Procedures for the Safe Operation of Helicopters in an Energized Wire Environment

This paper describes procedures for the safe operation of helicopters in an energized wire environment. The procedures are designed to respect the appropriate minimum distances that must be maintained between the extremities of the helicopter and energized and grounded parts when working on energized overhead lines and in energized substations. The required minimum distances, referred to as MAD (Minimum Approach Distances), have been derived from full-scale switching impulse sparkover tests using an MD500 helicopter insulated from the ground and operating at full throttle and with full fuel load onboard. Based on a large number of tests with the helicopter anchored to an insulating pedestal and positioned between phases of an energized line, worst-case situations were identified for two locations of the helicopter: (1) helicopter between energized phases and electrically bonded to one energized phase and (2) helicopter electrically floating (i.e., not bonded to either phase) and positioned at worst location between energized phases and between phases. Tests followed standardized testing procedures and provided the 50% sparkover voltage (crest value) U50, and the standard deviation (σ) of the distribution of sparkover voltage probability density function. The test data were analyzed and presented to experts in the live working community. The data have been adopted as the basis for inclusion in international standards (IEEE, IEC) for the use of helicopters in the energized wire environment. An example of the use of a helicopter in an energized environment is included.