Parallel Groove Clamp(PG Clamp) Guide
Do you know what is the parallel groove clamp?The parallel groove clamp is used for the connection of small and medium cross-section aluminum stranded wire or steel core aluminum stranded wire and the steel stranded wire of overhead lightning protection wire at a position that does not bear tension. It is also used for the jumper connection of non-linear poles. Power engineering materials (fittings) are used for interconnection of connecting wires, which are mainly used in power line engineering.
Reliable power supply is an important indicator of the power supply capacity of a power supply company, reflecting the degree of satisfaction of users’ power needs, and is also an important part of assessing power quality. The reliability of line equipment is an important factor affecting the reliability of power supply. Among them, the performance of the huge number of parallel-ditch clamps running in urban and rural power grids will directly affect reliable power supply. As the reliability of the parallel channel clamp is not high, the power supply company needs to increase the number of inspections, shorten the maintenance period, and increase the operating cost. If the parallel ditch clamp causes a malfunction or accident, it can cause a large-scale blackout and threaten the personal safety of urban and rural residents.
Parallel groove clamps are all non-force-bearing types, mainly including bolt-type parallel groove clamps, H-type (or C-type) parallel groove clamps, and wedge-type parallel groove clamps. Among them, bolt-type parallel groove clamps and There are two types: equal diameter and groove clamp and different diameter and groove clamp.
Electromechanical characteristics of parallel groove clamp
According to the provisions of the national standard GB2314 “General Technical Requirements for Electric Power Fittings” and the electric power industry standard DL/T 765.1 “Technical Conditions for Overhead Distribution Line Fittings”, the grip force of the non-load-bearing parallel groove clamp on the conductor shall not be less than the calculated breaking force of the conductor 10%, the conductivity shall not be lower than the resistance of the contacted wire. At the same time, in order to ensure stability and reliability, clear requirements are made for the resistance change index after the current is passed. Meeting these requirements can ensure that the line is in normal operation or overloaded. When a short circuit occurs, the parallel groove clamp does not fail before the wire, ensuring the safety and reliability of the circuit.
The current conduction between conductors can be analyzed from two aspects: the mechanical contact area of the conductor and the current conduction path. The mechanical contact area of the conductor: From a microscopic point of view, the surface of the conductor is composed of countless uneven peaks and valleys. The smoother the conductor surface, the smaller the height difference between the peaks and valleys. When two conductors are brought into contact by an external force, the contact is mainly in the form of peak-to-peak contact. Therefore, the actual mechanical contact area is much smaller than the nominal contact area of the clamp design, and the real mechanical contact area is about 7% of the nominal contact area.
Current conduction paths between conductors:
First, under the action of external pressure, the active aluminum oxide (Al2O3) layer on the aluminum-aluminum interface of the two conductors is squeezed or rubbed to cause it to locally rupture, causing aluminum electrons between the peaks and peaks of the surface. It flows freely and forms a certain conductivity. The greater the pressure, the more peak-to-peak points of contact and the lower the contact resistance. During the wire clamp installation and construction process, it is required to apply conductive grease containing copper and silver ions on the surface of the conductor to prevent re-oxidation of the cracked point of the oxide layer.
The second is the conductivity of active Al2O3 itself, so that the undamaged area also has a certain conductivity. At the same time, under the action of the external power source, the copper and silver ions in the conductive grease further penetrate into the active Al2O3 layer, so that the conductivity of the conductive interface after charged operation is slightly increased than the initial value, and the increase is generally 0.5%-9%.
The third is due to the better plasticity of aluminum. When the two interfaces are in pressure contact, part of the aluminum in the inner wall of the clamp will be plastically deformed and enter the stranded void of the outer layer of the wire, which increases the effective contact area and causes the intermolecular The interpenetration is more active, and as the number of aluminum atoms in the oxide layer further increases, the electrical conductivity at the electrical interface is improved.
Structure of bolt-type parallel groove clamp
The bolt-type parallel groove clamp is made of plate-plate structure and aluminum alloy material. Relying on the fastening pressure of the bolt, the connected wire is fixed in the upper and lower grooved splints to complete the connection, and then transmitted through flat washers and spring washers. Provides a relatively uniform and constant pressure to the connecting wires. It can be disassembled after installation. It is often used at the jumper or ground wire lap joint at the strain end of the line. To ensure that the clamp has sufficient and even pressure on the wire, it is grooved. The clamp generally adopts a two-bolt or three-bolt structure, and the installation requires uniform force when tightening the bolts. Sometimes in order to ensure the reliability of operation, two or three clamps are connected in parallel at equal intervals during line construction. The holding force of the bolt-type parallel groove clamp to the wire is about 10%-20% of the calculated breaking force of the wire.
Bolt-type equal-diameter parallel groove clamps generally only connect wires of the same diameter. The allowable wire span generally includes two adjacent specifications. For example, JB-4 parallel groove clamps are suitable for conductor cross-sections of 185mm2 and 240mm2. Therefore, a symmetrical design is adopted in the structure.
The bolt-type reducing and groove clamp allows continuous span combination of wires with a certain diameter range. The structure adopts an asymmetric design, and the pressure plate is designed to be adjustable from left to right to ensure that both different diameter wires can be contacted. A more stable pressure is obtained, but human factors have a greater influence on the degree of bolt tightening.
Structure of wedge-shaped parallel groove clamp
The material of the wedge-shaped parallel groove line is generally forged aluminum, which is composed of two parts: a bow-shaped body and a wedge; gun-shaped special tools are used for installation or disassembly, but cannot be reused. The inclination of the two sides of the wedge is the same as the inclination of the body, so that the wire can be uniformly stressed in the contacted section and self-locking between materials can be established; the bow-shaped body provides the elastic force required to maintain a stable pressure. The radius of curvature of the inner groove of the arcuate body and the radius of the outer groove of the wedge are slightly larger than the radius of the largest applicable wire. During installation, put the two connected straight wires into the corresponding positions on both sides of the main body, push the wedge to the mark line position by manpower, and then fire the special gun-shaped tool to generate an instant thrust to press the wedge into Work bit. The pressure on the wedge is mainly determined by the amount of charge in the special bullet, which reduces the influence of human factors on the installation quality, so the installation consistency of the wedge-shaped parallel groove clamp is better. The wedge-shaped parallel groove clamp can connect two wires of equal diameter and different diameter. The gripping force of the wedge-shaped parallel groove clamp on the wire is about 20%-45% of the calculated breaking force of the wire.
Post time: Nov-05-2021