where Е_{r.max.calc.и} = 10,4×d^-0,55×U/U_ph= 135.3 kV/cm – is maximal calculated field tension, defined by the conditions of unstable ionization.

      The number of insulation layers by the conditions of creeping discharge is:

,

where e×d_.– is maximal calculated field tension, defined by the conditions of creeping discharge;

e - is the dielectric constant o RIP insulation taken as 4,2.

      The dielectric thickness is taken δ=0.1cm.

      The number of isolation layers is taken by the minimal value of maximal calculated field tension, so  
 

      So we can take n=14.

Length of a ledge of the core inverted in apparatus: 

where k₁=1.4 – depreciation factor of durability. 

      The sum of lengths of ledges of one part of high-voltage bushier: 
 
 
 

      Let’s check up whether the received meaning Σλ_e satisfies the condition 
 

      The condition is satisfied, so we leave λ_l=2.064 cm

      The full sum of lengths of ledges is: 

 

      Length of a facing at a core: 

where for minimum conditions x=4.1.

      Length of null facing of the core: 

and parameter  

      The radius of null facing is: 

      The radius of n^th facing is: 

=6.56 cm

      Parameter A is: 

     and parameter: 

     Maximal tension in x layer:

      ,

     where layer voltage

     Layer length x is: 
 
 

     Table 3.2 – The results of layers calculation

      3.2 Calculating of china covers

 

      Length of the top tire cover is defined by the formula: 

      Length of the lower tire cover is defined by the formula: 

then

      Length of coupling 

      Inside diameter of the coupling is taken: 

      Outside diameter of the coupling is taken: 

      Inside diameter of tires 

      Outside diameter of tires 

      Diameter by sheds of insulator is 

      Number of sheds is: 
 

      The distance between sheds of insulator is: 
 
 

      Table 3.3 – Dimensions for rib calculating

 

      Figure 3.3 – The profile of a rib of a china insulator 

      Wet flashover test: 

      Layer voltage is: 

      Layer density is: 

      Medium radial density taken at maximum: 

      Skeleton volume is: 

      Maximal flange density: 
 

      3.3 Mechanical calculation

 

      Bushes treat to an operation of the bending loading affixed by the end of the air end. At calculations on a mechanical strength it is supposed that all loading is perceived by a chine tire cover and the internal part of lead does not carry mechanical loading.

      Width of a wall of a china tire cover is equal 35 mm;

      Moment of inertia: 
 
 

      where D=0.239 m, d=0.169 m – external and internal diameters of a china insulator accordingly.

      The moment of resistance to curving of bushes at round section: 
 
 

      Mechanical effort in section: 
 
 

      where M – flexing operating moment of an insulator: 
 
 

      The cross-section area of china cover: 
 
 

      Figure 3.4 – Dependence of limit strength of china at curving from cross-sectional area. 

      By the graph

      The condition is held 
 
 
 
 

      So the chosen parameters satisfy the request.

      3.4 Heat calculation

 

      At passage of a current on a current carrying core there is an allocation of heat in a core and in isolation owing to dielectric losses in it. At some temperature there is a thermal breakdown of isolation. Therefore it is important to define voltage at which there will be a breakdown of isolation, so-called thermal breakdown voltage which is defined: 
 
 

      where p₀ – losses in dielectric at temperature v₀, Wt/cm³;

      λ₁ – calorific conduction, Wt/(cm∙K);

      v_B – ambient temperature, °C.

      It is necessary to determine the following sizes: 
 
 
 
 
 

      where λ₂ – equivalent calorific conduction of a china cover and a layer of oil between RIP isolation and china, Wt/(cm∙K);

      r_i – outside radius RIP, cm;

      r₀ – outside radius of a current carrying pipe, cm;

      r_c – outside radius of a china cover, cm;

      k_T – factor of a heat dissipation from a surface of a china cover in air. 

Table 3.4 – Data for calculation of U_T.

 

Table 3.5 – Dependence of f_o(m).

 
 
 
 
 

      We can choose from the table by approximation f₀=0.6: 
 
 

      The received value should be in 1.5…2 times more then 1.1∙U_H.P. 

      So the demand is satisfied. 
 

 

4 DESIGN DESCRIPTIONS

 

      The job of the given academic year project consisted in constructing and calculation of high-voltage bushing insulator on the voltage 66 kV. The designed high-voltage bushing intended for installation on SF₆ factory-assembled switch-gear or switches - on voltage 330 kV. Bushing is installed on the height no more then 600 m on the sea level in normal pollution conditions. For a basis of projection it is chosen oil - filled hermetic high-voltage bushing insulator for transformers on voltage 66 kV.

      The current carrying circuit of high-voltage bushing insulator, comprise of a copper pipe. Lead has three isolation gaps: RIP condenser isolation, transformer oil and a china insulator. The upper part of high-voltage bushing insulator on voltage 66 kV will comprise of the following elements: the contact clip, the compensator of pressure, the upper china cover, a connective sleeve. The lower part: the lower china cover, the shield. Design of bushing is sealing. For indemnification of temperature changes of volume of oil the special equalizers built -in bushing serve. The internal insulation is executed as RIP isolation and placed in china covers filled by insulating oil. Bushing constantly is under superfluous pressure of oil.

On the connecting cartridge intended for fastening input are: clevis for rise of bushing, terminal for measurement of a tangent of a dielectric loss angle and capacities of an internal insulation which in a running time earthed the gate for adjustment of pressure and the measuring device with the manometer for the control of pressure over input. In the bottom part of bushing there is a shield. General view of construction is represented on the drawing 1. View of the lower china cover on sheet 2. View of current leading pipe on sheet 3.

 

CONCLUSION

 

      Result of execution of an academic year project became designed and calculated the high-voltage bushing insulator on 66 kV.

      Principal advantages of the given construction are that it is hermetic, hence there is no moistening and an intensive strain ageing of internal isolation of high-voltage bushing, it is reliable and safe. The following advantage of designed high-voltage bushing insulator is be relative the random distribution of voltage along a current carrying circuit. Disadvantage of the given construction is impossibility of recovery after breakdown. 

 

LIST OF REFERENCES

 
 

1. Methodical guide for course project on the "High-voltage apparatus" course for 8.092206 major - Electrical apparatus./Author A.Afanasiev.-Zaporozhue:ZNTU,2003. - 15 p.
2. Справочник по электрическим аппаратам высокого напряжения./ Под ред. Афанасьева В. В. - Л.: Энергоатомиздат, 1987.
3. Синявский В. Н. Расчет, конструирование и испытание изоляторов высокого напряжения. М.: Энергия, 1965.-112 с.
4. Справочник энергетика промышленных предприятий. Гольстрем В.А. ,Иваненко А.С.- К.: Техника»", 1997 г. - 562 с.
5. Дмитриевский В. С. Расчет и конструирование электрической изоляции. М.: Энергоиздат, 1981. 246 с.