The U.S. Environmental Protection Agency estimates losses of 60 to 80 billion kWh attributable to distribution transformer inefficiencies, which rob U.S. business and American consumers of approximately $4 billion per year. Typical distribution transformers are either core-type or shell-type. The gapless construction used in toroidal core transformers allows for smaller, more efficient, lighter, and cooler transformers with reduced electromagnetic interference and lower acoustic noise. The main technical advantage of toroidal core transformers is that the no-load loss is substantially reduced. These advantages have a greater impact for transformers that operate in lightly loaded (suburban and rural) areas because the no-load loss is very small. Since toroidal transformers can be made smaller than standard transformers, it is possible to replace oil immersed overhead transformers with dry toroidal units, reducing the potential for violent faults in addition to the environmental benefits of avoiding the use of oil.

The yearly commercial energy consumption in the federal government is about 42 billion kWh (approximately $2.5 billion). Assuming the replacement of all distribution transformers with one percent higher efficiency ones, the cost savings would be about 420 million kWh, or $25 million per year. The state and local governments annually consume about 132 billion kWh (approximately $9.3 billion) in their non-residential buildings. Hence, the potential savings are about $90 million per year. If the changeover to energy-efficient transformers applies nationally to non-governmental commercial buildings (annual electricity cost of $44.8 billion), it roughly results in savings of $450 million per year.

Toroidal transformers are not currently in use in distribution networks due to the lack of experience with toroidal design at medium and high voltages. Although it is quite well-known that toroidal transformers are more efficient than other types of transformers, manufacturers have failed to build them for high voltages compatible to power distribution grids. They have typically exhibited unacceptable failure when subjected to the “impulse test”. This test serves to give confidence to utilities that the transformer will not fail during the lightning strikes. The HIGHEST (HT) technology resolves the problem with the special patented electrostatic shield. The function of the electrostatic shield is to produce a more uniform distribution of the electrical stresses that the inter-turn and inter-layer insulation undergo during the impulse test. The HT technology enables to build a high efficiency toroidal transformer compatible with IEC and IEEE standards for dry-type distribution transformers for the first time. Currently, this technique is the only way to build the high efficiency toroidal transformers compatible with IEC and IEEE standards for dry-type distribution transformers. To the best of our knowledge, currently, there are no other academic groups or any companies developing the same technology.

The project outcomes are the new transient electro-thermal model, toroidal transformer design optimization, a new enclosure design, and establishing the Completely Self Protected (CSP) technology for dry-type transformers.

In practice the distribution power grids are subject to short-term and long-term overloads. The new transient electro-thermal model will help design toroidal transformers that will withstand such temporary abnormal operating conditions. Moreover, transient electro-thermal model will help identify overload capability of the transformers, thus, eliminating unnecessary installation of the additional units.

Design optimization study of the toroidal transformers allows to determine the most optimum design with the minimum cost.

The new enclosure design yields a compact geometry of the tank that will allow to reduce the amount of the insulating material. Moreover, experimental and computer simulation studies have shown that the new design of the tank offers better thermal performance. This will allow to design and manufacture smaller and lighter transformers with lower cost.

Currently most of the utilities prefer to purchase CSP transformers. CSP is a protection system for distribution transformers that protects the transformer against lightning surges, secondary faults, severe overloads, and provides visual warning for uneconomical loading conditions. The CSP design provides maximum protection against transformer failure and disruptive outages. It also protects the service provider from the extra costs of more complicated installation, unnecessary equipment, and power downtime. 

All CSP transformers are currently manufactured as oil-immersed transformers. This fact presents an opportunity as well as a challenge to CSP-HT. CSP system components available in the market are compatible to operate only in oil. Therefore, our task is to establish a CSP system in HT transformers according to the IEEE Standards for dry type transformers.

The main products of this project are three prototypes of toroidal distribution transformers of 7.62 kV (to be used in a 13.2 kV system) to 2x120 V secondary (standard utilization voltage); one is rated at 25 kVA and the other two at 50 kVA. Additional products include: two papers published in the IEEE Transactions, one patent has been filed, and one PhD student was supported during the execution of the project.

Last Modified: 09/06/2016
Modified by: Qiong Wu