Transformers; types, design, efficiency, reliability.

This course is about the case study dealing with the investigation on the causes of a failure of 400 kVA, 23/0,4 kV MV/LV dry type cast resin transformer feeding an office building of a bank group located in the center of Milan (Italy).

The fault occurred following planned maintenance works that required the whole installation to be switched off. The failure resulted in half the building being cut off power for 2 days. The reason of the fault has been found in the design of the transformer.

The course is going to present method of failure investigation in power transformers.

On July 1st 2015 the new European Regulation N 548/14 on power transformers entered into force. Also, it is the first time ever in the World when minimum energy performance of large power transformers has been regulated.

The Regulation establishes ecodesign requirements for placing on the market or putting into service power transformers with a minimum power rating of 1 kVA used in 50 Hz electricity transmission and distribution networks or for industrial applications.

Transformers are strategic assets in the electrical networks, playing an important role in achieving the ambitious energy efficiency targets set by the most industrialized countries. Considering Europe only, 16,7 terawatthours (corresponding to 3,7 megatons of CO2) will be saved in 2025 through reduction of no-load and load losses.

Although transformers are among the most efficient electrical devices, even slight improvements in their energy performances shall be highly valued, considering the amount of installed units and the fact that they are designed to operate for decades before being replaced.

In this lesson the requirements, the exceptions and market surveillance consideration of the regulation are presented and discussed in details.

The criteria for choosing the right transformer for given application have both technical and economic character. The main electrical parameters used to specify a transformer are:

  • rated power (and overload conditions)
  • rated voltage of the primary and secondary winding
  • short-circuit voltage
  • values of load and no-load losses

Another distinctive element is the choice of the type of transformer, dry or liquid immersed with implications for transformer rating. Specifying transformer ratings is related to network conditions such as:

  • loading
  • voltage and short-circuit values required in different places in the system
  • availability and continuity of supply
  • power requirements from particular loads
  • location of the loads in relation to the choice of the best (barycenter method) location of the transformer

This course gives overview how to include working conditions in specification of the transformer ratings.

Transformers are strategic assets in the public electrical networks and in private electricity systems, playing an important role in achieving the ambitious target set by the countries committed to global energy saving and emission reduction targets. In Europe only the cost-effective improvement potential through more efficient design has been estimated in about 16,2 TWh per year in 2025, which corresponds to 3,7 Mt of CO2 emissions.

Although transformers are among the most efficient electrical devices, even slight improvements in their energy performances shall be highly valued, considering the amount of installed units and the fact that they are designed to operate for decades before being replaced. In this context, energy performances can be regarded as a crucial accelerator for the penetration of new ideas and innovative solutions in the transformers business. In this course, the present energy performance programs running in different countries are reviewed, paying particular attention to the European market and recent EU Regulation no. 548/14.

Losses in transformers decide about their energy performance and although transformers are yet efficient devices the potential for energy saving is nearly 50% when considering all operating units globally. The focus will be energy losses in power transformers with particular reference to medium and low voltage units. Selecting the value of losses is a decision mainly of economic nature because losses are the main operational cost and higher the cost of electrical energy, higher the importance of losses. In this context it’s important to understand that:

  • No-load losses depend mostly on construction methods of the magnetic core (type of material and technology) and such operating conditions as magnetic induction, voltage and frequency at the same time they are independent of the load
  • The load losses depend on the characteristics of the windings as well as on the load

In principle, lower the losses, more benefits from the transformer, but the life cycle cost analysis is generally carried out by determining the capitalized cost of the unit which consists of:

  • The capitalized cost of the installed transformer (transformer cost and cost of installation)
  • The capitalized cost of the losses.

The analysis is going to determine the trend of losses over the life of the transformer, depending on the type of intended use (load chart, periods without load and out of service, future load growth), combining losses with the cost of energy which depend on the type of supply or generation cost. The course delivers methodology necessary to perform such life cycle cost analysis.

The design of a transformer requires not only electrical knowledge but also mechanical and heat engineering skills. For the success of a project the electromagnetic as well as the mechanical and thermal calculation are equally important and none of them can be neglected.

Furthermore, the study of any electrical construction is not a problem of pure physics, but an engineering challenge and involves economic equations which bring two contradicting criteria; the minimum cost of construction and the minimum cost of ownership into design considerations. As in many other engineering activities, designing a transformer is not a simple application of mathematical formulas. In such a case all transformers would have been identical.

This lesson gives an overview of the main issues involved in the design of power transformer in order to provide the students with the tool for understanding the power transformer build up and operation as well as main sizing considerations.

Transformers are an essential part of the electricity network: they convert electrical energy from one voltage level to another. This course is introducing the subject of transformers. The intention of the whole series is to promote lifecycle thinking when procuring transformers. Therefore, the focus will be on energy performance, reliability, asset management. This course covers:

  • Classification of power transformers
  • Principles of operation
  • How to order transformers
  • Technical reference standards
  • Main functional characteristics and corresponding requirements
  • Peculiarities for different applications

This lesson gives an overview of all main characteristics of Power Transformers in order to provide the students a powerful tool for power transformer proper selection.