Solomonik February 2003
36-WG11/Cavtat/147
L. L. Vladimirsky, E. A. Solomonik HVDC Power Transmission Research Institute (NIIPT) RUSSIAN GUIDELINES FOR SELECTION OF OUTDOOR INSULATION (Comments, supplements, and additions to 36-WG11/Capetown/139) In 2002 was published the 5th revised and enlarged edition of the Russian standard on selection of external electrical insulation, both in clean and polluted atmosphere areas. The standard is incorporated as Chapter 1.9 of the 7th edition of the «Regulations on Electric Installations». Starting from 1964, the guidelines of all Russian standards on selection of external electrical insulation have been as follows: - both in clean and polluted atmosphere areas, the insulation of overhead lines and switchgear is selected for normal service conditions, i. e. for exposure of wet polluted insulator surface to operating voltage stresses, which assures also reliable performance of the insulation under exposure to internal overvoltages; - application of the standards is the principal insulation selection method, dictated by tight schedules of electric facility planning and by wide-scale application of type projects; under these conditions it is generally unaffordable to select outdoor insulation for majority of facilities on the basis of project-oriented laboratory research and/or field-data based calculations; - while the national standards provide the basis for selection of outdoor insulation, use is also made of local or regional insulation level maps (pollution degree maps) plotted with the help of field research findings and generalized service records; - the mandatory design parameter is the specific effective creepage distance λe of insulator and insulating structures, which is calculated with allowance for a number of correction factors according to the insulator configuration, dimensions and design of insulation; - pollution hazards for outdoor insulation are quantified through the pollution level (PL) of the electric facility location; the PL determination procedure is the principal objective of any outdoor insulation selection manual; the right determination of PL ensures automatic selection of outdoor insulation; - the PL criteria are pollution source characteristics, which are most often the only adequate information available at the planning stage; - use of other criteria, such as the outdoor insulation performance records, flashover voltages of field-polluted insulators, characteristics of atmospheric precipitation or pollutant layer, in selection of external insulation is highly time- and labour-consuming; these inputs are mainly used in plotting insulation or pollution level maps; As compared to earlier editions, the 2002 standard features the following main differences: - the number of standard pollution levels was lowered from 7 to 4, while use of PL other than standard is still possible; - the standard specific effective creepage distance λe has been assumed to be identical for porcelain, glass, and polymer (composite) insulators; - requirements on the flashover performance of artificially polluted insulators, depending on the PL in the service area, have been included; - the standard values of λe have been assumed to be identical for line and substation insulation, as well as for all voltage ratings from 110 kV and above. The standards for selection of glass and porcelain insulating units and structures from their specific effective creepage distance λe with allowance for the PL of the location and the rated voltage of the installation are as shown in Table 1. Glass and porcelain insulating units and structures may be also selected from their wet polluted flashover performance data. Composite insulating units and structures are selected from their wet polluted flashover characteristics alone. The minimum creepage distance of composite insulators is stipulated in their specifications.
1
Solomonik February 2003
36-WG11/Cavtat/147
Table 1 Minimum specific effective creepage distance λe, cm/kV, of supporting insulator strings and rod units on steel and reinforced concrete line supports, external apparatus insulation and outdoor switchgear insulators Pollution level I II III IV
Voltage rating, kV up to 35 1.90 2.35 3.00 3.50
110-750 1.60 2.00 2.50 3.10
When selected from the flashover voltage, strings of 6 to 750 kV overhead lines, external insulation of electric apparatus, and insulator units of 6 to 750 kV outdoor switchgear must have wet polluted 50% AC flashover voltages not below those given in Table 2. Table 2. Polluted 50% AC flashover voltages of 6-750 kV overhead line insulator strings and 6-750 kV external insulation and outdoor switchgear insulators Voltage rating, kV 6 10 35 110 150 220 330 500 750
Minimum 50% flashover voltage, kV 8 13 42 110 150 220 315 460 685
The specific surface conductivity of the pollutant layer on glass, porcelain, and composite insulators must be assumed to be at least 5 µS for PL-I, 10 µS for PL-II, 20 µS for PL-III, and 30 µS for PLIV. Insulators exposed to limited atmospheric wetting and pollution, such as those of gas-insulated switchgear, must have 50% AC flashover voltages not below those shown in Table 3 when exposed to artificial wetting and pollution. The specific surface conductivity of the pollutant layer on glass, porcelain, and composite insulators must be assumed to be at least 1 µS for PL-I, 3 µS for PL-II, 7 µS for PL-III, and 10 µS for PL-IV. Table 3 Wet polluted 50% AC flashover voltages of insulators under limited atmospheric exposure Voltage rating, kV 6 10 15 20 35 Minimum 50% flashover voltage, kV 10 16 23 30 50 For ceramic and glass units the 2002 Regulations specify a specific creepage distance λe which is calculated with the help of several additional correction factors. These make allowance for effects on the pollution performance of the insulator profile, the maximum insulator diameter, and a special be2
Solomonik February 2003
36-WG11/Cavtat/147
havior of multiple-unit insulating structures, such as insulator strings and stacks. Thus the effective specific creepage distance λe of insulators and multiple-unit insulating structures is specified to be λe = λ ⋅ kL kD kK , where: − λ is the specific geometrical creepage distance according to IEC- 815 (1986); − kL, the correction factor making allowance for efficient use of the available creepage distance, i. e. taking into account the effect of the insulator profile on the wet polluted flashover voltage; − kD, the correction factor making allowance for the effect of the wet polluted insulator's diameter on the flashover voltage; the Russian standards take kD according to the IEC-815 (1986); − kK, the correction factor making allowance for the effect of the shape of a multiple-unit insulating structure with parallel and/or parallel-and-series arms on its wet polluted flashover voltage. The external insulation selected with the help of the factors kL, kD and kk has the needed reliability without excessive margins. The 2002 Regulations provide values of kL and kK for most common ceramic and glass units and insulating structures. It has been shown by tests that sometimes these factors depend on the pollution degree of insulators, however, the available block of data on the subject is not yet sufficient to be taken into account in external insulation selection norms. Factors kL for suspension cap-and-pin insulators with weakly and moderately ribbed bottom surface (0.9 ≤ L/D ≤ 1.4) are found from Table 4 according to the ratio of the geometrical creepage distance L to the cap diameter D. Table 4 Factors kL for suspension cap-and-pin insulators with weakly and moderately ribbed bottom surface L/D From 0.90 up to 1.05 Over 1.05 up to 1.10 Over 1.10 up to 1.20 Over 1.20 up to 1.30 Over 1.30 up to 1.40
kL 1.0 1.05 1.10 1.15 1.20
The factor kL of suspension cap-and-pin insulators for heavy pollution areas is found from Table 5. Table 5 Factors kL for special-purpose suspension cap-and-pin insulators Insulator profile Double wing Antifog cap-and-pin insulator Aerodynamic (hemispherical and conical) Bell-shaped (smooth inside and ribbed outside surface)
kL 1.20 1.25 1.0 1.15
The factor kL of suspension rod insulators is found from Table 6 according to the ratio of the creepage distance L to the length of the insulating body h.
3
Solomonik February 2003
36-WG11/Cavtat/147
Table 6 Factor kL of suspension rod insulators L/h kL
Under 2.5 1.0
2.5-3.0 1.10
3.01-3.30 1.15
3.31-3.50 1.20
3.51-3.70 1.25
3.71-4.00 1.30
In the case of external insulation in the form of single insulating structures (apparatus covers, post insulators, rod post insulators, bushings), the values for kL are found from Table 7 using also the ratio of the creepage distance L to the length of the insulating body h. Table 7 Factor kL for apparatus covers, post insulators, suspension rod units, bushings L/h kL
under 2.0 1.0
2.0-2.30 1.10
2.31-2.70 1.20
2.71-3.20 1.30
3.21-3.50 1.40
The factor kL for line and post pin insulators is taken to be 1.0 at a low profile and 1.1 at a high one. The values for kk are specified in the 2002 Regulations as follows: - kk = 1.0 for I-strings of suspension cap-and-pin and rod insulators and for single stacks of identical post insulators; - kk is taken from Table 8 for multiple-unit structures with electrically parallel arms without jumpers (double and multiple supporting and tension strings, double and multiple stacks); - kk = 1.0 for Λ and V strings with single arms; - kk = 1.1 for multiple-unit structures with series-parallel single arms (Y and strings, stacks of post insulators with parallel arms of unequal height, substation apparatus with insulating guys). Table 8 Factor kk for multiple-unit structures with electrically parallel arms without jumpers Number of parallel arms kк
1 1.0
2 1.05
3-5 1.10
The factor kк for structures with more than five parallel arms, for complex multiple-unit structures with parallel and series-parallel arms (such as strings with double bottom arms), for complex multiple-unit structures with metal jumpers, for structures made up by units of various configurations and generally for complex three-dimensional structures must be found individually by tests or calculation. The 2002 Regulations also provide recommendations on the optimum configuration of insulators in areas with various pollution intensity levels. For instance, suspension units should be selected in compliance with Table 9.
4
Solomonik February 2003
36-WG11/Cavtat/147
Table 9 Application areas of suspension insulator units of different shapes Insulator shape Pollution characteristics Cap-and-pin insulator with ribbed bottom Areas with PL-I and II, any kind of pollution surface (L/D ≤ 1.4) Smooth hemispherical and conical cap-and- Areas with PL-I and II , any kind of pollution; arpin insulators eas with saline soils and industrial pollution within PL-III Porcelain cap-and-pin and long-rod insulator Areas with PL-IV in the neighborhood of cement, shale-processing, iron and steel, potassium fertilizer, phosphate, electrode compound facilities Standard long-rod porcelain insulator (L/h ≤ Areas with PL-I, including areas with inaccessible overhead line routes 2.5) Double-wing cap-and-pin insulator Areas with saline soils and industrial pollution, PL-II to IV Cap-and-pin insulator with heavily ribbed Sea and salt lake coasts, PL-II to IV bottom surface and a protruding inner rib (L/D > 1.4), Anti-fog. Special-make long-rod porcelain insulator Areas with PL-II to IV, any kind of pollution; areas with inaccessible overhead line routes, PL-II (L/h > 2.5) and III Standard composite rod insulator Areas with PL-I and II , any kind of pollution, including areas with inaccessible overhead line routes Special-make composite rod insulator Areas with PL-II and III, any kind of pollution, including areas with inaccessible overhead line routes Table 10 shows basic 2002 criteria for determining the pollution level from characteristics of pollution sources. Additionally, instructions are given on selection of external insulation in low pollution areas. In areas which are not affected by industrial pollution sources, such as forests, tundra, forested tundra, prairies and the like, use can be made of insulators whose specific effective creepage distance is lower than that specified in Table 1 for PL-I. Listed as PL-I areas are territories which are affected by sources of industrial or natural pollution, including marshlands, mountains, low-salinity soil areas, and farmlands. With sufficient substantiation, insulators in industrial areas may be planned to have a longer specific effective creepage distance than that specified in Table 1 for PL-IV. It should be pointed out that the new standards provide a methodology of allowance for the wind rose in adjustment of boundaries of PL areas and a methodology of determining PL with superposition of pollution from several sources.
5
Solomonik February 2003
36-WG11/Cavtat/147
Table 10 Pollution source type 1. Industrial facilities 2. Seas and salt lakes 3. Thermal power plants and industrial boiler houses 4. Cooling towers and sprayer pools 5. Dust-generating dumps, warehouses, sewage treatment facilities, motor roads using large quantities of de-icing chemicals 6. Saline soils*
Pollution level criterion Kind of production, design annual output, thousand tons, distance from pollution source, m Design salinity of water, g/l, distance from pollution source, m Type and ash content of fuel, generation capacity, MW, height of chimneys, m, distance from pollution and water source, m Conductivity of circulating water, µS/cm, distance from pollution source, m Distance from pollution source, m
Characteristics of the topsoil, including water-soluble salt content and deflation level, distance to the saline soil area, m 7. Mountainous areas Altitude above the sea level, m * This requirement was last included in the 1990 USSR edition of the Regulations; it was eliminated from the 2002 Regulations as no longer important for Russia. The 2002 Regulations offer methodologies of calculating the pollution level at different distances from specific pollution sources, as a rule, with allowance for characteristics of the sources. Inputs for the calculations were obtained in the 1975-1990 period by generalization of long-term service statistics for electric apparatus operated in the neighborhood of industrial and natural pollution sources of the USSR. Also quoted in the 2002 Regulations is the methodology of determining the design industrial output and the list of industrial products, to be used as inputs in calculation of pollution levels. This methodology was developed by a large team of specialists of a number of agencies in different USSR republics. By way of illustration, Tables 11 and 12 show the norms for finding the pollution levels in the neighborhood of chemical pollution sources and in the salt lake and sea coastal areas. Table 11 Pollution levels in the neighborhood of chemical pollution sources
Design annual output, thousand tons up to 10 over 10 up to 500 over 500 up to 1500 over 1500 up to 2500 over 2500 up to 3500 over 3500 up to 5000
up to 500 1 2 3 3 4 4
Pollution level at distance from the pollution source, m over over over over over over 1000 1500 2000 2500 3000 500 up up to up to up to up to up to to 1000 1500 2000 2500 3000 5000 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 3 2 1 1 1 1 3 3 2 2 1 1 4 3 3 3 2 2
over 5000 1 1 1 1 1 1
6
Solomonik February 2003
36-WG11/Cavtat/147
Table 12. Pollution levels (PL) in coastal areas of seas and salt lakes over 10,000 m2 Design salinity of waDistance from coast Water basin PL ter, g/l line, km Non-saline up to 2 up to 0.1 1 up to 0.1 2 Low salinity over 2 up to 10 over 0.1 up to 1.0 1 up to 0.1 3 Medium salinity over 10 up to 20 over 0.1 up to 1.0 2 over 1.0 up to 5.0 1 up to 1.0 3 High salinity over 20 up to 40 over 1.0 up to 5.0 2 over 5.0 up to 10.0 1 To conclude, Table 13 gives a summary of Russian approaches to selection of external insulation. Table 13 Russian Approaches to Selection of External Insulation
1. 2.
3.
4.
Approach Determination of PL by standards. Selection of external insulation by standards Determination of PL by standards. Selection of external insulation from flashover characteristics of artificially polluted insulators. Determination of PL from results of field research and service experience. Selection of external insulation on the basis of results of field research and service experience. Selection of external insulation on the basis of results of field research (without determining PL).
Application Most widely used since 1964. Fairly widely used over the recent decade.
Was very widely used in the USSR. Seldom used now in Russia (for plotting of Insulation Level or Pollution Level Maps) Was used in the USSR for selection of insulation for particularly sensitive facilities. Virtually never used in Russia at present.
On the whole, the Russian approach to selection of external insulation in different polluted atmosphere areas is identical or close to the guidelines of the IEC Publication 60815, now being revised. However, differences in Russian and IEC positions suggest discussion of the issues at WG 11 TC 36 IEC.
Authors’ address: 1/39 Kurchatov Str., St. Petersburg, 194223, Russia E-mail
[email protected] Fax (7-812) 247-94-84 Tel. (7-812) 247-01-61, 247-94-08
7
