GENERATOR PHASE AND NEUTRAL REVERSAL - A COST EFFECTIVE WAY TO EXTEND THE LIFE OF YOUR WINDING -

摘要

A great number of generators was installed in the 80s and 90s in North America. With a typical life expectancy of 40 years, it is expected that most of these generators will need to be refurbished over the next 10 years. Investments made by Utilities over the last few years already confirm this tendency. Dealing with aging equipment, one of the main challenges for the Utilities is to find the best strategy to keep their units up and running, while planning for the next refurbishment. Among various maintenance options available, this paper discusses an efficient and cost-effective one, the generator phase and neutral reversal. By performing a physical inversion of the high and low voltage points within a winding, the “most-aged” bars/coils on the high voltage side are moved to the low voltage end of the winding and vice-versa. This simple and quick maintenance work can extend the life of an ageing winding. The first part of the paper will describe electrical ageing of high voltage stator windings. After discussing the available options to prevent and repair damages due to electrical ageing, the concept of the generator phase and neutral reversal will be introduced. The paper will describe what problems a reversal addresses, when it is most efficient and what its limitations are. The pre-requisites enabling a fast and effective implementation of phase reversal will be covered. We will also show how simple design features, considered at the design phase of a winding, can significantly speed-up the modifications required to implement a phase reversal. Lastly, a case study is presented: a phase and neutral reversal performed on a 28 MVA generator, with a 7 years-old winding, which solved a very high partial discharge levels issue, thus guaranteeing several years of trouble-free operation to the Owner.