ABSTRACT

 

      EN: 27 pages, 8 figures, 5 tables, 5 sources, 3 drawings.

      Subject of investigation – high-voltage bushing.

      Aim of the work – to learn to use engineering methods of calculation

of electrical devises with the constructor development and solving problem of producing all details and devise itself. The work on this term project is for better understanding for students of such course as "High voltage apparatuses" "SAD", and solving the problem of diploma designing.

      Bushes apply to a conclusion of wires of high potential from tanks of transformers, oil switches, and also for a lining of wires through walls of buildings.

This work was held with the usage of program package MathCAD. Usage of this program gives us possibility to accept more accurate results. The drawings were made by program package AutoCAD.

      For the realization of the purpose of this project was designed the high-voltage Bushing with RIP insulation.

      Given data:

Nominal voltage: U_n=66 kV;

Nominal current: I_n = 400 A; as soon as bushings are produced only for the nominal current 630 A we take this value as the input data.

Isolation:internal-external;

Environment: Air-oil;

Type of hermetization: Hermetic;

Type of apparatus: high-voltage bushing;

Load;P=5kN;

Device is installed on 600m 

BUSHING INSULATOR, HIGH-VOLTAGE BUSHING, CHINA COVER. INSULATION, RIP INSULATION, OIL-BARRIER INSULATION, CAPACITY PLATE, TRANSFORMER OIL 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

CONTENTS

TASK…………………………………………………………………………….…2

ABSTRACT 3

INTRODUCTION 6

1 CONSTRUCTIONS OF HIGH VOLTAGE BUSHINGS 7

2  DESCRIPTION OF CHOSEN CONSTRUCTION 13

3 CALCULATION OF INSULATOR 14

3.1 Calculation of isolation. 14

3.2 Calculating of china covers 19

3.3 Mechanical calculation 21

3.4 Heat calculation 22

4 DESIGN DESCRIPTIONS 25

CONCLUSION 26

LIST OF REFERENCES 27

 

INTRODUCTION

 

      Bushes are applied for terminal of wires of high potential from tanks of transformers, oil switches, and also for a lining of wires through walls of buildings. Hey are installed the bush on a cover of the tank or on a wall of the building the metal flange. Bushes can well work at height of no more then 1000м above sea and in an interval of temperatures from-40 up to +45° with relative humidity up to 85%. Corresponding designs of isolators can be used for other, heavier environmental conditions.

      Bushings are BI, intended for carrying out of current carrying parts of the device through his (its) earthed parts.

      Bushes (BI) have two executions: internal installation (either ends BI are indoors or the device) in accordance with GOST 20454-79 and external-internal installation (one end BI is outside of a premise or the device) in accordance with GOST 20479-83. From both cleaning cloth PI there can be a same environment (air -air) or different environments (air - oil or air - SFe gas).

      Aim of the work – to learn to use engineering methods of calculation

of electrical devises with the constructor development and solving problem of producing all details and devise itself. The work on this term project is for better understanding for students of such course as "High voltage apparatuses" "SAD", and solving the problem of diploma designing. 
 
 
 
 
 

      1 CONSTRUCTIONS OF HIGH VOLTAGE BUSHINGS

 

      Bushes (BI) have two executions: internal installation (either ends BI are indoors or the device) in accordance with GOST 20454-79 and external-internal installation (one end BI is outside of a premise (room) or the device) in accordance wilh GOST 20479-83. From both cleaning cloth BI there can be a same environment (air - air) or different environments (air - oil or air - SF$).

      Bushes (high-voltage bushings are BI, intended for carrying out of current carrying parts of the device through its grounded parts) in the elementary kind represent a cylindrical body from one dielectric or several layers of various dielectrics along which axis passes a current carrying core; outside in an average part the body is covered by the metal grounded flange serving for fastening of isolator to the case of the device or to walls of buildings.

      Bushes for outside installations have a china detail with far acting edges (wings) which are located in the top hamper of isolator intended for work in an outside atmosphere

      High-voltage bushings, as well as bushes, have external and an internal insulation. External insulation will consist of the top china cover taking place in an external atmosphere and tightly connected to the bottom china cover by the metal connecting cartridge and ring linings from rubber. High-voltage bushings can be established under a corner of an inclination to a vertical from 0-45 and 0 - 90° depending on their design.

      The top china cover has far acting edges (wings) intended for protection against a rain of sites of a surface, located under acting edges. Its both parts work for linear High-voltage bushing in the air environment, but one part settles down inside the building, and another outside.

      High-voltage bushings divide on their design on tight, leaky and oil-filled. The internal insulation of tight high-voltage bushings has no message with an environmental atmosphere. At leaky high-voltage bushings the oil filling in them, has the message with an environment through an oil bar and drier of air. The last detain humidifying and oxidation of oil. Oil-filled high-voltage bushings tight, but have the general (common) oil system with transformers and chokes on which they are established.

      To destination distinguish high-voltage bushings for transformers, chokes, oil switches and for pass through walls and overlapping (linear high-voltage bushings).

      High-voltage bushings for transformers and chokes establish under a corner from 0 up to 60°, for oil switches - from 0 up to 15°, and linear high-voltage bushings - from 0 up to 90°.

      High-voltage bushings make or without additional capacity C2 (the measuring condenser), or with the measuring condenser for connection of devices of measurement of a voltage and let out(release) on rated voltage 66, 110,150, 220, 330, 500 both 750 KB and rated currents 200, 320, 400, 630, 800, 1000, 1250, 1600, 2000 and 2500 And.

      Besides let out high-voltage bushings with normal and amplified (strengthened) external insulation. In the latter case the top cover has more advanced surface at acting edges. Thus the leakage path length of a current on a surface of a china cover considerably increases. High-vokage bushings with amplified (strengthened) external insulation are used in areas with a dusty atmosphere.

      The majority of high-voltage bushings is intended for work at temperature from-45 up to +40°C on a voltage from 66 up to 500 KB at height no more than 1000 m above sea level, and high-voltage bushings on a voltage 750 KB - no more than 500 m inclusive can work. Amplified (strengthened) designs of high-voltage bushings can work and in more heavy conditions of operation.

      All high-voltage bushings should have strictly certain mechanical, thermal and electric parameters.

      Now several constructional types of bushings can be regarded.

      Bushings for power transformers and reactors are manufactured with two types of internal insulation of the capacitor type: solid (RIP Resin Impregnated Paper) and paper-oil (OIP Oil Impregnated Paper).

      Solid insulation.

      Internal insulation is the main structural part of the bushing and presents an insulation core, which is formed by winding insulating paper on the central pipe with sliced conducting leveling plates. Facings are used for optimal distribution of electric field in the radial and axial directions, which ensures the highest values of electric strength of both internal and external insulation, including a transformer placed on the bottom of the bushing.

      The isolating core is formed by crepe winding. Then the feedstock is saturated with epoxide compound under vacuum with the following solidification under pressure. This way all gas including are removed. 

      Figure 1.1 – The construction of bushing with solid insulation

      After thermal processing and glazing of the outer surface the isolating core forms a solid heart on which the coupling is installed by press fit. For better sealing between the coupling and the core the interfaces are filled with epoxy.

      Advantages:

• high reliability;
• long operation life.

Disadvantages:

• impossibility of recovery after breakdown.

 

      Paper-oil insulation.

      Internal insulation is the main structural part of the bushing and presents an insulation core, which is formed by winding dielectric paper on the central pipe with sliced conducting leveling plates. Facings are used for optimal distribution of electric field in the radial and axial directions, which ensures the highest values of electric strength of both internal and external insulation, including a transformer placed on the bottom of the bushing.

      Before assembling the core is dried under vacuum. After assembling bushing is processed by vacuum and saturated with transformer oil.

      Advantages:

• low cost;
• ability of automation of the producing process

      Disadvantages:

• construction is complex;
• combustibility;
• process of drying and impregnation is long.

 

      Figure 1.2 – The construction of bushing with paper-oil insulation 

      Gas-filled bushings can include either capacitor plates or cylinder-disk system. The isolation is presented by air, nitrogen, SF6 and mixture of nitrogen and SF6.

      Advantages:

• high isolating properties;
• high blowout properties;
• quick recovery of electric strength;

Disadvantages:

• can be used only in sealing bushings;
• risk of liquefaction process.

 
 
 
 

      Figure 1.2 – The construction of bushing with gas insulation 

      As a pesult of processing I choose oil-filled bushing with RIP insulation as it is the newest technology. The description is in the next paragraph.

 

2  DESCRIPTION OF CHOSEN CONSTRUCTION

 

      The designed high-voltage bushing on voltage 66 kV and nominal current 630 A will have next construction. As soon as bushings are produced only for the nominal current 630 A we take this value as the input data.

      The current carrying circuit of high-voltage bushing insulator, will comprise of a copper pipe. Lead will have three isolation gaps: RIP condenser isolation, transformer oil and a china insulator.

      We have the composition of next insulating materials: -internal insulation is the RIP insulation composed from bakelite paper and epoxy compound; external insulation are the china covers.

      Lower china cover will not have ribs.

      As analogical construction the bushing was chosen ГКТIII-60-66/630 (See on figure 2.1).But designing bushing will have more dimension.

      The high-voltage bushing comprise of the following elements: the contact clip - 1, the compensator of pressure - 2, the upper china tire casing - 3, a connective sleeve –  4, the lower china tire casing - 5, the shield - 6. 

      Figure 2.1 – Bushing on 66 kV.

 

      3 CALCULATION OF INSULATOR

      3.1 Calculation of isolation.

 

      For calculation of isolation the insulation gaps must be calculated.

      The composition of next materials is presented:

• Internal insulation is the RIP insulation composed from resin impregnated paper;
• External insulation is the china covers.

      The insulation gap through the thickness of bakelite paper δ and also length of china covers L to preserve the surface discharge in the air. The next methodic is used ([3], p. 138-157). 

      Figure 3.1 – Calculated gaps 

Phase operating voltage : 
 
 

      Figure 3.2 – A location of facings in high voltage bushing isolator 

      The cross-section of a current carrying pipe is defined proceeding from meaning of an initial current and an economic current density.

      In table 3.2 the sections of a current carrying pipe given for a choice are resulted.

I_max – the greatest working current;

I_n – nominal current;

J – the accepted current density (for copper conductors J=0.9-1.2 A/mm²). 

      Table 3.1 – Currents for definition of section of a current carrying pipe.

 

      Let us choose copper pipe with external diameter d_out and internal d_in :

d_out=30∙10^-3 m;

d_in=20∙10^-3 m.

      When calculating the isolation of bushings the condition E=const is used and the next equality is used:

U = 1,1U_c,

where U_c=140 kV is test voltage in the dry state, when there should not be creepages at the edges of the equalizing facings. The coefficient 1.1 takes into account the deviation of the test voltage caused by test conditions and measurement accuracy.

U = 1,1∙140=154 kV

      The number of insulation layers is defined by the formula:

,

where d_min is the minimal dielectric layer thickness;

E_max.calc. is the maximal radial tension.

      The number of insulation layers by the conditions of unstable ionization is: