1.Generation of High DC Voltages _NEW

7/28/2019 1.Generation of High DC Voltages _NEW

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GENERATIONOF HIGH DC

VOLTAGESPresented By

AKHIL ASHOK

E8A8701


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CONTENTS

Introduction

Generation of High DC Voltages

Half and Full Wave Rectifier

Rectifier Valve Construction

Ripple Voltages with HW and FW Rectifier


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INTRODUCTION

What is HV?

Types of HV:

High DC Voltage (e-Microscope, X-Ray, etc.)

High AC Voltages of Power/High Frequency (about

1 million volt or more to test power apparatus rated

for EHT voltages)

High Transient or Impulse Voltages (to simulateover-voltages due to lightning or switching surges)


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GENERATIONOF HIGH DC VOLTAGES

Mainly used in

- Research work in Physics

- Insulation test on Cables and Capacitors

- Impulse Generator

How to Generate HDC?

For DC Voltages up to 100KV, Electronic Valve

Rectifiers are used.AC Supply to Rectifier tubes maybe Power Freq

or AF (AF low ripple avoid costly filters)


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HALFAND FULL WAVE RECTIFIER

Rectifier Circuits for producing HDC Voltages

from AC maybe:

Half Wave

Full Wave Voltage Doubler

Rectifier maybe e-tube (PIV =250KV) or solid

state device (PIV up to 20KV lab use silicon

diodes ).

For Higher Voltages units are used in series.

(special care should be taken in order to make

uniform distribution of transient voltage)


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The value of RC = 10 x Period of AC Supply

PIV at least 2Vm

To limit charging current an R in series with

transformer


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RECTIFIERVALVE CONSTRUCTION

Special construction

Protective Shield or Grid around the filament and

cathode.

Anode usually circular plate

Heater and Cathode experience large electrostatic

force during non-conduction period.


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To Protect various elements:

Anode firmly attached fixed to valve cover

A steel mesh structure or protective grid kept

at Cathode potential surrounds cathode and

filament (hence mechanical forces between A

& K reflected on grid only)


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RIPPLE VOLTAGESWITH HW AND FW

RECTIFIER

Fluctuation in output DC, V is called Ripple

Ripple depends on:

Supply Frequency

Time Constant

Reactance of Supply Transformer

In HW, Ripple Freq = Supply Freq

In FW, Ripple Freq = 2 x Supply FreqRipple Voltage can be kept low by proper choice

of C and Transformer Reactance for given load.


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TRANSFORMERRECTIFIERSETSFOR

ELECTROSTATIC PRECIPITATORS


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HIGHVOLTAGEBOARDRECTIFIERASSEMBLY


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REFERENCES

High Voltage Engineering

M M Naidu, V Kamaraju


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THANK YOU

Documents

1.Generation of High DC Voltages _NEW