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Attempt To Replace Spark Gap By Thyristor In Marx
Circuit
N.Rishi
P.S.Ponmurugavel
Power systems-S.EEE
sastra university
thanjore, india
[email protected]
Power systems-S.EEE
sastra university
thanjore, india
[email protected]
Abstract—A Marx circuit is a type of electrical circuit first
described by Erwin Marx in 1924, whose purpose is to generate a
high voltage pulse. It is extensively used for simulating the effects
of lightning in electrical equipment testing. In this paper we
proposed an attempt to replace the spark gap used in Marx
circuit by using thyristor.
R.Dilip kumar
Power systems-S.EEE
sastra university
thanjore, india
[email protected]
is applied only for a short time, solid state switches will not
heat up extensively.
Ac compensation for the higher voltages encountered, the
later stages have to carry lower charge too. Stage cooling and
capacitor re charging also go well together.
Keywords-marx circuit,thyristors,spark gap,firing,overvoltage.
I.
INTRODUCTION
A Marx generator is a clever way of charging a number of
capacitors in parallel, then discharging them in series. When
capacitors are fully charged, either the lowest gap is allowed
to breakdown from over voltage or it is triggered by an
external source (if the gap spacing is set greater than the
charging voltage breakdown spacing). This effectively puts
the bottom two capacitors in series, over voltage the next gap
up and so forth. When using a spark gap configuration it is
impossible to stop the discharging process. The discharge will
continue until the capacitors are almost completely discharged,
in simulation of lightning the time of interruption also
important. It is impossible to produce a flat top pulse with a
classic Marx generator circuit. To overcome this difficulty we
proposed this scheme, it uses latest thyristor technology. The
solid state technology was proposed in [3]. BJT was proposed
[4]. In this proposed technology it is possible to generate more
controllable Marx generator based on solid state switches also
it can be called as thyristor Marx generator or controllable
Marx generator. This will sacrifices some of the steep voltage
edge offered by spark gap since the raising edge will be
restricted by the solid state switches.
II.
REPLACEMENT OF SPARK GAP
The Marx technique has been used to generate several kilo
volts from a low charging source using solid state devices
(thyristors) as switching device instead of spark gap.
Particularly lower output voltages, the capacitors can be
charged in parallel from a common source through a series
inductor. The charging impedance has to withstand the full
output voltage for the top stage.
In solid state avalanche devices, a high voltage
automatically leads to high current. Because the high voltage
(a)Block diagram for replacement of spark gap
The block diagram for replacement of spark gap is
shown in figure (a). the inductance used in this proposed
circuit is to oppose the rate of change of current. The
capacitors are charged in parallel it is discharged in series by
triggering the thyristor switch. The connections are to be made
to change the series parallel combination vice versa. The
circuit diagram is displayed in simulation and results i.e.) next
section.
The transformer used in this proposed method is
reactive transformer. It is used to oppose the change current.
This transformer has to be designed both coils on same core.
The only application for mutual inductance in a dc system is
where some means is available to switch power on/ off to coil
induced voltage peaking at every pulse.
The mutual inductance relation is given by Neumann formula
M21=N1*N2*P21
Where, N1 is the number of turns in coil 1.N2 is the number of
turns in coil 2. And p21 is the permeance of space occupied by
flux.
The arbitrary inductance M=K (L1L2)/2. Where K is the
coupling co-efficient range between 0-1, L1 and L2 are the
inductance of coil 1 and coil 2 respectively.
III.
SIMULATION AND RESULTS
For simulating the proposed thyristor based Marx scheme
we gave 5000 volts as input. This 5000v is produced using
cockroft Walton voltage multiplier circuit. The input to the
cockroft Walton voltage multiplier is 230v given using a 1:1
transformer. In the cockroft Walton multiplier circuit we build
22 stages. The basic cockroft Walton three stage in shown
below fig.(b).
Figure (d) simulation diagram for proposed scheme.
Figure (b) model cockroft walton voltage multiplier circuit.
The output of cockroft Walton voltage multiplier is shown
in figure (c).
The firing pulses are shown in figure (e). And
corresponding output voltage for the proposed scheme is
shown in figure (f) below. Input to this circuit is given from
output of cockroft Walton voltage multiplier circuit i.e) 5000
volts dc. In this circuit diagram it is made to connect in
parallel when charging. and the capacitors are connected in
series when discharging by firing the thyristor. In the proposed
scheme we got 20000 volts output as shown below.
Figure(e) firing pulses to the thyristor switch
Figure(c) output of cockroft Walton voltage multipler taken
between last stage and ground.
The input transformer is made of ratio 1:1. The output is
that same of the input. The voltage output is higher in both of
the circuits but the current is very less
Simulation diagram for proposed thyristor based marx
circuit is shown in figure (d).
Figure (f) Output voltage of proposed marx circuit.
IV.
FUTURE WORK
To design a thyristor to withstand for higher voltage
up to desired level. For implementing as a practical circuit
we need to use light activated thyristors.
V.
ACKNOWLEDGEMENT
We thank Mr.S.Natarajan (A.P III)/S.EEE/Sastra university
who guided us to present this paper. And we thank
Mr.S.Mohmed ghouse for his kind co-operation.
VI.
CONCLUSION
In this paper an attempt has been made to replace the spark
gap by thyristors. Here we generate high voltage with low
initial input by means of ideal thyristor switch which is used in
high frequency application. For generating high voltage up to
160 kilo volts it is possible by increasing the number of stages
and also by increasing the range of input and capacitor values.
But the technical challenge is thyristor selection for very high
voltage.
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