Reliability implications of increased fault currents and breaker failures

Abstract

Increased power system fault currents impose stresses that may exceed the design rating of circuit breakers installed decades ago. Excessive stresses on the breakers increase their probability of failure. Breaker failures result in multiple simultaneous outages and are major contributors to system unreliability. As a result, it is desirable to quantify the contribution of increased fault currents to breaker failure. We propose a methodology that quantifies the effect of the relative statistical frequency of the different types of faults in the power system (from single-phase to three-phase faults) on the distribution of fault currents for a given circuit breaker and the implications on system reliability. The proposed work is illustrated with the IEEE 24-bus reliability test system where circuit breaker arrangements are explicitly modeled. The proposed methodology provides accurate fault current distributions through breakers (to closely reflect the expected fault conditions in the field) that help identifying common mode failures in cases of breaker failure. Applications of the proposed work include (a) identification of probabilistic models of common mode outages in real time and (b) reliability assessment of overdutied circuit breakers.

Analysis of the effect of location and failure rates of fault current limiters on substations reliability

“…Figure shows that the failure probability of Bs rises as the fault current passing through Bs increases . The failure rate of Bs depends on several factors, such as worn, degraded operation, arcing, and fault current.…”

“…4 | ANALYSIS OF FAILURE RATE REDUCTION OF COMPONENTS DUE TO USING FCL Figure 5 shows that the failure probability of Bs rises as the fault current passing through Bs increases. 21,[37][38][39] The failure rate of Bs depends on several factors, such as worn, degraded operation, arcing, and fault current. If λ B Fault current is the failure rate that occurs because of fault current passing through B, then reduction of fault current results in a decrease in the B's failure rate, because the λ B Fault current is removed.…”

Circuit breaker duty monitoring from the control center

“…This pdf is obtained using a Monte-Carlo simulation of faults that are placed in the test system one after the other, and by building statistics of the simulated fault currents using a discretized set of fault current ranges [7]. Weight factors based on the likeliness of the different types of faults (single-line, line-to-line, and three-phase) are considered too [8], as well as the dc offset and the frequency of faults on each line. An example of such a pdf is shown in Fig.…”