Introduction to Servo Stabilizer

Introduction to Servo Stabilizer :

The embedding of microprocessor chip technology and power electronic devices in the design of intelligent AC voltage stabilizers (or automatic voltage regulators (AVR)) led to produce high-quality, stable electric power supply in the event of significant and continuous deviation of mains voltage.

As advancement to the conventional relay type voltage stabilizers, modern innovative stabilizers use high performance digital control circuits and solid state control circuitry that eliminates potentiometer adjustments and allows the user to set voltage requirements through a keypad, with output start and stop facility.

This also led to make the trip timing or responsiveness of the stabilizers to a very less rate, typically less than a few milliseconds, in addition this can be adjusted with variable setting. Nowadays, stabilizers became an optimized power solution to many electronic appliances that are sensitive to voltage fluctuations and they have found working with many devices such as CNC machines, air conditioners, television sets, medical equipment, computers, telecommunication equipments, and so on.

What is a Voltage Stabilizer?

It is an electrical appliance which is designed to deliver a constant voltage to a load at its output terminals regardless of the changes in the input or incoming supply voltage. It protects the equipment or machine against over voltage, under voltage, and other voltage surges.

It is also called as automatic voltage regulator (AVR). Voltage stabilizers are preferred for costly and precious electrical equipments to protect them from harmful low/high voltage fluctuations. Some of these equipments are air conditioners, offset printing machines, laboratory equipments, industrial machines, and medical apparatus

Voltage stabilizers regulate the fluctuating input voltage before it could be fed to the load (or equipment which is sensitive to voltage variations). The output voltage from the stabilizer will stay in the range of 220V or 230V in case of single phase supply and 380V or 400V in case of three phase supply, within given fluctuating range of input voltage. This regulation is carried by buck and boost operations performed by internal circuitry.

There are huge varieties of automatic voltage regulators are available in today’s market. These can be single or three-phase units as required by the type of application and capacity (KVA) needed. Three-phase stabilizers come in two versions as balanced load models and unbalanced load models.

These are available either as dedicated units for appliances or as a big stabilizer unit for whole appliances in a particular place, say whole house. In addition, these can be either analog or digital type of stabilizer units.

The common types of voltage stabilizers include manual operated or switchable stabilizers, automatic relay type stabilizers, solid state or static stabilizers, and servo controlled stabilizers.  In addition to the stabilizing function, most stabilizers come with additional features such as input/output low voltage cutoff, input/output high voltage cutoff, overload cutoff, output start and stop facility, manual/auto start, voltage cutoff display, zero voltage switching, etc.

Why Voltage Stabilizers Are Needed?

Generally, each and every electrical equipment or device is designed for a wide range of input voltage. Depending on the sensitivity, the working range of the equipments are limited to a specific values, for instance, some equipments can tolerate ± 10 percent of the rated voltage while others ± 5 percent or less.

The voltage fluctuations (rise or dip of the magnitude of rated voltage) are quite common in many areas, especially at terminated lines. The most common reasons for voltage fluctuations are lighting, electrical faults, faulty wiring and periodic turning off the device. These fluctuations create mishap to the electrical equipments or appliances.

Long time over voltage will result

• Permanent damage to the equipment
• Insulation damage to the windings
• Unwanted interruption in the load
• Increased losses in cables and associated equipments
• De-rating life of the appliance

Long time under voltage will result

• Malfunctioning of the equipment
• Longer working periods (as in case of resistive heaters)
• Reduced performance of the equipment
• Drawing large currents which further lead to overheating
• Computational errors
• Reduced speed of motors

So the voltage stability and accuracy decide the correct operation of the equipment. Voltage stabilizers therefore ensure that the voltage fluctuations at the incoming power supply does not affect the load or electrical appliance.

How Voltage Stabilizer Works?

Basic Principle of voltage stabilizer to Perform Buck and Boost Operations

In a voltage stabilizer, voltage correction from over and under voltage conditions is performed through two essential operations, namely boost and buck operations. These operations can be carried manually by switches or automatically through electronic circuitry. During under voltage condition, boost operation increases the voltage to a rated level while buck operation reduces the voltage level during over voltage condition.

The concept of stabilization involves in adding or subtracting the voltage to and from the mains supply. For performing such task stabilizer uses a transformer which is connected in different configurations with switching relays. Some stabilizers use a transformer with taps on winding to provide different voltage corrections while servo stabilizers use an auto transformer to have wide range of correction.

To understand this concept, let us consider simple step down transformer of 230/12V rating and its connection with these operations are given below.