Marsz Electricals Pvt. Ltd.

Vashi, Navi Mumbai, Maharashtra

MARSZ manufactures Arc, Submerged Arc, Ladle, Induction furnace transformers upto 10 MVA, Upto 33kV, ONAN / OFWF cooling.

A high current furnace transformer is provided by having the low-voltage windings arranged in a closed delta configuration within the transformer enclosure. Bus bar terminals are mounted exterior to the enclosure for providing electrical connection with the low-voltage windings.

MARSZ Furnace transformers are used to step down from voltages between 11 and 33 kV to levels of several hundred volts only. This results in massive secondary currents. As an example a 30 MVA unit at 150 V would result in a secondary current of 115 kilo Ampere. For these high secondary currents special bushings are required to connect to the bus-bars. These bushings are specified with very specific arrangements to suit the bus-bar arrangement and cooling system. Furnace bus-bars are mostly water cooled. Due to the high secondary currents and resistive losses the furnace layout is such as to limit the bus-bar length.

The MARSZ furnace transformers are then located close to the furnace itself and if they are single phase units, arranged in a triangle around the furnace. This means that there is a high risk of fire, a high ambient temperature and this whole set up is located at a level associated with the third story of the building. The location above ground level encourages single phase units due to the structural limitations of the buildings. To reduce the fire risk the transformers are contained in rooms, which adds to the high ambient temperature.

MARSZ Furnace transformers are very much used in a production environment. Loading of these transformers is then very close to rated values and even beyond. This demands very reliable transformers. Shutdowns due to transformer problems are frowned upon. When shutdowns occur, the problem needs to be solved quickly. This in turn calls for good accessibility of the tap changer and other parts of the transformer. Large inspection covers in close proximity to the tap changer are often specified.

Due to the nature of the process MARSZ furnace transformers are specified with large tapping ranges. Thirty tap positions is not uncommon. Adding to the wide tapping range is the utilisation of the tap changer. Some users require up to 800 operations of the tap changer per day. This demands high maintainability and efforts to increase the maintenance intervals. On line tap changer oil filters are thus essential. To reduce downtime further, plug-in type diverters are specified. This allows a quick changeover of the diverter switch and an overhaul in a workshop environment with more time at hand.

Another aspect of the process is the large number of short circuits that these transformers are subjected to every day. Transformers associated with open arc furnaces can be subjected to a number of short circuits per melt as the material being melted collapses across the electrodes. Bus-bar flash overs are also a fact of life on most furnace installations. To add to this peril, MARSZ furnace transformers are required to have a lower than normal impedance. This gives rise to higher over-current factors. Very robust design in terms of the transformers’ ability to withstand the dynamic effects of repeated short circuits is required. Minimum impedance values for furnace transformers of the core type are in the order of 4 – 5 %. To achieve lower values, one would need a shell type transformer. Upper levels for impedance could be any value from 10 to 24 % depending on the configuration and tapping range.

Application in following industries :

Chemical, Pharmaceuticals, Steel, Textile, Engineering, Plastic, Cement, Refineries, Mining, Captive Power Projects, Hydro Power Projects, Wind Mill Farms, Construction Houses, Pharma, Electrical, Electronics, Renewable Energy, Automobile.

“VARIVOLT“ is the most effective device meant for operation from a nominal input voltage of 240V 1Ph & can give output voltage anywhere between 0 to 240V or 0 to 270V 1Ph by simple transformer action. Three such “VARIVOLT“ connected electrically in star and mechanically in tandem, become suitable for operation from a nominal input voltage of 415V 3Ph and can give output anywhere between 0 to 415V or 0 to 470V 3Ph.

“VARIVOLT” AUTO TRANSFORMER is a continuously variable voltage auto transformer, having a movable carbon tip, fixed to brush arm sliding on a silver plated commutator. Rotation of the brush arm by either manual or motor drive, delivers an output voltage from zero to or above line voltage. “VARIVOLT” conforms to I.S. 5142.

Salient Features:

• Rugged Construction : “VARIVOLT” Auto transformers are designed for heavy duty trouble free operation. All components are designed to give maximum life to the unit under extreme operating conditions. Except for carbon tips, no other part needs any specific maintenance . Even carbon tips do not require to be changed frequently. This practically makes the “VARIVOLT” a maintenance free electrical equipment.
• Excellent Regulation : The drop in voltage from “no load to full load” is minimal in “VARIVOLT” Auto-transformers. (See fig…II for regulation characteristics)
• High Efficiency : Careful copper, core selection and design assures the user of low watt loss, as compared to other controllers. 
• No Wave form Distortion : “VARIVOLT” provides an output voltage wave-form, which is a distortionless replica of the input voltage wave-form.
• Silver Plated Commutator : A special silver plating technique is used on the commutator, enabling it to withstand high overloads and maintain constant contact drop. It also ensures smooth operation, long life and increased resistance to corrosion.
• Over-load Capacity : Because of its careful designing, “VARIVOLT” can withstand many over-loads, Fig…I gives an idea of the maximum overloading allowed with its relevant time limits. When repeated overloading takes place, care has to be exercised to provide sufficient off time to reduce the temperature build up.
• Low Operating Torque : A glass smooth commutator, special sintered bushings for the shaft and perfect assembling of coils results in low operating torque for all “VARIVOLT” Auto-transformers.
• Smooth and Linear Output : As voltage between turns is small and as the brush arm is in constant contact with more than one turn, harmful sparking is avoided and output voltage can be set to a fraction of a volt from zero onwards.
• Low Magnetizing Current : By using an adequate section of high quality grain oriented silicon steel, the iron losses in “VARIVOLT”, are controlled to the minimum. The no load current in all “VARIVOLT” transformers, is invariably less than 3% of the rated current.
• Negligible Maintenance and Trouble Free Long Life : “VARIVOLT” has been carefully designed. No special care has to be taken to maintain “VARIVOLT” auto transformers in normal working environments. The only components needing inspection and maintenance are the carbon tips and the commutator. Timely replacement of carbon tips and cleaning off foreign particles and accumulated dust, from the commutators surface, will ensure a considerably long, maintenance free, and uninterrupted life to the unit. Normally “VARIVOLT” auto transformers up to 28 Amps. are offered in air cooled or oil cooled construction. Models of 40 Amps. & above are offered in oil cooled construction. In very special cases “VARIVOLT”, above 40 Amps, can be offered in air cooled construction. This is possible due to the special paralleling techniques adopted by us.

Auto Transformers – Our Speciality :

“VARIVOLT”  is now available in high current ranges from 225 Amps. up to 2000 Amps. in single, two and three phase models. Special paralleling techniques designed by us, have made it possible to surpass the previous current limit of 200 Amps. for toroidal Auto Transformers.

The following are the salient features of High Current “VARIVOLT” Auto Transformers :-

• Special forced current paralleling techniques, result in current sharing of each coil ±2%.
• Flanged type pressed steel radiators, are supplied separately packed, making the units easy for transportation.
• Gear Driven High Torque A.C. Synchronous Motor drive.
• Terminals in the form of bus-bars.
• All other features of oil cooled auto transformers.