Basic requirements for suspension clamps for power fittings

The overhead clamp of the overhead power line is used to fix the wire on the insulator string or to suspend the lightning protection line on the linear pole tower. It is also used to support the transposition conductor on the transposition tower, and the jumper is fixed on the tension and corner tower.

The national standard GB2314-1997 "General technical conditions for electric power fittings" puts forward the following technical requirements for the suspension clamp:

(1) The overhanging clamp has a drape angle of not less than 25°.

(2) The radius of curvature of the suspension clamp is not less than 8 times the diameter of the installed conductor.

(3) The percentage of the grip strength of the suspension clamps on the different conductors and the rated tensile strength of the conductors (corresponding to GB1179-1974 standard conductors) shall not be less than the values ​​in the table. The steel-cored aluminum stranded wire (corresponding to GBll7 cont. 1983) has an increased cross-section of aluminum steel.

1. Overhang angle of the suspension clamp

Due to the undulating path of the transmission line, the line spacing is different, and the load such as temperature and ice coating changes, the wires on both sides of the suspension point of the tower produce different overhang angles. The so-called overhang angle is usually the average of the overhanging angles on both sides. The transmission line passes through a flat zone, generally with a drape angle of 5°-8° and 10°-12°; when the line passes through the mountain height difference, the overhang angle can reach 20°-25°, and the overhang angle exceeding 25° is extremely Less. Specific conditions such as wire, span, height difference, etc. used in line engineering. It is ideal to design a suspension clamp suitable for a variety of different conditions of the line. However, this will not achieve the purpose of generalizing and standardizing the suspension clamp.

The current standard suspension clamp considers general general conditions, the dangling angle is calculated to be 27°, and the actual use range is 25°, below. When the actual overhang angle of the line exceeds this range, measures should be taken, such as using a double clamp, adjusting the tower position, the tower height, or designing a special clamp with a large overhang angle.

2. Holding strength of the hanging clamp

When the suspension line is in normal operation or disconnection, the conductor should have sufficient holding strength to avoid the cable slipping off the clamp after the adjacent cable is broken, resulting in insufficient safety distance for the spanning structure.

The grip strength of the suspension clamp is determined by the wire breakage tension. The thread tension is related to the maximum tension of the wire. In general, the wire breakage tension of the wire is 50% to 60% of the maximum tension of the wire; and the wire breaking tension is 40% of the rated tensile strength of the wire. The suspension clamp for overhead lightning protection line shall have a grip strength not less than half of the maximum tension of the lightning protection line.

3. Mechanical strength of the suspension clamp

The suspension line clamps under the normal operation of the line, and mainly bears the total load composed of the vertical load and the horizontal wind load of the wire. The suspension clamp shall meet a certain safety factor (k = 2.5) when the conductor is subjected to the maximum load.

The mechanical strength of the shaped suspension clamps is serialized according to the strength grade of the metal fittings, and the margin is large. Except for the extra heavy ice area, the general area can meet the requirements. Therefore, when the project is selected, it is generally only necessary to check the allowable maximum vertical span Sv of the clamp.