Power Transformers and Per-Units

This webinar, through slides, discussions, and numerical examples, starts with the different aspects, construction, and operation of ideal and practical two-winding single-phase transformers. The discussions start with an introduction to the characteristics and construction of ideal transformers and develop equations that relate primary and secondary voltages and currents for these transformers. Reflection of load from one side of the transformer to the other side is covered, as well as the dot notation of polarity.

Coverage continues with the introduction of real (practical) transformers along with their electrical model. Copper and core losses for these transformers are calculated, and the relation between core dimension, core permeability, and number of turns with different electrical parameters of the transformer are discussed. Two important test protocols, namely the short-circuit test and open-circuit test, which allow calculation of the most important electrical parameters of transformers, are explained.

The per-unit system, which is an important tool in the analysis of power systems, is explained in detail. The rationale for working with per-unit values and the advantages of their use are emphasized. Change of base, which is an important aspect of introducing equipment into a power network, is explained. Finally, the application of the per-unit system to three-phase balanced systems is covered.

Coverage moves on to the topic of three-phase transformers, their configurations, primary/secondary voltage and phase relations, and the application of per-unit values to circuits containing such transformers. Next, autotransformers are covered, as well as the advantages and disadvantages of their use in power networks. Coverage of three-winding transformers and their equivalent circuit and primary/secondary/tertiary current/voltage relations form the final subject of this webinar.

Each topic is immediately followed by well-chosen numerical examples and detailed steps leading to the solution of each to further enhance the learning experience of the participants. This webinar is intended for electrical engineers, as well as design personnel who are interested in learning the fundamentals of the operations of power transformers.