Higher frequency of inspection: The current practice of periodic inspection and condition based maintenance or replacement, can be continued with a higher frequency of inspection.
The inspection frequency in the MV/MV substations can be increased to once per year. This will give the same frequency as in the HV/MV substations. A higher inspection frequency will reduce the risk of failure of a relay, but it will also give higher costs. An even higher inspection frequency will give too much workload and is not considered to be realistic.