01 electric fields (elham hejrani's conflicted copy 2011-11-01) (in konflikt stehende kopie von...

Insulation for Energy Systems

ProfessorSergey Lopatkin

Office 00B18

e-mail:

Lopatkin@tpu.ru

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Significance of electrical insulationOverview of high voltage applicationsHigh voltage in electric power engineeringCourse syllabus

Content

Significance of electrical insulation

Reliability of energy systems Safety Efficiency

Applications of high voltage insulation– transmission lines, – cables, – transformers, – capacitors, – electrical machines

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4

High Voltage Applications

Light Engineering

Voltage up to 6 kV

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High Voltage Applications

Cathode-Ray Tubes:

TV sets, computer monitors, oscilloscope, etc.

(up to 25 kV)

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High Voltage Applications

Rail Transport:

subway, railway

(up to 27 kV)

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High Voltage Applications

Technology: electrostatic precipitation, separation, painting, electrohydraulic stamping, water cleaning, electroerosion electropulse

machining

(10-100 kV)

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High Voltage Applications

X-ray equipment

for medicine and industry

(up to 200 kV)

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High Voltage Applications

Scientific research

(millions Volts)

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High Voltage Applications

Electric power engineering

3, 6 – 1150 kV

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History of electric power engineering

1870 – invention of the DC generator 1882 – first large-scale use of electricity –

Edison's Pearl Street System; provided electric lighting for Lower Manhattan

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First DC power system

1) Current in transmission line: IL ≈ PLoad / V2

2) Voltage decay: V = V1 – V2 = IL Rline

3) Power loss: P = IL V = IL2

Rline = (PLoad / V2)2Zline

G

Transmission line

Rline V2V1

PLoad

Generator Load

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Ways to increase perfomance

P = (PLoad / V2)2Rline

1. increasing the operating voltage of a system

2. decreasing the impedance of a line

Impedance (DC): Rline = r L / S, where

r – specific resistance of the wire,

L – length of the line, and

S – cross-sectional area of the wire

already optimal

not effective

not effective

G

Rline V2V1

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Modern AC power system

1884 – invention of a transformer 1890 – 28 miles 10 kV line Deptford – London

Power transfer capability (PLoad ≈ V22 / Zline)

V(kV) 400 700 1000 1200 1500

P(MW) 640 2000 4000 5800 9000

G

Transmission line

ZlineV2V1

PLoad

Generator

LoadTransformerTransformer

V3

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Major AC power systems

10 50110

220287

380

525

735

1150

0

200

400

600

800

1000

1200

1400

1880 1900 1920 1940 1960 1980 2000

Year of installation

AC

vo

lag

e, k

V

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Application of the HVDC systems

Connection of Asynchronous AC Systems Long and Submarine Cables

Transmission lineDC

ACInverterRectifier

AC

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Major DC power systems

0

100

200

300

400

500

600

700

1950 1960 1970 1980 1990 2000

Year of installation

DC

vo

lta

ge

, kV

Demands to electrical insulation

Reliability Safety Efficiency

Ways to achieve: Design Manufacturing Maintenance

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Three questions to be answered

What is the electrical stress distribution that the materials will experience within the device?

What are the processes in insulation under these stresses that influence breakdown strengths of the materials?

How does the reliability change through the life of the device as a result of a reduction in the material breakdown strength (aging) and a change in the electrical stress distribution?

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Course structure

THEORY Electrical discharge in gas, liquid and solid dielectrics

(physics, theory, factors affecting discharge voltage, breakdown, corona discharge, flashover, partial discharge, treeing).

Design of high voltage insulation (transmission lines, cables, transformers, capacitors, electrical machines).

Testing techniques for insulation maintenance.

EXAM

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Textbooks

High Voltage Engineering Fundamentalsby E. Kuffel, W. S. Zaengl, and J. Kuffel

High Voltage Engineering by M.S. Naidu

Hochspannungstechnik. Theoretische und Praktische Grundlagen by M. Beyer, W. Boeck, K. Möller, and W. Zaengl

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ELECTRIC FIELD IN INSULATORS

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Contents

Electric field concept Electrical discharge and breakdown definitions Electric fields classifications

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Electric field related equations

Potential induced by charge in the medium

= q / (40 R)

q – charge

– permittivity of the medium

0 – electric permittivity of vacuum (8.85 10-12 farad/m)

R – distance

Voltage between the points 1 and 2

V = 1 – 2

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Electric field related equations

Electric field strength

E = –grad = –V / x

= – ∫l E dl

The force of electric field

F = q E

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Electrical discharge and breakdown

Electrical breakdown – loss of insulating ability

Electrical discharge – process (the stage) of breakdown

Dielectric strength of insulator: the maximum electric field strength, which the

material can withstand without breakdown the voltage at which the current starts increasing

to very high values and breakdown occurs

Breakdown voltage – applied voltage at the moment of breakdown

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Lightning

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Multiple Lightning

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Examples: spark discharge

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Examples: arc discharge

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Examples: long arc discharge

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Parameters affecting breakdown voltage

electric field distribution, pressure, temperature, humidity, nature of applied voltage, imperfections in dielectric materials, material and surface conditions of electrodes, time of voltage application,and others

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Electric field classification

Dependence on time of application: constant alternating pulsed

oscillating impulse aperiodic or unipolar impulse

t

E

t

E

t

E

t

E

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Electric field classification (space)

Е

0 D

Е

uniform

Е

0 D

Е

Е

0 D

Е

strongly non-uniformslightly non-uniform

Non-uniformity factor КN = ЕMAX / EAV

EAV = V / D; ЕMAX = f(voltage, shape, size, distance)

КN = 1 КN ≤ 3КN > 3

E = V / D E ≈ V / D E = f(x,y,z) E = f(x,y,z)

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Methods for estimating the potential and electric field distribution

the direct measurement of potential distribution

analytic calculations the numerical methods of calculations using

digital computers

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Calculation of maximum electric field

Planes

Concentricspheres

Sphere vs. plane

Twospheres

Coaxial cylinders

Cylinder vs. plane

Parallelcylinders

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Electrodes symmetry

Symmetric and asymmetric electrodes Symmetric electrodes are two electrodes of the

same shape and size and there is no electrode grounding

Asymmetric electrodes are two electrodes of the different shape or size, or one of them is grounded

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Solve the next problem

Sphere vs. plane

Given: r = 1 cm; a = 10 cm; U = 100 kVCalculate1. non-uniformity factor;2. at a given r the value a that provides slightly non-uniform field;3. at a given a the value r that provides slightly non-uniform field