DC High Speed circuit-breakers (DC-HSCB’s) and Protective Relays (PR’s) are present in all sorts of rail infrastructure. National or urban railways, tramways or metro’s, they all rely on this equipment to protect them from disastrous situations. The circuit-breakers can be installed either on board of the trains or on the trackside, in traction power substations. Protection Relays are, in most cases, part of the fixed installation. Needless to say that the DC-HSCB and PR are critical parts of the rail infrastructure. In the best case a faulty unit can cause the trains to stand still, in the worst case it can blow up parts of the infrastructure and cause casualties.
The life-cycle of circuit-breakers is long, some of the units still in operation are more than 50 years old. The first digital protective relays were introduced in the eighties. Proper testing of DC-HSCB and PR is a hot topic these days as a result of a number of incidents on various LRT and tramway systems (STEVO Electric, 2015). This paper describes some issues with testing and how to resolve them.