January 5, 2018

Internal arc testing of transformer bushings

Abstract This article discusses a special test on transformer bushings which has been introduced in the technical specifications of the Italian Transmission Operator. This test...

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Abstract

This article discusses a special test on transformer bushings which has been introduced in the technical specifications of the Italian Transmission Operator. This test is used to increase the safety in case of an internal electric arc fault in a bushing, which might explode posing threat to human life and the surrounding equipment.

Keywords: internal arc, withstand, short circuit, turret, bushing

1. Introduction

Safety is a very important factor to be taken into consideration in every area of life. In high voltage industry, where failure of electrical equipment may cause fatal accidents leading to catastrophic consequences and possible loss of life, safety aspects need to be considered from the inception of each product development.

High voltage (HV) and ultra-high voltage (UHV) plants and components play an important role in health and safety issues and the associated environmental aspects. Bushings, as components of HV and UHV systems, have been given a lot of attention in this regard and special tests have been introduced by utilities to prove their performance is safe even in drastic conditions.

All technologies that are applied in the bushing industry today have a very high level of operational reliability based on their long history and manufacturing experiences. While the traditional OIP (Oil-impregnated Paper) insulation technology is over 80 years old, the RIP (Resin-impregnated Paper) technology is more recent, but it has already reached over 25 years of service. Over the time, both technologies have been refined and adjusted in all aspects, and consequently, they are very reliable today. However, the progress in technology allows us to take further steps for improvement in other areas, including health and safety.

2. Test requirements

Recently, the Italian Transmission Operator, known worldwide as one of the leading companies in technical expertise, has taken a step in this direction, requesting to have the bushings which are able to withstand the effects of an internal arc following a failure that involves the rated short circuit current of the network.

This test is typical for other HV components, such as current transformers where the effects of an explosion due to an internal arc are really disastrous, acting as a bomb. For these components, this test has been performed for a long time and is well established by International Standards; however, it is new for bushings. A transformer bushing, even when equipped with a composite insulator which drastically reduces the effects of an internal failure, could blow out like a rocket, propelling the material or the insulator itself into the air. So, the request was made to use the composite insulators and perform an induced internal arc-fault test in order to raise the safety level of bushings against any kind of explosion.

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