Advance H gh Vo tage Eng neer ng

Lecture # 1

Basics of High Voltage, Electric Field, its Estimation &

Electrode Configurations      

Hidaytaullah khan Phd Scholar CIIT

Islamabad

Course Books  

0 High Voltage and Electrical Insulation Engineering (June 2011 Edition) by Ravindra & Wolfgang (IEEE Press)

0 High Voltage Engineering Fundamentals (2nd Edition) by E.Kuffel, W.S.Zaengl, J.Kuffel

  

Reference Books   

• Advances in High Voltage Engineering (IET) Edited by A.Haddad & D.Warne

High Voltage Engineering by C.L. Wadhwa 0 High Voltage Engineering by M.S.Naidu (4th Edition)

        

Why High Voltage (Engineering)?    

It’s the knowledge of the behavior of dielectrics (insulator) — electrical insulation when subjected to high voltage

  

No concept of a complete Insulator – Even a good Insulator can conduct under High Voltages

 

  

Result is to minimize the volume of the electrical insulation requirements and trouble-free life of high voltage apparatus.

   

A totally different Domain (Engineering) when High Voltage are applied. Stray Capacitances & Inductances come into play.

HVAC & HVDC Transmission • Flexible AC Transmission System (FACTS) based on High Power

GTO and IGBT’s    

• Examples of FACTS system include Fixed Series Capacitors (FSC) Thyristor Controlled Series Capacitor (TCSC) and STATCOMS

• Link for FACTS devices http://www.siemens.com.pk/pt_ac.html    

• List of HVDC Projects http://en.wikipedia.org/wiki/List_of_HVDC_projects

Basic Definitions to Start With     

• Electron • Proton • Ion • Ionization

 

• Electric Charge • Space Charge

 

• Volume Charge Density ρv

• Electric Discharge • Electric & Magnetic Field • Electromagnetics

Di-Electric & Electric Material

  

0 What the difference between these ?    

• Electric Material – capable of developing (conducting) electric charge or current

 

 

• Di-Electric Material – not capable of developing (conducting) electric charge or current but admits electrostatic and magnetic lines of force

 

• Di-Electric Material Properties– Relative Permittivity εr , Type of Material & Amplitude of Voltage Applied

 

 

Electrical Breakdown    

0 Failure of Electrical Insulation Properties (flow of current) of an Insulator or Di-electric                

Local Breakdown confined locally to a part of an Insulator

(Partial Breakdown)

Global Breakdown complete rupture or failure of insulator

properties (Electrical Breakdown)

 

Corona:  Partial Electrical Breakdown (discharge)     

0 Stable Partial Breakdown (PB) in Gaseous Di-electrics

  

• Types: Audible & Visible Corona        

Streamer:   

Extension of Corona at Distance  

Shower of Discharge (Streamer Corona) Example: Discharge of Cloud (Lightning)

 

Aurora:  

Luminous phenomenon consisting of streamers or Arches of Light at Polar Regions

   

• Explained under “Faraday’s Glow Discharge”  

• Atoms in Ionosphere stuck by High Energy Electrons Coming from Sun (cosmic Radiation)

  

• Aurora Australis (Southern Hemisphere)  

• Aurora Borealis (Northern Hemisphere)

 

Aurora:    

Di-electric Property: Capacitance         

0 Is the field between the plates of a Capacitor Uniform?     

• Permittivity of a Di-electric is Constant ?    

Stray Capacitance    

• How to minimize it?

Electric Field            

• Electric Charge is considered static when there is no movement of charge

 

• Field produced by Static charge or Direct Voltage is known as Electro-static field

 

• Field produced by power frequency Alternating voltage is known as quasi-stationary Electric field

Dielectric Breakdown depends on

    

& Composition of dielectric material, presence of impurities imperfections in the dielectric

 

& Pressure  

& Humidity  

& Temperature  

& Electric field configuration (shape of the electrodes, their size and gap distance)

 

& Electrode material  

& Duration  

& Magnitude and the waveform of the applied voltage

Electric Field Lines & Equipotential Lines  

                                      

Field Between Sphere or Cylinder and Plane

Electric Field Lines & Equipotential Lines    

      

Field on a Bundled Conductor Cross Section

Electric Field Intensity or Stress        

Electrostatic Force per unit positive test charge q placed at a particular point p in a dielectric

    

Electric Field Intensity E = F / q [N/C] or [V/m]    

More commonly used unit are KV/cm or KV/mm    

Potential Difference between two points a an b? How to find it in terms of Electric Field E

Electric Field Intensity or Stress           

Uab = Ua - Ub  

Uab = <a - <b   

Uab = Work done in moving a Unit positive charge from point b to point a

 

 

Uab is positive if Work is done which means <a

is at a higher potential

Electric Field Intensity or Stress       

Electric Field intensity E is given by the rate of change of potential with distance

            

              

Maximum value of the rate of change of potential is obtained when the direction of E is opposite to the direction in which potential is increasing rapidly

The maximum magnitude of the Field Intensity can there be obtained when the direction of the increment of the distance is opposite to the direction of E

Electric Field Intensity or Stress                                      

Electric Field intensity E is numerically equal to the potential

gradient

 

  

Partial Breakdown in Di-electrics  

• Gases: CORONA (Stable)    

• Solid and Liquid: INTERNAL BREAKDOWN    

Surface Breakdown or Tracking    

When Partial Breakdown takes place on the surface of a solid or a liquid its called as Surface Breakdown or Tracking

    

Partial Breakdown Inception Voltage Ui

 

  

Classification of Electric Fields  

                                     

η is Schwaiger Factor (Dimensionless Quantity)

Classification of Electric Fields                  

Dielectric Between Parallel Plates

Classification of Electric Fields                  

Sphere-Sphere Electrodes

Classification of Electric Fields                  

Needle-Needle Electrodes

 

 

Degree of Uniformity of Electric Fields  

    

1            

-          

Schwaiger Factor

Degree of Uniformity of Electric Fields    

Geometrical Characteristic Factor (p)

 

 

Divergence      

“The divergence of the vector flux density A is the outflow of flux from a small closed surface per unit volume as the volume shrinks to zero

    

OR  

     

Divergence at a point (x,y,z) is the measure of the vector flow out of a surface surrounding that point

Divergence for Fields (continued) 

t .- ep--. J

Imaginary - - --...

t't / \

-

 

Vector Field: A

Surface (S) / t "   

I ' / \

, /' 1

 

Vector Field: B Imaginary

Surface (S) / I "   

I

ep • J

, /t' l .......... - / - /

  

Vector Field: C Imaginary Vector Field: D

Imaginary -   

Surface (S) / " Surface (S) / t t t"' '

1

I f ep f I \ 1 t t I

I /\. \ I f ep !I

- \ •-

/ I

Divergence for Fields 

+--+

ar ao r+ . -( + . - (

 

Vector Field: E Imaginary

Surface (S) -t-.... /

 

I \             

di D = a Dx-

    a Dy

-

-  

aD:.

a - ay a -     

1 a 1 aD¢ aD. div D = -- p D cylindrical p ap P p a<t> a-:

    

. I a I a . I aD dtv D =-:; - ( rD, mO D0 pheri al)

r- r tn B tn B 8if>

Curl for Fields 

 

The curl of any vector is a vector, and any component of the curl is given by the limit of the quotient of the closed line integral of the vector about a small path in a plane normal to that

component desired and the area enclosed, as the path shrinks to zero.”

  

OR   

We can describe curl as circulation per unit area. The closed path is vanishingly

small, and curl is defined at a point

Curl  

 

Curl for Fields 

-V x < p +

 

Curl      

curl H = ( a H. aaHx ·)

+ ( a Hx - -a---H=.:. ) <J , + ( -a-H--,. - a Hx a-

ay a- a- ax 1 · ax ay ..

     

1 aH aH <> aHp aH p CJ<P a - a- ap

--- 1 CJHP c lindric

+ p a<P

;

      

1 aHr in o a<fJ

 ( pherical)

 

 

 

Maxwell’s Equation

 

               

Today’s Text Covered from (Chapter 1) of IEEE Press Book (Ravindra Book) + Up-til Article 2.4

(Chapter 2)    

and    

Chapter 1 of Kuffel Book