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TRANSCRIPT
High Voltage Engineering
Course Code: EE 2316
9/23/2017 Prof. Dr. Magdi El-Saadawi 1
Prof. Dr. Magdi M. El-Saadawi
www.saadawi1.net
E-mail : [email protected]
www.facebook.com/magdi.saadawi
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 Materials29/23/2017
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 Examples39/23/2017 Prof. Dr. Magdi El-Saadawi
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High voltages (d.c., a.c., and impulse) are required for
several applications.
Electrostatic precipitators المرسبات الكهروستاتيكية , particle
accelerators in nuclear physics, etc. require high voltages
(d.c.) of several kilovolts and even megavolts.
High a.c. voltages of one mega volts or even more are
required for testing power apparatus rated for extra high
transmission voltages (400 kV system and above).
High impulse voltages are required for testing purposes to
simulate overvoltages that occur in power systems due to
lightning or switching surges. Prof. Dr. Magdi El-Saadawi
2.1. Introduction
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The main concern of HV is for the insulation testing.
Hence, generation of high voltages in laboratories for
testing purposes is essential.
Normally, in HV testing, the current under conditions of
failure is limited to a small value (less than an ampere in
the case of d.c. or a.c. voltages and few amperes in the case
of impulse or transient voltages).
But in certain cases, like the testing of surge diverters
,or the short circuit testing of switchgearموجهات الصواعق
high current testing with several hundreds of amperes is of
importance. It may reach to several kiloamperes. Prof. Dr. Magdi El-Saadawi
2.1. Introduction
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There are various applications of high d.c. voltages in
industries, research medical sciences etc. HVDC
transmission over both overhead lines and underground
cables is becoming more and more popular.
The most efficient method of generating high D.C. voltages
is through :
➢ the process of rectification employing voltage multiplier circuits.
➢ Electrostatic generators
Prof. Dr. Magdi El-Saadawi
2.2. Generation of High D.C. Voltages
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The simplest circuit for generation of high direct voltage is
the half wave rectifier shown in Fig. 2.1
Here RL is the load resistance and C the capacitance to
smoothen the d.c. output voltage
If the capacitor is not connected, pulsating d.c. voltage is
obtained at the output terminals whereas with the
capacitance C, the pulsation at the output terminal are
reduced.
Assuming the ideal transformer and small internal
resistance of the diode during conduction the capacitor C is
charged to the maximum voltage Vmax during conduction of
the diode D.Prof. Dr. Magdi El-Saadawi
2.2.1 Half-Wave Rectifier Circuits
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2.2.1 Half-Wave Rectifier Circuits
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When high d.c. voltages are to be generated,
voltage doubler or cascaded voltage multiplier
circuits are used.
➢Vilard voltage doubler Circuit
➢Greinacher voltage doubler circuit
➢Cockroft-Walton Voltage Multiplier Circuit
Prof. Dr. Magdi El-Saadawi
Voltage Multiplying Circuits
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if the transformer is grounded at A instead of B as
shown in Fig. 2.1 (a). Such a circuit is known as
voltage doubler due to Villard for which the output
voltage would be taken across D. This d.c. voltage,
however, oscillates between zero and 2Vmax and is
needed for the Cascade circuit.
Vilard Circuit
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Suppose B is more positive with respect to A and the diode
D1 conducts thus charging the capacitor C1 to Vmax with
polarity as shown in Fig. 2.2.
During the next half cycle terminal, A of the capacitor C1
rises to Vmax and hence terminal M attains a potential of
2Vmax.
Greinacher voltage doubler circuit
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Thus, the capacitor C2 is charged to 2 Vmax through D2.
Normally the voltage across the load will be less than 2Vmax
depending upon the time constant of the circuit C2RL.
Greinacher voltage doubler circuit
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Cockroft-Walton Voltage Multiplier Circuit
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• The portion ABM’MA is exactly
identical to Greinacher voltage
doubler circuit and the voltage
across C becomes 2Vmax when M at
voltage 2Vmax.
• During the next half cycle when B
becomes positive with respect to A,
potential of M falls and, therefore,
potential of N also falls becoming
less than potential at M’ hence C2 is
charged through D2. Next half cycle
A becomes more positive and
potential of M and N rise thus
charging C2 through D2.
• Finally, all the capacitors C’1, C’2,
C’3, C1, C2, and C3 are charged.
Cockroft-Walton at No Load Operation:
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• The voltage across the column of
capacitors consisting of C1, C2, C3,
keeps on oscillating as the supply
voltage alternates. This column,
therefore, is known as oscillating
column.
• However, the voltage across the
capacitances C’1, C’2, C’3, remains
constant and is known as smoothening
column.
• The voltages at M’, N’, and O’ are 2
Vmax, 4 Vmax and 6 Vmax. Therefore,
voltage across all the capacitors is
2Vmax except for C1 where it is Vmax
only.
Cockroft-Walton at No Load Operation:
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• The total output voltage is:
2nVmax
where n is the number of stages.
• Thus, the use of multistage
arranged in the manner shown
enables very high voltage to be
obtained.
• The equal stress of the elements
(both capacitors and diodes)
used is very helpful and
promotes a modular design of
such generators.
Cockroft-Walton at No Load Operation:
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Cockroft-Walton Generator Loaded:
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Cockroft-Walton Generator Loaded:
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Fig. 2.5
A Cockroft–Walton
d.c. generator for
voltages up to
900 kV/10 mA
with fast polarity
reversal at ETH
Zurich
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Solved Examples p. 48
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Solved Examples p. 48
Video Link
https://www.youtube.com/watch?v=DI8Yt1AQrH8
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