Failure Rate Of Transformers Research Articles

Transformer real-time reliability model based on operating conditions

Operational reliability evaluation theory reflects real-time reliability level of power system. The component failure rate varies operating conditions. The impact of real-time operating conditions such as ambient temperature and transformer MVA (megavolt-ampere) loading on transformer insulation life is studied in this paper. The formula of transformer failure rate based on the winding hottest-spot temperature (HST) is given. Thus the real-time reliability model of transformer based on operating conditions is presented. The work is illustrated using the 1979 IEEE Reliability Test System. The changes of operating conditions are simulated by using hourly load curve and temperature curve, so the curves of real-time reliability indices are obtained by using operational reliability evaluation.

Development of Probabilistic Models for Computing Optimal Distribution Substation Spare Transformers

This paper presents probabilistic models developed based on the Poisson probability distribution for determining the optimal number of transformer spares for distribution transformer systems. The outage of a transformer is a random event and the probability mathematics can best describe this type of failure process. The developed models have been illustrated using illustrative 72-kV distribution transformer systems. Industry-average catastrophic transformer failure rate and a 1-year transformer repair or procurement time have been utilized in the examples considered in the paper. Among the models developed for determining the optimum number of transformer spares, the statistical economics model provides the best result as it attempts to minimize the total system cost including the cost of spares carried in the system.

A method for modeling nonlinear core characteristics of transformers during transients

An EHV transformer's insulation system must be designed to withstand stresses generated during transient events. Computer models are employed for predetermination of these stresses. The lack of accurate and consistent computer models for use by both utilities and manufacturers, is felt to contribute to the relatively high failure rate of EHV transformers. This paper develops a detailed nonlinear transformer model and a solution method that improves the accuracy with which the effect of the nonlinear characteristic of the magnetic core during transients can be predicted. This model is based on linearization of the core's saturable characteristic during solution time intervals. This paper describes a nonlinear, single phase, detailed transformer model and its verification against measured data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lightning-caused distribution transformer outages on a Florida distribution system

The data obtained from the Electric Power Research Institute (EPRI) Research Project (RP) 2542-1 on the characteristics of lightning surges on distribution lines are presented. This project was conducted to measure the lightning-caused currents and voltages that occur on distribution lines and to quantify the distribution system damage that occurs because of lightning. During the 3 yr data-gathering period, 2448 distribution transformers were monitored. The estimated lightning-caused transformer failure rate was 0.25%, and the estimated lightning-caused transformer fuse operating rate was 0.43%. Although these data are useful in the operation of distribution systems, further reducing the transformer failure rate will require that the exact failure mechanisms be established. It is noted that the research to determine the failure mechanisms will require a long measuring period and thus can be expected to be expensive. >