Earthing – substation fire and station transformer customers supply transfer voltage issue

At midnight on 7 April 2010, a substation fire cut power to 1500 residences and businesses. Main Roads and the Public Transport Authority responded to ensure that traffic lights and boom gates had generators installed ready to minimise impacts to the public and traffic. Investigations established that a fault in the area and failure of the earthing arrangement lead to the fire and damaged 11 kV indoor switchgear beyond repair. During the ensuing investigation, over 45 customers were identified as being supplied from the substation station transformer, raising concerns amongst internal stakeholders about transfer voltage hazards to customers. A working group was established to respond urgently and considered various suggestions, such as installing a distribution pole-top transformer or separated earth. It was noted that if the supply arrangement to the customer needed changing, other zone substations with this particular setup would also need to be changed (significant cost implications); it was queried whether this is an unacceptable risk. Some key challenges during this project were identifying the causes of fire, realistic risk assessment, maintaining positive communication channels among stakeholders to manage risk, preventing unnecessary action and a lack of background technical information for this old substation. This paper explains the systematic problem identification process to prevent future incidences in consultation with stakeholders and a special earthing design approach for substation and distribution accompanied by field testing, which lead to a robust risk management strategy. This case illustrates that acceptable levels of people safety were in place and also the prevention of unnecessary actions, which can cost utilities and customers.