NATIONAL INSTITUTE OF INDUSTRIAL ENGINEERING, MUMBAI

CABLE CONSTRUCTION & MANUFACTURING PROCESS

UNDER THE GUIDANCE OF

Dr. KVSS NARAYANA RAO

Submitted By

PRASENJIT HOJAI                                       SARVESH HIREMATH

ROLL NO-66                                                 ROLL NO-88

Cable Construction & Manufacturing Process

                                               fig-power cable parts

Power Cable mainly subdivided into parts-

1. Conductor

2. Insulation

3. Metallic Sheath

4. Bedding

5. Armouring

6. Outersheath

Conductor

Copper or Aluminium used for the Conductors obtained in the form of rods. The 8.0 mm Copper or 9.5mm aluminium rods. After testing, rods are drawn into wires of required sizes. These wires are formed into final Conductor in the stranding machines under strict Quality Assurance Program. 

Insulation

Cross linked polyethylene compound or PVC is insulated over Conductor by Extrusion  process.  XLPE insulated cores are cured by steam curing in vulcanizing chamber to provide thorough cross-linking.

The raw materials & thickness of Insulation are maintained under strict Quality Control and conform to B.S. 5467 / IEC 60502 Part-1 or B.S. 6346 / IEC 60502 Part-1 Standards for XLPE & PVC cables respectively. 

Laying Up

The insulated cores are laid up with a right hand, or alternating left & right hand, direction of lay in the sequence of the core numbers or colours. Where ever necessary non-hygroscopic PP / PVC Fillers & binder tape are used to form a compact and reasonably circular cable. 

Bedding

All armoured cables have extruded PVC bedding. The PVC used for bedding is compatible with the temperature of Insulation material. 

Armour

When armouring is required, the armour consists of single layer of Galvanised steel wire. The armour is applied helical, with a left hand direction. We also provide other armours such as steel strip, tape or tinned copper. Single core cables are armoured with Aluminium or copper wires.

OuterSheath

The standard cables are manufactured with Extruded black PVC Type-9 of B.S. 7655 or ST-2 of IEC 60502. Outer sheath is embossed or printed with the information required by the related standards. Special FR, FRLS compounds are used for outer sheathing of cables, to suit customer’s specification requirements.

Cable Manufacture

An extruded cable production line is a highly sophisticated manufacturing process that must be run with great care to assure that the end product will perform reliably in service for many years. It consists of many sub processes that must work in concert with each other. If any part of the line fails to unction properly, it can create problems that will lead to poorly made cable and will potentially generate many metres of scrap cable. The process begins when pellets of insulating and semiconducting compounds are melted within the extruder. The melt is pressurised and this conveys material to the crosshead where the respective cable layers are formed.  Between the end of the screw and the start of the crosshead.it is possible to place meshes or screens, which act as filters. The purpose of these screens was, in the earliest days of cable extrusion, to remove particles, or contaminants that might be present within the melt. While still used today, the clean characteristics of today’s materials minimize the need for this type of filter. In fact, if these screens are too tight, they themselves can generate contaminants in the form of scorch or precross linking.

Nevertheless, appropriately sized (100 to 200-micron hole size) filters are helpful to stabilize the melt and protect the cable from large foreign particles that most often enter from the materials handling system.

The most current technology uses a method called a true triple extrusion process where the conductor shield, insulation and insulation shield are coextruded simultaneously. The cables produced in this way have been shown to have better longevity (Figure 3) [7]. After the structure of the core is formed the cable is crosslinked to impart the high temperature performance. When a CV tube is used fine control of the temperature and residence time (linespeed) is required to ensure that the core is crosslinked to the correct level.

 Jackets

In most MV, HV and EHV cable applications, the metal sheath/neutral is itself protected by a polymeric oversheath or jacket. Due to the critical performance needed from the oversheath, there are a number of properties that are required, such as good abrasion resistance, good processability, reasonable moisture resistance properties, and good stress cracking resistance. Experience has shown that the material with the best composite performance is a PE-based oversheath, though PVC, Chlorosulfonated Polyethylene and Nylon have been used as jacket materials.

Tests on XLPE cables retrieved after 10 years of operation show that the mean breakdown strength falls by almost 50% (from 20 to 11 kV/mm – HDPE & PVC, respectively) when PVC is used as a jacket material. Many utilities now specify robust PE based jackets as a result. The hardness of PE is also an advantage when protection is required from termite damage.

Jackets extend cable life by retarding the ingress of water and soluble ions from the ground, minimizing cable installation damage and mitigating neutral corrosion. Ninety three percent of investor-owned utilities in the USA specify a protective jacket. The semiconductive jacket or oversheath is recommended for high lightning incident areas or joint-use trenches where telecommunications cables co-exist with power cables.

Inspection and Test Plan for Power Cable

The inspection and test plan for power cable article provides you information about power cable test and power cable inspection in manufacturing shop.

• Witnessing voltage and insulation resistance tests or alternative spark tests.

• For 33Kv cable, witness dielectric power factor voltage test.

• Dimensional checking on sample off-cut i.e. construction consistency, insulation thickness, external sheath screen, armours and mans of main components.

• Visual checking in respect of cable formation, core and external sheath colors, marking legibility.

• Testing on material sample i.e. conductor coating, insulation external jacket for elongation, heat strocle blending and characteristics of armour, metal and sheath components including zinc coating.

Third Party Inspection for Power Cable Configuration

Third party inspector checks the power cable configuration in accordance to drawing and datasheets. Following items is taken in account:

• Cable type
• Number of conductors
• Conductor size
• Conductor color coding
• Insulation type and size
• Fillers
• Water stoppers
• Armour
• Shield
• Outer diameter
• Other specified elements/dimensions
• Cable identification

References:-

•    Electrical Power Cable Engineering by  Bruce S. Bernstein and William A. Thu
•    L.V. Power and Control Cables by Oman Cables Industry
•   TR-101670 “Underground Transmission Systems Reference Book: 1992 Edition,” Electric Power Research Institute
•  http://ieeexplore.ieee.org/Xplore/home.jsp

Benefits of TR-XLPE Cable

TR-XLPE Cable

INTRODUCTION

                  Utility companies worldwide are striving to reduce the life cycle costs of their medium voltage distribution systems in response to economic and environmental drives. The use of tree retardant XLPE insulation has allowed utilities to achieve long service life under severe operating conditions. This has led to improved life cycle economics and has minimized social and environmental issues resulting from cable replacement activities.

                   It was recognized that XLPE, as well as other polymers, undergo a degradation process, called water treeing, when exposed to moisture and an electrical stress. Two different approaches were used, at about the same time, to solve this problem. In North America, a novel additive formulation approach was used to impart water treeing resistance. The resulting product, called additive TR-XLPE or “TR-XLPE,” was introduced in the early 1980’s and has shown excellent field service performance. In Europe, blends of polyethylene with ethylene alkyl acrylate copolymers were used to impart resistance to water treeing degradation. This product, called “Copolymer XLPE”, was also introduced in the early 1980’s and has had excellent field service performance.

 DISCUSSION

                   Tree-retardant crosslinked polyethylene (TR-XLPE) was designed to overcome the water treeing deficiency of high molecular weight thermoplastic polyethylene and crosslinked polyethylene (XLPE). In addition to significantly retarding the growth of water trees, TR-XLPE was designed to maintain XLPE’s high dielectric strength and low electrical loss. Laboratory testing has consistently demonstrated the excellent resistance of TR-XLPE against degradation in wet electrical aging. Accelerated cable testing methods have further proven the performance enhancement of TR-XLPE in wet environments.

                  Evaluations of field aged cable continue to support the performance advantages of TRXLPE over other insulation compounds. Unjacketed high molecular weight thermoplastic polyethylene and cross-linked  polyethylene (XLPE) cables began failing prematurely with water treeing being associated with the cable failures.

 Water Tree Growth Patterns in XLPE

 Water Tree Growth Patterns in TR-XLPE

Figure 1

 Figure 2

                    Figure 1 highlights the water tree growth shapes of XLPE and TRXLPE in the laboratory test after aging 90 days at room temperature with the microphotographs being taken at 40X magnification. Figure 2 highlights the length of the water trees grown in XLPE and TR-XLPE in this laboratory test with days of aging. This lab test has now been accepted by the industry and adopted as ASTM D6097-97. As demonstrated by the water tree shapes in Figure 1, the TRXLPE grows smaller and constrained trees compared to conventional XLPE.Following the laboratory demonstration of improved water tree resistance, TR-XLPE demonstrated improved performance.

                    If Emphasis was placed on cleanliness and retention of electrical breakdown test after aging in water. Researchers found that blends of the polyethylene resin used in XLPE with copolymers, based on ethylene alkyl acrylate copolymers, resulted in improved resistance to electrical breakdown after aging in water under electrical stress. The resulting product, called “Copolymer XLPE” has also had excellent field service performance for MV cables.

CONCLUSIONS

                   It was recognized that XLPE, as well as other polymers, undergo a degradation process, called water treeing, when exposed to moisture and an electrical stress enhancement. Additive based “TR-XLPE” was introduced in the early 1980’s and has shown excellent field service performance. Multiple accelerated wet electrical tests have consistently demonstrated the improved retention of dielectric strength achievable with TR-XLPE over other insulation materials. These tests have led to TR-XLPE being the predominant insulation used for medium voltage underground distribution cables. “Copolymer XLPE” was introduced inthe early 1980’s and has also had excellent field service performance for medium voltage cables. The TR-XLPE technology used has been shown to have comparable or better performance than copolymer XLPE standard tests such that the growth of TR-XLPE insulation is expected.The expectation for improved cable life and reliability has led to significant interest in TR-XLPE to achieve these expectations. Usage of TR-XLPE is growing as performance-based tests have been implemented. As the long life performance expectations for medium voltage underground cable systems increase, there is an increasing motivation to use TR-XLPE as the insulation of choice to achieve these objectives.

REFERENCES

• Lawson, J.H. and Vahlstrom Jr., W. “Investigation of Insulation Deterioration in 15 kV Polyethylene Cables removed from Service, Part II.”
  IEEE Trans. PAS Vol. 92, March/April, 1973, pp. 824-831.
• Bahder, G., Katz, C., Lawson, J.H., and Vahlstrom Jr., W. “Electrical and Electromechanical Treeing Effects in Polyethylene and Crosslinked Polyethylene Cables.”                                      IEEE Trans. PAS Vol. 93, May/June 1974, pp. 977-986.
• Global Trends and Motivation Toward the Adoption of TR-XLPE Cable Authors: P.J. Caronia, A. Mendelsohn, L.H. Gross, J.B. Kjellqvist
  The Dow Chemical Company, 1 Riverview Drive, Somerset, N.J. 08873

Effects of Design on Ergonomics

Introduction

                The design of hand tools has a significant influence in the development of upper limb musculoskeletal disorders. By improving the ergonomic properties of hand tools the health of users and their job satisfaction might be positively affected.Any hand tool design must consider the users’ limitations, and provide a right fit for the users. A typical example would be Tongs. In metal forming industries where workers need to use tongs to retrieve workpieces from ovens. Ideally, the tong should be able to grasp objects easily, with a minimum amount of gripping force. In reality, many people may find tongs to be awkward to use as the ability of tongs to grasp objects are generally poor.Undesirable tong design may lead to low user acceptance of tongs, which can lead to catastrophic accidents. Initially, the hand tool must be perceived to be usable, ergonomic and visually appealing in order for the users to benefit from the tools. The perception of ergonomics, usability and aesthetics will be assessed for two different tool designs, R1 ( traditional tong design) and R2 (proposed design alternative).

                                                    The existing tong design available (R1)

                                                          Proposed alternative design (R2)
                                                   
Upper limb disorders and hand tool Ergonomics

                  A mismatch between the user perception and the actual performance of the product may be detrimental to the product’s future success and survival.An upper limb musculoskeletal disorder (ULD) is chronic in nature, and it occurs gradually over time. Several causes of ULD are; repetitive tasks, forceful exertions, vibrations, or sustained or awkward positions. ULD is the general term that is used to describe any disorder experienced in upper limbs. ULD also is used to describe the types of tissue injuries such carpal tunnel syndrome and tennis elbow. An overuse syndrome is also associated with ULD. The most effective intervention that takes place would be workplace redesign.Examples are work associated activities such as using keyboard and mouse. The term includes a group of disorders that most commonly develop in workers using excessive and repetitive motions of the head and neck extremity. The other causes of ULD are remaining in a fixed postures and poor workplace ergonomics. ULD happens when excessive and repetitive motions, coupled with high forces are exerted by the upper limbs. ULD may cause disability, to workers, resulting in loss productivity and other serious consequences. Recovery from ULD may take years, and even then complete recovery may not be possible. The most effective intervention that takes place would be workplace redesign. As the old saying goes, prevention is better than cure, therefore the design of hand tools are of paramount importance.

Method Study

             As there are many types and designs of tongs in the market, it is difficult to narrow down exactly the best tong design as that will depend on the type of objects being handled, and the nature of the task itself. Therefore, instead of evaluating every single type of tong, a particular type of tong was chosen to be evaluated.R1 is used in a materials engineering lab, where round, cylindrical steel specimens ranging from 2-3 cm in diameter, and 1 cm in height are handled. Sometimes, R1 is used to handle semi circular work pieces with the same diameter and height.In the proposed design, instead of having a single tool, the proposed design has two parts, a tray and a gripper. The tray is specially designed for the gripper to securely hook the tray. In this way, instead of directly gripping the workpiece, the workpiece would be placed on the tray and the tray would then be inserted into the furnace or oven using the gripper.
                  The proposed design (R2) and the existing design (R1) were evaluated in terms of ergonomics and usability using a questionnaire that consisted of several questions. Participants were shown the pictures of R1 and R2 in the questionnaire. Based on the pictures, the questions were rated using a Likert type scale, ranging from 1 (least agreeable) to 6 (most agreeable). The neutral option was discarded to prevent participants from taking a neutral stance. While at the same time, the aesthetics aspect of the proposed design and the existing design were evaluated using a scale from 1 to 10, where 1 indicates least beautiful and 10 the most beautiful. The questionnaire was distributed to 50 students. The pictures of R1 and R2 were included in the questionnaire. The responses for each of the questions were then converted into agreement/disagreement percentage ratings, where responses from 1 to 3 were treated as a disagreement, and responses from 4 to 6 were treated as an agreement.

Discussion

           72% of the respondents agreed that R2 will accomplish task more quickly than R1 (64%). This is also shown in the ratings for productivity, where 80% of the participants agreed that R2 will help them to increase productivity compared to R1 (66%). Productivity increase can be associated with a quick task accomplishment, and this is clearly evident in the results. The ratings for numbness and peak pressures on the hand are fairly consistent, where 64% of the respondents agreed that R1 will cause peak pressures on the hand compared to R1. The ratings for numbness did not exhibit that much difference, since perceiving numbness from pictures can be rather difficult (54% for R1 vs 50% for R2).
            Other ratings given by the participants indicated their preference for R2 design. The statements 'easy to operate tool' and 'easy to perform handling task‖ were rated slightly different from each other, although the meaning of the question is quite similar. For the statement ' easy to operate tool', R1 was rated at 82% vs 84% for R2, in which the difference was very slight (2%). Whereas, in the statement 'easy to perform handling task' a rating of 66% was given for R1, and 78% for R2. Perhaps, in the statement 'easy to operate tool' was more ambiguous in its meaning, so the rating difference was small compared to 'easy to perform handling task', which indicated a bigger difference in the ratings. Questions concerning grip force supply and force transmission yielded a similar pattern; R2 is favored more by the participants, where 70% of the participants believed that R2 would require less gripping force compared to R1 design (58%). This is due to the fact that R2 has special hooks at the end that can be inserted into the sides of the tray allowing for a more secure grip compared to R1, where the grip force required for handling R1 would depend on the type of object being handled.
              The weak correlation between product aesthetics and the perception of ergonomics may be explained by the difficulty in perceiving ergonomic features. Ergonomic features are hard to perceive, for example grip force requirement and handle length. These two features can only be measured by physically touching and holding the tool itself. However, their understanding of product aesthetics does not need any further clarification. Consumers do know what a visually appealing product is by just looking at the product. On the other hand, there is no complete theory or model that can accurately predict how consumers come to perceive a product to be visually appealing or vice-versa.

Conclusion
              Design have effects on .... but it can affect the productivity. Also design should be user friendly so that people working with that equipment will not get irritated. The study has shed some light into the relationship between perceived ergonomic, usability and product aesthetics. As there has yet to be an established connection between perceived ergonomics, usability and product aesthetics, buying decisions may be purely driven by aesthetics considerations, thus this may lead to usability and ergonomic problems in the future for consumers. Products that are deemed to be ergonomic and usable, has to convey that impression to the potential users. As there are a certain percentage of consumers purchasing products online, the products will have to convey the impressions of good ergonomics, usability, and aesthetics.


Reference 

"The Influence of Different Hand Tool Designs on the Perception of Aesthetics,
Ergonomics and Usability"
By
M. S. Syed Mohamed
International Journal of Business and Social Science
Vol. 3 No. 3; February 2012