A strong test and maintenance program will keep protective relays in a high state of readiness and help utilities avoid equipment damage and prolonged downtime. Adjustments checking (iv) Breakers tripped by manual contact closing. Relay voltage. Relay systems protect high voltage equipment and transmission lines, providing safety and system stability. This guide provides recommended. ABB has developed a preventive maintenance concept for the well-established SPACOM, RE500 and Relion series relays. These relays have been in the market for more than 20 years.