Insulation

Prof. Dr.-Ing. Volker Hinrichsen
M.Sc. Mohammad Hossein Nazemi

Winter Term 2010/2011

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Hochspannungstechnik
High-Voltage Technology / Chapter 1 -1-

Introduction of High-Voltage Laboratories

Office area Workshop area,
Small Test Hall,
Seminar Rooms
Large Test Hall

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Accredited test lab for Um = 800 kV

1.2-MV transformer cascade

3.2-MV impulse voltage generator
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Our Technical Assistants (Wissenschaftliche Mitarbeiter; WiMi) ....

Sébastien Blatt Katarina Samuelsson
Thomas Wietoska Jan Debus Thomas Rettenmaier
Mohammad Hossein
Nazemi

Michael Tenzer
Max Tuczek
Patrick Halbach Karsten Golde Masi Koochack-Zadeh
Sebastian Suchanek

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Frau Hasenei Frau Brunner

Our secretary ........ Our book-keeper ........

Our workshop ……

Herr Veith Herr Homa Herr Ullrich Herr Noll Herr Graulich

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High-Voltage Technology I: Subjects

1 Objectives, applications, selection of voltage level
2 Generating high alternating voltages
3 Generating high direct voltages
4 Generating high impulse voltages
5 Measuring high voltages
- alternating-
- direct-
- impulse
12 Traveling waves on lines
6 Electrical fields
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High-Voltage Technology II: Subjects

7 Layered dielectrics

8 Control of electrical field stress and potential distribution

9 Dielectric breakdown of gases (air, sulphur hexafluoride)

10 Surface discharges, pollution flashover

11 Lightning discharges and lightning protection

13 Dielectric breakdown of solids, fluids and in vacuum

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High-Voltage Technology I: Recommended Books

Download of the slides (English and German)
and the lecture notes (German only):

www.hst.tu-darmstadt.de

UN: student
PW: vorlesung

Can be lent out from us (please contact Mrs. Koochack-Zadeh)
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Can be lent out from us (please contact Mrs. Koochack-Zadeh)

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Further recommendations:

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High-Voltage Technology / Chapter 1 - 10 -

High-Voltage Technology I: Time Schedule
1 21.10.2010 Chapter 1 Introduction 2 Excursions:
2 28.10.2010 Chapter 1 Introduction - Siemens
3 04.11.2010 Chapter 2 Generating high alternating voltages Schaltanlagenwerk
4 11.11.2010 Chapter 2 Generating high alternating voltages Frankfurt
5 18.11.2010 Chapter 3 Generating high direct voltages - ABB GIS-Fertigung
6 25.11.2010 Chapter 3 Generating high direct voltages Großauheim
7 02.12.2010 Chapter 4 Generating high impulse voltages Thursdays; starting 09:30;
8 09.12.2010 Chapter 4 Generating high impulse voltages until 16:00
16.12.2010 Cancelled two auxiliary dates needed
23.12.2010 Christmas holidays



9 13.01.2011 Chapter 5 Measuring high voltages



12 03.02.2011 Chapter 6 Electrical fields

13 10.02.2011 Chapter 6 Electrical fields

14 17.02.2011 Miscellaneous

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High-Voltage Technology I: Examination

Exercises:
• 2 Mini-Tests during lecture time
• each test up to 10 points max. 20 points

Lecture:
• only oral examination
• max. 80 points

in sum max. 100 points

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Objectives of High-Voltage Technology

High-voltage engineering or technology deals with
• physical phenomena
• technical problems,
which arise with
• natural presence
• generation
• application
• measurement
of high voltages.

High-voltage engineering has gained most of its importance for
electrical power systems. The permanent supply of electric energy, at
any time, at virtually any location, economical and of high quality
and reliability, could not be realized without the use and nearly perfect
control of high voltages as it is fact today.

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Presence of "high voltage"

In technical systems ......

as continuous operating voltage .....

a.c. systems 50 Hz or 60 Hz up to Us = 1200 kV

Actual (since 2008)
PR of China:
Us = 1100 kV
India (under construction):
Us = 1200 kV

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as continuous operating voltage .....

HVDC transmission up to ± 800 kV

Actual in PR of China:
± 800 kV (since 2009)
(Plans for ± 1000 kV)

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as overvoltages .....

of power frequency ...

• due to earth faults

• „Ferranti effect“ = voltage increase at the end of a long,
unloaded transmission line (or after load rejection)
due to voltage drop across the inductances caused
by capacitive charge currents

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as overvoltages .....

transient ...

• due to intentional or unintentional switching operations

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as test voltage .....

alternating voltage up to 2 MV

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direct voltage up to several MV

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impulse voltages up to 6 MV
(lightning, switching impulse
voltage)

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further applications .....

high frequency alternating voltages for long wave transmitters
(aerial voltages up to several 10 kV)

direct voltages:
charge carrier accelerators up to several 106 eV
dust filters, enamel spraying systems up to 100 kV
ultra-vacuum electron tubes up to several 100 kV

pulse power technology in physical research

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In nature ......

as direct voltage ......
lightning electricity: cloud voltages up to 100 MV
electrostatic charges: charge separation up to
several kV

as impulse voltage ......

overvoltages by
lightning strokes

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Definition „High-Voltage“

In general, a power system is termed a "high-voltage" system if
operated at alternating phase-to-phase voltages above 1 kV (rms
value) or at direct voltages above 1.5 kV.

Furthermore, for power systems the terms medium voltage, high
voltage and extra high voltage (even ultra high voltage) have been
established, depending on the "Highest voltage for equipment Um" of a
system.

Voltage

"Medium voltage (MV)" 1 kV < Um <= 52 kV

"High voltage (HV)" 72.5 kV <= Um < 420 kV

"Extra high voltage (EHV)" 420 kV <= Um <= 800 kV

"Ultra high voltage (UHV)" Um > 800 kV

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Goals of High-Voltage Technology

Basic goal of high-voltage technology in power systems and related
equipment: insulation of components at high potential from each other
and from ground.

The insulation must be able to reliably withstand all
• electrical
• mechanical
• climatic
• other
stresses during the scheduled lifetime of equipment of up to 50 years.
At the same time the construction and design must be economical
and optimized in terms of cost, meaning that materials are utilized to
their technical and physical limits. Safety margins are usually not
paid for and would be on the manufacturer's cost.

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Goals of High-Voltage Technology - Issues

to determine the voltage stress during service in terms of type,
amplitude, time duration and frequency of occurence

to understand the physical phenomena, which lead to dielectric
breakdown of the insulation (gaseous, liquid or solid), and to derive
design rules for the construction of high-voltage equipment

to optimally utilize insulation by well founded knowledge of material
properties (with particular focus on longevity) and their permanent
development and improvement, as well as by reasonable shaping of
electrodes and insulation arrangements

to develop well-suited test methods and diagnostic tools and to
standardize them in internationally accepted standards (e.g. IEC)

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Goals of High-Voltage Technology - Issues

Insulation coordination and overvoltage protection

Generating and measuring high alternating, direct or impulse voltages
(and currents) in the laboratory and on-site

to perform design, type, acceptance and routine tests on individual
equipment or complete switchgear

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High-Voltage Technology – Involved Disciplines

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Transmission Voltage Levels

In order to transport electric power over wide distances the transmission
voltage has to be chosen high.

Power in the three-phase system:
P power (VA)

P = 3 ⋅ ULE ⋅ I = 3 ⋅ U Δ / 3 ⋅ I = 3 ⋅ U Δ ⋅ I ULE line-to-earth voltage (V)
UΔ phase-to-phase voltage (V)
I current through conductor(A)

Increase of power by

increase of voltage

or
increase of current

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The power losses of transmission are basically proportional to
the power of two of the current:

PV = I ⋅ R 2 PV power loss per phase (VA)
I current through conductor (A)
R resistance of conductor (Ω)

Go for high transmission voltage!

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What are the cost of transmission losses?
Example calculation: costs of 1% transmission losses
The power of the nuclear power plant Biblis (both units)
shall be transmitted: P = 2 400 MW = 2.4 · 109 W
Thereof 1% losses: Pv = 24 MW

Full load operation 24 h per day: daily working losses
Wv = Pv ·T = 24 MW · 24 h = 576 MWh = 576 000 kWh

Assumption: 1 kWh 1.5 cent daily cost of losses Kv,d = 8 500 €/d

Operation of the plant about 330 days per year

Annual cost of losses "Biblis" Kv,a ≈ 2.8 Mio. €/a
Annual cost of losses "Biblis" Kv,a ≈ 2.8 Mio. €/a
For all Germany: 1% of 600 TWh = 6 TWh losses
Annual cost of losses “Germany" Kv,a ≈ 90 Mio. €/a
Annual cost of losses “Germany" Kv,a ≈ 90 Mio. €/a
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Limitation of Short-circuit Power

Yet another reason for a high-voltage system:
Formation of sub-grids by an overlaid transmission voltage
backbone limits the short-circuit power of a system.

110 kV 110 kV

110 kV 380 kV

110 kV 110 kV

Short-circuit currents that can be handled nowadays: 80 kA

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The transmission voltage cannot arbitrarily be increased as the
effort of insulation also increases with voltage.

An optimal transmission voltage can be defined.

The optimal transmission voltage results from cost considerations.

The cost of a long distance power transmission is made up from

• operating cost

• cost of equipment
• cost of overhead line conductors
• cost of insulation
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Details given in the exercise P

s
1 2
Assumptions: • Power transmission from „1“ to „2“
• Distance s = const.
• Transmitted power P = const.

• Operating cost KV ~ 1/U

• Cost of equipment
• Line conductor KL ~ 1/U

• Insulation Kis ~ U

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U

• Operating cost KV ~ 1/U

• Cost of equipment
• Line conductors KL ~ 1/U

• Insulation Kis ~ U

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Rules of thumb for optimal transmission voltage:

a) Uopt = f(P):

Uopt (kV) = 15 ... 20 ⋅ P (MVA)

U2
Coincidental consistance with natural load of a line: Pnat =
Z

Z = Surge impedance of the line
L' Z = 250 Ω (420 kV, four-bundle conductors)
Z=
C' Z = 400 Ω (123 kV, single conductors)

U = Z ⋅ Pnat = 16...20 ⋅ Pnat

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Rules of thumb for optimal transmission voltage:

b) Uopt = f(s):

Uopt (kV) = s(km)

Not applicable for short distances as in that case the cost
of transformers have considerable additional impact on cost.

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Guidance values for transmission voltage, transmittable power
and transmission distances:
Transmission
Power Distance
voltage
30 MVA
Um = 123 kV (≈ demand of a 100-200 km
30 000-people town)

125 MVA
Um = 245 kV (small unit of 200-400 km
a power plant)

600 MVA
Um = 420 kV (large unit of 400-800 km
a power plant)

2000 MVA
Um = 800 kV (nuclear power plant, 1000 km
two units)

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Development of Transmission Voltages

Year Voltage (kV) Place Kittler

1891 15 Lauffen-Frankfurt / D
1907 50 Stadtwerke München / D
1911 110 Lauchhammer-Riesa / D
1929 220 RWE RhIntroduction / D
1932 287 Boulder Dam / USA
1952 380 Hårspranget-Hallsberg / S
1959 525 UdSSR
1965 736 Manicouagan-Montréal / CA
1985 1200 Ekibastuz - Kokchetav/UdSSR
*) Field test: 2000 km long transmission line; half of it was operated at 1200 kV for several
years. Another field test in Japan: 1100 kV for more than 10 years.
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Standardized Transmision Voltages (IEC 60071-1)

IEC standard 60071-1 specifies standardized values of Um or Us:
72.5 kV
123 kV
145 kV
170 kV
245 kV
300 kV
362 kV
420 kV
550 kV
800 kV
1100 kV
1200 kV

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International Highest Transmission Voltages
Country Voltage (kV)
in service planned or in test phase)

Indien: 1200 kV (under constr.)
China: 1100 kV (since 2008)
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System Voltages in Germany
Planned for the future

7.2 kV

420 kV 123 kV 12 kV 0.4 kV
24 kV
245 kV
36 kV
72 kV

Grids and facilities of other voltage levels are actually in use in high amount
but will not be expanded. Different philosophies for existing installations:

"downrating" or "uprating".
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The German Interconnected
Power System

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Largest German Transmission System Operators (2005)

As per Oktober 2010:
1 EnBW Transportnetze AG
2 transpower stromübertragungs gmbh (TenneT)
3 Amprion GmbH
4 50Hertz Transmission GmbH

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Interconnected Electrical Power Systems
Interconnection - Pro's ....

Location of power plants to be chosen independent
from load centers.

Particular characteristics of different types of power plants (basic-,
intermediate-, peak load-) can better be taken into consideration.

Less spare power installation required

Less impact of system faults and occasional loss of
power plants to the user

Higher overall quality of power supply (voltage- and frequency control)
In Germany: f = 50 Hz +/- 50 mHz!!!!

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Interconnected Electrical Power Systems
Interconnection - Pro's ....

Timewise (daily, yearly) and geografical (North-South, East-West)
load levelling

Free choice of power supplyer independent from location

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The European Interconnected Power System – entsoe 2010

Head Organization ENTSO-E
(European Network of Transmission
System Operators for Electricity)

5 Regional Groups (RG) =
"Synchronous Areas" or
"Synchronous Zones"
RG Continental Europe (former UCTE)
= largest interconnected system
in Europe
> 600 GW installed
> 400 GW assured
Regulation Zone Germany =
4 TSO (Transmission System Operators)
Source: entsoe

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Equipment in High-Voltage Power Systems

From the supplier to the user ....

For transmission of 1000 MW:
I ≈ 20 000 A I ≈ 1 500 A

10 kV ... 27 kV 72.5 kV ... 550 kV 12 kV ... 36 kV 0.2 kV ... 0.4kV
"High and Extra High Voltage" "Medium Voltage" “Low Voltage"

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Typical single line circuit diagram of a transformer substation
220/66 kV (245/72.5 kV)
Overhead lines
Earthing switch

Disconnector

Circuit breaker

Double bus bar 220 kV

Transformers 220/66/11 kV
To 0.4-kV
station service
system

Double bus bar 66 kV

Overhead lines or cables

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Side view of a typical 420-kV open air substation

Distances in [m]

420-kV substation with overhead tubular double busbars in diagonal arrangement
1 ... Bus bar system I 2 ... Bus bar system II 3 ... Busbar disconnector
4 ... Circuit breaker 5 ... Current transformer 6 ... Line disconnector
7 ... Line trap 8 ... Capacitive voltage transformer
T ... Bay width T1 ... Width of incoming bay T2 ... Width of outgoing bay

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420-kV gas insulated switchgear (GIS)

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Generators

Transformers
Circuit breakers
Disconnectors and earthing switches

Surge arresters
Voltage and current transformers, combined instrument transformers
Post insulators (station posts)

Line insulators

Cable, cable terminations, cable joints

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FACTS

Flexible AC Transmission Systems
Installations for power flow control between two AC sub-grids
by control of voltage, phase angle and impedance

jX
1 2
U1, α1 U2, α2

Increased use of power electronics, e.g.:

Thyristors with off-state voltages up to 8 (10) kV
LTT‘s = Light Triggered Thyristors
IGBT‘s = Integrated Gate Bipolar Transistors
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High-Voltage DC Transmission (HVDC)
Fields of application:

Interconnection of asynchronous grids: 50- and 60-Hz-systems or
systems of different frequency control characteristics

Extremely long transmission distances (> 1000 km), which else would
require high efforts of compensation measures (such as FACTS) for
reactive power control and stability

Sea cable links of more than 40 km, which would have a too high
demand of reactive power in case of AC operation (charging power of
cable capacitance!)

Grid extensions in load centers, which else would lead to an intolerable
increase of short-circuit power (which cannot be handled by the
equipment, e.g. circuit brakers)

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System voltages:

Overhead lines: usually +/- 500 kV (up to +/- 800 kV)

Sea cable links: +/- 400 kV ... +/- 450 kV

Modes of operation:

"Back-to-back"

Long distance transmission

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Voltage Stress in Power Systems
5
Possible voltages without arresters
Magnitude of (over-)voltage / p.u.

4
Withstand voltage of equipment

3

2

1
Voltages limited by arresters

0
Lightning overvoltages Switching overvoltages Temporary overvoltages Highest system voltage
(Microseconds) (Milliseconds) (Seconds) (Continuously)

Duration of (over-)voltage
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Classes and shapes of stressing voltages and overvoltages acc. to
IEC 60071-1 "Insulation co-ordination", Table 1

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• IEC 60071-1 specifies Standard Insulation Levels for equipment.
• The standard insulation level is defined by a set of two different types
of Standard Voltages.
• Two different Voltage Ranges are distinguished:
Range I: Um = 1 kV up to and including Um = 245 kV
(Distribution and transmission systems)
⇒ Standard short-duration power-frequency
withstand voltage
⇒ Standard lightning impulse withstand voltage *)
Range II: Um above 245 kV
(Transmission systems)
⇒ Standard switching impulse withstand voltage **)
⇒ Standard lightning impulse withstand voltage *)
*) "BIL" acc. to IEEE Std. 1313.1 **) "SIL" acc. to IEEE Std. 1313.1

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Standard Insulation Levels acc. to IEC 60071-1

Range I:
Um = 1 kV up to and including Um = 245 kV

The standard voltage values are
all the same for
• Phase-to-earth-,
• Phase-to-phase-,
• Longitudinal
insulation!

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Standard Insulation Levels acc. to IEC 60071-1

Range II:
Um above 245 kV

Different standard voltage
values for
• Phase-to-earth-,
• Phase-to-phase-,
• Longitudinal
UHV: insulation!

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What is an Impulse Voltage in High-Voltage Technology?

Shape of a lightning impulse voltage

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What is the meaning of Un, Us and Um ?
Definition acc. to IEC 60071-1 („Insulation co-ordination“)

= Un acc. to 28/169/CDV (Draft IEC 60071-1 Ed. 8)

= Us acc. to 28/169/CDV (Draft IEC 60071-1 Ed. 8)

R Voltage phasor diagram Example: German
e.h.v. system

„Phase-to-phase voltage“ Un = 380 kV
„Delta voltage“ Us = 420 kV
Um = 420 kV (usually!)

Line-to-earth voltage:
U = U / 3 = 242 kV
LE s
S T
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What is the meaning of Un, Us and Um ?
Definition acc. to IEC 60071-1 („Insulation co-ordination“)

R Voltage phasor diagram Example: German
e.h.v. system

„Phase-to-phase voltage“ Un = 380 kV
„Delta voltage“ Us = 420 kV
Um = 420 kV (usually!)

Line-to-earth voltage:
U = U / 3 = 242 kV
LE s
S T
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Design of Electrodes and Insulators

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Insulation coordination

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24-hour load cycle

Peak load

Intermediate load

Daily maximum demand

Base load
Daily minimum
demand

Day time

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Climatic Stress

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Sonstige Beanspruchungen ….

Growth of algea, moss .....
Growth of algea, moss .....

Vandalism ....
Vandalism ....

Animal attack ...
Animal attack ...

Transportation ....
Transportation ....

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Other Stress ….

Algae and moss .....

Earthquakes ....
Transportation ....
Vandalism ....
Animal attack ...
Short-circuit current forces ....
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Equipment: Transformers

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Equipment: Circuit Breakers

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Equipment: Disconnectors, Earthing Switches

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Equipment: Surge Arresters

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Equipment: Instrument Transformers
Optical current transformer
(making use of
electro-optical
"Faraday effect")

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Equipment: Line Insulators

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Equipment: Cables, Cable Terminations, Cable Joints

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Thyristors with Off-State Voltages up to 8 (10) kV

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Light Triggered Thyristors

"Reliable Power Supply for California"

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First AC Power Transmission Lauffen - Frankfurt 1891
Später: 15.000 V

1000 Lamps
+
1 artificial
waterfall !!
oil filled!

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Erasmus Kittler

Professor
Dr. Erasmus Kittler

Very first faculty of
electrical engineering
worldwide, 1882

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Erasmus Kittler

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Enamel Spraying System operated at 100 kV

Quelle: Phoenix Contact März/April 2003

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Insulation

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