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High Voltage Introduction
Professor Ahdab Elmorshedy
Cairo University, Faculty of
Engineering
High Voltage
What is high voltage? Why is it needed?
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High voltage
Potential, V:
Electrical location of a point according to a
reference.
unit: volt
Voltage, U:
unit: volt
Potential, V:
Electrical location of a point according to a
reference.
unit: volt
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Voltage, U: potential difference
unit: volt
Alternating voltage
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Direct voltage
Direct Voltage
Impulse voltage
Impulse Voltage
High voltage
U > 1000 Volt = 1 kiloVolt
High voltage (HV)
U 1000 Volt = 1 kiloVolt
Low voltage (LV)
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High voltage towers
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Standard Suspension Insulator - Ball & Socket
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Standard suspension Insulator - Tongue & Clevis
Technical Data
0216- 0216-
Catalogue Number
70 80
Porcelain Disk Diameter / mm 255 255
Unit Spacing / mm 146 146
Creepage Distance / mm 295 295
Electromechanical Failing Load / kN 70 80
Standard Coupling According to IEC 471 16c 16c
Long-rod Insulator
Catalogue Number 1503
IEC 60433 Designation L70E
Nominal Creepage Distance / mm 655
Electromechanical Failing Load / kN 70
Nominal System Voltage / kV 20
Dry 50% Flashover Positive / kV 221
Lightening Voltage Value Negative / kV 231
Impulse Withstand Positive / kV 212
Voltage Voltage Value Negative / kV 222
Avg. Flashover 90
Wet Power Frequency Voltage / kV
Withstand 81
Radio Interference Voltage at 1 MHz / V 5
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1 kV < U 52 kV
Medium Voltage, MV
52 kV < U 300 kV
High Voltage, HV
300 kV < U 800 kV
Extra High Voltage, EHV
800 kV < U
Ultra High Voltage, UHV
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High voltage levels
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In Egypt:
Medium Voltage: 11, 22 kV
High Voltage: 66, 132, 220 kV
Extra High Voltage: 500 kV
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High DC voltage
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Why do we need high voltage
1. More Power
Electrical power: P = V*I
Electrical energy: W = P*t
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Why do we need high voltage
2. Distance Between Energy Source and the
Consumer
In order to cover voltage drops in long distances.
As the line is resistive, a voltage drop will occur
along the line. The voltage at the generator, UG,
is higher than the voltage at the load, UL.
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Why do we need high voltage
3. Reducing Losses
If R is the overall line resistance, the following
power transmission losses, P, occur:
Relating the power losses to the transmitted power,
we obtain the relative power losses:
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Equation illustrates the inversely proportional
relationship of the transmission losses to the square
of the line voltage.
To keep losses low, power transmission lines are
operated at voltages which should, theoretically, be
as high as possible.
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Why do we need high voltage
3. Reducing Losses
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Why do we need high voltage
4.Reducing Dimensions & Cost
Increasing the line voltage also implies an
increase of the insulation costs associated with
components such as transformers.
Decreasing losses imply increasing equipment
costs.
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Historical development
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High voltages
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AC
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DC
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High Voltage Engineering
Dielectric stress and withstand strength of
insulation materials
Overvoltage protection and coordination
Transients, continuous
Power system component design
Technical & economical optimization
Diagnostics
Testing and measurements
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HV SOURCES
HVDC: CW GENERATOR-CASCADE GENERATOR
Cockcroft and Walton used this circuit design to power
their particle accelerator in 1932, performing the first
artificial nuclear disintegration in history (The
experiment produced definitive evidence for Einsteins
formula E = mc2)
(Responsible for development of the atomic bomb)
Nobel Prize in Physics in 1951
Greinacher, a Swiss physicist described the same
principle 1919
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Impulse MARX GENERATOR
Impulse generator:
Single stage structure can reach 200 300 kV
For higher voltages n stages are stacked on top
of each other
Multi stage generator first introduced by Erwin
Marx in 1923
Used for simulation of lightning or switching
transients.
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Safety
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What went wrong?
29 % live voltage even though it was supposed
to be disconnected.
26 % Something fell, slid, or accidentally
touched a live component
18 % Technical fault
Other reasons, forgetfulness
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Electrical accident risks in electrical work
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VOLTAGE LEVELS
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CURRENT
Reaction limit, 0.5 mA Causes small muscular
cramps.
Cramp limit, 10 mA
A human being can suffer short-duration higher
current without damage.
Children and women are more sensitive to the
effects of current than men.
There are also significant individual
differences.
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Typical resistance value from hand to hand or
from hand to foot is about 500 1000 .
Most dangerous current paths are across the
chest or from hands to foot, because the heart
is on the current path.
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SYMPTOMS
Slight muscular cramps, slight nervous
disorders, increase of blood pressure
Stronger cramps, you cannot break free of the
live equipment
Ventricular fibrillation and dropping of blood
pressure
Loss of consciousness
Contraction of heart
Slight skin burns
Serious skin burns, poisoning of nerve cells
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Electrical current can cause deep burns or
other serious inner injuries, which are not
possible to see outside.
Electric arc near a person can also cause skin
burns and eye injuries.
In the worst case symptoms can appear a
several days after an electric shock.
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Ventricular Fibrillation
AC is more dangerous than DC or impulse
voltages
When the frequency of the current is 50-60 Hz,
the most common cause of death is the
ventricular fibrillation.
During the ventricular fibrillation the blood
pressure decreases and there is lack of oxygen
in lungs and brains.
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If the influence time of current is longer than
the operational cycle of the heart and the
current is sinusoidal (50-60 Hz), very low
current can cause ventricular fibrillation.
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Standards
EN 50110-1: Operation of electrical installations
Importance of the professional skills, how to
give advise for the work and how to be sure that
the voltage is not on.
List of operations, which are allowed for
professionals to perform as live work.
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The live working zone surrounding bare live
parts and the vicinity zone are determined at
different voltages.
Requirements for temporary ground and
grounding devices.
Training of emergency first aid is recommended
to all those who assist or manage electrical work.
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Electrical Safety
Two approaches for protection against electric
shock
Prevent (accidental) contact to live parts
Limit voltage and current duration or maintain
exposed voltage below dangerous levels
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Allowed touch voltage UTp as a function of
current duration during earth fault in a HV
system
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Grounding (Earthing)
Grounding is essential for the safe operation of
networks
(Power) System earthing functional earthing and
protective earthing of a point or points in an electric
power system (IEC)
Functional earthing earthing a point or points in
a system or in an installation or in equipment, for
the purposes other than electrical safety (IEC)
Component included in the electrical circuit (e.g.
LV neutral point) is earthed.
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Protective earthing earthing a point or points
in a system or in an installation or in equipment,
for purposes of electrical safety (IEC)
Components not included in the electrical
circuit that are susceptible to voltage are
earthed.
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Example of earths surface voltage profile and
voltage when current flows in earth electrodes
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Overhead Lines
Overhead line accidents occur most often on 20 kV
lines.
Large number of 20 kV lines
Situated close to residential areas
Not as easy to notice as large transmission lines
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Allowed electrical work for ordinary electricity
consumers (if you know what you are doing)
Replacing household fuses
Connecting lighting fixtures to ceiling connectors
Replacing broken socket plugs
Replacing intermediate switches in power cords
Manufacturing and fixing of single phase extension
cord
Removal of socket and lighting covers
50 V AC and 120 V DC electrical work, e.g.
installing solar panels
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