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Home | Blogs | Transformers: The Electrical Engineering Marvel
Fri Aug 16 06:45:14 UTC 2019

Transformers: The Electrical Engineering Marvel

Transformers, as the name suggests, transform electrical voltage into another level through the conversion of magnetic energy into electrical energy, and were invented in 1885, based on the theory of induction. Transformers have emerged as the primary electrical device in the power transmission and distribution (T&D) industry. The high importance of modern-day Electrical Transformer, Power Transformers and Distribution Transformers is attributable to their adaptability to conditions, versatility in range and significant advancement in design to achieve greater efficiencies in Transformer Winding and optimal induction and resistance losses. 

Structure:

The main structure comprises of a Magnetic Core made of high-permeability laminates made of silicon steel or permalloys, and Transformer Windings, usually of low-resistance Copper or enameled magnet wires, each insulated from the other as well as with the core. Core Transformers are characterized by windings surrounding the center, while the core surrounds the winding in a Shell Transformer. These Transformers need to stay cool by various means, and hence, different technologies have emerged.

Uses of Transformers:

Some of the main uses of an Electrical Transformer include changing voltage levels as per need at generation or during transmission or at the User-end changing Direct Current (DC) into Alternating Current (AC) and isolation of different electrical circuits to prevent catastrophe. 

Types of Transformers:

The underlying purpose of Transformers is to help transfers electrical energy from one circuit to another, between the Power Plants and the end-users. Hence, there is an undeniable need for various types of Electrical Transformers. They can be categorized variously based upon design, supply, purpose, use, and capacity; viz., Core Transformers, Shell Transformers, Single Phase Transformers, Three Phase Transformers, Step-Up Transformers, Step Down Transformers, Power Transformers, Distribution Transformers, etc.

 Design Basis:

  • Core Transformer - Both, the Primary and Secondary Transformer Windings are coiled outside the Magnetic Core to increase efficiencies in high frequencies. But, it has limited uses in open-air conditions.
  • Shell Transformer - The Magnetic Core surrounds the Transformer Windings, which are coiled on a central limb and therefore has one magnetic circuit that is better for higher voltage applications. But, it needs forced external cooling to dissipate energy and hence it is costlier.

 Supply Types:

  •  Single Phase Transformers - They consist of only one Primary and one Secondary Transformer Winding thus providing two different or equal voltages, and are normally used as Step Down Transformers to lower the input voltage to domestic voltage values suitable for electrical and electronic appliances and devices. Separate Single Phase Transformer units can be combined together to provide the same results as a Three Phase Transformer
  •  Three Phase Transformers - They consist of three Single Phase Transformers connected together in a fixed configuration or as the winding of three Single Phase Wires on a Single Core producing three sets of primary and secondary windings. This type is far more economical and efficient than a bank of three Single Phase Transformers and is easier to install generally used as a Distribution Transformer. The disadvantages of such a transformer are the high repair and standby unit costs.

 Purpose Types:

  •  Step Up Transformers - Power generated at low voltages is very economical. While it is possible for such low voltage electricity to be transmitted to consumer end, the transmission losses over the vast distances are substantial due to higher current, making it costly and putting pressure on generation capacities. Therefore, it is ideal for producing electricity at low voltages and transmitting it at higher voltages to the receivers. A Step Up Transformer converts the produced low voltage to a higher voltage before transmission from the generators to the Power grid.
  • Step-Down Transformers - Power transmitted from the plants to the receivers is at a higher voltage to reduce T&D losses. But such voltages cannot be supplied to consumers due to the inadequacies of end-use appliances to sustain such voltages and the safety hazards involved with such high voltage electricity. Therefore, another device or series of devices are needed to reduce the voltage to acceptable and different voltages. A Step-Down Transformer achieves this purpose.

Use Basis:

  •  Power Transformers -These transformers are generally used in transmission network for stepping up Low voltage high current to a high voltage low current and are usually big in size with high insulation levels They are suitable for high voltage (greater than 33KV) power transfer applications to the substation or the public electricity supply and act as a bridge between the power generator and the primary distribution grid. Typically Power TransformersareThree Phase Transformers.
  •  Distribution Transformers -These transformers have a comparatively lower rating and are used to distribute electricity by stepping down the voltage for domestic or commercial use. They are suitable for low voltage industrial purpose(less than 33KV) and domestic purpose (440v-220v). They are typically smaller in size, easier to transport, and easy to install. Distribution Transformers can be further categorized based on insulation or location.
  • Instrument Transformers- Also known as an Isolation Transformers, they are used to transform and step down current as well as voltage levels. Their primary use is to safely isolate the secondary winding when the primary has high voltage and current supply to protect the measuring instruments, meters, or relays. They can be further divided into two types: Current Transformer and Potential Transformer.

 Cooling Basis:

  • Oil-Filled Transformers - Transformers up to 3 MVA capacity and usually installed at power distribution sub-stations need their Core Assembly and Winding Coils to remain cool. They are immersed in oil, which circulates in and around the coils, its temperature lowered by air-cooled radiators or water heat exchangers.
  • Air-Cooled Transformers - Heat generated in this type of transformers is kept cooled through blowers and induction fans forcing colder air over the Core Assembly. 

Technological Advancement in Transformer Industry:

Power Industry has realized the urgent need to address the significant losses in Generation and T&D caused due to material, dissipation of heat and therefore, to increase efficiencies in the Electrical Transformer Industry and to reduce costs of manufacturing and operating.

Newer research and inventions have resulted in power being transported across longer power lines with higher voltages, but that has also necessitated the production of better designed, more reliable and higher capacity Power Transformers and Distribution Transformers with newer Technologies. 

Transformer Core:

  •  Material - Newer emphasis on thinner core material and Laser Scribing on the core grain has resulted in decreasing losses in currents at the time of generation. Also, different steel grades are being employed to respond to differential losses in different areas and reduce costs.
  • Configuration - The use of laminated cores has allowed different and asymmetric core configurations to obtain greater flexibility of shapes and sizes without compromising on its magnetic properties.
  • Lap Joints - Multiple Step Lap configuration is now being used to offset losses incurred at Limb joints of the core.

Environmental Issues:

One of the basic challenges has been to reduce noise in Transformers caused by mechanical vibrations. Recent developments in this area include:

  • Obtaining bigger Core area by reducing the density of core flux 
  • Choosing better efficiency of core material
  • Identifying frequencies of resonance by analysis of core and tank and using techniques of noise damping or redesigning of the core.

 Winding Designs:

  •  Material - There has been greater use of Copper-Silver Allow in coil wires instead of pure copper to reduce annealing and to increase short circuit withstanding capacities.
  •  Conductor Bundling - Newer technical discoveries have resulted in trans-positioning of bundled conductors to reduce circulating current problems.
  •  Conductor Bonding - Newer Epoxy coating material are being used to bond the conductor bundles to add withstanding strength against separation due to short circuits.
  •  Insulations- Highly advanced Cellulose insulation tapes and laminated pressboards are being employed for windings to withstand higher temperature degradations.

Insulation Systems:

  •  Oils - Natural esters are in advanced stages of testing in Power Transformers as they have a higher flash point, lower costs and lesser flowability in leakage situations than normally used mineral oils.
  • Gas to Liquid- Synthetically produced from Natural Gas, these new oils have low sulfur and aromatic content to provide better response, longer life, and higher conductive properties to increase transformer efficiencies.
  • Gas Insulation -Special gases, which are non-inflammable and non-explosive, are being used to ensure safety in public use. They are also less contaminable.
  • Cooling Systems -Newer designs of internal oil guides and flow ducts are helping to better transformer performance. In addition, the Oil Directed Air Forced system of cooling has proved to be most effective, especially in Large Power Transformers.

External Components:

  • Bushings - Most modern-day transformers prefer Dry Type Resin Impregnated Paper Bushings over Oil Insulated Paper to derive superior performance and reduced chances of failure.  
  • Tank - Rounded tanks demand lesser oil and are symmetrical to coil designs, providing better efficiencies; Lighter Tank material is being explored to reduce weight.

Nanotechnology:

The concept of nanotechnology is being experimented and developed as additives to the oils to improve heat transfer and resistance as also to identify and locate micro gas detectors. 

Conclusion:

The multiple advancements in Transformer Technology will benefit the global electrical community by promoting conservation of resources, reducing life cycle costs of transformers and optimizing capital costs and therefore, lowering electricity tariffs in the long run for the consumers.

 

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