Impregnated Paper Cables Research Articles

Wireless partial discharge tracking on cross-linked polyethylene MV and HV cables

Medium voltage (MV)/high voltage (HV) cable lines are high-value assets and require substantial costs for their installation or replacement. For this reason, the capability to assess the condition of cable lengths and accessories on site is of great importance. Cross-linked polyethylene (XLPE) insulation is extensively used for MV, HV, and extra-high voltage (EHV) class cables [1] thanks to its excellent voltage-endurance and thermomechanical properties. In particular, XLPE-insulated cables feature substantially lower losses, easier manufacturing and jointing procedures, better environmental compatibility, and higher operating temperature compared with impregnated paper cables, which lead to lower costs in procurement and operation [2], [3].

Research on the breakdown under type test of non‐pressurized paper‐insulated HVDC cables

AbstractOne of the most interesting and important problems, met during the development of non‐pressurized impregnated paper cables for high voltage direct current, arose from the introduction of a long‐duration type test at thermal cycles under a DC steady voltage of twice the working voltage. DC cables manufactured according to a traditional paper insulating technique showed during the cooling phase of a thermal cycle a catastrophic fall of the dielectric strength of the order of 50 %. The reason for this fall is analysed both theoretically and experimentally and the way to overcome the obstacle is explained and discussed.

Dielectric Phenomena Related to the Use of Carbon Black Paper Screening in High-Voltage Fully Impregnated Paper Cables

Carbon black (CB) paper screening is today commonly used in oil-filled cables since, besides the well-known advantages already experienced with solid-type cables, it provides a considerable increase of the a-c dielectric strength. CB paper, however, causes an increase of the ``ionization factor.'' These phenomena are studied and the conclusion is drawn that they are closely interrelated. This fact is shown to be related to movements of charged particles in oil gaps adjacent to CB paper. Measurements and theoretical calculations are in good agreement.

Terminal risers for impregnated paper cables

CONSIDERABLE DIFFERENCES of opinion and corresponding differences in practice exist about the safe height for vertical terminations of solid-type paper-insulated cables. The limitations are vacuum formation at the top of well-sealed risers, leads stretching at their base, and moisture effects if the potheads are not hermetically sealed.

Terminal Risers for Solid-Type Impregnated Paper Cables

Terminal Risers for Solid-Type Impregnated Paper Cables

The breakdown mechanism of impregnated paper cables

A new technique of cable examination has been developed. Incipient faults have been studied before actual breakdown with the aid of a microscope, the papers having been freed from oil and dyed to show up the waxing. The types of waxing observed are classified, and their part in breakdown is discussed. The deterioration is always found to be in connection with the conductor, generally through the gap of the first paper. The occurrence of the maximum deterioration at a distance from the conductor is explained, and a diagram showing the path of failure in an actual case is given.The conclusion reached is that failure originates from the ionization in a void in contact with the conductor, but that subsequent breakdown takes place by carbonization of the compound. Such carbonization requires time for its completion and is the chief factor in the voltage/time-to-breakdown curve. It takes place both longitudinally, over the surface of the paper, and perpendicularly through it.The results obtained in the laboratory are compared with those in service, and the types of failure are described.The effect of d. c. stress on cables is discussed and the advantages of routine d. c. testing of feeders are explained on this basis.

Ionization Studies in Paper-Insulated Cables---II

This is the second report to be presented before the Institute of the research investigation of ionization phenomena in paper-insulated, high-voltage cables, which is being conducted at the Harvard Engineering School under the auspices of the Impregnated Paper-Insulated Cable Research Committee. This paper is a report of progress and will be followed by further reports as the work progresses. The power dissipated as ionization loss in cables is much more harmful than the power dissipated in the solid dielectric. The paper presents methods of separating this ionization loss from the total dielectric loss occurring in high-voltage impregnated paper cables, the methods being verified experimentally. It consists essentially of seven parts as follows: (1) A description of the apparatus and the method of impregnating cable paper whereby test specimens having practically no occluded gases can be produced. It is necessary to prepare and test samples in this manner in order to determine the law of their dielectric properties over a wide range of voltage gradient. It is only by knowing this law that it becomes possible to separate the ionization loss in the cable from the total dielectric loss. These experiments show that with three typical but widely different types of impregnating compounds, the power factor and capacitance are constant up to gradients as high as from 250 to 300 volts per mil; the power loss is proportional to the voltage squared under these conditions. These results are illustrated with curves.

Dielectric problems in high-voltage cables

The paper deals with several important problems of particular theoretical and practical interest at the present time in connection with the design, manufacture, and operation of high-voltage impregnated-paper cables. In the first place, the phenomenon of dielectric absorption is discussed as a question of fundamental importance and as a basis for a proper understanding of dielectric losses. It is shown how dielectric resistance must be carefully defined in order to be of any value as a characteristic of cable quality, or in analytical discussion, and the results of experiments are given to show that whilst the usually accepted absorption expression departs from the truth, it can be used within limits. Experimental work on absorption in different dielectrics and on the effect of moisture and temperature on the constants is also described. The dependence of alternating dielectric losses on direct-current characteristics is discussed, and the author suggests a conception of the former in which they can be explained as I2R losses, without retaining the difficulties of a dielectric hysteresis. Several new points are brought to light and supported by experimental evidence in a discussion of the relationship between d.c. and a.c. losses. The nature of the ?V? curve connecting dielectric power-factor and temperature is investigated, and an explanation of the ?V? curve is suggested based on the I2R theory of losses. The paper also discusses the rise of power factor with voltage, the important effect of time on the breakdown strength, and the bearing which this has on the effect of surges in a system. In conclusion, some suggestions are made on the nature of breakdown and the assessment of cable quality.

High-voltage impregnated paper cables

D. W. Roper: A point which should be more prominently set forth is that as the operating voltage of a cable increases, the quality must improve. What is needed at the present time is some method of measuring the quality of the insulation and determining the maximum operating voltage for which a given quality of cable is suited, and to which it should be limited. There are also needed some other tests to be applied to cable at the factory in order to determine whether it will be satisfactory for the service for which it is intended. Apparently some further research as well as co-operation between the manufacturing and operating companies is needed in order to develop the proper tests for this purpose.

High-voltage impregnated paper cables

High-voltage impregnated paper cables

High-Voltage Impregnated Paper Cables

A limit of carrying capacity was reached in high voltage cables due to high dielectric losses, and in order to overcome this limitation, science had to be called upon to introduce measurements and tests to control this quality. The exact experience gained in the development of these tests by scientific men working in cooperation with the men of practical experience enabled the cable industry to attack the next limitation that confronted it, namely, dielectric strength. The industry has already made considerable progress, and the present problem is the complete elimination of occluded air and vapor from the insulation. Air films have been regarded as causes of low dielectric strength, due to ionization of the air and consequent formation of hot spots. It is advanced, herein, that a more useful conception of the danger of air films, is that they promote internal surface leakage. It has also been generally believed that air films can be detected by the slope of the voltage power-factor characteristic. It is contended herein that such is not the case. It is pointed out that the foundation for future developments has been laid by the equipment and organization of American cable manufacturing plants for accurate quality control by continual testing of raw and process materials.