Long term performance of gas-insulated switchgear operating under tropical conditions

Long term performance of gas-insulated switchgear operating under tropical conditions

Pharmatrisanti, A.

Smit, J.J. (promotor)

Electrical Engineering, Mathematics and Computer Science

Electrical Sustainable Energy

2012-06-08

For the past two decades, electricity utilities have struggled to provide high quality electrical power to their customers while keeping on spending effectively the expenses for operating and maintaining the power system. Unfortunately, under tropical conditions, operation circumstances affect the equipment so that either its lifetime is cut shorter or its failure rate is higher. One of the affected equipment is GIS installations. Because of its important function in a power network, a need to investigate how the tropical circumstances affect the GIS installations has raised. This thesis focuses on the assessment and the understanding of how the tropical circumstances influence GIS long term performance. This knowledge is hence applied to develop a maintenance methodology for these circumstances to enable better tropical GIS performance. In order to improve the maintenance methodology, the degradation mechanisms need to be identified. FMECA method is applied so that parameters which indicate premature function loss can be defined and hence being monitored. Furthermore these degradation processes have to be controlled to attain a better GIS performance. This means that the processes have to be measured. In order to do so, series of experiments were conducted under both homogeneous and inhomogeneous electric field conditions. Gas pressure, gas humidity and gas temperature as well as electrical stresses were varied to measure the change of the electrical withstand of the insulating gas. Next, the health index and degradation level of the equipment are assessed. A model, namely condition and life assessment are introduced. This concept utilizes knowledge rules and norms obtained from field experiences as well as experimental results. To complete the model, a weighting factor is introduced to represent how high the influence of parameter or GIS system is. From our experiment we learn that the major factors of influence are the following parameters: • gas pressure • moisture content • decomposition products For these parameters the respective weighting factors were determined through experiments. In asset management strategy, prioritizing work delivery is as important as determining health and degradation levels. This can be fulfilled by conducting risk assessment both to equipment and utility’s business values. A model of risk assessment is introduced. Verification of the models is carried out by using of data of a utility which installations are operated under tropical circumstances. In addition to the verification, an example of how the models are used is given as well.

gas-insulated substations
tropical influences
long term performance

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doctoral thesis

(c) 2012 Pharmatrisanti, A.