Improving availability of distributed PMU in electrical substations using wireless redundant process bus

Protection and measurement systems in electrical substations are requested to have high availability. When considering an all-digital substation protection system, all the components and infrastructure devices (instrument transformers, processing units, merging units, intelligent electronic devices, communication network and synchronization source) contribute to the overall availability level. In particular, in this paper the availability of a distributed phasor measurement unit inspired by the standards IEC 61850, is investigated. A cost-effective solution to enhance distributed PMU reliability by means of redundancy using an IEEE 802.11 wireless network is proposed. The process bus has a wireless backup for both time synchronization protocol and sampled values packets carrying measurement information. Results are reported for a wireless network that uses software based timestamping for PTP synchronization.