Because electrical utility companies carry out such a large proportion of their operational work on live equipment, this is justification for a separate chapter to be written to highlight some of the challenges of arc flash hazard management. I produced a report into electrical flashover incident energy for Northern Powergrid in 2010 and the work was seen as ground-breaking by peers in the industry at the time. I believe that the report, and the subsequent approach by Northern Powergrid led to a hugely successful outcome which is something that I would like to share in this chapter.
11.1 So, what makes electrical utilities special?
Live work is routinely carried out on overhead lines and low voltage cables and equipment in a way that is seldom seen on industrial and commercial electrical installations. In fact, the majority of work on low voltage systems is carried out live, and the justification for live working is a balance between the risk to consumers and the risk to employees. Management of the arc flash risk is broadly organised by competence, training, rules and protection.
Operations that are fairly unique to electrical utilities are; a) live low voltage underground cable jointing where skilled employees have to prevent the risk of electric shock and burns in all weathers and often hampered by traffic and the general public, b) low voltage overhead work given the same other hazards as well as work at height by climbing or access platforms, c) link box procedures which often involve manually paralleling supplies from different transformers, d) working on open framed live low voltage feeder pillars and e) high voltage live line work. Some of the above operations are frequently carried out under emergency situations brought on by weather related events. This can mean that employees are working in the teeth of a gale.
11.2 Project Overview
Northern Powergrid owns, constructs, maintains, repairs, and replaces assets for electrical distribution across the North East, Yorkshire, and North Lincolnshire region of the United Kingdom to 8 million people across 3.9 million homes and businesses. Its network consists of more than 61,000 substations, has around 30,000 kilometres of overhead lines, almost 67,000 kilometres of underground cables and has over 2000 employees. Northern Powergrid’s network has a connected transformer capacity of over 38,000 MVA that operates at voltage ranges from 132 kV down to 240 volts.
The company was reviewing personal protective equipment (PPE) procurement with a view to rebranded uniforms and commissioned the project in order to assist in the design of clothing systems and arc protection. The objectives were:
- To determine incident energy levels as part of a risk assessment strategy for a variety of work tasks by putting together a number of scenarios and circuit configurations.
- Link the above calculations into personal protective equipment requirements to protect against personal injury from electrical flashover.
Working with the Northern Powergrid Field Standards Division, various models were developed to simulate system conditions against site activities and determine the estimated incident energy levels that could be encountered by employees undertaking work on or near energised equipment on the Northern Powergrid system. Various working activities and complex network configurations were examined to create data on which future PPE requirements could be designed and also provide further information for risk assessments. The modelling took place on the low voltage (400 volts) and secondary high voltage (11,000 and 20,000 volt) networks.
The first question was, how to carry out the prediction part of the 4P approach to arc flash risk assessment? It was a hugely complex interconnected network after all, and there was some initial doubt about whether meaningful results could be produced. I was helped by two factors. Firstly, the willingness and cooperation of directors, managers and frontline employees to engage with the project, and secondly, like most distribution networks within the UK, a conservative approach had been adopted towards their construction over the years. This meant that systems, and therefore circuit configuration and protection tended to follow well trusted norms.
Working to the above strategy, various models were created to simulate site activities. This would determine incident energy levels as part of a risk assessment strategy for a variety of work tasks by putting together a number of scenarios, tasks and circuit configurations. The calculations would be useful in informing preventative strategies and indeed produced some surprising information in respect of the effects of fault levels and working distances. This would eventually link the above calculations into Personal Protective Equipment (PPE) requirements to protect against personal injury from electrical flashover.