Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T4/00—Overvoltage arresters using spark gaps
  • H01T4/16—Overvoltage arresters using spark gaps having a plurality of gaps arranged in series
  • H01T4/20—Arrangements for improving potential distribution
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/12—Overvoltage protection resistors

Definitions

• This invention concerns improvements in or relating to surge arresters (diverters) by which is meant a device, such as is commonly connected between power supply lines and earth, which under normal conditions represents an open circuit but which, in response to voltage overload conditions occasioned for example as the result of a lightning strike on a power line, rapidly switches to a conductive condition so as to divert the transient power surge to earth and then recovers to its former condition following cessation of the transient in question.
• surge arresters diverters
• Conventional surge arresters commonly comprise, in accordance with the definition given in the International Electrotechnical Commission's recommendation document IEC 99-1 1970, a single or multiple gap connected in series with one or more non-linear resistors.
• Most surge arresters commonly comprise a series of gaps, associated with each of which may be provided means for expanding and thereby quenching an arc truck acros the respective gap, together with a parallel grading circuit for grading the voltage distribution across the series gaps in the event of an overvoltage occurring across the arrester;
• Figure 6 of British Patent Specification No. 1 232 005 for example shows one form of such a conventional surge arrester.
• the grading circuit has two prime functions, namely to ensure that the applied power frequency voltage is reasonably evenly distributed across all of the series gaps and to maintian the required voltage distribution under impulse and switching surge conditions until gap sparkover occurs, and commonly comprises grading components such as linear resistors, non-linear resistors, and/or capacitors connected across the gaps, these grading components commonly being attached to the gaps as separate and non-integral components.
• the series gap arrangement has commonly had to be such as to permit the grading components to be suitably located with respect to, and electrically connected to, the series gaps.
• a more recent development in the field of surge arresters is the gapless or metal oxide type which can comprise (i) a number of non-linear metal oxide resistors in series, (ii) a single or multiple spark gap connected in series with one or more metal oxide resistors, or (iii) a number of metal oxide resistors in series with one or more additional such resistors electrically shunted by means of a spark gap or other by-pass component.
• the voltage grading in such surge arresters may be either inherent in the resistor arrangement as in the first and third possibilities (i) and (iii) above mentioned, or as in the previously mentioned conventional arresters for the second possibility (ii) abovementioned.
• the present invention resides in the concept of providing an electrically-resistive metal oxide glaze on the internal surface of the bore of the porcelain insulator housing normally employed for accommodating surge arrester components, and providing the surge arrester internal assembly with electrical connections between the gaps and/or grading components and the resistive coating at various locations throughout the length of the bore.
• the resistive glaze in the internal bore of the porcelain housing is utilised, at least in part, as the grading circuit for the arrester series gaps.
• the conventional gap grading circuits will, in accordance with the invention, be replaced in whole or in part by the resistive glaze, and with metal oxide or gapless type arresters the resistive glaze or other layer can, in accordance with the invention, be used to reinforce the inherent grading current by provision of electrical contact at regular intervals along the internal bore of the porcelain housing between the resistive glaze and the internal surge arrester components.
• the only connections between the electrically resistive layer provided on the internal surface of the housing and the internal components of the surge arrester, namely the assembly of series connected spark gaps and resistor blocks, are made at the top and bottom ends of the complete assembly.
• the resistive layer thus can have a voltage grading effect only when a plurality of such surge arresters are connected together in series, and has no grading effect in regard to the individual internal components of an individual surge arrester.
• Figure 1 schematically illustrates a prior art arrangement comprising linear-resistor grading circuits
• Figure 2 schematically illustrates a prior art arrangement comprising non-linear resistor grading circuits
• Figure 3 schematically illustrates a prior art arrangement comprising non-linear resistor and capacitor grading circuits
• Figure 4 schematically illustrates a first embodiment of the invention
• FIG. 5 schematically illustrates a second embodiment of the invention.
• the arrangements shown each comprise four series gaps G1 to G4 with grading circuits comprising respec tively series connected linear resistors R 1 to R 4 conn ected to shunt the gaps (Fig. 1), series connected non-linear resistors NLR 1 to NLR 4 connected to shunt the gaps (Fig. 2), and combinations of non-linear resistors NLR 1 to NLR 4 and capacitors C 2 , C 3 coupled to the gaps (Fig. 3).
• non-linear voltagedependent resistors may be series connected with the gaps as is well known.
• Figure 4 represents schematically a first embodiment of the invention comprising an otherwise conventional series gap, linear grading resistor type surge arrester as shown schematically in Figure 1, but wherein the resistors R 1 etc. are comprised by sections of a metal oxide resistive glaze such as of oxides of tin or iron or combinations thereof provided on the internal surface of the bore of the insulator housing.
• the shedded porcelain insulator housing is designated 2
• the electrically resistive glaze is designated 1
• resilient contact fingers to the glaze 1 are designated 3
• spark gaps are designated 4.
• voltage-dependent non-linear resistors could be series-connected with the respective spark gaps intermediate adjacent gaps, the resistors constituted by the glaze shunting the spark gaps.
• Figure 5 illustrates schematically a metal oxide or gapless arrester wherein the metal oxide resistive glaze on the internal surface of the porcelain housing is used to reinforce the inherent grading current by virtue of electrical contact being made at regular intervals along the internal bore of the housing.
• reference numeral 1 designates the resistive glaze
• 2 designates the housing
• 3 designates the contacts to the glaze 1
• 4 designates the non-linear resistors.
• the use of the metal oxide resistive glaze can eliminate at least a proportion of the expensive grading components conventionally provided; (ii) the internal assembly of the arrester is simplified; (iii) the use of the resistive glaze as a comp onent of the grading circuits provides for a greater surface area for dissipating grading circuit watts loss thereby enabling greater grading currents to be utilised with resultant enhanced performance; (iv) the uniform resistive glaze will additionally sex ve to screen internal components from external influence and this will reduce internal ionization levels; (v) the invention can readily be adapted to conventional porcelain insulator housings without requiring dimensional changes; (vi) the internal assembly of conventional surge arresters can be utilised with only the minimum of modification to provide for the electrical contacts to the resistive glaze;

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Thermistors And Varistors (AREA)

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Publications (1)

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• 1981
  • 1981-08-25 EP EP19810902380 patent/EP0065951A1/en not_active Withdrawn
  • 1981-08-25 JP JP56502801A patent/JPS57501454A/ja active Pending
  • 1981-08-25 WO PCT/GB1981/000168 patent/WO1982000926A1/en not_active Application Discontinuation
  • 1981-08-27 CA CA000384729A patent/CA1162232A/en not_active Expired

Non-Patent Citations (1)

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