Distribution Transformers

A distribution transformer is a transformer that provides the final voltage transformation in the electric power distribution system, stepping down the voltage used in the distribution lines to the level used by the customer. The invention of a practical efficient transformer made AC power distribution feasible; a system using distribution transformers was demonstrated as early as 1882.
If mounted on a utility pole, they are called pole-mount transformers. If the distribution lines are located at ground level or underground, distribution transformers are mounted on concrete pads and locked in steel cases, thus known as pad-mount transformers.
Distribution transformers normally have ratings up to 200 kVA, although some national standards can describe units up to 5000 kVA as distribution transformers. Since distribution transformers are energized for 24 hours a day (even when they don't carry any load), reducing iron losses has an important role in their design. As they usually don't operate at full load, they are designed to have maximum efficiency at lower loads. To have a better efficiency, voltage regulation in these transformers should be kept to a minimum. Hence they are designed to have small leakage reactance.

Power Transformers

Station & Multi-winding to suit specific needs & L.T. Transformers for generating Stations.
Upto 10 MVA ,3 Phase , Upto 33Kv , ONAN/ONAF/OFAF /OFWF Cooling

A power transformer is characterized by inner and outer low voltage winding sections and a high voltage winding section disposed there between. The low voltage windings are comprised of a plurality of pancake coils, and the high voltage winding are comprised of a plurality of conductor strands spirally wound for a plurality of coil layers. The low and high voltage winding sections are laterally spaced with the low voltage windings disposed in side-by-side positions and adjacent to the high voltage windings. The high voltage windings have a smaller turn height than the low voltage windings and have conductor strands of smaller gauge than the pancake coils of the low voltage windings.

A Power transformer is an electrical device that transfers energy between two or more circuits through electromagnetic induction.
A varying current in the transformer's primary winding creates a varying magnetic flux in the core and a varying magnetic field impinging on the secondary winding. This varying magnetic field at the secondary induces a varying electromotive force (EMF) or voltage in the secondary winding. Making use of Faraday's Law in conjunction with high magnetic permeability core properties, transformers can thus be designed to efficiently change AC voltages from one voltage level to another within power networks.

Transformers range in size from RF transformers less than a cubic centimeter in volume to units interconnecting the power grid weighing hundreds of tons. A wide range of transformer designs is encountered in electronic and electric power applications.

Furnace Transformers

Arc, Submerged Arc, Ladle , Induction ,
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.

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 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.

[earthing-transformer]

Neutral Earthing transformers are normally provided in 3-phase system, which is without neutral and earth fault protection.

Neutral earthing transformer has zig-zag (interstar) winding to achieve the required zero phase impedance. In addition an auxiliary winding can also be provided to meet the requirement of auxiliary power supply.

ONAN /ONAF cooling with conventional pressed steel radiators. The range includes up to 33 KV systems and as per the site requirements.

A Earthing ( zigzag) transformer is a special purpose transformer with a zigzag or 'interconnected star' winding connection, such that each output is the vector sum of two phases offset by 120°.
 

Its applications are for the creation of a missing neutral connection from an un-grounded, 3-phase system to permit the grounding of that neutral to an earth reference point and also harmonic mitigation, as it can suppress triplet (3rd, 9th, 15th, 21st, etc.) harmonic currents, to supply 3-phase power as an auto transformer (serving as the primary and secondary with no isolated circuits), and to supply non-standard phase-shifted 3-phase power.

Nine-winding three-phase transformers, typically have 3 primaries and six identical secondary windings which be used in zigzag winding connection as pictured. As with the conventional delta or wye winding configuration three-phase transformer, a standard stand-alone transformer containing only six windings on three cores can also be used in zigzag winding connection, such transformer sometimes being referred to as a zigzag bank. In all cases, six or nine winding, the first coil on each zigzag winding core is connected contrariwise to the second coil on the next core. The second coils are then all tied together to form the neutral and the phases are connected to the primary coils. Each phase, therefore, couples with each other phase and the voltages cancel out. As such, there would be negligible current through the neutral point, which can be tied to ground.

Hermetically sealed transformer is a transformer design which has no conservator. Here the dielectric insulating fluid in the transformer tank is completely sealed and is in zero contact to the atmosphere. The design avoids air in the transformer tank thereby avoiding sludging and oxidation of the dielectric fluid.

Hermetically sealed transformers are totally maintenance free and are particularly suited for use in exposed outdoor environments such as moisture, salt or dust laden atmospheres. They are used extensively in chemical plants, oil and gas terminals where poor accessibility makes regular maintenance impracticable. Transformers immersed in synthetic coolants are suitable for use indoors with adequate ventilation or near to the load center where oil would not be considered environmentally acceptable.

Normally these type of transformers are accommodated by devices that measure heat related volume variations. Gas cushion is used to compensate the volume variation due to heat. Normally the gas is nitrogen. This gas is thermally uncoupled from the dielectric liquid.

The CSS are designed, manufactured, fully assembled, wired and operationally tested in our workshops, therefore site works are minimal.

The CSS are compact and consist of power factor correction equipment, ring main unit / load break switch, circuit breakers, switchboards and dry / oil type transformers encased in robust enclosures with easy access to equipment. 
The CSS can be ideally installed in residential and commercial complexes, industrial environments, utilities where free space is a major constraint.

Features :

• Factory built and tested
• Easy and simple to install reducing the on-site operations
• Ready for network connection
• Design complies to IEC 61330
• Maintenance free SF6 insulated Ring Main Unit for MV networking
• SCADA compatible equipments
• Available with oil cooled/dry type transformers upto 2500kVA
• Rust, corrosion and weather proof enclosure
• Independent access for all the compartments for routine maintenance

Reactor Transformers

Air cored series & Shunt Reactor, Upto 2 MVA , Upto 33Kv, ONAN / AN
A variable transformer, reactor having a core combining at least two complete core elements with a common yoke; primary winding divided into two independently fed sets of phase coils wound in opposite direction, arranged on symmetrical legs of core elements and separated by the common yoke; secondary winding with each phase coil divided into two wound in opposite direction portions carried by symmetrical core legs, adjacent to the primary coils and separated by common yoke. The secondary short-circuited reactor winding is reduced to at least one close loop member with loop portions separated by the common yoke. The single, poly phase apparatus has at least one primary coil per set that includes a controllable device in circuit relation therewith to enable control of one primary coil relative to the other, either in current magnitude or in current phase shift. The controllable device being either a silicon control rectifier or transistor.

CLICK ON IMAGE TO SEE ENLARGE VIEW

In cast resin dry type transformers, the complete encapsulation of primary and secondary winding in epoxy resin prevents penetration of moisture into windings. The cast resin offers very good protection against adverse ambient conditions. These transformers can work without disruption of service at 100% humidity.

Due to the high grade insulation material, coils are non hygroscopic & the transformer can be switched on directly without pre-drying even after a long period of service interruption.
Contrary to the conventional dry type transformers the cast coil transformers are better in respect of impulse voltage withstand strength.

Higher dynamic short circuit withstands strength as compared to oil immersed and conventional dry type transformers because of fibre glass reinforced epoxy encapsulation. No partial discharges can occur during operation. The insulation material used is glass fibre reinforced with epoxy resin of class 'F' which can withstand wide temperature variation. Due to high quality insulation material the transformer is practically non-inflammable by an electrical arc, special fire protection measures are not required.

Due to encapsulation of coils with cast resin the coils dimensions are stable & no coil tightening is required to maintain the short circuit strength. Also no check of oil level and electrical insulation/oil is required. This leads to saving in cost on account of maintenance.
As cast resin transformers are solidly cast, problem associated with oil filled transformers like oil leakage and pilferage of oil is completely avoided.

Industrial, Substation & Distribution purpose Manufacturing range Upto 2MVA 22 KV naturally air cooled.

A dry type transformer has an iron core, vacuum pressure resin impregnated high voltage windings and low voltage windings . The low voltage winding is constructed with conductors. Dupond nomex insulating material includes an apparatus to secure the windings in place during a vacuum and pressure resin impregnation process. The result is a coil that exhibits high short circuit protection due to the tightly bond conductors comparable to completely resin encased molded transformers at a substantially reduced cost.