Failure Bunching Phenomena in Electric Power Transmission Systems

Abstract

The physical environment in which a component resides can have a significant effect on the resulting reliability of the system. This is particularly true in electric power systems containing overhead transmission lines. Extreme weather conditions can create significant increases in transmission element stress levels leading to sharp increases in the component failure rates. The phenomenon of increased transmission line failures during bad weather is generally referred to as 'failure bunching'. This condition should not be misconstrued as a common mode failure. This is an entirely different phenomenon and one that is important for multi-circuit transmission lines on single tower structures. This paper illustrates the inclusion of weather conditions in the reliability analysis of parallel redundant systems. A series of weather models are presented with application to electric transmission lines. The reliability effects of incorporating common mode failures in multi-circuit tower structures and independent events incorporating normal, adverse, and major adverse weather considerations in separated parallel line configurations are illustrated and examined.The applications described in this paper are to electric power transmission lines. The concepts of stress related failure bunching and common mode failures are, however, applicable to a wide range of engineering systems.

On the three-state weather model of transmission line failures

“…Values quoted for common mode failures in reference [1] are in the range of 0.1 to 1 per cent of the rates modelling independent failures. It is therefore acceptable from a practical point of view to define C not by equation (14) but by…”

“…(In the examples considered in reference [1], C has essentially been defined by equation (15) rather than equation (14). )…”

“…Various models were used in reference [1] to evaluate asymptotic reliability characteristics of systems of power transmission lines exposed to changing weather conditions. The weather conditions were assumed to take values in a space with three states according to a Markov process; they were termed normal, adverse, and major adverse.…”

“…The engineering aspects of the systems considered here are well covered in reference [1] and it is not intended here to justify the assumptions or to (re)interpret the results. This paper unifies and extends the models from reference [1] and descibes a method for their symbolic and numerical implementation.…”

“…This paper unifies and extends the models from reference [1] and descibes a method for their symbolic and numerical implementation.…”