Latest servo stabilisers and CVTs are smarter, more energy efficient and have longer life span

Today, these products are packed with features like IC controlled circuits, high and low voltage cut-offs for compressor protection, and time delay between shutdown and restart for additional safety to connected equipment. They are also easy to install and operate

By Kartiki Negi

Tuesday, October 07, 2014: Servo stabilisers are very reliable and are known for their durability. They are compact and quite portable; hence, they are suitable for applications like computing, entertainment, aerospace, etc. Constant voltage transformers (CVT), on the other hand, effectively regulate voltage variations, suppress transients and bridge short interruptions/dips.

The latest in the market

Both CVTs and servo stabilisers have unique advantages. A servo stabiliser automatically corrects voltage at regular intervals. When supplied with constant voltage, synchronous motors operate very efficiently. They protect expensive equipment from the menace of voltage fluctuations, thus lowering the cost of maintenance.

The advantage of using CVTs is that they are extremely reliable and rugged since they have no moving parts. They are capable of controlling a higher input voltage range at lesser loads, unlike servo stabilisers, which have a fixed controlling range. Stabilisers have relays, which when switched cause the output voltage to be interrupted for a short time. This type of interruption or transient many not be good for computers. In comparison, CVTs ensure a clean, spike-free and controlled output voltage. “CVTs have a very short changeover time and are very smooth, while servo stabilisers are not so smooth, and the impact of this can be easily seen in instruments when voltage is very high or low. There are slight fluctuations and some noise in the instrument, which are easily visible to the naked eye,” says Yogesh Dua, director, upsINVERTER.com.

Servo stabilisers: In January 2014, Convergence Power Systems launched the SVX series of servo voltage stabilisers, which range from 1 kVA to 1000 kVA. “Our products in the 1 kVA -5 kVA range have applications in security scanning equipment, medical diagnostic equipment, packing conveyor machines, etc. Our stabilisers ranging from 10 kVA-1000 kVA find application in the domestic, industrial and machinery domains. Faster voltage correction speeds with more precise regulation are the advantages of these designs,” says Sreekumar, director, sales and marketing, Convergence Power Systems Pvt Ltd.

Elent Electronics’ servo voltage stabilisers range from 1 kVA to 50 kVA for single phase stabilisers and 5 kVA to 1000 kVA for three phase stabilisers. These variants offer features such as no output waveform distortion, fast correction of output voltage, automatic voltage-20 V/sec, auto/manual operation facility, high efficiency, etc. “These stabilisers are compact and modular, making it easy to install, operate and service,” says Ramotar Singh, director, Elent Electronics Pvt Ltd.

Cosmostat Industries’ existing servo controlled voltage stabiliser is designed and manufactured as per IS 9815 specifications for stable supply. Its fast correction ratio against quick voltage fluctuations ensures trouble-free operation for high precision electrical and sophisticated electronic equipment. It offers a rate of correction that is greater than 10 to 50 volts/second with an efficiency greater than 97 per cent. With a synchronous motor drive for high reliability, its waveform distortion is zero. It comes with an auto manual selector switch to select the mode the stabiliser needs to work in. In the event of the automatic controls failing, the unit can be used under manual control. Push button switches are used to increase and decrease the output voltage of the servo stabiliser when in manual mode.

Constant voltage transformers: In August 2014, upsINVERTER.com launched its constant voltage AVR, which is used to provide constant output for sensitive instruments and for voltage compensation. It is an IGBT-based system with an isolated transformer that has a very short changeover time compared to servo stabilisers. “Electronic equipment like spectrophotometers, PH-meters, x-ray machines and recorders are all affected by a high mains voltage, whereas refrigerators, deep freezers, incubators and other compressors are affected by a low mains voltage. Industries that run for 24 hours also get affected by voltage fluctuation. So these transformers are used to provide a regulated constant voltage to the devices. This CVT can be used to eliminate high fluctuations in AC supply and provide a constant voltage to the device,” says Yogesh Dua.

Servokon Systems’ existing HT AVR (high tension automatic voltage regulator) stabilises voltage directly on HT 11 kV or 33 kV lines and range upto maximum 5000 kVA. It is used in factories, hospitals, the IT industry, malls, etc. “This product guarantees 99 per cent efficiency; it is a highly reliable product with an expected life of more than 30 years,” says Zakir Hussain, director, Servokon Systems Ltd.

Vertex Power Solutions offers a constant voltage single phase transformer, which uses a tank circuit composed of a high-voltage resonant winding and a capacitor, to produce a nearly constant average output with a varying input. The ferromagnetic approach is preferred because of the lack of active components, and the reliance is on the square loop saturation characteristics of the tank circuit to absorb variations in average input voltage. The ferromagnetic action is a flux limiter rather than a voltage regulator, but with a fixed supply frequency, it can maintain an almost constant average output voltage even as the input voltage varies widely. Besides, the input supply is completely isolated from the output by means of an isolation transformer. This CVT is suitable for various applications like computers, data processing equipment, audio/video equipment, photo processing equipment, bio-medical equipment, telex machines, EPABX systems, fax machines, cash registers, electronic typewriters, etc.

How to choose the right product

There are several specifications one must keep in mind when buying an appropriate servo stabiliser or a CVT. One must make sure that the product has the correct specifications with regard to its rating, technical aspects like output voltage regulation, correction speed, etc.

Before selecting a servo stabiliser, one should ascertain how much power it uses. By taking an inventory of all the essential electrical loads and doing a basic electrical load evaluation, one can get a fair idea of how much power the system needs to produce.

Second, prospective buyers should be aware about the power fluctuation scenario, that is, the minimum and maximum voltage from the main AC supply. In brief, one has to select the input voltage window and the power consumption of the appliance. So, when selecting any stabiliser or CVT, the following aspects need to be checked:

• Input voltage range

• Output voltage range

• KVA rating

• Type of load: balance/unbalance

• Type of voltage: balance/ unbalance

• Type of protection required

• Type of cooling: Air/oil

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