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R & D Review


No.94 November 1998

WFLEX® Coaxial Cables

We have developed a new coaxial cable WFLEX® which has approximately 80% expanded polyethylene insulation and an annularly-corrugated copper outer conductor.
The features of WFLEX coaxial cable are as follows.

  • With a deep ring-corrugated outer conductors having a short pitch, the WFLEX cables are softer than conventional corrugated copper tube coaxial cables. They can be bent to a tight radius using less force than the conventional cables required.
  • Attenuation is approximately 40% less than braided coaxial cables of the same size.
  • The characteristics do not deteriorate over time because of the stable attenuation and phase characteristics (delay).
  • Connectors are easy to mount securely because the cables are ring-corrugated.
  • The corrugated copper tube of outer conductor is a highly effective barrier to RF leakage which exceeds the measurable test sensitivity limit.

With good reputation from our customers, it has been used for jumper cable of portable telephone base stations, personal handyphone system transmission line, cable for Beam Position Monitor System for KEKB.
This paper describes the profile characteristics and experimental results of WFLEX coaxial cable for practical use.
[Key words] Coaxial cables, Highly foamed polyethylene, Ring-corrugated copper tube, Jumper cable, Cable for Beam Position Monitor System

The Development of Unshielded Twisted Pair Cables for Giga-bit Ethernet System

The Giga-bit Ethernet system has held public attention as a high-speed network standard for the next generation. This standard allows that the system to transmit digital signals of a billion bits per second, that is, it has 10 times ability of fast-Ethernet system.
This paper introduces estimation results of unshielded twisted pair cables which has been developed as a transmissive equipment used for the giga-bit Ethernet system.
[Key words] Giga-bit Ethernet, High-speed network, Category 5

Development of a New Sub-duct for Optical Cables

Recently, it is becoming difficult to ensure the duct for optical cables whose demand is largely growing. As a method for solving this problem we suggest an optical cable installed into a sub-duct which is put into the space of duct for power cables. In this paper we report on the development of a new sub-duct which allows longer length installation by pushing, a new reel and a new head for the sub-duct to prevent insertion into pre-installed power cables.
The performance of the new duct was verified by using of model duct route set up in our factory. The results are as follows:

  • A new sub-duct which has an outer diameter of 34mm can be installed for more than 150m by pushing into the duct with an inner diameter of 125mm and which has a power cable of 6.6kV CVT 325mm2 pre-installed.
  • 600 fiber cables can be inserted into an Φ 34 sub-duct whose inner diameter is 27mm.
  • After installing the sub-duct into the duct, drawing out and pulling in the pre-installed power cable caused no problems.

[Key words] Optical cable, Sub-duct, Duct route, PVC pipe, High stiffness, Installation

Development of Tin-codoped Germanosilicate Narrow-band Reflective Fiber Bragg Gratings Written Through the Coating

Fiber Bragg gratings which uses the photo induced refractive index change of the core of optical fibers are being largely studied in optical communications and fiber sensor systems. Generally, the coating is removed when fabricating fiber Bragg gratings.
In this paper we report on a direct fabrication of a narrow-band reflective fiber Bragg gratings without removing the coating, using a tin-codoped germanosilicate fiber and an UV transparent coating. The optical transmission characteristic of the fabricated fiber Bragg grating had maximum reflectivity of more than 99%, FWHM : 0.12nm and side-robes suppression of more than 25dB on a grating length of 24mm. We also tested the mechanical strength of the fabricated fiber Bragg gratings. The average breaking stress was 4.9GPa, n value was 20.
[Key words] Fiber Bragg grating, Written through a fiber coating, Tin-codoped, UV-transparent resin.

Development of Optical Cable Amplifiers

In this paper, a new type of erbium-doped fiber amplifier is demonstrated. A small size optical fiber amplifier installed in a flexible stainless-steel tube is mechanically coupled to an optical fiber cable which can be regarded as a part of the cable. This cable amplifier can be handled like ordinary optical fiber cables when wound on drums or during cable installation. We developed two types of cable amplifiers, technologies to unite an optical amplifier with the cables are shown in this paper. One cable amplifier which contains an ordinal optical fiber amplifier of 300mm in length and 26.5mm in diameter has a length of 415mm and a diameter of 37mm. The other has a length of 610mm and contains two compactly assembled amplification units. Conventional optical fiber amplifiers are designed to be installed inside structures such as central offices. However, the new cable amplifier can be placed anywhere along the optical cable. The cable amplifier can be expected to open new fields for communication systems.
[Key words] Erbium-doped fiber amplifier, Flexible, Small diameter, Cable amplifier

Development of Compact Y-joints for 22kV XLPE Cables

With increasing electric power demand, 22kV underground distribution network is expanding. Under present conditions, compact type accessories with a simple erection procedure is required for lack of working space and to shorten the erection time.
The new type of compact Y-branch-joint ( Y-joint ) for 22kV XLPE cables has been developed with a new construction, new materials and by reducing parts. This new type of compact Y-joint is drastically reduced in size and erected by simple procedure compared with the existing Y-joint. Sufficient reliability has been confirmed by the success of development tests.
[Key words] Simplification of election procedure, Compact accessories, Silicone rubber, Monocoil spring

Study of the Partial Discharge Detection Frequency Selection by Impedance Frequency Characteristics (f-Z characteristics)

Recently, the use of general frequency signal detectors for measuring the partial discharge is increasing, and it is possible to select the detection and amplification frequency in a specific range. For lumped constant specimen it is not necessary to give special regard to selecting the detection frequency, but for distributed constant specimen such as stator winding of power generators and power cables, it is necessary to select the optimum amplification frequency according to the specimen characteristics.
For selecting the optimum amplification frequency, this paper reports on methods of using the frequency characteristics of the impedance of various samples.
[Key words] Partial discharge detection, Detection frequency for discharge, f-Z characteristics, Detection frequency selection

The Degradation Diagnosis of Polymeric Materials by Ultrasonic Waves
- Part 1, Degrading Mechanisms of Polymeric Materials and the Degradation Diagnosis of Low Voltage Cables by the Ultrasonic Method -

Polymeric materials for sheath and insulation of the low voltage cables are degraded under various conditions, major cause being "heat". The mechanisms of heat degradation of typical polymeric materials for cables, polyvinyl chloride (PVC), polyethylene (PE/XLPE) and ethylene propylene rubber (EPR), can be explained as follows;

  • PVC : Volatilization of plasticizer and aggregation (major), and elimination of hydrochloride from PVC resin(minor).
  • PE : Molecular weight loss by oxidation and aggregation of polar groups.
  • XLPE : Molecular weight loss by oxidation, increase in crystallinity caused by scission of crosslinkings and aggregation of polar groups.
  • EPR : Volatilization of the process oil (initial stage), aggregation of polar groups formed by oxidation and curing.

Many kinds of low voltage cables have been used under various conditions in the plants and works. A certain cost for the maintenance of those cables is unavoidable for keeping their reliability and stable operation. Therefore, a degradation diagnosis technique is required for the maintenance of low voltage cables at low costs. The diagnosis must be able to estimate the degree of degradation of the cables non-destructively without any service interruption. We, at Mitsubishi cable industries have developed a new degradation diagnosis method for various low voltage cables, the ultrasonic method. The ultrasonic method allows diagnosis of degradation in various kinds of cables easily without any service interruption and any special skills. With this method the propagation velocity of ultrasonic in the cable sheath are measured, and the change in elastic property and density by degradation can be detected without reference to the structure or size of cables. It should be useful in the preventive maintenance of plants and facilities.
[Key words] Polymeric material, Polyvinyl chloride, Polyethylene, Crosslinked polyethylene, Rubber, Low voltage cable, Degradation, Diagnosis, Ultrasonic

Development of Ultra Wide Band Electromagnetic Wave Absorbers

This paper describes the properties and the design concept of two newly developed absorbers, the TM series absorber used in EMI/EMS anechoic chambers and the Emfader used especially in interior materials for intelligent buildings.
With the progress of advanced electromagnetic wave technologies, higher frequencies from GHz to the millimeter wave bands are being used for such devices as cellular phone systems.
FP series absorbers for microwave use have been developed since ten years ago. Now we have a line-up of absorbers for the entire frequency band from MHz to the millimeter wave.
[Key words] Electromagnetic wave absorber, GHz band, Millimeter wave, EMI/EMS, Anechoic chamber, Intelligent building

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