What is a compression dead end clamp?
A clamp used to splice conductors and ground wires by a compression process (hydraulic compression or explosive compression) is called a compression dead end clamp (also marketed in some catalogues as a dead end tension clamp or tension clamp). As a type of high tension clamp used on overhead lines, it is classified into hydraulic type and explosive-compression type.
The commonly used hydraulic-type compression dead end clamp (a form of cable tension clamp for overhead conductors) mainly consists of a body tube, jumper plate, jumper clamp, and steel anchor. The body tube is manufactured from a hot-extruded aluminum tube; the jumper plate is manufactured from a hot-extruded aluminum plate; the jumper clamp is formed by flattening a portion of the aluminum tube; and the steel anchor is generally forged from high-quality carbon structural steel.
The installation of a hydraulic-type compression dead end clamp on an energized line is shown in Figure
The steel anchor is used to splice and anchor the steel core of an aluminum conductor steel-reinforced (ACSR) conductor. By pressure crimping, the steel anchor undergoes plastic deformation, so that the steel anchor and the steel core of the ACSR become integrated as one body. After that, the aluminum strands of the ACSR and the aluminum tube are crimped to complete the compression process.
The compression dead end clamp features convenient installation, etc. (For high-voltage line applications, some suppliers may list similar products under high tension cable clamp.)Compression Dead End Clamp can be further subdivided into the following types:
Hydraulic-Type Compression Dead End Clamp for Conductors
Hydraulic-type compression dead end clamps for conductors include: hydraulic-type compression dead end clamps for ordinary ACSR conductors, hydraulic-type compression dead end clamps for (83) standard ACSR conductors, and compression dead end clamps for aluminum-alloy stranded conductors, etc. These tension clamps are widely used where reliable end anchoring is required.
Hydraulic-Type Compression Dead End Clamp for Ordinary ACSR Conductors
The structure of the hydraulic-type compression dead end clamp for ordinary ACSR conductors is shown in Figure 1.
Figure1: Structure of hydraulic-type compression dead end clamp for ordinary ACSR conductor
(a) Structure (I); (b) Structure (II)
Hydraulic-Type Compression Dead End Clamp for (83) Standard ACSR Conductors
The hydraulic-type compression dead end clamp for (83) standard ACSR conductors is also vividly called the "submachine-gun type". It is an improved type of the (74) standard hydraulic-type ACSR dead end clamp. For the improved type, the outer diameter of the steel anchor tube is the same as that of the straight tube, and the same specification of compression die can still be used during crimping. In this structure, the steel anchor ring is located at the rear of the steel tube; the ring band bears the entire tensile force of the conductor, while the steel tube only bears the tensile force of the steel core. The structure of this clamp is shown in Figure2.
Figure2 Structure of hydraulic-type compression dead end clamp for (83) standard ACSR conductor
(a) NY-150–400 hydraulic-type ACSR compression dead end clamp;
(b) NY-150–800 hydraulic-type ACSR compression dead end clamp
The (83) standard hydraulic-type compression dead end clamps for ACSR conductors include NY-150–400 and NY-150–800 types. Their structures are basically the same, as shown in Figure2.
Compression Dead End Clamp for Aluminum Stranded Conductors
The compression dead end clamp for aluminum stranded conductors consists of an aluminum tube body and a steel anchor. Figure3 shows the structure, physical product, and installation view of the compression dead end clamp for aluminum-alloy stranded conductors.
Figure3 Compression dead end clamp for aluminum-alloy stranded conductor: structure and physical product
(a) Structure of compression dead end clamp for aluminum stranded conductor;
(b) Compression dead end clamp for aluminum stranded conductor
Compression Dead End Clamp for Ground Wires
On overhead transmission lines, a load-bearing clamp that connects overhead ground wires (shield wires) by compression is called a compression-type dead end clamp for overhead ground wires (also referred to as an earth wire tension clamp). It is used for installing GJ-35 to GJ-150 steel stranded wires, and is used as the terminal fixation of shield wires on non-tangent towers or as the terminal fixation of guy wires (sometimes described as a tension wire clamp / tension wire clamps). The structure of this clamp is the same as that of the (83) standard conductor dead end clamp: the steel tube of the steel anchor only bears the tensile force of the steel core, and the entire tensile force of the conductor is borne by the ring band of the steel anchor.
Compression dead end clamps for ground wires are generally formed directly by a steel anchor, and are likewise divided into hydraulic type and explosive-compression type.
Hydraulic-Type Compression Dead End Clamp for Ground Wires
The structure drawing and physical photo of the NY-G hydraulic-type compression dead end clamp for ground wires are shown in Figure4.
Figure4 NY-G hydraulic-type compression dead end clamp for ground wires
Anti-Corrosion Compression Dead End Clamp for Steel Stranded Wires
The structure of the anti-corrosion dead end clamp for steel stranded wires is similar to that of the ground-wire dead end clamp, as shown in Figure5. It is made by sleeving an aluminum tube over the steel tube after compression, and crimping both ends. The anti-corrosion dead end clamp for steel stranded wires is a national standard series product. The model numbers include NY-50G, NY-70GF, NY-80GF, NY-100GF, NY-120GF, NY-125GCF, etc. Meaning of model code: N-dead end; Y-compression; F-anti-corrosion (with cover); G-steel stranded wire; C-single-wire tensile strength grade C (1370 N/mm²); numbers-nominal cross-sectional area of steel stranded wire. For example, model NY-125GCF indicates a compression dead end clamp suitable for steel stranded wire with a nominal cross-sectional area of 125 mm², and single-wire tensile strength grade C (1370 N/mm²).
Figure5 Structure of anti-corrosion dead end clamp for steel stranded wire
Explosive-Compression Type Compression Dead End Clamp
A load-bearing clamp that uses explosive crimping to splice conductors on overhead transmission lines and on busbars of power plants and substations is called an explosive-compression type compression dead end clamp. In addition to bearing the full tensile force of the conductor or shield wire along the line direction, it also serves as a conductor to transmit current. After installation, an explosive-compression type compression dead end clamp cannot be disassembled, so it is also called a permanent dead end clamp, i.e., the second type of dead end clamp. It must be used when installing large-cross-section ACSR conductors with a first-type dead end clamp, but the grip strength of the clamp cannot meet the specified requirements.
The structure drawing of the explosive-compression type compression dead end clamp are shown in Figure6.
Figure6: Explosive-compression type compression dead end clamp: structure drawing
When using explosive compression, either single explosive compression or double explosive compression may be used (i.e., first crimp the steel anchor, then sleeve the aluminum tube and explosively crimp the aluminum tube). Before explosive compression, strip the aluminum at the rear of the exposed steel core at the conductor end so that 10 mm of the inner aluminum layer is removed, and insert it into the anti-burn hole of the steel anchor to prevent the steel core from being burnt during explosive compression, as shown in Figure7.
Figure7: Anti-burn hole at the steel anchor outlet of the explosive-compression type compression dead end clamp
Other Dead End Clamps
Dead End Clamp for Expanded-Diameter Conductors
When splicing conductors using a dead end clamp, to ensure good quality after the metal flexible tube is compressed, the steel anchor should be inserted into the hollow metal flexible tube before the compression operation.
During installation, the expanded-diameter conductor passes through the clamp aluminum tube, then the sleeve tube is sleeved on; a filler rod is inserted into the hollow part of the inner aluminum material of the conductor; the steel stranded wire at the pulling connection end of the conductor is placed into the ring gap mentioned above and wrapped with the dead end rod; then the clamp aluminum tube is moved to an appropriate position of the sleeve tube to complete the installation.
Dead End Clamp for Large Crossings
Dead end clamps for large crossings commonly include two types: the snail dead end clamp and the lead-poured dead end clamp.
From the structural characteristics, when installing the snail dead end clamp, the conductor is wound into the snail-shaped spiral groove (3–4 turns) and then fixed by bolts. As the radius of curvature continuously decreases, the tail-end tension of the conductor will gradually decrease. At this time, the additional stress caused by bending increases, but the total stress will not exceed the allowable value. A neoprene rubber liner is provided in the groove of the snail dead end clamp to protect the conductor from abrasion. The tensile force value of the snail dead end clamp is calculated according to Eq. (3-1). The tail-end tension T2 of the conductor after passing through the clamp is borne by the bolts.
The lead box of the lead-poured dead end clamp is made of steel. During installation, first sleeve the conductor into the conical steel sleeve, then bend the strand ends into hooks, and then pour in molten lead-based alloy. After cooling, the installation is completed.
Dead End Clamp for Jumpers
To solve problems of jumpers on transmission lines such as easy overturning, electromagnetic interference, and large power loss, a dead end clamp for jumpers may be used. This clamp eliminates the potential difference between jumpers, thereby reducing power loss of the jumper, reducing energy consumption, and greatly reducing the drag of the jumper; at the same time, it also reduces the electromagnetic interference of the jumper itself, reduces the vibration amplitude of the jumper, and is beneficial to the safe operation of transmission lines.
A typical installation view of a jumper dead end clamp is shown in Figur8, which is the installation view of a 30° jumper compression dead end clamp. On 500 kV lines, for the four-bundle conductors of the jumper arranged in a square on a dead-end tower, in order to avoid impact and abrasion at the down-lead points of the upper and lower subconductors, the jumper of the upper and lower conductors adopts a 30° installation method. The structure drawings of the four-to-two jumper clamp (Group 1), four-to-two jumper clamp (Group 2), and six-to-four jumper clamp are shown in Figures9 to11, respectively.
Figure8 Installation view of 30° jumper compression dead end clamp
Figure9 Structure of four-to-two jumper clamp (Group 1)
Figure10 Structure of four-to-two jumper clamp (Group 2)
Figure11 Structure of six-to-four jumper clamp (six conductors, two downleads)
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