High voltage .ppt

8/9/2019 High voltage .ppt

1/30

MULTI-STAGE IMPULSEGENERATORS


2/30

INTRODUCTION

The single-stage impulse generator circuit is

inconvenient and impractical for generation ofvery high voltages because of various reasons

like requirement of a very high dc voltagesource ,difficulties encountered in switching ofvery high voltages,physical size of the circuitelements etc.

To overcome these difficulties , in 1!" #ar$

suggested a multistage impulse generator circuit.


3/30

A typical four-stage ipulse

ge!erator circuit


4/30

PRINCIPLE O" OPERATION

The dc voltage %o charges the stage capacitors &1

through the high value charging resistors '1 as well as

through resistors '!,which are much smaller than the

resistors '1. (fter a long time period, the points (,).&,* will acquire

the potential of the dc source %o,w.r.t the earth point +.

The points ,,,/ will remain at earth potential .

The load capacitance &b remains at earth potential

during charging of state capacitors.


5/30

0et the charging voltage attain a value of say ,%o.

2hen +1 breaks down there will be a momentaryredistribution of charge potential on capacitor &1connected across (.

ts top plate falls to zero potential while its lower platesuddenly changes to 3%o.

4uddenly there appears a potential of !%o across the gap+! and this gap instantly breaks down. The process isrepeated .

5or an n-stage impulse circuit the output impulse voltageacross &b will be 36n%o. -is voltage efciency

It is essential that Switching gaps are adjustable tomake breakdown almost simultaneously


6/30

ANALYSIS OF THE MULTI-

STAGE CIRCUIT

When all the gaps G1G!G" and G# havebroken down the spark resistance in eachgap may be regarded as negligiblecompared to the resistances $1 and $!%

& and G' and () and I* and + are at e,ualpotentials so that the links '()I and *+may all be omitted%

or an n-stage impulse circuit )s . )1/n 0 $e.n$!


7/30


8/30

COMPONENTS

1. *& &harging 4et

!. &harging 'esistors

". +enerator &apacitors and 4park +aps

7. 2ave 3shaping 'esistors and &apacitors

8. Triggering 4ystem

9. %oltage *ividers

:. +as insulated impulse generators


9/30

1.a dc (variable) supply for charging hesage capaciors!for his use co"binaion

of sep up r"r and reci#er. Charging i"eno less han $!1% second. Charging

should be suiably conrolled (hyrisorconrolled)

&.'se non inducive ire ound resisors.They should be placed such ha hey canbe easily echanged * replaced

+.Paper i"pregnaed capacior of loinducance and high capaciy for fasdischarge..


10/30

RATING O" IMPULSE GENERATORS

mpulse generators are rated by

;1


11/30


12/30

A Marx Generator is a clever way ofcharging a number of capacitors inparallel, then discharging them in

series. Here R1and R2are the wave shapingresistors.


13/30

Mar ,eneraor (&$%-)


14/30

Need for Modi#caion

Rating of the control resistors requiredis high.

Hence cost is high.Also the efficiency is low.


15/30

Modi#ed Mar Circui

Here the resistances R1and R2are incorporated in the unit.

R1is divided in to n equal parts of R1/n and put in series

with the gap G. R2is divided in the n equal parts and arranged across eachcapacitor after gap G.


16/30


17/30

/dvanages * 0i"iaions

This arrangement saves space.

Rating of the resistors(R1& R2)required is reduced.

Cost is reduced.

Efficiency is increased.

Wide variation of the wave shape isnot possible.


18/30

GENERATION OF

SWITCHING SURGES


19/30

Switching surges are overvoltages in power systems that occurdue to sudden opening or closing of a circuit breaker or due toarcing at a fault point in the system

Switching surges are short-duration transient voltages

Their magnitude is dependent on the system voltage

Switching surges are slow rising impulse having a wave-fronttime of 0.1 to 10millisecond and a tail time of 1 to severalmilliseconds

Standard switching impulse voltage is defined as2502500micro sec wave with the same tolerances for time tofront of !250 " 50# micro sec and time to half value of!2500 " 500# microseconds


20/30

Several circuits have been adopted for producing

switching surges.

They are grouped as

1.$mpulse generator circuit modified to give longer

duration waveshapes

2. %ower transformers or testing transformers e&cited

by dc voltages


21/30


22/30

D.C

G R1

C1 R2 C2 CX

V0

t

The values of R1 and R2 for producing waveshapes of long duration

such as 100!1000"s or #00!#000"s will range fro$ 1 to %&'oh$s and% to 20 &'oh$s respectivel(


23/30

GENERATION OF

IMPULSE CURRENTS


24/30


25/30


26/30


27/30

3 Mai"u" value of i"pulse curren isnor"ally independen of and C forgiven energy :15&C&.and

e;ecive inducance 0.3 / lo value of inducance 0 is

needed o ge high curren

"agniudes for given chargingvolage .


28/30

GENERATION OF HIGH

IMPULSE CURRENTS


29/30


30/30

IMPULSE CURRENT

GENERATOR / dc charging uni giving variable volage ocapacior ban-.

Capaciors each ih lo self inducance

capable of giving high shor circui currens. /n addiional air cored inducor for highcurren value.

Proper shuns and oscillograph for

"easure"en purposes=and / riggering uni and spar- gap for iniiaion

of curren generaion.

Date post:	01-Jun-2018
Category:	Documents
Upload:	mohammed-mansoor
View:	216 times
Download:	0 times

High voltage .ppt

Documents