Optimization of power transformers based on operative service conditions for improved performance

Abstract

Utilities are demanding nowadays that power transformers manufacturers comply with different performance and reliability requirements in order to provide a good service to electricity consumers in terms of quality of supply in addition to other requirements in line with modern society needs of environment protection. There is an increased trend in recent years to legislate and regulate in energy efficiency, noise emissions and other environmental related aspects that are driving utilities and manufacturers to work together in different stages of the transformer life. One important goal of this collaborative effort is to achieve an optimized definition and transformer design by adapting the main requirements and specifications to the actual service conditions. This paper presents some concepts that can be used to specify, define and optimize power transformers looking at the most common service conditions where they will spend the majority of their operative life. The main associated advantages for the utilities are related to improved asset utilization (rationalized use of transformer materials with longer life expectancy because of a more balanced hot spot temperature across the regulating range, additional overload capabilities), energy efficiency and environmental benefits (optimized losses with less auxiliary consumption, reduced sound levels). Power transformers and autotransformers are typically defined and specified looking at the operative needs of a particular utility considering the adequate power rating, impedance, regulation range and using the international standards as a reference when coming to performance, tolerances, test and final acceptance. The transformer design is optimized based on the requirements and specification (losses, operating temperatures, sound level) and considering the most restrictive operative and testing conditions (i.e. in an extreme tap changer position, maximum ambient temperature), normally without evaluating in detail the performance at the most common service conditions. Under this traditional approach, the transformers will spend most of their operative lives working at the typical service conditions that are different to those used for transformer optimization. In this paper, some guidelines are presented to optimize the transformers looking at their typical working conditions exemplified with two case examples. The first one focused on the thermal balance between windings and the second related to the optimization of the cooling system and sound level, that will serve to illustrate the main advantages of the concept: • Increased life expectancy because of a balanced hot spot in all operating conditions. • Improved overloading capabilities. • Reduced noise levels in typical service conditions. • Rationalized use of transformer materials. • Reduction of overall cooling equipment power consumption. • Increased redundancy of cooling equipment.