course code: ee 2316saadawi1.net/uploadedfiles/extra_files/0le932n8o3.pdfvan de graaff generator pp....

High Voltage Engineering

Course Code: EE 2316

10/3/2017 Prof. Dr. Magdi El-Saadawi 1

Prof. Dr. Magdi M. El-Saadawi

www.saadawi1.net

E-mail : [email protected]

www.facebook.com/magdi.saadawi

http://www.saadawi1.net/

http://www.saadawi1.net/

ContentsChapter 1

Introduction to High Voltage Technology

Chapter 2

Generation of High Voltages and Currents

Chapter 3

Measurement of High Voltages and Currents

Chapter 4

Breakdown Mechanism of Gases, Liquid and

Solid Materials210/3/2017

Chapter 2

Generation of High Voltages and Currents

2.1. Introduction

2.2. Generation of High D.C. Voltages2.2.1 Half-Wave Rectifier Circuit

2.2.2 Cascade circuits

2.2.3 Electrostatic Generators

2.3. Generation of High A.C. Voltages2.3.1 Cascaded Transformers

2.3.2 Series Resonant Circuit

2.4. Generation of Impulse Voltages and Currents2.4.1 Impulse Generator Circuits

2.4.2 Multistage Impulse Generator Circuit

2.4.3 Components of a Multistage Impulse Generator

2.5. Solved Examples310/3/2017 Prof. Dr. Magdi El-Saadawi

10/3/2017 4

Electrostatic generators convert mechanical energy into

electric energy directly.

The electric charges are moved against the force of electric

fields.

In Fig.: An insulated belt is moving with uniform velocity

in an electric field of strength E(x).

Prof. Dr. Magdi El-Saadawi


Principle of electrostatic generators

10/3/2017 6Prof. Dr. Magdi El-Saadawi

Construction of

Van De Graaff

Generator pp. 26

Principle of

Operation of

Van De Graaff

Generator pp. 27


Van de Graaff

Generator

( Paris , 1994)


5 MV Van de

Graaff generator

built in 1937 by

the Westinghouse

Electric company

in Pennsylvania

10/3/2017 13

• Advantages:

– Very high voltages can be easily generated

– Ripple free output

– Precision and flexibility of control

• Disadvantages:

– Low current output

– Limitations on belt velocity due to its tendency for vibration. The

vibrations make it difficult to have an accurate grading of electric

fields

• Applications:

– in nuclear physics laboratories for particle acceleration

– accelerating electrons to sterilize food and process materials,

– producing energetic X-ray beams in nuclear medicine



10/3/2017 14

The two main methods are:

transformers and resonant circuits.


2.2. Generation of High A.C. Voltages


(1) Iron core.

(2) Primary L.V. winding.

(3) Secondary H.V. winding.

(4) Field grading shield.

(5) Grounded metal tank

and base.

(6) H.V. bushing.

(7) Insulating shell or tank.

(8) H.V. electrode

10/3/2017 19

For voltages higher than 400 KV, the insulator of the

transformers must be stronger and will take large space and

will be costly so:

It is desired to cascade two or more transformers depending

upon the voltage requirements. (Fig. 2.9)

It is to be noted that the individual stages except the upper

most must have three-winding transformers


2.3.1 Cascaded Transformers

10/3/2017 20

The primary of the first stage transformer is connected to a low

voltage supply. The tertiary winding (excitation winding) of first

stage has the same number of turns as the primary winding, and feeds

the primary of the second stage transformer.

The potential of the tertiary is fixed to the potential V of the

secondary winding.

The secondary winding of the second stage transformer is connected

in series with the secondary winding of the first stage transformer, so

that a voltage of 2V is available between the ground and the terminal

of secondary of the second stage transformer.

Similarly, the stage-III transformer is connected in series with the

second stage transformer. With this the output voltage between

ground and the third stage transformer, secondary is 3V.




Horizontal

Configuration


Vertical

Configuration

10/3/2017 25

Disadvantages of this scheme:

- Expensive and requires more space (for horizontal configuration).

- The lower stages of the primaries of the transformers are loaded more as

compared with the upper stages.

Advantages of this scheme is that:

- Natural cooling is sufficient

- The transformers are light and compact.

- Transportation and assembly is easy.



10/3/2017 26

Resonance may occur in the circuit suddenly and the

current will then only be limited by the resistance of the

circuit and the voltage across the test specimen may go up

as high as 20 to 40 times the desired value.

With series resonance, the resonance is controlled at

fundamental frequency and hence no unwanted resonance

occurs.

The development of series resonance circuit for testing

purpose has been very widely welcome by the cable

industry as they faced resonance problem with test

transformer while testing short lengths of cables.



10/3/2017 30

Advantages of series resonance circuit.

(i) The power requirements in KW of the feed circuit is very

small.

(ii) The series resonance circuit suppresses harmonics and

interference to a large extent.

(iii) In case of a flashover or breakdown of a test specimen

during testing on high voltage side, the resonant circuit is

detuned and the test voltage collapses immediately. The

short circuit current is limited by the reactance of the

variable reactor



10/3/2017 31

Advantages of series resonance circuit.

(iv) No separate compensating reactors (just as we have in

case of test transformers) are required. This results in a

lower overall weight.

(v) When testing SF6 switchgear, multiple breakdowns do

not result in high transients.

(vi) Series or parallel connections of several units is not at all

a problem. Any number of units can be connected in

series without bothering for the impedance problem

which is very severely associated with a cascaded test

transformer. In case the test specimen requires large

current for testing, units may be connected in parallel

without any problem.Prof. Dr. Magdi El-Saadawi



400 KV

AC

resonant

system

Video Link

https://www.youtube.com/watch?v=uGRXnVtyUHo

https://www.youtube.com/watch?v=Xqt2gAalV4Y

https://www.youtube.com/watch?v=87qTGPh1kaw





https://www.youtube.com/watch?v=87qTGPh1kaw

course code: ee 2316saadawi1.net/uploadedfiles/extra_files/0le932n8o3.pdfvan de graaff generator pp....

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