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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
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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
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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
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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
2.2.3 Electrostatic Generators
Principle of electrostatic generators
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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
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2.2.3 Electrostatic Generators
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Van de Graaff
Generator
( Paris , 1994)
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5 MV Van de
Graaff generator
built in 1937 by
the Westinghouse
Electric company
in Pennsylvania
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• 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
Prof. Dr. Magdi El-Saadawi
2.2.3 Electrostatic Generators
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The two main methods are:
transformers and resonant circuits.
Prof. Dr. Magdi El-Saadawi
2.2. Generation of High A.C. Voltages
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(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
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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
Prof. Dr. Magdi El-Saadawi
2.3.1 Cascaded Transformers
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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.
Prof. Dr. Magdi El-Saadawi
2.3.1 Cascaded Transformers
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Horizontal
Configuration
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Vertical
Configuration
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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.
Prof. Dr. Magdi El-Saadawi
2.3.1 Cascaded Transformers
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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.
Prof. Dr. Magdi El-Saadawi
2.3.2 Series Resonant Circuit
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2.3.2 Series Resonant Circuit
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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
Prof. Dr. Magdi El-Saadawi
2.3.2 Series Resonant Circuit
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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
2.3.2 Series Resonant Circuit
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400 KV
AC
resonant
system
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Video Link
https://www.youtube.com/watch?v=uGRXnVtyUHo
https://www.youtube.com/watch?v=Xqt2gAalV4Y
https://www.youtube.com/watch?v=87qTGPh1kaw
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