Course Code: EE 2316 - saadawi1.netsaadawi1.net/upLoadedFiles/extra_files/nmco81maoc.pdf · The...
Transcript of 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
9/17/2017 Prof. Dr. Magdi El-Saadawi 2
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
9/17/2017 7
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
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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.
Prof. Dr. Magdi El-Saadawi
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.
Prof. Dr. Magdi El-Saadawi
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.
Gases, Liquids, and Solids as Insulators
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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
Gases, Liquids, and Solids as Insulators
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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.
1.6. Basic Equipments
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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.
1.6. Basic Equipments
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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.
➢
1.6. Basic Equipments
Figure: (Left) a capacitive voltage transformer
30
➢ Circuit breakers and fuses
– The duty of circuit breakers and fuses is to rapidly
interrupt fault current.
1.6. Basic Equipments
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.
1.6. Basic Equipments
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Circuit breakers and fuses
➢ 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.
1.6. Basic Equipments
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Circuit breakers and fuses
➢ 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.
1.6. Basic Equipments
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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
1.6. Basic Equipments
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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.
1.6. Basic Equipments