In general, residential areas experience very low voltage during the day and normal voltage during the night and industrial areas experience very low voltage during the day and very high voltage during the night. 

However, most of the electrical equipment and loads are designed to operate for a voltage variation of up to ±10 %, 

Servo-controlled stabilizers using toroidal core transformers can regulate the output voltage within ±1 % of the standard voltage. Furthermore, they allow smooth variation in the voltage without steps or interruptions. They can be designed for a wide variation of voltage with ease. They also have reasonably quick correction times.

We provide onsite testing of servo stabilizers to verify their working condition.

Physical Inspection. First, we Inspect all the components and see that they are of approved make and proper rating.

Insulation Testing. Then, we test the insulation between the terminals and the body of the stabilizer with a 500 V megger. The insulation should be greater than or equal to 5 MΩ when measured at the ambient not exceeding 45°C.

Load Testing. Lastly, we test the stabilizer with actual equipment load so that the full load condition is available for a minimum of six hours with the available input voltage. During this test, we record the output voltage and temperature to see that they are within limits.

The main failure points in the servo stabilizer are the autotransformer and servo motor. So they should be of reputed makes.

The selection of variac with the proper rating also plays an important role in the satisfactory performance of the stabilizer. We advise derating the nameplate rating by 10-15% for air-cooled systems as many stabilizers fail on account of the failure of the variac operating under the adverse condition of very low input voltage and high load current.

The other important reason for the failure of the voltage stabilizer is the wear and tear of the carbon brushes in the variac or the reduced spring tension of the carbon brushes which requires periodic inspection for remedial action.