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Project: T173700 #3721
 

Gradient control around bucket trucks and forestry vehicles is extremely important to ensure a safe environment for workers and the public and to protect power system equipment. Utility safety rules require bucket trucks to be adequately grounded by bonding the vehicle to the system neutral, overhead ground wires, or a ground rod. However, grounding the vehicle through a temporary ground rod may not guarantee line protection operation during a fault condition, depending on its resistance to earth. Feller bunchers, on the other hand, are constantly moving, making it impractical (if not impossible) to bond the vehicles to tower footings, wood pole risers, or ground rods. Existing standards such as IEEE and IEC provide guidance for grounding aerial devices, but these rules and procedures are not comprehensive and leave a number of unanswered questions which might result in incorrect decisions and hazardous conditions. Thus, this report: (i) provides an analytical review of the touch and step potentials around bucket trucks and tree fellers during various construction and maintenance activities; (ii) calculates touch and step potentials around tree fellers during direct contact to the energized lines; (iii) calculates touch potentials during the installation of temporary protective grounds (TPGs) in bracket grounding; (iv) calculates touch potentials on structures away from TPG, (v) identifies areas of concern regarding existing grounding practices; and (vi) provides recommendations for grounding practice to improve safety of worker around aerial devices in close proximity with power lines.

Keywords:

Bucket truck grounding, Tree feller grounding, Bracket grounding, Temporary Protective Grounds, Capacitive coupling, Inductive coupling, Touch potentials, Equipotential zones.