Coordination of Power and Metal Pipelines Using Risk Based Safety Principles
Annual Conference
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Electrical power lines and substations impress continuous and transient voltages and currents on adjacent or parallel metal pipelines during normal operation of the power system and also during earth fault events. The impressed pipeline voltages present a potential risk of damage to the pipelines and dangerous electric shock to people in contact with the pipeline metal.
Power line towers and substation fences/enclosures are subject to dangerous touch voltages during fault events. The electrical power industry has developed a risk based approach to managing the safety risk to people in contact with such metalwork. It considers the likelihood of a person being present in the hazard zone at the same time as the fault event. This calculated likelihood is used to determine whether mitigation is required to eliminate the risk or reduce it to as low as reasonably practicable.
The requirements for managing the safety risk to people in contact with metallic pipelines is specified in AS/NZS4853, which adopted the electrical power industry’s risk based approach to managing touch voltage risk in 2012. This revised approach to safety risk assessment and mitigation has now been applied to extensive buried metal pipeline networks in New Zealand.
The buried pipeline networks are generally well insulated from ground, electrically continuous along their length and unearthed as this facilitates the application of effective impressed current cathodic protection. These characteristics have however made it necessary to consider a large portion of the pipeline network when assessing the impact of changes to only small portions of the power system and complicate the coordination requirements between the electrical power and pipeline utilities.
This paper describes how risk based safety principles have been implemented on metal pipeline networks in New Zealand and what data needs to be transferred between pipeline and power utilities to facilitate effective coordination.