What are Automatic Voltage Regulators (AVR)?

In electrical power system, there is a device called Automatic Voltage Regulator (AVR) used to adjust the voltage levels within a desired limit. In other words, an automatic voltage regulator is an electronic circuit that is primarily used for regulating the output voltage of an electric generator, so that we can obtain a constant voltage even when the load is fluctuating.

This tutorial will explain the construction, working, needs, advantages, and applications of automatic voltage regulators (AVRs). So, let’s start with the basic introduction of automatic voltage regulator.

What is an Automatic Voltage Regulator?

An AVR or Automatic Voltage Regulator is an electronic circuit or device that is used at the output side of a generator to control the output voltage. The primary function of an automatic voltage regulator is to stabilize the voltage so that we can get a constant voltage at output.

In the case of electric generators, the load variation affects the output voltage i.e., the output voltage of an electric generator fluctuates with the variations in the load. Therefore, to stabilize this fluctuating voltage of the generator, we use the automatic voltage regulator.

The use of automatic voltage regulator also results in improved efficiency and reliability of the supply system.

For voltage regulation, an automatic voltage regulator is typically used in the following major places in a power supply system −

• At the output side of a transformer

• At the output side of a generator

• Between the feeder and load, etc.

In actual practice, the automatic voltage regulators are used at multiple locations in a power system.

Functions of Automatic Voltage Regulator

As mentioned above, the primary function of an automatic voltage regulator is to regulate the voltage within a predefined limit. However, in an electrical system, it also contributes in several other functions.

Some of the common functions of an automatic voltage regulator are listed below −

• To maintain the output voltage of a generator within a desired limit.

• To provide protection against undesirable conditions like voltage spikes, surges, and overloading.

Construction of Automatic Voltage Regulator

The block diagram of a typical automatic voltage regulator is shown in the following figure.

It consists of the following major components −

• Voltage detector

• Comparator and error detector

• Control circuit

• Power amplifier

Let us understand the function of each of these components of an automatic voltage regulator.

Voltage Detector

It is also known as a voltage sensing element. The main function of this device is to detect the output voltage of the generator. The primary component of a voltage detector in AVR is a potential transformer (PT). Thus, the voltage regulator can also reduce the output voltage of the generator to a value safer to measure.

Comparator and Error Detector

This is an electronic circuit which compares the output voltage of the generator with a reference voltage. If there is any difference between these two values, then it produces an error signal, which is further sent to a control circuit to make required adjustments.

Control Circuit

The control circuit of the automatic voltage regulator performs processing of the output of the comparator and error detector as per the error signal generated. As a result, it produces a control signal which is then sent to a power amplifier.

Power Amplifier

The power amplifier of the AVR amplifies the control signal so that it can drive the excitation system of the generator effectively. The excitation system adjusts the magnetic field in the generator and hence the output voltage.

All these components of the automatic voltage regulator work together and provide a constant voltage as the generator output.

Working Principle of Automatic Voltage Regulator

The working of an automatic voltage regulator is based on the principle of error detection. According to this principle, when the output voltage of a generator or any other equipment deviates from a specified voltage level, then an error signal is generated by the AVR. This error signal instructs the other components of the AVR to make required adjustments and maintain the voltage within a specified limit.

Desirable Characteristics of Automatic Voltage Regulator

The following are some major desirable characteristics of an ideal automatic voltage regulator −

• An ideal automatic voltage regulator is supposed to have a good voltage regulation so that it can do voltage adjustments withing a specified limit.

• A high-quality automatic voltage regulator has a fast response time so that it can quickly detect the voltage variations and do necessary adjustments.

• A good automatic voltage regulator has high accuracy and maintains the output voltage within an acceptable range.

• An ideal automatic voltage regulator should have a good load regulation, so that it can give a stable voltage under changing load conditions.

• An automatic voltage regulator should have high efficiency so that there would be minimum losses within the AVR.

• An automatic voltage regulator should have capabilities to cancel the noise interference.

• The components of an automatic voltage regulator must be of high-quality so that it has high reliability and longer life.

All these are some key characteristics of an AVR that make it an ideal one.

Advantages of Using Automatic Voltage Regulator

In an electrical system, the use of an automatic voltage regulator contributes in several advantages. The following are some main advantages of an automatic voltage regulator −

• AVR helps to obtain a stable output voltage that prevents damages of sensitive devices due to voltage variations.

• Automatic voltage regulator improves the power quality and reliability.

• It minimizes the impact of load variation and voltage fluctuation in the system to improve the overall performance of the system.

• Automatic voltage regulator also helps in minimizing faults due to over-voltage and under-voltage.

Applications of Automatic Voltage Regulator

Automatic voltage regulators are widely used in various electrical systems like transformers, generators, feeders, etc. Some common applications of automatic voltage regulators are listed below −

• In electric generators, AVRs are used to stabilize the output voltage.

• Automatic voltage regulators are also used in electric feeders to reduce the voltage fluctuations.

• Automatic voltage regulators are also in industrial machinery to stabilize the supply voltage for efficient operation.

• In telecommunication systems, the automatic voltage regulators are used to provide stable and reliable power supply required to operate sensitive equipment.

• Automatic voltage regulator is also used in parallel operation of alternators to provide protection against overload.

• Automatic voltage regulator is also used in electrical systems to provide protection against electric surges and spikes.

Conclusion

In conclusion, an AVR is an electronic device that is used for regulating or controlling the voltage of an electrical system like output voltage of a generator. It stabilizes the fluctuating voltage and improves the reliability of the system. In this article, I have explained all the important concepts related to automatic voltage regulator.

FAQs Related to Automatic Voltage Regulator

In this section, I have answered some most commonly asked questions related to automatic voltage regulator.

1. What are the top 5 features of automatic voltage regulator?

The following are the top 5 features of the automatic voltage regulator −

• Optimal voltage regulation

• Broad input voltage range

• Low internal impedance/resistance

• Compatibility with the specified load

• Voltage accuracy as per the load requirements.

2. What is the working principle of AVR?

The working principle of automatic voltage regulator is based on error detection. Where, the actual output voltage is compared with a reference voltage to detect the error.

3. Can automatic voltage regulator increase voltage?

The automatic voltage regulator is responsible for regulating the excitation system. Thus, it can decrease or increase the voltage to maintain it within a specified range.

4. What is the difference between AVR and stabilizer?

An automatic voltage regulator adjusts the output voltage of a generator or feeder according to the load requirements. Whereas, a stabilizer only stabilizes the fluctuating voltage at a certain value.

5. What are the two types of automatic voltage regulators?

The following are two types of automatic voltage regulators used in electrical systems −

• Linear automatic voltage regulator

• Switching automatic voltage regulator