Short answer
The job of a tensioning device (automatic tension compensator) is to keep the tension of the contact wire and messenger wire constant while temperature changes make the conductors expand and contract, so that contact wire height, elasticity and wave propagation speed stay stable. Three common forms: pulley type (balance weights plus a pulley set, a classic layout that is easy to inspect), ratchet type (high transmission ratio with breakage braking to stop runaway, common on upgraded and high-speed lines) and spring type (stored spring energy replaces balance weights, saving ground space, common in tunnels and urban areas).
Selection points
Select by the tension class of the tensioning section (for example 10 kN, 15 kN, 20 kN or 30 kN), by the travel of the compensating rope and by the installation space available. For ratchet devices the braking performance must be checked (the distance the balance weight drops after a wire break). Spring compensators suit locations where space is tight or balance weights are awkward to install. The device body and its fittings follow the current edition of the TB/T 2075 series (Parts 12, 13, 14, 17 and 23).
Related products
Pulley tensioning device | Ratchet tensioning device | Spring tensioning device