalanced load models.

Stabilizers can be used on an individual basis to stabilize voltage for a single device, or they can be employed to safeguard larger units, whether in residential, commercial, or industrial settings. Furthermore, stabilizers can be either analog or digital, offering various features such as input/output voltage cutoffs, overload protection, manual or automatic operation, voltage display, and zero voltage switching, among others.

Why is there a need for voltage stabilizers?

Electrical equipment and devices are typically designed to operate within a specific range of input voltage. Depending on their sensitivity, this operating range may be constrained to specific voltage tolerances. Some equipment can withstand variations of ±10% of the rated voltage, while others may tolerate only ±5% or even less.

Voltage fluctuations, which can occur at multiple points, especially at the connection points to the load, are a common occurrence. These fluctuations result from various factors, including lightning, electrical faults, faulty wiring, and periodic device shutdowns, and they can pose significant challenges to electrical equipment and devices.

The consequences of applying excessive over-voltage to a load include permanent equipment damage, insulation deterioration, unwanted load interruptions, increased losses in cables and related equipment, and a reduced device lifespan. On the other hand, applying low voltage to a load can lead to equipment failure, longer operating times (e.g., for resistance heaters), diminished equipment performance, larger electrical currents causing overheating, calculation errors, and reduced engine speed.

The stability and accuracy of voltage are critical factors in ensuring the proper operation of electrical equipment and devices. Voltage stabilizers play a crucial role in ensuring that voltage fluctuations in the input power supply do not adversely affect the connected load or electrical device.

How do voltage stabilizers work?

Voltage stabilizers rely on two fundamental operations: buck and boost. These operations are executed based on whether the input voltage is higher or lower than the desired output voltage. This can be done manually using switches or automatically through electronic circuits.

The key concept behind voltage stabilization involves adjusting the input power source's voltage, either by adding or reducing it to reach the desired voltage at the output. To achieve this, voltage stabilizers employ transformers connected to relays or solid-state switches in various configurations. Some stabilizers utilize transformers with taps on the coil to provide different voltage corrections, while servo motor stabilizers use auto-transformers to offer a broader range of corrections.

To illustrate these operations, consider the example of a 230/12 V step-down transformer, which can be configured for both boosting and bucking voltage. The diagram below illustrates the configuration of a boosting transformer. In this setup, the secondary winding's polarity is arranged to directly augment the primary voltage. Consequently, when there is an under voltage situation, relays or solid-state switches activate to introduce extra voltage to the input voltage by adjusting the transformer (whether it's a servomotor or auto-transformer).

The diagram below depicts the arrangement of a step-down transformer (Buck), where the secondary coil's polarity is configured to directly subtract from the primary voltage. Thus, when under voltage surge conditions occur, relays or solid-state switches activate to supply extra voltage by adjusting the transformer (be it a servo motor or auto-transformer).

The diagram below illustrates a two-stage voltage stabilizer, featuring a pair of relays responsible for providing a consistent AC supply to the load during both over-voltage and under-voltage conditions. These relays facilitate the execution of buck and boost operations for two specific voltage ranges, such as one for low voltage (e.g., 195 V) and the other for over-voltage (e.g., 245 V).

In cases where the stabilizer utilizes transformer technology with various taps, the appropriate tap on the transformer is engaged depending on the input voltage. Conversely, when the stabilizer employs an auto-transformer, a servo motor is employed to adjust the voltage levels. This is necessary because the auto-transformer features a single coil, and adjusting voltage levels involves the servo motor moving within the transformer coil's windings.

Voltage stabilizers have evolved into indispensable components in various contexts, from household electrical appliances to industrial and commercial systems. In the past, manual voltage stabilizers were employed to amplify or diminish input voltage in order to generate a consistent and desired output voltage. These early stabilizers relied on electromechanical relays for the purpose of disconnection and re-connection.

However, as technology advanced, electronic circuits were introduced to automate the stabilization process. Another widely embraced category of voltage stabilizers is servo motor stabilizers, which continuously and seamlessly correct voltage deviations without relying on mechanical switches or keys.

Types of voltage stabilizers:

There are several types of voltage stabilizers:

  1. Relay Type Stabilizers: These voltage stabilizers regulate voltage by connecting various taps of the transformer to the load, allowing for amplification or attenuation.

  2. Servo Motor Controlled Stabilizers: These stabilizers employ servo motors to continuously correct voltage variations, typically achieving high output voltage accuracy.

  3. Static Voltage Stabilizers: Static stabilizers use electronic power converters to precisely regulate voltage without moving parts, offering high efficiency and reliability.

The choice of stabilizer type depends on factors such as the required accuracy of voltage regulation, speed of correction, and the specific needs of the connected equipment or devices.

Distinguishing between Voltage Stabilizers and Voltage Regulators:

Voltage stabilizers and voltage regulators serve similar purposes, namely maintaining a stable voltage output. However, they differ in their primary functions:

  1. Voltage Stabilizer: A voltage stabilizer is designed to deliver a constant output voltage without altering the input voltage, regardless of changes in the load current.

  2. Voltage Regulator: A voltage regulator, on the other hand, maintains a constant output voltage without modifying the load current.

Selecting the Right Capacity for a Voltage Stabilizer:

Choosing the correct capacity for a voltage stabilizer involves considering several factors:

  • Determine the power consumption specifications of the equipment for which you need a stabilizer, either from the device's nameplate or its user manual.
  • Calculate the required KVA capacity of the stabilizer by multiplying the device's voltage by its maximum rated current.
  • Add a safety margin of around 20-25% to the calculated KVA capacity to accommodate potential future load additions.
  • Account for the power factor when calculating the KVA capacity, especially if the device's rating is given in watts.
  • For residential applications, voltage stabilizers ranging from 200V to 10kV are typically sufficient. In contrast, commercial and industrial applications may require single-phase or three-phase stabilizers with higher ratings.

These steps can help you choose the appropriate size of voltage stabilizer for your specific electrical appliances or equipment, ensuring efficient and reliable operation.

Prasun Barua

Prasun Barua is an Engineer (Electrical & Electronic) and Member of the European Energy Centre (EEC). His first published book Green Planet is all about green technologies and science. His other published books are Solar PV System Design and Technology, Electricity from Renewable Energy, Tech Know Solar PV System, C Coding Practice, AI and Robotics Overview, Robotics and Artificial Intelligence, Know How Solar PV System, Know The Product, Solar PV Technology Overview, Home Appliances Overview, Tech Know Solar PV System, C Programming Practice, etc. These books are available at Google Books, Google Play, Amazon and other platforms.


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