A stringing block is a sheave used to support and let the movement of a cable that is being installed. It is normally used overhead but there are also particular designs used at the entrance to a channel system.
Stringing Block 6711E with standard socket suspension
The high strength Aluminum/MC Nylon stringing blocks is exactly designed for installation of distribution conductors and is usually used at the first and last span poles or on any additional distribution application where a weightier load or a greater conductor bending radius is needed such as on 45O – 90O turns or the heavy compound angles. With a diversity of suspension fittings, the 6711E stringing block can be fitted to slings, on-chain davits, or also with the voluntary adjustable base, which can be installed on cross-arms.
Features of Stringing block:
The most common features of stringing blocks are
- The Gate opening latch is a one-hand operation.
- The Gate Latch is designed for a very safe, smooth single motion hot stick operation allowing the conductor to be detached from the same side.
- Lengthy rope guards prevent the rope from snagging between the frame and sheave.
- Surrounded top to protect rope or conductor in case of any uplift.
- All edges are easily contoured to prevent damage to the rope or conductor.
- Elective grounding block with an extended shaft for ground clamp connection.
Optional Block Accessories
The accessories of conductor stringing block are
- Chain davit
- Nylon suspension for the sling.
- Cross arm base for maximum 127 mm x 127 mm cross arm.
Block Dimension:
Sheave Diameter – 508-916mm
Sheave Width – 100-110mm
Groove Radius – 254-458mm
Sheave Root Diameter – 408-800mm
Groove Depth – 100-116mm
Throat Width – 73mm
Throat Height – 86mm
Block Height – 359mm
Block Width – 194mm
Types of Conductors used in overhead electric transmission line
A conductor is one of the most significant components of overhead lines. Choosing a proper type of conductor for overhead lines is as significant as selecting economic conductor size and economic broadcast voltage. All good conductors should have the subsequent properties:
- high electric conductivity as in stringing block
- high ductile strength to endure mechanical stresses
- relatively lesser cost without flexible much of other properties
- lower heaviness per unit volume
Conductor Materials
Copper was the favored material for overhead conductors in previous days, but aluminum has substituted copper because of the much lower cost and lightweight aluminum conductor associated with a copper conductor of the same confrontation.
Following are some of the materials that are good conductors.
Copper:
Copper has high conductivity and better tensile strength. So, copper in hard-drawn beached form is a great option for the above lines. Copper has a very high current density which means more current resounding capacity per unit cross-section area. Therefore, copper conductors have a comparatively smaller cross-section area. Also, copper is sturdy and has high scrap value. However, due to its advanced cost and non-availability, copper is infrequently used for overhead power lines.
Aluminum:
Aluminum has 60% of the conductivity of copper; which means, for the same resistance, the width of an aluminum conductor is about 1.26 times that of a copper conductor. Though, an aluminum conductor has almost half the heaviness of an equivalent copper conductor. Also, the tensile strength of aluminum is very less than that of copper. Seeing combined factors of cost, conductivity, strength, weight, etc., aluminum has a good edge over copper. So, aluminum is being widely used for overhead conductors.
Cadmium-copper:
Cadmium-copper alloys cover approximately 99% of copper and 1.5% of cadmium. The addition of about 1% cadmium to copper upsurges the tensile strength by up to 50% and conductivity is condensed only by 15%. Therefore, these conductors can be useful for very long spans. However, due to the high cost of cadmium, such conductors may be inefficient in many cases.
Types of Conductors
Aluminum conductors have an edge over copper conductors seeing combined factors of cost, conduction, tensile strength, weight, etc. Aluminum conductors have totally replaced copper conductors in the above power lines because of their lower cost and weight.
Next are four common types of overhead conductors that are used for the above transmission and distribution to carry produced power from generating stations to end-users. Usually, all types of conductors are in beached form to upsurge flexibility. Solid wires, excluding for very small cross-sectional areas, are very problematic to handle and, also, they tend to set at the point of support because of fluctuation in winds.
The types are
- All Aluminum Conductor
- All Aluminum Alloy Conductor
- Aluminum Conductor, Steel Reinforced
- Aluminum Conductor, Alloy Reinforced
All Aluminum Conductor
This type is also referred to as ASC which is Aluminum Stranded Conductor. It is made up of elements of Electrical Conductor grade aluminum. This has a conductivity of about 61% International Annealed Copper Standard. Despite having good conductivity, because of its comparatively poor strength, it has limited use in transmission and rustic distribution lines. But it can be seen in urban areas for supply where spans are usually short but higher conductivity is compulsory.
All Aluminium Alloy Conductor
These conductors are made from aluminum alloy 6201 which is a high-strength Aluminium-Magnesium alloy. This alloy conductor bids good electrical conductivity with better mechanical strength. Because of the lighter weight, this may be used for distribution purposes. But it is not usually preferred for transmission and these conductors can be employed in coastal areas because of their outstanding corrosion resistance.
Aluminum Conductor, Steel Reinforced
This consists of a solid steel core with one or more layers of high purity aluminum wires wrapped in a spiral. The core wires may be zinc-coated steel. The central core provides extra mechanical strength and, henceforth, sag is significantly less than all other conductors. These conductors are available in an extensive range of steel content. These are very widely used for all transmission and distribution purposes.
Aluminum Conductor, Alloy Reinforced
This conductor is formed by packaging strands of high purity aluminum on high strength. This has better electrical as well as mechanical properties than equal ACSR conductors and may be used in overhead transmission as well as in distribution lines.