course code: ee 2316 - saadawi1.netsaadawi1.net/uploadedfiles/extra_files/nmco81maoc.pdf · the...

High Voltage Engineering

Course Code: EE 2316

9/17/2017 Prof. Dr. Magdi El-Saadawi 1

Prof. Dr. Magdi M. El-Saadawi

www.saadawi1.net

E-mail : [email protected]

www.facebook.com/magdi.saadawi

Assessment Schedule

➢Assessment 1 test in Lecture week 4

➢Assessment 2 Midterm exam week 7

➢Assessment 3 test in Lecture week 10

Weighting of Class Grading (Total 75 marks for

this Part )

▪ Lecture Exams (2 Scheduled Exams) 8 marks

▪ Midterm Exam 10 marks

▪ Reports and Sheet 7 marks

▪ Final Exam 50 marks


Students’ Assessment كيفية تقييم الطالب

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 Materials39/17/2017

Chapter 1

Introduction to High Voltage Technology

1.1. Introduction

1.2. Voltage Classification

1.3. Advantages of Increasing of Voltage

1.4. EHV and its advantages

1.5. Voltage Stresses

1.6. Basic Equipment

1.7. Testing voltages

49/17/2017 Prof. Dr. Magdi El-Saadawi

Introduction

to

High Voltage Technology

Chapter 1


9/17/2017 6Prof. Dr. Magdi El-Saadawi

1.1. Introduction

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The Main effect of voltage increase are:

a) Weight of copper used for transmission.

b) Efficiency of the line.

c) The line voltage drop.

Prof. Dr. Magdi El-Saadawi

1.3. Advantages of increasing of voltage


a) Weight of copper used for transmission


b) Efficiency of the line


c) The line voltage drop

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For P and l remaining constant:

➢The increase in voltage causes saving copper losses,

increase in efficiency, and decrease the voltage drop.

but also

➢ the improved power factor decreases the copper losses,

decreases the volume of copper used and increase the

efficiency of the line.


1.4. Advantages of EHV

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EHV (400 KV, 760 KV, and 1000 KV) transmission are

increasingly used for very long distances or for inter

connections between two or more separate power systems

to achieve sharing of installed reserve and other economic

aspects.

At doubled voltage, a transmission circuit can carry

approximately twice as much power at the same current.

At doubled voltage, a transmission circuit can carry

approximately four times as much power at the same

percentage voltage regulation and percentage losses.


1.4. Advantages of EHV

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• Conductor:

– The element which carries the current and is subjected to

the high tension “high voltage”.

• Insulating material

– The element which prevents the current to flow through

the undesired parts.

– The dielectric strength of an insulating material is an

important factor which specifies the importance of the

insulator.

– Understanding of the failure of the insulation will be

possible by the study of the possible mechanisms by

which the failure can occur.

HV science focuses on two main factors

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• Gases as Insulators:

– Air at atmospheric pressure is the most common gaseous

insulation.

– Many types of gases used as insulators include: air,

nitrogen, SF6, CO2, vacuum, …. etc.

– They are used as insulators in high voltage equipment,

e.g. transformers, circuit breakers (SF6 circuit breakers),

switchgear, etc.

– Breakdown occurs in gases due to the process of

collisional ionization.

Gases, Liquids, and Solids as Insulators

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• Liquids as Insulators:

– Dielectric liquids are used as electrical insulators in high

voltage applications, e.g. transformers, capacitors, high

voltage cables, and switchgear

– Liquids serve dual purpose of insulation and cooling.

– They have the advantage that a puncture path is

self−healing تعالج نفسها ذاتيا .

Temporary failures due to over voltages are reinsulated

quickly by liquid flow to the attacked area.

– Some examples of dielectric liquids are transformer oil,

liquid oxygen, liquid nitrogen, and purified water.


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• Solids as Insulators:

– Solid dielectric materials are used in all kinds of

electrical circuits and devices to insulate one current

carrying part from another when they operate at different

Voltages.

– Many types are used in overhead transmission lines and

underground cables as studied in 2nd grade


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– The voltage stresses on power systems arise from various

overvoltages. These may be of external or internal origin.

– External overvoltages are associated with lightning

discharges and are not dependent on system voltage.

– Internal overvoltages are generated by changes in the

operating conditions of the system such as switching

operations, a fault on the system or fluctuations in the

load or generation.

– In designing the system's insulation, the two areas of

specific importance are:

• the voltage stresses which the insulation must withstand.

• the response of the insulation which subjected to these voltage

stresses.

–

1.5. Voltage Stresses

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➢ Power lines: towers, conductors, and insulators.

– ….

➢ Underground power cables

– ….

➢ Power transformers

– ….

1.6. Basic Equipments

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➢ Bushings

– It is sometimes required to take a high voltage conductor

through a wall or the tank of a transformer.

– In such cases a bushing is required to support the high

voltage conductor and to provide the necessary insulation

in the axial and radial directions.

– In this case the voltage distribution is non-linear in both

the axial and radial directions.

– The voltage gradient (E) is also high close to the high

voltage conductor and this could cause discharges in

those regions.


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Instrument transformers

➢ Voltage transformer (VT)

– Voltage transformers are typically power transformers

with a rating of 110 kV: 110 V, a ratio of 1000:1 for

measuring, metering and protection purposes

➢ Current transformers (CT)

It is a type of

transformer that

is used to measure

AC Current.


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Instrument transformers

➢ A capacitor voltage transformer (CVT)

– It is a transformer used in power systems to step down

extra high voltage signals and provide a low voltage

signal, for metering or operating a protective relay.

➢


Figure: (Left) a capacitive voltage transformer

30

➢ Circuit breakers and fuses

– The duty of circuit breakers and fuses is to rapidly

interrupt fault current.


Figure: Schematic representation of the interruption of the fault current

by a circuit breaker and associated protection relays

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Circuit breakers and fuses

➢ Air blast circuit breakers – In air blast circuit breakers, compressed air at pressures

as high as 1 Mpa is used to blow out the arc as the

contacts are separated.

– While the contacts are open, full system voltage appears

across the contact and the required insulation is provided

by the pressurized gas.


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➢ SF6 circuit breakers

– The insulation and arc quenching tasks are both performed

by SF6 gas which has high insulation characteristics

– The gas also has the ability to assist arc quenching, تبريد

due to its thermal and electronegative properties.


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➢ Fuses

– Fuses are mainly used up to voltage 22 kV.

– High rupturing capacity fuse elements are used.

– The fuses are often pole-mounted as drop-out fuse link

assemblies.


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➢ Isolators

– When working on apparatus, such as circuit breakers, it is

necessary to disconnect the apparatus from the live system

and to apply visual earths.

– For this purpose, isolators and earthing switches are

provided.

– Isolators are different from circuit breakers in that they

should be operated under no load current and they have no

arc quenching capacity.

– Isolator are off-load devices while, circuit breaker are an

on-load device.

– Isolator is a switch operated manually, which separate the

circuit from the power main


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➢ Surge arresters and Lightning arresters

– The power system is subject to transient overvoltages due

to lightning and switching.

– Lightning arresters, also called surge diverters, are applied

to limit the peak voltages to values that cannot damage the

equipment to limit overvoltages.

– Lightning arresters are usually fitted with grading rings to

ensure a more uniform voltage distribution over the height

of the arrester.


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course code: ee 2316 - saadawi1.netsaadawi1.net/uploadedfiles/extra_files/nmco81maoc.pdf · the...

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