Course Code: EE 2316 - saadawi1.netsaadawi1.net/upLoadedFiles/extra_files/ohlmmemmg.pdf · A simple method of controlled tripping consists of making the first gap a three electrode

High Voltage Engineering

Course Code: EE 2316

10/7/2017 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 Materials210/7/2017

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 Examples310/7/2017 Prof. Dr. Magdi El-Saadawi

10/7/2017 4

➢Definition: An impulse voltage is a unidirectional voltage

which rises rapidly to a maximum value and falls more or

less rapidly to zero as shown in Fig. 2.15• In case of oscillations in the wave shape, a mean curve should be considered.

wave front time

=1.25 (t2 – t1)

wave tail time = (t3 – t0)

Prof. Dr. Magdi El-Saadawi

2.4. Generation of Impulse Voltages and Currents

10/7/2017 5

– The wave front is the average rate of rise of voltage between

the points where the voltage is 10% and 90% of the peak value.

Lighting Impulse Voltage wave

– The standard wave shape specified in BSS and ISS is

1/50 micro sec. wave

a wave front of 1 micro sec. + 50%

a wave tail of 50 micro sec. + 20%

– 100 kV, 1/50 micro sec. wave means that peak value of 100 kV

– The wave shape recommended by the American Standard

Association is 1.5/40 micro sec.

– Here wave front time is taken as 1.67 times the time taken by the

wave to rise from 30% to 90% of its peak value and wave tail time

is computed as in BSS or ISS i.e. it is given as (t3 – t0)


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Switching Impulse Voltage wave

– The standard wave shape specified in BSS and ISS is

250/2500 micro sec. wave

a wave front of 250 micro sec. + 20%

a wave tail of 2500 micro sec. + 60%

Prof. Dr. Magdi El-Saadawi


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Lighting

Impulse

Voltage

wave

Switching

Impulse

Voltage

wave

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– An exact equivalent circuit of a single stage impulse

generator is shown in Figure 2.16 represents

2.4.1 Impulse Generator Circuits

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➢C1 capacitance of a d.c generator

➢L1 inductance of the generator and the leads connecting the

generator to the discharge circuit.

➢R1 inherent series resistance of the capacitances and leads

and often includes additional lumped resistance for output

waveform control.

➢L3, R3 are the external elements which may be connected at

the generator terminal for waveform control.

➢R2 and R4 control the duration of the wave.

R4 also serves as a potential divider when a CRO is used

for measurement purposes.


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➢C2 and C4 represent the capacitances to earth of the high

voltage components and leads.

C4 also includes the capacitance of the test object and of

any other load capacitance.

➢L4 represents the inductance of the test object and may also

affect the wave shape appreciably.

➢Usually for practical reasons, one terminal of the impulse

generator is solidly grounded. The polarity of the output

voltage can be changed by changing the polarity of the d.c.

charging voltage


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➢Two simplified and practical equivalent circuits of impulse

generator circuits are shown in Fig. 2.17 (a) and (b).

➢R2 = discharge resistance C1= discharge capacitance

➢R1 = damping resistance C2= load capacitance


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➢The maximum stored energy is

➢ For the analysis we may use the Laplace transform circuit

sketched in Fig. 2.17 (c), which simulates the boundary

condition, that

➢for t ≤ 0 C1 is charged to V0 and

➢for t > 0 this capacitor is directly connected to the wave-shaping

network.


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• A single stage circuit is inconvenient to obtain

higher and higher impulse voltage because:(i) The physical size of the circuit elements becomes very large.

(ii) High d.c. charging voltage is required.

(iii) Suppression of corona discharges from the structure and leads

during the charging period is difficult.

(iv) Switching of vary high voltages with spark gaps is difficult.


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Fig. 2.18 shows a 3-stage impulse generator circuit due to

Marx employing ‘b’ circuit connections.

➢ The impulse capacitors C1 are charged to the charging

voltage V0 through the high charging resistors Rc in

parallel.

➢ When all the gaps G break down, the C1 capacitances are

connected in series so that C2 is charged through the series

connection of all the wave front resistances R1 and finally

all C1 and C2 will discharge

➢ Usually Rc >> R2 >> R1.

➢ If in Fig. 2.18 the wave tail resistors R2 in each stage are

connected in parallel to the series combination of R1 , G

and C1 , an impulse generator of type ‘a’ is obtained.



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(i) d.c. Charging Set

The charging unit should be capable of giving a

variable d.c. voltage of either polarity to charge the

generator capacitors to the required value.

(ii) Charging Resistors

These will be non-inductive high value resistors of

about 10 to 100 kilo-ohms. Each resistor will be

designed to have a maximum voltage between 50

and 100kV.


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(iii) Generator Capacitors and Spark Gaps

These are arranged vertically one over the other with

all the spark gaps aligned. The capacitors are

designed for several charging and discharging

operations.

On dead short circuit, the capacitors will be capable

of giving 10 kA of current.

The spark gaps will be usually spheres or

hemispheres of 10 to 25 cm diameter. Sometimes

spherical ended cylinders with a central support may

also be used.


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(iv) Wave-shaping Resistors and Capacitors

Resistors will be non-inductive wound type and

should be capable of discharging impulse currents of

1000 A or more.

Each resistor will be designed for a maximum

voltage of 50 to 100 kV. The resistances are bifilar

wound or non-inductive thin flat insulating sheets.

In some cases, they are wound on thin cylindrical

formers and are completely enclosed. The load

capacitor may be of compressed gas or oil filled with

a capacitance of 1to10 μF.


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(v) Triggering System

This consists of trigger إثارة أو اشعال spark gaps to cause

spark breakdown of the gaps

A simple method of controlled tripping consists of

making the first gap a three

electrode gap and firing it from a controlled source.

(vi) Voltage Dividers

Voltage dividers of either damped capacitor or

resistor type and an oscilloscope with recording

arrangement are provided for measurement of the

voltages across the test object.



300 KV

Impulse

Generator


2.4-MV

impulse

generator


Indoor impulse

generator,

20-stage,

4-MV, 200-kJ,

with

encapsulated

sphere gaps

(Rio de Janero)


Video Link

https://www.youtube.com/watch?v=IrQsghadA8A


https://www.youtube.com/watch?v=IrQsghadA8A

Documents

Course Code: EE 2316 - saadawi1.netsaadawi1.net/upLoadedFiles/extra_files/ohlmmemmg.pdf · A simple method of controlled tripping consists of making the first gap a three electrode