January 7, 2016

Test systems for automated testing of distribution transformers – Part I

Abstract Distribution transformers are used worldwide and in very large quantities as a link between regional medium-voltage networks and local low-voltage distribution systems. To ensure...

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Abstract

Distribution transformers are used worldwide and in very large quantities as a link between regional medium-voltage networks and local low-voltage distribution systems. To ensure quality, the required electrical characteristics must be demonstrated through extensive testing procedures on each distribution transformer in the production. This paper gives an overview of the equipment for automated testing of distribution transformers. There are also various options presented for a significant reduction of the required test time which can be achieved by optimizing the interaction of automatic switching devices, intelligent system control and largely intuitively designed test sequences.

Keywords: automated testing, distribution transformer, transformer testing, high-voltage test equipment, factory testing

1. Introduction

The distribution of electrical energy is divided into multiple interconnected power grids, which are operated at different voltage levels. These include, as for example in the European Union, an extra-high-voltage grid (> 110 kV), a high-voltage grid (110 kV), a medium-voltage grid (< 36 kV) and local low-voltage grids (400 V). The transmission of electrical energy and voltage matching between different voltage levels requires the use of transformers.
Distribution transformers, which are connected to medium-voltage grids, are used for general low-voltage power supply of buildings and industrial users. They are also used in cases where electrical energy that is generated in small power stations, such as solar farms or wind farms, is fed directly into the medium-voltage grid.
In contrast to large transformers, distribution transformers are produced and used worldwide on a much larger scale. From an economic point of view, the demands in terms of production and electrical testing differ greatly among these transformer types, since the time required for each production step represents a certain cost factor. Manufacturers thus strive to reduce the individual times to a technically feasible minimum. Since every single distribution transformer must undergo intensive electrical testing before it can be delivered to the customer, the test system used must also be able to perform tests within the shortest possible period of time, so that the production process is not slowed down.

2. Factory testing of distribution transformers

Together with the quality assurance processes, the routine tests that have to be conducted on each distribution transformer after production serve to demonstrate that the customers’ requirements in terms of the electrical parameters have actually been satisfied. Additional testing is conducted in the form of type tests before a newly developed transformer type can move to the series production stage. Such type tests are performed once on a prototype that is representative of the corresponding production series to demonstrate that it has all of the required properties.

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