The pulling and braking systems should operate smoothly and
should not cause any sudden jerking or bouncing of the conductor. Each system
should be readily controllable and capable of maintaining a constant tension.
Pullers and tensioners may be mounted separately or in groups for bundled
conductor installation.
The controls should allow the independent adjustment of
tension in each conductor. It is recommended that the tensioner have an
independently operated set of bullwheels for each subconductor when stringing
bundled conductor, particularly when more than two subconductors per phase are
being installed.
Pullers should be equipped with load-indicating and
load-limiting devices. The load-limiting device should automatically stop the
puller from acting further if a preset maximum load has been exceeded.
Tensioners should be equipped with tension indicating devices.
Capacity selection of the puller and tensioner is dependent
upon conductor weight, the length to be strung, and the stringing tensions. The
capacities of the puller and tensioner should be based on the conductor, span
length, terrain, and clearances required above obstructions.
In general, stringing tensions will be about 50% of sag
tensions. Sag tensions should never be exceeded during stringing. Tensioner bullwheels must be retarded so that
conductor tension may be maintained at various pulling speeds.
Positive braking systems are required for pullers and
tensioners to maintain conductor tension when pulling is stopped. Failsafe-type
braking systems are recommended.
There are basically two types of pulling machines used in
the construction of transmission lines being strung under tension. These are
defined as bullwheel and drum-type or reel-type pullers.
Some drum-type or reel-type pullers are available with level
wind features to provide uniform winding of the line. Some drum-type and all
reel-type pullers provide easy removal of the drum (or reel) and line to
facilitate highway mobility.
This feature also provides the advantage of
interchangeability of drums. The control of payout tension of the pulling line
is a desirable feature of many pullers.
Mobility of the pullers and tensioners is important to
minimize downtime between pulls. Also critical are the setup and leveling
features of the units.
The overhead ground wire tensioner is normally a separate
unit from the conductor tensioner as the requirements are independent of each
other.
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