Reliability of Standby Equipment with Periodic Testing

Abstract

The reliability of standby equipment subjected to periodic testing is studied. Analytic expressions have been derived for reliability measures, such as: mean accumulated operating time to failure, mean number of tests between two consecutive failures, mean time to failure following an emergency start-up, and probability of failing to complete an emergency mission of a specified duration. These results are useful for assessing the reliability of standby equipment such as combustion turbine units of an emergency power supply at a nuclear generating station or hospital. The mean accumulated operating time to failure of the standby equipment depends on the test duration, the starting failure probability, and the mean and variance of the times to failure of an identical equipment in the continuous operation mode. It is considerably less than the mean time to failure of an identical equipment in the continuous operation mode. This is primarily due to starting failures. Bounds of the mean accumulated operating time to failure of standby equipment can be obtained from knowledge of the mean number of tests between two consecutive failures, and test duration. The mission failure probability and the mean time to failure of the standby equipment following an emergency start-up strongly depend on the probability distribution of the times to failure of an identical equipment in continuous operation mode.