Transmission line unavailability due to correlated threat exposure

Abstract

Blackouts in the power system are rare events that can have large consequences for society. Successful preparation and prevention of such events calls for models capable of predicting their occurrence. The simultaneous outage of multiple components is of special interest in an N-1 secure transmission grid. Spatio-temporal correlation in probability of failure for components can cause blackouts to occur more often than anticipated. This paper demonstrates a new method of calculating time-series of component unavailability due to external threats based on historical data. The time-series of unavailability can be used to predict the expected occurrence of contingencies throughout the year. A test case is presented where an hourly time series of wind dependent failure probabilities and historical outage durations of transmission lines are combined to illustrate the proposed method. The results show that the simultaneous unavailability of multiple transmission lines may be significantly larger than estimated using traditional reliability analysis.

Reliability of Supply and the Impact of Weather Exposure and Protection System Failures

“…In this section, a general and compact method for calculating reliability indices including protection system misoperations is postulated, using both approximate methods and a time-series method, based on the definitions of fault types as originally proposed in [17]. The basis for approximate methods is [34] in Section 3.1, and that for a time-series approach is [10] in Section 3.2.…”

“…These can be applied to calculate systems reliability indices for cut-sets. Two methods are presented here: an approximate method of system reliability using annual failure rates including protection system failures, and a method to calculate time series of probability of failure due to different fault types, which can be used together with [10] to calculate unavailability of cut-sets.…”

“…FT1 and FT2 are only dependent on information of the line itself and is repeated for reference here 7and (8). FT3 and FT4 are calculated by using the associated probability matrices (9) and (10). The multiplication of the matrices with the line failure rate vectors gives vectors of FT3 and FT4 failure rate contributions from all source lines at the target line.…”

“…In [10] an analytical technique is used to calculate time-series of expected unavailability of transmission lines due to wind conditions, instead of using a Monte Carlo approach. For each hour, the probability of failure of the transmission line is paired with a distribution of outage duration.…”

“…Major blackouts are often due to multiple component outages, caused by environmental factors [1][2][3][4][5], and/or dependent failures such as protection system failures [6]. The increased probability of failure of one or more components in a short period of time due to extreme weather has been termed failure bunching, and models have been developed to capture such effects in power system reliability studies by using both analytical methods and Monte Carlo simulation methods [7][8][9][10]. Large blackouts are often a consequence of complex series of events, such as cascading failures [11].…”