Electrical stress control

Details Electrical stress control Electrical stress control

1998-09-17

2000-09-26

Dawson, Robert

Electricity: conductors and insulators

Conduits, cables or conductors

Combined

524432, 428389, 428418, 428416, 428450, 428463, 423622, 523459, 264 60, 264 56, H02G 15064, H02G 15103, H02G 15184

Patent

active

061245496

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the control of electrical stress, and in particular to a composition of matter for effecting electrical stress control, and its application to the jointing or termination of electrical power cables, for example.
Electrical equipment, including power cables, operating at medium voltage, say about 10 kV and above, can be subject to electrical stresses that may not be sufficiently controlled by a material that is essentially only electrically insulating. It is known to employ stress control material particularly for such applications. Such material may be classed as `linear` or as `non-linear`. A linear stress control material obeys Ohm's law:
A non-linear material obeys a generalised form of this equation material under consideration.
EP-B-0121986 (Raychem), for example, discloses the termination of a high voltage cable in which a layer of linear stress control material is used in combination with a layer of non-linear stress control material. The material for each layer may be selected from a variety of materials comprising filled polymers.
A paper published in the Proceedings of the 8th CIMTEC Ceramic Congress and Forum on Materials Symposium, Florence, Jun. 29 to Jul. 4, 1994, by Strumpler, Kluge-Weiss and Greuter of ABB, entitled Smart Varistor Composites, describes a material comprising doped ZnO varistor powder as a filler in a polymeric matrix. Proposed applications of the material are exemplified as the suppression of voltage transients or field grading in bushings and cable terminations. The filler is prepared by sintering the powder under conditions ranging from 935.degree. C. to 1320.degree. C. and 4 hours to 20 hours respectively. The shape of the filler particles is said to be almost spherical. It is indicated that agglomerates can have diameters from about 3 micrometers to about 300 micrometers, and that by sieving before or after sintering, a special size fraction can be chosen. The sample prepared is sieved to a particle size of <200 micrometers. The resultant material has a non-linear current/voltage characteristic.
FR-A-2547451 (Electricite De France) discloses a non-linear resistance material for use in distributing voltage in a cable termination. The material comprises a bond or binding agent, which may be a polymeric material, and a ceramic powder based on doped zinc oxide. In this publication, the mass percentage of the powder (the zinc oxide), and its particle size are shown to be the two essential characteristics of the material, with the zinc oxide forming at least 50% of the total mass, and at least 50% of the grains of the powder having a diameter greater than 100 .mu.m. The material is shown to be non-linear, with the field strength varying smoothly with current density. The ceramic powder is obtained by crushing a pellet of the material that has been sintered at high temperature (800-1500.degree. C.). That is to say, the initial particles of zinc oxide are compressed at high temperature into a coherent solid body, or pellet, of the kind used as a varistor in high voltage lightning arresters, which is then crushed by means of a planetary agate marble crusher to form the powder. Such crushing results in particles of irregular and usually jagged shape. The non-linearity of the resulting powder is shown to improve as its particle size increases, at a constant percentage (85%) of powder in the total composition. A particle size between 140 .mu.m and 200 .mu.m is preferred to a size of 100 .mu.m to 140 .mu.m. Samples having a particle size of less than 100 .mu.m are shown to be significantly less non-linear.
U.S. Pat. No. 4,297,250 (Westinghouse) discloses a method of making a ZnO powder composition exhibiting non-linear V-I characteristics. A mass of agglomerated particles is pressed to provide a cohesive pressed green body that is then heated at between 1050.degree. C. and 1400.degree. C. for a time to sinter the particles together. The sintered body is then crushed to provide finely divided powder particle fragments. The fragments are sieved and heated a

REFERENCES:
patent: 3631519 (1971-12-01), Salahshourian
patent: 3644662 (1972-02-01), Salahshourian
patent: 4275261 (1981-06-01), Fillie et al.
patent: 4297250 (1981-10-01), Gupta et al.
patent: 4418240 (1983-11-01), Chazelas
patent: 4431861 (1984-02-01), Clabburn et al.
patent: 4458103 (1984-07-01), Irie et al.
patent: 4551915 (1985-11-01), Larsson
patent: 4731199 (1988-03-01), Matsuo et al.
patent: 5276080 (1994-01-01), Oku
Patent Abstracts of Japan (PAJ) and World Patent Index (WPI) abstracts of JP 6-116502 (Apr. 1994).
Strumpler et al., "Smart Varistor Composites," Proceed. 8th CIMTEC Ceramic Cong. & Forum New Mater. Symp., pp. 15-22 (Jun. 29, 1994-Jul. 4, 1994).
WPI Abstract No. 89-170570/198923 (abstract of JP 1-113466 (May 1989).
WPI Abstract No. 89-216536/198930 (abstract of JP 1-153770 (Jun. 1989)).
WPI Abstract No. 92-052346/199207 (abstract of JP 3-295110 (Dec. 1991)).
Search Report for International Application No. PCT/GB97/00092 (Apr. 14, 1997).
Search Report for Application No. GB 9600819 (Apr. 10, 1996).

Affiliated with

Also associated with

Rating

Electrical stress control does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Electrical stress control, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrical stress control will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2101920