Unorganised servo stabiliser market: Buyers should go for quality and credibility


No matter how much technology advances and how much engineers try to come up with advanced substitutes, it seems that the market for servo stabilisers will forever remain the same. In fact, almost all leading servo stabiliser manufacturers claim to be growing by 50 per cent. According to industry analysts, more than 400 manufacturers exist in India, catering to almost all types of industries—large, medium and small, and the market is growing by 15-20 per cent. This industry is unorganised with a large number of smallscale units manufacturing servo stabilisers and related components like variable transformers, microcontroller-based control units, etc.

By Srabani Sen

Friday, October 15, 2010: The market for servo stabilisers is continuously growing, yet, because of a surfeit of manufacturers, margins are low. “If a worker leaves us, he goes and starts a small unit on his own and is considered a manufacturer. But since he is not an engineer, he can only copy the technology from others. However, it will be difficult for him to produce good quality products as he lacks much knowledge. This sector is so unorganised, there is no data on the exact number of manufacturers in the field,” states Piyush Garg, managing director, Piyush Electronics & Electricals (P) Ltd.

How a servo stabiliser functions

Piyush Garg, MD, Piyush Electronics &Electricals

The voltage variations, which have become a common phenomenon in the current power supply system, cause havoc in sensitive and sophisticated equipment. “Voltage stabilisers are meant to take care of this problem and protect the equipment. They ensure a longer life of the equipment and also drastically cut down electricity consumption of the equipment leading to continuous reduction in electricity bills. Thus, they play an important role in energy conservation, which is the need of the hour,” says H Kamruddin, managing director, Servokon Systems Ltd.

Servo voltage stabilisers feature a microcontroller based circuit to control the AC synchronous servo motor. The motor is mechanically attached to the arm of a continuously variable auto transformer which feeds to the primary of a control buck boost transformer. The stabiliser output voltage is compared with the reference voltage and the resultant error signal controls the servo motor, providing true proportional control systems rather than on/off circuits, states Garg. “The use of the servo voltage stabiliser is the only way to control erratic supply voltage conditions. It can control all types of loads like inductive, resistive or capacitive,” he adds.

Servo stabilisers use an advanced electronic servo motor concept to control a motorised variable transformer. Due to the motorisation, there is a small delay in voltage correction. However, output voltage accuracy is usually 1 per cent with input voltage changes going up to 50 per cent. These machines are not affected unduly by the power factor or the frequency variation. This type of technology tends to be extremely effective when considering large three phase applications, as it can maintain its accuracy for all three phases, both line to line and line to neutral, irrespective of the input voltage balance and the load balance at any power factor. They are also able to withstand large inrush currents, normally experienced with inductive loads. However, due to the mechanics of this type of stabiliser, periodic maintenance is required.

RK Dhawan, MD, Green Dot Electric

“Servo voltage stabilisers save life of costlier appliances, CNC machines, electrical equipment, medical equipment, motors,  lab equipment, etc, through  generally available mains AC supply. The supply fluctuates regularly or goes in dip and bounces due to sudden loads and off loads on the supply voltage. The fluctuations both on low and high side are harmful to electronic and electrical equipment. It is, therefore, essential to have correct voltage for various equipment both to save energy, save life, improve performance and save from damages of high voltages,” explains R K Dhawan, managing director, Green Dot Electric Ltd.

“Servo stabilisers can correct voltage fluctuations before the latter damages your hi-tech machines. Hence, they are required in all offices, showrooms, factories and residences. They give a perfectly stable output supply even under severe conditions of unbalanced voltage. It is a highly customised and tailor made product, available to suit input voltage variations of individual customers,” says Akil Siddiqui, marketing manager, Cosmostat Industries.

Various design topologies

Haji Kamruddin, MD, Servokon Systems

According to Kalpana Adhikari, director, NPP Energy Ltd, servo stabilisers available in the Indian market are manual, semi automatic (logic circuit controls), and fully automatic with microcontroller based control driver. These servo stabilisers are of two types—air cooled and oil cooled. Also commonly used are servo stabilisers with the DG set MCCB panel, the three phase servo stabiliser with and wthout an ampere meter, the single phase servo stabiliser with auto cut system, the three phase unbalanced servo stabiliser, etc. “Now, depending upon the input fluctuation, servo motors adjust the output of the auto transformer to provide a stabilised output,” she adds.

An ISO 9001:2000 and ISO 140001:2004 certified company, NPP Energy Ltd was established in 1991 and makes servo stabilisers from 1 kVA to 1000 kVA. Piyush Electronics & Electricals, which had started manufacturing servo stabilisers in 1995, produces servo stabilisers from 0.5 kVA (for homes) to 1500 kVA (for industry). It also designs the circuits and manufactures all the components of servo stabilisers, in-house. It makes both air cooled as well as oil cooled models. “Air cooled servo stabilisers are expensive and high maintenance is required, whereas oil cooled ones require less maintenance and are not as expensive as air cooled ones,” points out Garg.

Kalpana, director, NPP Energy

Green Dot Electric manufacturers microcontroller based voltage stabilisers from 2 kVA to 2000 kVA. “Our servo stabilisers  are made with ultra isolation transformer and have soft start function and surge protection. These products guarantee 98 per cent electrical efficiency and high speed correction up to 100 volt per second,” says Dhawan. Green Dot also claims that its stabilisers have lowest footprint in the industry and no wave shape distortions. “These stabilisers are generator compatible with permanent magnet burn proof motor.

The specially designed control system is microcontroller based and its displays have 18 parameters in 3 digit, 7 segment digital displays. The panel displays 12 diagnostic indications  and  voltage per phase—input, voltage per phase output and load per phase. The panel by selection can also display input voltages of all three phases, output voltage of all three phases and output currents of all three phases. The reliability has been built into any and all components including a class of variable transformer that have been built-in heat sinks and self adjusting and self aligning carbon brush systems,” adds Dhawan.

Founded in 1989, Cosmostat manufactures single phase and three phase balanced and unbalanced servo stabilisers. “Servo voltage stabilisers from Cosmostat are specifically designed, incorporating the latest solid state technology to protect equipment from undesirable voltage fluctuations,” states Siddiqui. “Our products come with an audio alarm, which has alerts for both high and low inputs. These stabilisers will automatcally cut off with high and low voltage, and have a single phase preventer and over voltage protection,” adds Siddiqui.

Akil Siddiqui, marketing manager, Cosmostat Industries

Established in the 1990s, Servokon has come a long way and manufactures servo stabilisers from 1kVA to 5000 kVA. “We offer a wide gamut of products such as servo voltage stabilisers, servo controlled stabilisers, automatic voltage stabilisers and many more. Our range of equipment is specially designed to give high performance and is extremely efficient, durable, accurate and user friendly. Owing to their qualitative features, our products are widely in demand by industries, schools, other educational institutions, hospitals, hotels, malls, etc,” says Kamruddin. “Besides, our products are approved by reputed national inspecting agencies like Engineers India Limited (EIL), Department of Industries (Haryana) and RITES, adding to their credibility. We have also been accredited with the ISO 9001:2000 certification,” he adds.

Technological innovations

Despite the servo stabiliser sector in India having matured a little over time, not many technological innovations have taken place. Says Garg, “These days, manufacturers have replaced age old logic control cards with a brand new technology—microcontroller-based control drivers. The whole circuit has been made compact and put inside a microcontroller, which has been made programmable. The same microcontroller will work in any capacity of servo stabiliser. These also need no maintenance. Another technological change is that ‘EI’ core designs have been replaced with ‘MITRED CRGO’ core designs for buck boost transformers. This provides the best efficiency.”

Dhawan, however, advocates that double wound buck boost transformer can be eliminated and instead a tapped auto transformer (TAT) can be used to improve the efficiency and save energy. “We have eliminated the buck boost transformers as it improves efficiency by 3 per cent. We use TAT design, which gives efficiency up to 99.9 per cent at certain positions against 97-98 per cent in buck boost transformer designed stabilisers. ISI is being approached for incorporating standard on TAT design of servo stabiliser.  We have designed stabilisers upto IP 54 environmental protection and that can be placed in the sun, rain and on rooftops,” adds Dhawan.

An ISO 9001 certified unit, which does 20-30 per cent exports every year, Green Dot is trying to shift to hybrids of static and servo stabiliser for faster speeds of correction and other gains. The future servo stabilisers will have technological breakthrough as they have copper contacts instead of carbon contacts along with inter turn shorting current blocking technology (ITSCB). These will provide life long non-wearable current collection system and virtual no heating on load for high value currents. Basically, even stabilisers upto 500 kVA and 1000 kVA will not incorporate transformer oil. Rather in sleek panel design, stabilisers with no wave shape distortion or use of ISBT incorporating inverter based voltage stabilisers will be the future of this line.

“Working hand in hand with technology and innovation, we have developed the most futuristic servo stabilisers, which are suitable for inconsistent voltage and moist humid/dusty environments,” points out Kamruddin. “We have now shifted to digital microcontroller based stabilisers from analogue meters. All our servo stabilisers come with the auto cut system,” he adds. Servokon manufactures all the components required for the servo stabilisers. “This helps us to maintain the highest level of quality, and most importantly, we can ensure delivery on time,” he adds.  “People are experimenting with new technology but so far have not been successful. Some have made it with IGBT based transformers but it is not economical,” says Adhikari.

Tips for buyers

Since the servo stabiliser industry is unorganised, buyers should be very careful while making a purchasing decision. The credibility of the company should be looked into, and it is also essential to have some knowledge about the product.  “Before selecting the stabiliser, the customer needs to know how much power they use. By taking an inventory of all the essential electrical loads and doing a basic electrical load evaluation, one can get a good idea about how much power a system needs. One also needs to know about the power fluctuations, that is, t he maximum and minimum voltage that you get from the main AC supply, says Siddiqui.

Says Garg, “While ordering servo voltage stabiliser care should be taken to ensure that servo voltage stabiliser capacity is 20 per cent more than maximum load. Always ask for break down voltage (BDV) test report for the transformer oil being filled in the unit. Buck boost transformer should have been designed with ‘MITRED CRGO core’ for better efficiency of the product. Also, insist on having a complete testing as suggested in the standards. Last but not the least, one must make sure that the manufacturer has used all branded products, especially AC synchronous servo motors. This is one of the prime components of the stabiliser.”

The price of a servo stabiliser depends on certain major factors at the customer’s end. These are the maximum load capacity (kVA), supply voltage (both on the minimum and maximum), and the type of cooling (air/oil cooled). Says Adhikari, “Sometimes, buyers don’t know what their requirements are. We have to go and inspect their site and suggest the appropriate capacity of the servo stabilisers.”

Adds Kamruddin, “Sometimes customers give us wrong specifications and when the stabiliser fails to handle the load, they blame us. So we send our engineers to the site of installation and come up with our own specifications.

“Buyers usually look for low cost products,” complains Dhawan. “In such a scenario, manufacturers go to the extreme and try to compromise on quality, but we are determined about our quality standards and do not compromise on it. Hence, we try to educate the customers and advice them not to go beyond certain specifications; that low cost products will prove to be expensive in the long run,” sign off Dhawan.

Different applications of servo stabilisers

  • Communication devices: Radio transmitters, televisions, cameras, video recorders, radar navigational devices
  • Computers and calculating machines: Personal computers, workstations, servers, peripherals like tape and disc devices, printers, card punches, unit recording machines
  • General laboratory equipment: Spectrometers, photographic processing equipment, chromatographs, etc
  • Electro medical equipment: X-rays, intensive care units, electro cardioscope, sterilisers, etc
  • General office equipment: Duplicating machines, photocopiers, telex machines, faxes, teleprinters, phototypesetters, general heating, lighting, production and process control equipment
  • CNC machines, air compressors, textile machines, lightings, X-ray and medical equipment, engineering units, computers, pump sets, transmitters and many other similar applications

Source: Piyush Electronics & Eletricals (P) Ltd

Advantages of using servo stabilisers

  • Quick, steady and accurate correction of voltage
  • Constant output voltage, despite load current variations
  • Balanced output voltage, irrespective of unbalanced input
  • Overall energy saving—above 98 per cent efficiency
  • Increased life of your equipment, reduced heating
  • Operational features include additional metering, surge suppression, voltage cut off, low and high voltage overload protection by MCCB or MCB
  • Single phase prevention, bypass of servo with main line, audio visual alarms, inbuilt isolation transformer, etc
  • Corrects voltage fluctuations before it can damage your machines
  • Gives perfectly stable output even under severe conditions of unbalanced voltage

Major components of servo voltage stabilisers

  • Auto transformer/variac/dimmerstat
  • Buck boost transformers
  • AC synchronous servo motors
  • Microcontroller based control drivers

Source: Piyush Electronics & Electricals (P) Ltd

Types of servo stabilisers

  • Manual
  • Semi automatic (logic circuit controls, older technology)
  • Fully automatic (microcontroller based control drivers) –air cooled and oil cooled

Products Information

Name of manufacturer

Types of servo stabilisers

Price range

Important features

Contact details

Cosmostat Industries

2 kVA to 2000 kVA

Price varies depending on maximum load capacity, supply voltage, and cooling type (air/oil cooled)

Solid state technology, audio alarm, automatic cut off with high and low voltage

Mob: 9311442855, Email: [email protected], Website:

Green Dot Electric Ltd

2 kVA to 2000 kVA


Microcontroller based, soft start function and surge protection a LV/HV/OL/IPH/R. Ph cut offs for 3 independent motor controls & air cooled upto 1000 kVA & optional isolation/ultra isolation transformer

Ph: 26222088

Mob: 9810117725,
Email: [email protected], [email protected],


NPP Energy Ltd

1 kVA to 1000 kVA


Voltage limit indicator, accuracy of 0.5% to 1%

Mob: 9355587062, Email: [email protected], Website:

Piyush Electronics & Electricals (P) Ltd

0.5 kVA to 1500 kVA


Microcontroller based, fully programmable, high efficiency, computerised design

Mob: 9711811306, Email:[email protected], Website:

Servokon Systems Ltd

1 kVA to 5000 kVA


High performance, extremely efficient, durable, accurate and user friendly

Mob: 9310630786 Email: [email protected]


Note: The names of companies are in alphabetical order

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