kV Cables Research Articles

Effects of Internal Conductor to Enclosure Arcs on SF6 Gas Insulated Transmission Lines

The effects of internal conductor to enclosure arcs on SF6 gas insulated transmission lines (GIL) were tested using 154 kV and 275 kV cables. Tests were conducted on the 154 kV cable with arc currents of 1 KA RMS and 2 KA RMS for durations of 1 ~ 4 seconds, and on the 275 kV cable with an arc current of 50 KA RMS for durations of 0.1 ~ 0.4 seconds. Various characteristics of these cables were measured, such as the velocity of arc travel, melting trends of the enclosure wall, the decomposition of SF6 gas, the pressure and temperature curves, damage to cable components, and the residual performance capability of damaged components. The data, from these measurements, the findings of these tests, contribute to the improved design and maintenance of GIL systems.

An Attempt at Predicting Cable Breakdown Voltage from Dielectric Measurements

For twenty slightly different ethylene propylene (EP) insulated model cables, an 0.8 correlation coefficient was found between dielectric strength after aging and both tan6 after aging and the change with aging of insulation resistance constant (IRK). Aging consisted of 3.5 months immersion of 60 cable specimens in 90°C water with 2 MV/m 60 Hz electrical stress continuously applied. However, tan6 and IRK measurements made regularly on EP and crosslinked polyethylene (XLPE) insulated 15 kV cables, similarly aged at 2 MV/m in 90°C water, did not predict how long a cable would withstand the aging stresses.

Development of radiation crosslinking process for high voltage power cable

This work has been done to develop an electron beam crosslinking process for high voltage power cable by solving problems of the foaming and discharge breakdown of thick polyethylene insulation during irradiation. When a polyethylene plaque (d=0.92, MI=1.0) of 4 mm thick corresponding to the wall of 6.6 kV cable was irradiated by 1.5 MeV electrons, the temperature went up to 95°C and foaming was observed at a dose of 20 Mrad. On the other hand, irradiation of 24 Mrad was required for sufficient heat resistance (75% gel formation) of polyethylene. Although an addition of conventional polyfunctional monomers reduced the crosslinking dose (10 – 12 Mrad), discharge breakdown occured at relatively low doses. The present work reveals that both foaming and discharge breakdown are efficiently prevented by the use of dipropargyl succinate (DPS). A 6.6 kV type cable specimen insulated with polyethylene containing 2 phr of DPS was irradiated by 1.5 MeV electrons. While the cable had properties comparable to those of a steam cured one, very few voids were observed in the insulation.

EPRI-Manufacturers 500/550 KV Cable Research Project-Potheads NO. 2 - Summary of Field Test Performance at Waltz Mill

This paper presents the test history and results of the post test examination of four G&W EHV potheads installed on cables A and B during the original two year field evaluation program for the 500/550 kV oil pipe cable systems and the extended testing at 750 kV, or elevated cable conductor temperatures, at the Waltz Mill test facility. This research project was sponsored by the Electric Power Research Institute (EPRI).

Procedure to increase voltage rating of field installed 15 kV cable by replacement of nitrogen with sulfur hexafluoride

This paper presents the results of a study to establish the feasibility of increasing the operating voltage and MVA rating of an installed 15 kV cable system by replacing the nitrogen with sulfur hexafluoride gas. The results of laboratory and field studies indicate that such a conversion is feasible and can be accomplished in the field if the ionization starting potential of the cable is measured during conversion to prove the safe operation at the higher voltage. It is concluded that the ionization starting potential of a 15 kV cable system can be raised by a factor of approximately 1.5 at 15 psig (10.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> N/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) after conversion to sulfur hexafluoride gas.

Development and trials of the 400 kV integral pipe-cooled cable system

The need for reduction in wayleave requirements for cables for undergrounding of CEGB 400 kV very-heavy-duty lines has led to the development of the integral pipe-cooled cable system. The thermal design of the system is described and the various practical problems, pertaining to the installation of larger 400 kV cables in pipes, are outlined. Two field-trial installations have been constructed, the second being designed to resolve problems of cable movement which were not fully solved due to practical limitations in the first trial. The main results of both trials are reported. The applications, limitations and economic advantages of this cable system are briefly discussed.

Synthetic polymer papers suitable for use in EHV underground cable insulation

This relates to the applicability of Tenax <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sup> paper made of poly(2,6-diphenyl-p-phenylene oxide) fibers to EHV cable insulation. Tenax paper shows excellent thermal stability in DDB impregnant even at 150° and its impulse strength has been improved significantly. Long-term dielectric test on model cable suggests that Tenax paper insulation may provide an EHV cable capable of operating at 25 kV/mm and 120°. Some experimental 275 kV cables are manufactured and offer much valuable imformation. Additional calculation based on the data available indicates that Tenax paper insulated oil-filled cables rated at lOO0 KV may offer much power capability advantage.

EPRI ߞManufacturers 500/550 kV cable research project cable A ߞEffect of increased conductor temperature

The original ERC - Manufacturers, 500/550 kV Cable Research test schedule was successfully completed [1] in August 1972 and most of the basic data has been presented [2]. A follow-on program designed to search for end-points has run its course and it is now appropriate to describe the events and consider their significance in EHV system design. Cyclic thermal loading has been postulated as a cause of EHV Cable system problems. This paper relates specifically to test specimen A and its performance in a high thermal load study at the Waltz Mill test facility [3]. The end point was reached but the failure mode appeared to be one of mechanical origin and will require further tests.

High voltage cables with extruded insulationߞStatistical controls and reliability evaluation

Design characteristics of high voltage cables with extruded insulation can be established by use of the failure probability distribution of the insulation materials involved The evaluation of the distribution parameters is discussed and the validity of the theory for a wide range o f cable dimensions is proved. Also discussed is the importance that, in order to ensure cable reliability, these parameters should remain constant for time intervals ranging from a few minutes to many years. Finally it is shown by analysis of the relative influence of the distribution parameters how it is possible to establish the insulation requirements for the design of 60 to 138 kV cables.

Internally force-cooled power cables; optimum working temperature in the range 70–358 K

Current ratings are compared for both copper and aluminium conductors, internally cooled with a variety of coolants, working in the temperature range 70 K to above ambient. Capital and running costs are then estimated for optimised designs of cable cooled with some of the more promising of these coolants. It is shown that there is no economic advantage in the deep refrigeration of the conductors, and that the optimum temperature of of operation for a force-cooled cable is near to ambient. With 400 kV cables, the preferred coolant is a low-viscosity mineral oil. Water may also merit consideration as a coolant, but further study is needed of the problems of segregation from the dielectric, and design of feed joints and terminations. 1000 kV cables are also considered, but because of the high cost of reactive compensation, unit capital costs are higher than for 400 kV cables. The preferred coolant for 1000 kV cables is a low-viscosity mineral oil. With oil-cooled cables, some economic, advantage can be gained by refrigerating to coolant-inlet temperatures of down to about −40°C.

Special Report on Development and Installation of 138 kV Cable Systems for Tests EEI Waltz Mill Station

A group of papersl presented at the 1970 Winter Power Meeting outlined the EEI-Manufacturer's 500/550 KV Cable Research Project, at the Waltz Mill Testing Facility, under the direction of the Electric Research Council. A description of the station layout and voltage supply was given in the lead paper2 of that series and need not be repeated here.

Development and Installation of 138 KV Cable Systems for Tests at EEI Waltz Mill Station: Cable 23

This paper covers the General Electric Company's development, testing and installation at the Waltz Mill Station of a 138 kV solid dielectric power cable and associated splice. The cable described is unique in the industry in that (1) it utilizes a new insulation with higher breakdown strength, (2) is the only cable at Waltz Mill to use a mineral filled cross- linked polyethylene, and (3) has its insulation shield intimately bonded to the insulation.

Mathematical Analysis of Direct Buried Rural Distribution Cable Impedance

The results are presented of a computer study of the impedance of direct buried cable with current flow in the earth taken into account. The cable considered is solid insulation, concentric neutral, primary cable used for rural underground distribution. The effects of earth resistivity, line length and neutral conductivity are examined. Impedance values for 15 kV and 25 kV cable are given for sizes # 2 through #4/0 AWG.

EEI-Manufacturers 500/550 KV Cable Research Project. Pothead No. 2-High Pressure Oil Paper Pipe Type

The design concept of the G & W 500 kV capacitor graded potheads supplied for the E. R. C.-Waltz Mill field testing program is basically the same as those supplied for a similar field testing program to evaluate 345 kV cable systems.

EEI-Manufacturers 500/550 KV Cable Research Project. Cable A - High Pressure Oil Paper Pipe Type

This paper describes the design, manufacture and tests on a 500/550 kV cable and joint. The cable successfully withstood 1550 kV impulse and 1290 kV switching surge established by Electric Research Council for the Waltz Mill field tests. The 60 Hz tests demonstrated the cable with either a splice, insulated to 2 times the insulation O.D. or 1.5 times the insulation O.D. had adequate ac dielectric strength.

EEI - Manufacturers 500/550 KV Cable Research Project. Pothead No 1 - Capacitance Graded Type

Design innovations required for a pothead to terminate 500-kV pipe-type cable are explained. The laboratory test program which demonstrated required dielectric strength is described. Finally, field installation experience is discussed.

EEI-Manufacturers 500/550 KV Cable Research Project. Waltz Mill Testing Facility

The Waltz Mill test facility is part of the Electric Research Council's program for research on underground transmission. At this station prototype samples can be tested at voltages ranging from 115 kV to 1 100 kV. The station was designed to provide flexibility and control of accelerated life tests of sample insulation systems and other evaluations required to demonstrate serviceability of prototype transmission systems. Initial samples being tested are 500-kV paper insulated, pipe-type cables. Test loops are not underground, but are installed above ground. Artificial earth environment is provided by computer controlled heaters and thermal lagging on the test pipes. Up to 2000 amperes can be circulated in the conductor of each sample to simulate loading conditions. Computer logging of temperature data and other quantities plus power factor measurements provide a history of sample performance during the two year test period. Test sample installation procedures are described.

EEI-Manufacturers 500/550 KV Cable Research Project. Cable B-High Pressure Oil Paper Pipe Type

A 550 Kv. paper insulated pipe cable is on test. Maximum stress is 425 v/mil (17 kv/cm). A semi-synthetic taped joint operates at 315 v/mil and dissipation factor about 40% lower than the cable. A telemetered temperature monitoring system gives a direct reading of average conductor temperature. Design and manufacturing details are given.

Gas-pressurised lapped-polythene dielectric for extra-high-voltage power-cable systems

The paper describes an experimental investigation of the electrical, physical and mechanical properties of lapped-polythene dielectric. From the levels of impulse-breakdown stress and discharge-inception stress obtained, the use of this dielectric appears to be a promising method of operating low-permittivity low-loss insulation at stresses comparable with those currently employed in paper-insulated power cables at the highest transmission voltages. After consideration of other design aspects, a specification for 275 kV cable is given, based upon the experimental results obtained. The problem of providing terminations is also considered, and work leading to the design and testing of 275 kV capacitance-graded sealing ends is described.

The 400 kV grid system for England and Wales

The paper describes, in Part 1, a study of probable long-term requirements of the main transmission system in England and Wales. The possibility of continuing to extend at 275 kV is compared with the alternative of introducing a higher voltage, either 400 or 500 kV, and the reasons for deciding to adopt 400 kV as the next step in transmission voltage are given.The research work associated with the development of overhead lines suitable for operating at 400 kV in England and Wales is described in Part 2 of the paper, while Part 3 gives a summary of the main features of the design of the 400 kV substation equipment, overhead lines and cables which will be used to implement the proposals.