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.