Introduction to 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.
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.
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
Servo Controlled Voltage Stabilizers
These are simply termed as servo stabilizers (work on servomechanism which also known as negative feedback) and the name suggests it uses a servo motor to enable the voltage correction. These are mainly used for high output voltage accuracy, typically ±1 percent with input voltage changes up to ± 50 percent. The figure below shows the internal circuit of a servo stabilizer which incorporates servo motor, auto transformer, buck boost transformer, motor driver and control circuitry as essential components.
In this stabilizer, one end of buck boost transformer primary is connected to the fixed tap of the auto transformer, while other end is connected to the moving arm that is controlled by the servo motor. Secondary of the buck boost transformer is connected in series with incoming supply which is nothing but stabilizer output.
Electronic control circuit detects the voltage dip and voltage rise by comparing the input with built-in reference voltage source. When the circuit finds the error, it operates the motor that in turn moves the arm on the autotransformer. This could feed the primary of buck boost transformer such that a voltage across the secondary should be the desired voltage output. Most servo stabilizers use embedded microcontroller or processor for the control circuitry to achieve intelligent control.
These stabilizers can be single-phase, three-phase balanced type or three-phase unbalanced units. In single phase type, a servo motor coupled to the variable transformer achieves the voltage correction. In case of a 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. In an unbalanced type of servo stabilizers, three independent servo motors coupled with three auto transformers and they have three separate control circuits.
There are various advantages of using servo stabilizers compared with relay type stabilizers. Some of these are higher correction speed, high precision of stabilized output, capable to withstand inrush currents, and high reliability. However, these require periodic maintenance due to the presence of motors.