A Brief Discussion On The Application Of Tension Clamps In Circuits
In the construction of 10kV and below power lines, tension clamps are often used at power line terminal poles, branch poles, tension poles, and corner poles. Commonly used tension clamps include bolt-type aluminum alloy tension clamps (NLL) and forgeable cast iron tension clamps (NLD). Their main specifications are as follows:
The selection of Load isolation switch is mainly determined according to the different conditions of the power line conductors. There are two common situations.
1. Selection of line tension clamps when LGJ and LJ conductors are used.
When LGJ or LJ conductors are used, since the tension clamps are clamped on the outer diameter of the conductor when used, the type of tension clamp used should be selected according to the outer diameter of the conductor. For example, LGJ-185/30 conductors are used in power lines. After calculation, it can be known that its outer diameter is 18.88mm. From the above table, it is known that the tension clamps that should be used are NLL-4, NLL-5 or NLD-4.
It should be noted that the outer diameter of the LGJ conductor is calculated by adding the aluminum wire cross section of 185mm and the steel core cross section of 30mm, not simply by the aluminum wire cross section of 185mm. LGJ conductors of the same specification have different steel core cross sections and conductor outer diameters, so the tension clamps used for LGJ conductors of the same specification are not necessarily the same. If it is an LJ conductor, since it does not have a steel core, the cross section of the aluminum stranded wire can be used to calculate the outer diameter of the conductor.
In addition, since the tension clamp is clamped on the outer diameter of the conductor, we require the outer layer of the LGJ or LJ conductor to be wrapped with aluminum tape during construction to prevent damage to the conductor during crimping.
2. Selection of line tension clamps when using insulated conductors.
In densely populated, tree-rich, and polluted areas, we are increasingly using insulated conductors to replace bare conductors. Compared with bare conductors, it has the advantages of high safety and reliability, reduced line loss, and less corrosion of the conductor. When using insulated wires, we need to pay attention to the fact that the tension clamp is clamped on the outer diameter of the "wire" rather than the outer diameter of the "conductor" when used, so the model of the tension clamp used should be selected according to the outer diameter of the wire rather than the outer diameter of the conductor. For example, in the power line, JKLGYJ-150/8 steel core reinforced cross-linked polyethylene insulated overhead cable is used. After calculation, it is known that its conductor outer diameter is 15.30mm. Adding its insulation thickness of 3.4mm and conductor shielding thickness of 0.5mm, it can be known that its conductor outer diameter is 23.1 mm. According to the above table, the tension clamp that should be used is NLL-5. If we select the equipment clamp based on the conductor outer diameter of 15.30mm at this time, then the selected equipment clamp cannot be used at all.
In addition, when installing the tension clamp, we must tighten the screws evenly, and require that there is no increase in the stress of the wire at the contact surface between the installed wire and the metal original, so as to prevent the wire from being damaged by breeze vibration or other wire oscillation and ensure that the gripping force of the tension clamp on the wire is not less than 95% of the wire breaking force.
