Latest coil transformers are more efficient and compact

While toroidal transformers are much more efficient than their conventional counterparts, switched mode power supplies (SMPS) are moving towards higher switching frequencies so that the size of the transformer is reduced. Besides, new core materials are being introduced, making coil transformers more compact and reliable

By Kartiki Negi

Thursday, August 14, 2014: The latest coil transformers available in the Indian market are mostly custom built for power electronics of higher frequencies and use thin laminations CRGO, amorphous, nano crystal or ferrite, powder iron cores. These transformers come with higher frequencies and offer higher levels of efficiency. “Transformer technology has made long-range electric power distribution practical. Without the ability to efficiently step voltage up and down, it would be cost-prohibitive to construct power systems for anything but close-range (within a few miles at most) use,” says Ashok K Jain, CEO, Anant Enterprises.

What’s new in the market

Toroidal transformers are the latest in the market. They are much more efficient than the conventional E-I variants. Switched mode power supplies (SMPS) are moving towards higher switching frequencies so that the size of the transformer is reduced. Besides, new core materials are being introduced, such as iron dust powder cores, high flux density cores, MPP cores, and amorphous cores to reduce the overall size of the transformer, thus making the assembly more compact and reliable, informs Ashok K Jain. Adds Suresh Hebbar, CEO, Electro Magnetic Devices, “Coil transformers with higher frequencies have the advantage of being more efficient, while being lighter and smaller.”

Toroidal transformers: Toroidal transformers consist of a circular ring-shaped magnetic core of a highly magnetic permeable material such as iron powder or ferrite, around which wire is coiled to make an inductor. Toroidal coils are used in a broad range of applications in AC electronic circuits.

Voltamp Controls India Pvt Ltd offers a range of high quality toroidal transformers with twin 115V AC primary windings and a wide choice of secondary voltages. The primary windings can be connected in series or in parallel to cater to 115 V or 230 V 50/60 Hz AC inputs. All leads for both primary and secondary (primary and secondary winding) are double-insulated enamelled wire that have stripped wire ends, which reduces assembly time. There are no air gaps in the core and no vibrating laminations. The reluctance is low, resulting in very low magnetising currents and savings in power consumption. Another benefit of this gapless core is the reduced level of radiated electrical noise (hum field). “The simple construction of the toroid, and the resultant lower weight compared to the conventional laminated transformers, makes this range particularly attractive for compact power supplies and slimline equipment,” says Rahul Kulkarni, design engineer, Voltamp Controls India.

Anant Enterprises also offers big auto transformers in toroidal technology with ratings up to 6000 VA.

SMPS transformers: In 2013, Anant Enterprises developed SMPS transformers for the security systems sector. These transformers are used in SMPS for CCTV and DVR systems. “Coil wound components for SMPS come with line filters, switching transformers and inductors. These line filters may be EE-, UU- or toroidal core-based, while switching transformers may be RM core, pot core or EE core-based. The switching frequency varies from 16 kHz to 100 kHz,” explains Ashok K Jain.

Potted transformers: Transformers can be potted into circular shells or potting boxes to give additional protection in adverse environmental conditions and to provide an attractive uniform package. Plastic enclosures or metal shells are used for improved electromagnetic and electrostatic screening. In February 2014, Anant Enterprises introduced a series of potted transformers for high reliability and robustness.

High frequency high voltage transformers: Electro Magnetic Devices offers high frequency transformers with amorphous and ferrite cores. “These have sandwiched interleaved coils that use thin wire bunches called litz wires. As SMPS are being designed to work at frequencies of >200 kHz, the transformers that go into them have to be carefully made so that they work efficiently at the required frequency levels. The careful selection of raw materials is also very important; otherwise, the transformer may saturate at higher frequencies,” says Suresh Hebbar. These transformers are also used in AC to DC converters (battery chargers and DC power supplies), DC to DC converters (charge controllers, buck and boosters), DC to AC converters (inverters for solar, wind-powered UPS systems, etc), and AC to AC converters, apart from drives and transmission systems.

With the advent of fast switching devices (IGBTs, FETs, etc), the switching software technology is evolving towards more efficient and compact power converters that are suited to the high frequency magnetic components.

Aluminium foil transformers: Several industries turned to aluminium as an alternative to copper wire because it is in good supply, has a stable price and is less expensive than copper. The heat storage capacity of aluminium is more than that of copper. Since aluminium wound transformers have a superior thermal storage capacity compared to copper wound units, they can withstand more surges and overload currents (normally exhibited when a motor starts) than copper units.

Unitech Transformers Pvt Ltd offers aluminium foil wound transformers that reduce overall material costs by 15 to 20 per cent. The company offers capacities up to three-phases and a voltage range of 100-800 kVA. Unitech also offers UPS system output transformers that are made using aluminium strips that are wound, which can easily be used in cars, air compressors, engineering machinery and air separation equipment, directly. They can also be used in various other products such as radiators, condensers and evaporators. They can directly be processed into different aluminium ingots aluminium strip. The firm offers capacities of 30, 40 and 60 kVA.

Alfo Electric also offers aluminium foil transformers in 1 kVA to 500 kVA power ranges. These are a cost-effective, efficient replacement for copper wound transformers.

Copper wound transformers: Voltamp Controls India offers copper wound transformers which are semi-automatic and are also called 16 kVA transformers. These transformers are known for their long service life and high performance. According to the company, the products are manufactured using very high quality raw material procured from reliable vendors in the industry.

Dry type three-phase double wound transformers: Krishna Electricals offers high efficiency three-phase dry type transformers up to 200 kVA, which the company claims are manufactured from premium quality lamination and electrolytic grade super enamelled/DFGC copper wire. These dry type transformers are also offered with cold rolled grain-oriented steel, and come with various accessories such as earthing terminals and bi-directional wheels that have low noise levels.

How to choose the right transformer

A good number of players in the market offer coil transformers for various applications. Buyers may, therefore, get confused when choosing the right product for their applications’ needs. Here are some tips that will help you to choose the right coil transformer.

• Transformers are mostly chosen depending on the applications, such as mains frequency and AC requirements in domestic and general isolation applications. “High frequency versions are mostly used by OEMs for SMPS, and in power electronics and drivers,” says Suresh Hebbar. Besides, since the life of a transformer is around 12 years, the life of the application must match that time period.

• Coil transformers should have proper voltage current ratings with suitable frequencies, insulation class (temperature) and isolation (spike or hi pot withstand-for) safety purpose with adequate margins. Low loss cores and copper enamelled conductor transformers have good efficiency and regulation when optimally designed for the given specifications.

• They should meet BIS, IEC, CE, and UL standards.

• One can also look for additional safety for thermal cut outs or overload fuses built in to avoid burn outs and fire hazards.

• One should be sure of the frequency required. A lower frequency transformer can work at a slightly higher frequency, i.e., 50 Hz can work at 60 Hz, but operating it at a lower-than-specified frequency saturates the core, resulting in large core losses and heat, which may lead to burn out.

• Current and voltage specifications should suit the application in order to work in worst-case environmental conditions and load patterns.

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