Life assessment and life extension of high voltage equipment in transmission substations.

Abstract

In order to sustain transmission grid availability and reliability it is imperative that the

condition of vital and costly high voltage equipment is ascertained on a continuous or

regular basis. It is necessary to establish the effective diagnostic tools or surveillance

devices that can be used to assess equipment condition.

Emphasis has been placed on refining well-established and more novel but

developing condition assessment techniques. It is important to note that condition

assessment of equipment also allows the opportunity to predict failure. Based on a

complete and systematic assessment, the failure of defective equipment may be

evident or predicted in time, thus preventing a forced outage and loss of valuable

'system minutes'. It has also become necessary to extend the life of existing

equipment since most of them are reaching the end of their useful life. Replacement

strategies have proven to be ineffective due to financial and resource constraints

experienced by utilities.

Life extension is the work required to keep equipment operating economically beyond

its anticipated life, with optimum availability, efficiency and safety. One of its principal

components is condition assessment, with the possibility of predicting remnant life.

As a result, refurbishment projects are then raised. Refurbishment by replacement,

uprating, modifications or change of design of certain key components to extend the

life usually requires a substantial amount of capital to be invested. These projects

must be economically justified.

This thesis focuses on establishing condition assessment techniques for major power

equipment such as power transformers. Assessment techniques for instrument

transformers and circuit breakers are included, since these are commonly replaced

or modified under refurbishment projects.

An experimental investigation was carried out to determine the effectiveness of

integrating data of two diagnostic techniques i.e. dissolved gas analysis (on-line) and

acoustic detection of partial discharges. It was found that there is a correlation

between data obtained from an acoustic detection system and an on-line single gas

(Hydrogen) analyser. By integrating the data of both on-line monitoring systems, the

diagnostic process is further enhanced. In addition, the location of a fixed discharge

source was verified by using an acoustic detection system. Further, the sensitivity of

the acoustic technique to partial discharge inception voltage, relative to the

established electrical detection technique was determined for the experimental

arrangement used. The results obtained indicated that this is an effective technique

for the evaluation of activity within a transformer structure.