High voltage electrical systems can be extremely dangerous if you do not know what you're doing. Generally, high voltages are only seen in utility services, mining operations, and large industrial processing plants and therefore the dangers are not as well known as you may think. It is important for all workers, not just electrical workers to understand the safety of working in and around high voltage areas. In this article, we outline the common problems and some possible solutions when working in these high-risk environments.
You are required to understand the exclusion zones associated with high voltage equipment if you are an untrained person. This also includes work performed outside the exclusion zones, where potential may arise for the plant to incidentally contact high voltage equipment. A ‘safety observer’ is required where this is the case to monitor the operator’s movements of the plant or equipment to ensure the exclusion zones are not breached. For specifics for untrained personnel, it is important to understand the associated ‘Code of Practice – Working near overhead or Underground Electric Lines’.
For trained personnel, the dangers can be managed with the correct implementation of High Voltage Isolation and Access Procedures (HVIA). Once the purpose of the switching operations has been established, E.g/ Access High Voltage Equipment for Repairs, a switching sheet can be designed to suit the installation. The switching sheet is written by a competent and authorized HVIA technician and checked by a supervisor and the switching coordinator for potential errors. This ensures safe switching operations and no details are overlooked that may impinge on the safety of the workers.
Once the switching sheet has been approved, the first steps are to isolate, test, and earth the high voltage apparatus that is required to be accessed for works. This process is referred to as the ‘forward switching’ operations. With high voltage equipment not only is it necessary to isolate the equipment from the supply but earthing of the equipment must be implemented to discharge any residual voltages on the apparatus by nearby energized equipment. The safety of the workers is ensured using operator earthing locks and ‘Do Not Operate’ signage placed on the point of isolation.
The equipment is tested and proved de-energized, and an ‘Access Permit’ is issued to the work crews. The Access Permit Recipient becomes the person in charge of the isolation and all work crews lock onto a lock box that contains the keys from the forward switching operator earth locks. This ensures that equipment cannot be operated until all workers have signed off the permit and removed their locks from the lock box. Once works are completed, a similar permit is issued called a ‘Test Permit’. This permit allows the work crew to verify the works are complete and it is safe to re-energize. Once all permits have been surrendered and canceled the switching operators can commence the re-energization phase.
The re-energization phase of the switching is referred to as the ‘Reverse Switching’. In the reverse switching generally the same process as forward switching is followed but in the opposite order. This ensures all equipment has been returned to ‘as found’ conditions without missing any important steps. It is important to verify supply is restored and any control equipment is operational before leaving site. Sometimes the sudden loss of supply can cause electronic equipment to fail which requires re-setting (usually communications equipment).
Implementing these HVIA procedures it greatly minimizes the risk of potential hazards present in high voltage equipment and ensures the safety of all associated work groups. If your site has high voltage equipment that you are unsure how to operate safely, we can provide fully qualified and competent personnel to manage your isolations for you.