tvn en generation of high voltages 2 0 rp

8/2/2019 TVN en Generation of High Voltages 2 0 RP

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High Voltage Engineering

Generation of High Voltages


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Lectures

Generation of High Voltages

Measurement of High Voltages

Electrostatic Field and Field Stress Control

Electrical Breakdowns and Discharges

Non-destructive Insulation Tests

Overvoltage

Insulation Coordination

Overvoltage protections

Transient behavior of transformer windings

4/8/2011 High Voltage Engineering 2


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References

Kuffel E., Zaengl W.S., Kuffel J.: High VoltageEngineering Fundamentals, Second edition,2000

Wadhwa C.L.: High Voltage Engineering, NewAge International Publishers, New Delhi, 2007

Naidu M.S.: High Voltage Engineering,

McGraw-Hill, 1995 Denno K.: High Voltage Engineering in Power

Systems, CRC Press, 1992



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High Voltage Sources

Three main types of generators

DC

AC

Impulse

Very small currents

Less then an ampere (AC, DC)

Few amperes in case of impulse or transient voltages

Special tests needs a generator with hundeds of

amperes high-current generators



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DC High Voltage Generation

Mainly used for pure scientific research work and fortesting equipment related to HVDC transmissionsystems or electrostatic precipitation

High d.c. voltages are even more extensively used in:

applied physics (accelerators, electron microscopy, etc.),electromedical equipment (X-rays)

industrial applications (precipitation and filtering ofexhaust gases in thermal power stations and the cement

industry; electrostatic painting and powder coating, etc.) communications electronics (TV, broadcasting stations)



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Simple rectifier circuits

The single-phase half-wave rectifier with

voltage smoothing



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Bi-phase half wave rectifier circuit



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Output of Full Wave Rectifier



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Cascade circuits



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Electrostatic Generator

Electrostatic generators convert mechanicalenergy directly into electrical energy

Electrical charges are moved in this generator

against the force of electrical fields -> gaininghigher potential energies and consumingmechanical energy

Van de Graaff - electrostatic belt-drivengenerators today use in nuclear physicsresearch laboratories



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Van de Graaff Generator

Charge is sprayed onto an insulating moving

belt by means of corona discharge points

The charge is conveyed to the upper end

where it is removed from the belt by

discharging points

The largest generator operates with 25 MV,

and was tested up to internal flashovers with

about 31MV



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Generation of High AC Voltages

Electric power transmission with high a.c.voltages predominates in our transmissionand distribution systems

Range from about 10 kV r.m.s. only up tomore than 1.5MV r.m.s. today

The testing voltages are usually single-phase

voltages to ground with pure sinusoidal shape The ratio of peak-to-r.m.s. values equals 2

within 5 %



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Testing Transformers



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Cascaded Transformers



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Series Resonant Circuit

Usually for testing of objects which represent

a high capacitive load and which have low and

stable losses (hv cables)

Conventional test systems with compensating

reactor are larger and expensive

High short circuit impedance of the voltage

source (in case of breakdown the channel is

not excessively damaged)



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Series resonant system



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Series Resonant Circuit with Variable

Frequency

Usually for field testing of cables, rotating

machines or GIS

Further reduction of weight and size



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Impulse Voltage Generator

Two more frequently causes of disturbances in

power systems:

Lightning overvoltages (x MV, up to 100 kA)

Switching phenomena (amplitudes are derived

from operating voltage)

Actual shape of both overvoltages varies it is

necessary to simulate these transients bysimple way for testing purposes



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Full Impulse Waveform



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Chopped Impulse Waveform



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Single-Stage Impulse Generator


Initial conditions:


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Solution for output voltage u2:


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Influence of Parameters


.00005 0.00010 0.00015 0.00020t

0.1

0.2

0.3

0.4

0.5

u

hR1

.00005 0.00010 0.00015 0.00020t

0.1

0.2

0.3

0.4

0.5

u

iR2

iC1

.00005 0.00010 0.00015 0.00020t

0.1

0.2

0.3

0.4

0.5

u

iC1

.00005 0.00010 0.00015 0.00020t

0.1

0.2

0.3

0.4

u

hC2


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Multi-Stage Impulse Generator

(Marx Connection)



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Impulse Voltage Generators


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