Tommie Lindquist

Estimation of disconnector contact condition for modelling the effect of maintenance and ageing

In order to optimize the maintenance of electric power equipment, models of equipment reliability as a function of age and maintenance are necessary. As a first step towards the development of these kinds of models, this paper proposes a quantitative method for establishing the condition of disconnector contacts by the use of thermography, which is a well- established diagnostic practice used in preventive maintenance programmes. Results from two sets of thermography measurements carried out in the Swedish transmission grid are presented. Statistical distributions for the uncertainties when using the method are estimated from the measurements. A method for converting temperature rises measured at non steady state loading conditions to a corresponding steady state temperature rise have been devised using a simple thermal model. The probability of sending an unaged contact to maintenance is estimated using Monte Carlo simulations based on the statistical distributions of the uncertainties. Finally, it is shown that by using the method proposed in this paper it is possible to estimate the contact condition of disconnectors, including Monte Carlo simulated confidence intervals.

Hazard rate estimation for high-voltage contacts using infrared thermography

Infrared thermography is the most common way to assess the condition of high-voltage electrical contacts in electric distribution and transmission systems. However, thermography has one major drawback as contacts carrying low or no load may not be assessed. This paper proposes a method to save and make use of thermography measurements to estimate statistical distribution parameters for the time to failure for a population of electrical contacts. The statistical distributions may then be used to support maintenance decisions for the sometimes large proportion of contacts that may not be assessed directly due to low load. As the measurement results accumulate over the years more accurate predictions can be made. The proposed method is illustrated using three test cases applied to a population of high-voltage disconnectors with randomly generated thermography measurements. The main conclusion of the paper is that using the proposed method will provide maintenance decision support for high-voltage apparatus that may not be assessed directly by thermography.

A method for age modeling of power system components based on experiences from the design process with the purpose of maintenance optimization

This paper introduces a first step towards establishing the effect of maintenance on component reliability. The concept of relative age is introduced and defined as well as a method to establish this relative age of electric power system components for the purpose of Maintenance optimization. The proposed method is demonstrated by modeling the relative age of a sub-component for a circuit breaker (CB). The modeling is based on the results from a major CB reliability study and a survey of all CB failures in the Swedish National Grid during the period from January 1/sup st/, 1999 to July 31/sup st/, 2003. The results from this application study show that it is possible to model the reliability of power system components by using results from development tests and calculations from the design process along with failure and maintenance data.

Reliability functions and optimal decisions using condition data for EDF primary pumps

There are many examples in which proportional hazards modelling (PHM) is used to accurately model the effects of the operating environment on an items lifetime. Using such techniques it is possible to find an economically optimal moment of replacement based on condition monitoring data. However, in a nuclear power plant, the problem is somewhat different as it is not possible to stop the process and perform preventive maintenance at the most economical moment in time. The problem of interest in such cases has more to do with whether the item will last until the next scheduled plant shutdown or not. This paper presents some developed and implemented theory to calculate the conditional reliability function of an item given the current equipment age and the current values of the condition-monitoring variables. A case study of a shaft seal for a reactor cooling pump (RCP) using data from several French nuclear power plants operated by the Electricite de France (EDF) is also presented

Reliability centered asset management

This paper describes three projects aimed at the development of optimal maintenance strategies in power systems. A poster will be compiled from the information herein.