Reliability Analysis of Two Protection System Configurations for High Voltage Transmission Lines

Protection systems play a crucial role in power systems. The increasing demand for electric power leads to the complexity of the network and, therefore, to an increasing search for the improvement of the reliability of the high voltage (161 kV and over) line system protections. In order to achieve the required reliability level, the redundancy technique is often used. Two alternatives of redundancy are usually used. The first one is the use of two distance-protections connected in parallel, named as configuration {z, z}, and the second one is the use of one distance-protection and a differential-protection connected in parallel, named as configuration {z, Delta} . These two configurations are compared, in the paper, based on their calculated reliability. The comparison was made using new developed Markov stochastic models. Based on these models, the CIGRE reliability index for protection systems was computed for each configuration. It was shown that the configuration {z, z} is more reliable than the configuration {z, Delta} . Therefore, for high voltage line protection, where redundancy is required, it is recommended to use the configuration {z, z}.