Russian Guidelines for Selection of Outdoor Insulation

Nov 22, 2002 - III. 3.00. 2.50. IV. 3.50. 3.10. When selected from the flashover voltage, wet polluted strings of 6 to 750 kV overhead lines, external insulation of.
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E. Solomonik (presented by C. Engelbrecht)

36-WG11/Capetown/139 22/11/02

Russian Guidelines for Selection of Outdoor Insulation L. L. Vladimirsky, E. A. Solomonik, E. N. Orlova HVDC Power Transmission Research Institute (NIIPT), 1/39, Kurchatov Str., St. Petersburg, 194223, Russia

Abstract Reported are the guidelines and criteria for the selection of outdoor line and substation insulation according to the standing Russian norms (2001). The paper deals with: − determination of the insulation pollution level close to sources of industrial or natural pollution from types and characteristics of these sources; − selection of line and substation insulators from their polluted wet flashover characteristics depending on the pollution level of the anticipated service area; − selection of the insulation level of electric installations from specific effective creepage distances. Quoted are correction that make allowance for effect of the configuration of line and substation insulators and insulating structures on the needed geometrical creepage distance. Examples are given of recommended insulator types (with respect to the configuration of the insulating body) for areas with different pollution types and levels.

At present, line and substation insulation must be selected in Russia following the standing 1990 ‘Instructions on the Selection of Insulation of Electric Installations RD 34.51.101-90’. At present, work is under way on a new updated version of another standard that will make, after approval, an 'Insulation of Electric Installations' chapter in the 2000 seventh edition of the Russian 'Regulations on Electric Installations', referred to further as 'Regulations’. Given in this chapter of ‘Regulations’ are recommendations on all matters of application of insulators on overhead power transmission lines and in switchgear rated from 6 to 750 kV in Russia. The recommendations are given for four standard pollution levels, as specified by the RD document. According to ‘Regulations’, glass and porcelain insulating units and structures are selected from their specific effective creepage distance λe with allowance for the pollution level (PL) of the location and the rated voltage of the installation (Table 1). Composite insulating units and structures are selected, according to ‘Regulations’, from their wet polluted flashover characteristics alone. 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 Voltage rating, kV Pollution level up to 35 110-750 I 1.90 1.60 II 2.35 2.00 III 3.00 2.50 IV 3.50 3.10

When selected from the flashover voltage, wet polluted strings of 6 to 750 kV overhead lines, external insulation of electric apparatus, and insulator units of 6 to 750 outdoor switchgear must have 50% power frequency flashover voltages not below those given in Table 2. Table 2. Minimum effective wet polluted 50% flashover voltages of 6-750 kV overhead line insulator strings and 6-750 kV external insulation and outdoor switchgear insulators Voltage rating, kV 50% flashover voltage, kV 6 8 10 13 35 42 110 110 150 150 220 220 330 315 500 460 750 685

The specific surface conductivity of the pollutant layer must be assumed to be at least 5 µS for PL-I, 10 µS for PLII, 20 µS for PL-III, and 30 µS for PL-IV. Insulators of the U2 category, exposed to limited atmospheric wetting and pollution (such as those of gasinsulated switchgear) must have 50% flashover voltages not below those shown in Table 3 when exposed to artificial wetting and pollution. The specific surface conductivity of the pollutant layer 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. Minimum effective wet polluted 50% flashover voltages of U2 insulator units Voltage rating, kV 6 10 15 20 35 50% flashover voltage, kV 10 16 23 30 50

It is essential to point out that the standards set identical requirements for glass, porcelain and composite insulators. In accordance with new Russian standards, 6 to 35 kV overhead lines must use, as a rule, suspension cap-and-pin and composite insulators. 110 to 750 kV overhead lines and 35 to 750 kV substation busworks must use, as a rule, glass units. Use may be also made of porcelain suspension capand-pin insulators, porcelain rod insulators, as well as composite rod insulators. For ceramic and glass units the Regulations specify a specific creepage distance λe which takes into account the requirements of IEC Publication 815 «Guide for the selection of insulators in respect of polluted conditions», but uses, however, several additional correction factors. These make allowance for effects on the pollution performance of the insulator profile, the diameter, and a special behavior of

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multiple-unit insulating structures, such as insulator strings and stacks. Thus, the Russian standards recommend that the effective specific creepage distance λe be found for insulators and multiple-unit insulating structures, using the following three correction factors: λe = λ ⋅ kL kD kK , where: − λ is the specific geometrical creepage distance according to IEC- 815; kL, the correction factor making allowance for efficient use of the available creepage distance, i. e. taking into account the shape of the insulator surface; − 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 IEC815; − kK, the correction factor making allowance for the effect of a wet polluted multiple-unit insulating structure with parallel and/or parallel-and-series arms on the flashover voltage. The insulation selected with the help of the factors kL, kD and kk has the needed reliability without excessive margins. Russian standards 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 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 and including 1.40

kL 1.0 1.05 1.10 1.15 1.20

The factor kL for suspension cap-and-pin insulators intended for heavy pollution areas is found from Table 5. Table 5. Factors kL for special-purpose suspension cap-and-pin insulators kL Insulator profile Double wing

Antifog cap-and-pin insulator Aerodynamic (hemispherical and conical) Bell-shaped (smooth inside and ribbed outside surface)

1.20 1.25 1.0 1.15

In the case of external insulation in the form of single insulating structures (apparatus covers, post insulators,

long-rod insulator units, bushings), the values for kL are found from Table 6 using the ratio between the creepage distance L and the length of the insulating body h. Table 6. Factor kL for apparatus covers, post insulators, suspension rod units, bushings L/h

under 2.0

2.0-2.30

2.31-2.70

2.71-3.20

kL

1.0

1.10

1.20

1.30

3.213.50 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 by the Russian standards 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 7 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 ∆ and V strings with single arms; - kk = 1.1 for multiple-unit structures with series-parallel single arms (Y and A strings, stacks of post insulators with parallel arms of unequal height, substation apparatus with insulating guys). Table 7. 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 Y strings with double 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 Russian insulation selection standards 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 8. The standards give detailed instructions on determination of PL close to specific pollution sources, as a rule, making allowance for characteristics of these sources. By way of illustration, Table 9 gives PL determination criteria in the vicinity of chemical and other industrial pollution source facilities. Table 10 shows similar guides for saline coastal areas. Also quoted is a procedure for determining the PL from the design output of industrial facilities and a full list of polluting products of various industries.

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Table 8. Application areas of suspension insulator units of different shapes Insulator shape Pollution characteristics Areas with PL-I and II, any kind of pollution Cap-and-pin insulator with ribbed bottom surface (L/D ≤ 1.4) Smooth hemispherical and conical cap-and-pin insulators Areas with PL-I and II , any kind of pollution; areas with saline soils and industrial pollution within PL-III Porcelain cap-and-pin insulator Areas with PL-IV in the neighborhood of cement, shale-processing, iron and steel, potassium fertilizer, phosphate, electrode compound facilities Areas with PL-I, including areas with inaccessible overhead line routes Standard long-rod porcelain insulator (L/h ≤ 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 bottom surface and a Sea and salt lake coasts, PL-II to IV protruding inner rib (L/D > 1.4), Anti-fog. Areas with PL-II to IV, any kind of pollution; areas with inaccessible overSpecial-make long-rod porcelain insulator (L/h > 2.5) head line routes, PL-II 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 9.

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

Pollution levels in the neighborhood of industrial pollution sources Pollution level at distance from the pollution source, m over 500 over 1000 over 1500 over 2000 over 2500 up to 500 up to 1000 up to 1500 up to 2000 up to 2500 up to 3000 1 1 1 1 1 1 2 1 1 1 1 1 3 2 1 1 1 1 3 3 2 1 1 1 4 3 3 2 2 1 4 4 3 3 3 2

over 3000 up to 5000 1 1 1 1 1 2

Table 10. Water basin Non-saline Low salinity Medium salinity

High salinity

Pollution levels (PL) in coastal areas of seas and lakes over 10,000 m2 Design salinity of water, g/l Distance from coast line, km up to 2 up to 0.1 up to 0.1 over 2 up to 10 over 0.1 up to 1.0 up to 0.1 over 10 up to 20 over 0.1 up to 1.0 over 1.0 up to 5.0 up to 1.0 over 20 up to 40 over 1.0 up to 5.0 over 5.0 up to 10.0

PL 1 2 1 3 2 1 3 2 1

over 5000 1 1 1 1 1 1