Why Must The Pre-twisted Wire Be Aligned With The Direction Of Force On The Pin Of The Tension Fitting?

At the construction site of power transmission lines, workers usually focus on the appearance and tightness of armor rod preformed after installation, but the direction of force on preformed armour rod and the tension fitting pin is easily overlooked. This detail directly affects whether the armor rods can achieve the grip strength specified in its design.

Mechanical Principles of Force Direction

armor rods for acsr relies on its helical structure to encase the conductor and transmit tension. When the end of armor rods transmission line connects to the tension fitting pin, the direction of the tension force must be along the helical axis of the pre-stirred wire. The gripping force of the pre-stirred fitting comes from the radial contraction of the helical segment under tension. This contraction causes the pre-stirred wire to tightly grip the conductor, generating friction. If the direction of the tension force deviates from the pin axis, bending stress will occur on the stressed side of the pre-stirred wire, resulting in uneven contraction of the helical segment, and some helical segments may even become loose.

• Reduced tension transmission efficiency: A loose helical section cannot effectively tighten the conductor.

• Local stress concentration: Abnormal load at the contact point between the pre-twisted wire and the conductor.

• Increased fretting wear: Long-term operation may lead to pre-twisted wire breakage or conductor damage.

Key control points during installation:

Pre-installation inspection:

Before installation, check if the pre-twisted wire specifications match the conductor model. The fit between the inner diameter of the pre-twisted wire and the outer diameter of the conductor is crucial; too tight will damage the conductor, while too loose will result in insufficient grip. Also, confirm that the direction of the tension fitting pin hole is consistent with the direction of force at the hanging point.

Alignment during installation:

Align the center mark of the pre-twisted wire with the installation starting point on the conductor and wrap it evenly along the conductor surface. When inserting the pull ring at the end of the pre-twisted wire into the pin, adjust the hardware position so that the pull ring plane is perpendicular to the pin. The pre-twisted wire itself has a right-hand helix; ensure the rotation direction conforms to the product design requirements during installation.

Most early failures of pre-twisted wires are not due to product quality issues, but rather to installation direction deviations. The newly revised DL/T 763 standard provides more detailed specifications for the structural types and test methods of pre-stretched wires. Field personnel must understand and implement these installation guidelines to minimize potential line hazards.