Page 69 - 6748

A helicopter hovers between the towering pylons of an extra-high-voltage power line. In a
cradle, suspended several metres below the aircraft, stand two line men, shrouded in hooded,
stainless-steel threaded hot suits. Just a few feet away is a live electric cable, fizzing with
400,000 volts. One of the men, holding a short metal wand, reaches out towards the cable.
Pocket-sized lightning bolts arc through the air. There's no discernible electric shock, just a slight
tingling sensation. A lead is then clipped to the live cable to maintain an electrical connection
with the cradle and helicopter. The line men are now on, and maintenance work on the live
power line can begin.
c In pairs, discuss the main precautions you think should be taken during live line
maintenance work by helicopter with regard to the following hazards.
12 Collisions and snagging (getting caught/trapped)
13 Hazards from electrocution and heat
14 Mechanical failure (helicopter and equipment)
d 7.4 Krisztof, an electrical engineer, is describing live line maintenance by helicopter for a
TV documentary. What precautions does he describe for each of the three types of hazard
in Exercise 6c?

Krisztof: The main hazard, when manoeuvring a helicopter close to power lines, is the risk of a
collision with the line. So before commencing work, it's essential for the crew to have detailed
information about weather conditions, especially wind direction and speed. Operating in very
windy weather is obviously out of the question. The pilots involved in live line work are highly
trained and experienced and their expertise is arguably the
crucial factor in ensuring safety. Another hazard is snagging,
as at certain times the platform will momentarily be attached
to the power line and to the helicopter, leaving the aircraft
tethered. It's essential, therefore, that the cable is equipped
with a tension release mechanism, so that if the helicopter
pulls away suddenly for any reason, the cable can break free.
To prevent electrocution and burns from arcing currents, the
crew on the platform wear hot suits. These have stainless-steel
threads which channel the electricity around the technician's
body, allowing the 400,000 volt supply to flow between the
power line and the platform. The suits also have a fireproof
lining, to provide protection from heat. And eye protection is
worn, as a protection against flashes from electric arcs.
Again, training is one of the key factors in ensuring safety. As
a precaution against mechanical failure, the suspension cable,
platform and all associated equipment are systematically
inspected before each operation, to check for damage. And the
helicopter is maintained in line with aviation regulations. One
additional precaution is taken regarding the helicopter's
engines: only twin-engine craft are used for live line work, so
that if an engine fails, the pilot can still land safely.

7 In pairs, think of an operation you are familiar with
that requires safety precautions. Student A, you are a
safety officer; explain the precautions to a new employee.
Student B, you are a new employee. Swap roles and
practise again.

67