Design and Development of a Compact Trip
Pulse Generator
Madhu Palati1, G. R. Nagabhushana
1, and Archana Sharma
2
1Dept. of Electrical & Electronics Engineering, School of Engineering and Technology, Jain University, Bangalore-
562112, India 2Energetics and Pulse Power Section, APPD, BARC, Mumbai, Maharashtra-400085, India
Email: [email protected]
Abstract—Pulsed power engineering has found many
applications of great importance in areas of defense, nuclear
physics, civilian, industrial and medical etc. In all these
applications Marx generators are the primary source of
generation of pulsed voltage/current. For the erection of
Marx generator, a proper triggering mechanism is
implemented for the first spark gap electrode, which gives
consistent breakdown for all the remaining spark gaps in
the Marx column. This paper discusses the design and
development of a simple, inexpensive and compact trip pulse
generator. This triggering mechanism provides the control
triggering to operate the Marx generator at definite time.
The experimental results reveal that the output voltage of
trip pulse generator is able to make air breakdown in the
first electrode gap.
Index Terms—Marx generator, spark gap electrodes,
voltage
I. INTRODUCTION
Fast pulses (nano and sub-nanosecond rise times) have
many applications both civilian and defense. Most
common method of generating high voltage pulses is
using a Marx generator. The Marx generator (proposed
by Prof. Erwin Marx in 1923 at the Technical University
of Braunschweig, Germany) works on the principle of
charging several capacitors in parallel and discharging
them in series so that voltages add up. The schematic of a
four stage Marx generator is shown in Fig. 1.
Figure 1. Schematic diagram of a four stage Marx generator
The capacitors get charged through the charging
resistors, RC. After reaching the desired voltage the first
spark gap is self triggered. However, if controlled
triggering is required, the first gap is usually triggered by
an external means using a three electrode gap or
Trigatron gap based triggering scheme. Twice the voltage
Manuscript received June 24, 2015; revised March 22, 2016.
(due to two capacitors coming in series) appears across
the second spark gap, and breakdown occurs in that gap.
This repeats for subsequent stages of Marx and is known
as “erecting of Marx”. Therefore the stage voltage of
each capacitor gets added up and appears across the load.
The ideal no-load output voltage across the load is equal
to n*Vc, where n is number of stages and Vc is the stage
charging voltage
The design, development, limitations and work carried
out on triggering of the first spark gap electrodes of the
Marx generators for generation of fast pulses, by the
earlier researchers has been briefly discussed in next
paragraph:
Osmokrovic et al. [1] discussed the testing of two three
electrode spark gap models, first model with third
electrode inside the main electrode and the second model
with a separate third electrode. Several characteristics
were determined experimentally and comparative
analysis was made.
Sack et al. [2] discussed about the drawback of three
electrode gap i.e. the trigger electrode gets subjected to
more wear compared to the main electrode because the
arc gets concentrated on the small surface of the trigger
electrode. The design of trigger device for over-volting
the first gap was replaced by charging inductor with a
pulse transformer in combination with a pulse generator.
Sack et al. [3] presented the design of trigger generator
for over voltage triggering of first gap of Marx generator
used in repetitive applications. Pulse transformer
equipped with IGBT switches was used to generate
trigger pulses to cause over voltage across the first spark
gap electrodes.
Sack et al. [4] discussed the short life of conventional
triggered spark gaps. A new trigger method has been
developed and presented some preliminary experimental
results by inclusion of triggering system for the existing
Marx generator
Choyal et al. [5] designed & developed the first gap
triggering mechanism for a 300kV Marx generator by
means of pulse transformer, which produced a 6kV pulse
and was applied between the first spark gap electrodes.
The UV light is passed through all the gaps that caused
pre-ionization of all remaining gaps, resulted in
simultaneous sparking of all gaps. A hollow ceramic tube
of 1.2mm diameter was inserted through the bore of one
of the first spark gap electrodes. A 0.5mm wire was
International Journal of Electronics and Electrical Engineering Vol. 4, No. 6, December 2016
©2016 Int. J. Electron. Electr. Eng. 505doi: 10.18178/ijeee.4.6.505-509
controlled triggering, pulse generator, breakdown trip
inserted in the hollow ceramic tube to form the third
terminal for which a negative voltage of 6kV was applied.
Thomas Baby et al. [6] developed the triggering
mechanism with pulse repetition frequency ranging from
0.1Hz to 1kHz. Pulses of 5µs duration with rise time less
than 1µs were generated from the timer circuit. This
voltage pulse is fed to the gate of the SCR that was wired
to the primary of a pulse transformer, which produces a
transient voltage of 4kV and is fed to the trigger pin of
the spark electrode.
Rowan Sinton et al. [7] developed a custom built first
stage spark gap i.e. a three electrode gap. By varying the
gap length, it was able to trigger reliably ranging from 10
to 90kV. The trigger signal was delivered thru a fiber-
optic cable.
From above, it is very clear that triggering mechanism
is required for triggering the first electrode gap. In this
paper an attempt is made to develop a custom made trip
pulse generator for triggering the first electrode gap of a
10 stage Marx generator of rating 200kV, 20J.
II. METHODS OF CONTROLLED TRIGGERING
The methods for controlled triggering of first stage of
Marx generator are listed below:
Using a three electrode gap
Using a trigatron gap
Spark gaps with movable frame
A. Three Electrode Gap
The first stage spark gap of a Marx generator is fitted
with a three electrode gap and is shown in Fig. 2. The
central electrode is maintained at a potential in between
that of a top and bottom electrode of three electrode gap.
Breakdown is achieved at any instant by applying a
trigger pulse of peak voltage not less than one fifth of the
charging voltage to the central electrode. This three
electrode gap requires more space and an elaborate
construction [8], [9].
Figure 2. Tripping circuit with three electrode gap
By closing the switch S, the thyratron conducts and
Capacitor C produces a decaying pulse of positive
polarity to initiate the Oscillogram time base and negative
pulse through the capacitor C1, which gets applied across
the top electrode and central electrode and the gap
conducts.
B. Trigatron Gap
In this arrangement, one of the spark gap i.e. earthed
electrode has a bore at center and the schematic and
tripping circuit of trigatron gap are shown in Fig. 3 and
Fig. 4 respectively. The trigger electrode is fitted into this
hole through a bushing on application of trip pulse to the
trigger electrode by means of tripping circuit, the field
gets distorted between the HV electrode and the earthed
electrode results in spark over in the main gap. This
method requires lower trip pulse voltage compared to
three electrode gap scheme [8], [9].
Figure 3. Schematic of tripping circuit with trigatron gap
Figure 4. Tripping circuit using a trigatron gap
The capacitor C1 is charged to 5 to 10kV, when the
switch S is closed a pulse is applied to CRO through the
capacitor C2 and at the same time Capacitor C3 gets
charged and a trigger pulse is applied to the trigatron gap.
The delay time for triggering can be obtained by varying
R3 and C3 and the residual charge can be discharged into
high resistance R2 [10].
C. Trigatron Spark-Gaps Mounted on Movable Frame
In this arrangement, one of the spark gaps electrode are
mounted on a movable frame, once the capacitors gets
fully charged, the spark gap distance is reduced by
moving the movable frame. In order to have consistency
of sparking, irradiation from an ultraviolet lamp is
provided from the bottom to all the gaps. This method is
difficult and does not assure consistent and controlled
triggering [8], [9].
Most often Trigatron gap scheme is used, and this is
expensive. In our work, the principle of three electrode
gap is used to breakdown the air gap in the first spark gap
electrode.
Another method of triggering first stage spark gap
electrode without third electrode is explained by Eugene
et al. [11] and the schematic circuit is shown in Fig. 5.
International Journal of Electronics and Electrical Engineering Vol. 4, No. 6, December 2016
©2016 Int. J. Electron. Electr. Eng. 506
Figure 5. Schematic of trip circuit without trigger electrode
The ground side charging inductor of the first stage of
Marx generator is replaced by a pulse transformer which
is auxiliary connected to the pulse generator. The pulse
transformer super imposes a voltage pulse to the charging
voltage of the first stage capacitor C1 of Marx generator.
Therefore this over voltage across the first spark gap
causes the spark gap to fire.
III. EXPERIMENTAL MODEL
Control triggering circuit i.e. Trip pulse generator is
designed for triggering the first spark gap electrode of the
existing Marx at our laboratory. The schematic view of
the Marx with trip pulse generator and schematic of trip
pulse generator are shown in Fig. 6 and Fig. 7
respectively.
Figure 6. Schematic view of Marx generator with trip pulse generator
Single phase supply is fed to the primary of isolation
transformer (230V/110V) and the secondary side voltage
is rectified to DC and the 1000µF capacitor gets charged.
When the switch gets closed, the capacitor discharges
into the ignition coil. Ignition coil consist of primary coil
of less number of turns and are of thick wire and
secondary coil of more number of turns and are of thin
wire. When the input voltage from the capacitor is
applied to the primary thru the switch, it creates strong
magnetic field in the primary and when the supply from
the capacitor is suddenly disconnected, this will cause the
magnetic field to collapse and induce high voltage
transient in the secondary coil.
Figure 7. Schematic of trip pulse generator
The output transient of ignition coil is applied to the
set of five capacitors connected in series each of rating
0.01µF, 4kV. Twenty resistors of carbon type, each of
rating 100kΩ,2W are connected in series and the whole
series combination of these resistors are connected across
the set of the capacitors mentioned above, to avoid the
reverse flow of current. Also, to discharge the remaining
stored energy into these resistors after post application. A
10 ohms wire wound non-inductive resistor, is connected
in series with this combination to limit the current. The
high voltage lead is connected to the copper rod of 3mm
diameter. ±10mm adjustment for vertical and horizontal
displacement of the copper rod is provided in the stand, to
focus the spark at the first stage spark gap. Fig. 8 shows
the experimental setup of the trip pulse generator.
Figure 8. Experimental setup of Marx generator with trip pulse generator
IV. RESULTS & DISCUSSIONS
The end of the copper rod of the trip pulse generator is
placed very close to the one of the electrodes of the first
spark gap of the Marx generator. The output of the Trip
pulse generator is tested using P6015A, 1000X High
voltage probe of Tektronix make. Control triggering is
done by using the control button, by pressing the control
button, the spark occurs between the tip of the copper rod
and one of the electrodes of the first spark gap. The High
voltage waveform is captured by the HV probe and is
International Journal of Electronics and Electrical Engineering Vol. 4, No. 6, December 2016
©2016 Int. J. Electron. Electr. Eng. 507
displayed on the Digital storage oscilloscope and the
same is shown in the Fig. 9.
The distance between the copper rod and the spark gap
electrode was 5mm and 1000X probe was used to
measure the waveform, from the waveform the
magnitude of the output pulse is 16kV (each unit is of 5V
and multiplication factor of probe is 1000, for 3.2 units
the voltage is 16kV).
Figure 9. Experimental output voltage of the trip pulse generator
The air density factor, δ [8] is given by:
𝑑 = 𝑝
760 [
293
273+𝑡] (1)
k = d (2)
Vo (corrected) = Vo (STP)* k (3)
% 𝐸𝑟𝑟𝑜𝑟 =𝑉𝑜 (𝑐𝑜𝑟𝑟𝑒𝑐𝑡𝑒𝑑)−𝑉
𝑉𝑜 (𝑐𝑜𝑟𝑟𝑒𝑐𝑡𝑒𝑑)∗ 100 (4)
where p is the pressure in torrs, t is the room temperature
in degrees centigrade, k is the correction factor, VO (STP)
is the breakdown voltage of air at standard temperature
(20°C) and pressure (760 torrs), VO (corrected) is the
corrected value of breakdown voltage of air at room
temperature and pressure and V is the experimental value
at room temperature and pressure. The measured room
temperature t is 26°C and pressure p is 750 torrs. From
(1), the air density factor is 0.968. For values of d greater
than 0.95, correction factor is same as air density factor
[8]. Therefore, from (2) the value of correction factor is
same as air density factor. The breakdown voltage of air
VO (STP) for a sphere gap spacing of 5mm is 16.8kV and
VO (corrected) calculated from (3) is 16.26kV.
The obtained value from experimental waveform and
the calculated value are in agreement and the change is
very nominal i.e.0.26kV and % error calculated from (4)
is minimal i.e. 1.6%. This voltage was sufficiently
enough to break the first gap of the Marx generator
available at our laboratory and at the remaining gaps the
voltage got added up and self breakdown took place
simultaneously.
V. CONCLUSION
In this work an attempt has been made to develop a
simple compact, inexpensive and portable trip pulse
generator for controlled triggering of the first stage spark
gap of the Marx generator. The trip pulse generator gave
an output voltage of 16kV for a 5mm gap between the
electrodes of the trip pulse generator & the Marx first
stage spark gap electrode. The experimental and
theoretical values of the voltages are in close agreement.
After the occurrence of breakdown of first spark gap, the
remaining spark gaps of Marx generator were self
triggered due to overvoltage across them. Based on the
requirements, the output voltage of the trip pulse
generator can be increased by adding the capacitors
mentioned in the circuit.
ACKNOWLEDGMENT
The work has been carried out by the financial support
of Department of Atomic Energy (DAE), Board of
Research studies in Nuclear Sciences (BRNS). We are
highly thankful for them. Author is grateful to the
Director, EEE HOD & Management of School of
Engineering & Technology, Jain University, Bangalore
for their constant support and encouragement, in carrying
out this research work.
REFERENCES
[1] P. Osmokrovic, N. Arsic, and N. Kartalovic, “Triggered three
electrode spark gaps,” in Proc. IEEE 10th Pulsed Power Conference, July 3-6, 1995, pp. 822-827.
[2] M. Sack, R. Stangle, and G. Miller, “Overvoltage trigger device
for Marx generators,” Journal of the Korean Physical Society, vol.
59, no. 6, pp. 3602-3607, December 2011.
[3] M. Sack and G. Miller, “Design and test of a modular trigger
generator for over-voltage triggering of Marx generators,” in Proc. IEEE Power Modulator and High Voltage Conference, June 2012,
pp. 320-323.
[4] M. Sack, C. Schultheiss, and H. Bluhm, “Wear-Less trigger method for Marx generators in repetitive operation,” in Proc.
IEEE 14th Pulsed Power Conference, June 15-18, 2003, pp. 1415-
1418. [5] Y. Choyal, et al., “Development of a 300kV Marx generator and
its application to drive a relativistic electron beam,” Sadhana, vol.
30, no. 6, pp. 757-764, December 2005. [6] T. Baby, T. Ramachandran, P. Radhakrishnan, V. P. N. Nampoori,
and C. P. G. Vallabhan, “A low inductance long life triggered
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[7] R. Sinton, V. H. Ryan, W. Enright, and P. Bodger, “A Marx
generator for exploding wire experiments,” in Proc. Asia-Pacific
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[8] M. S. Naidu and V. Kamaraju, High Voltage Engineering, 4th ed.,
Tata McGraw Hill, 2009, p. 182. [9] E. Kuffel, W. S. Zaengl, and J. Kuffel, High Voltage Engineering
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[10] C. L. Wadhwa, High Voltage Engineering, Third ed., New Age International Publishers, 2010, pp. 119-120.
[11] E. Vorobiev and N. Lebovka, Electro Technologies for Extraction
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Madhu Palati received the B.Tech degree in
Electrical & Electronics Engineering from Sri Venkateshwara University, Tirupati, India, in
2003 and M.E from M.S.University, Baroda,
India in 2005. He has worked as a software Engineer in Keane India Ltd, Gurgaon for a
period of one and half years and in IBM
Private Limited, Bangalore for a period of three years. He is currently working as
Assistant Professor and also working towards
the PhD degree in the department of Electrical & Electronics
International Journal of Electronics and Electrical Engineering Vol. 4, No. 6, December 2016
©2016 Int. J. Electron. Electr. Eng. 508
Engineering, School of Engineering & Technology, Jain University, Bangalore.
G. R. Nagabhushana received the B.Sc.
degree from Mysore University, Mysore, India,
in 1960, and the B.E. (Electrical), M.E. (Electrical High Voltage Engineering), and
Ph.D (High Voltage Engineering) degrees
from the Indian Institute of Science, Bangalore, India, in 1963, 1965, and 1973,
respectively. He was with the Department of
High Voltage Engineering, Indian Institute of Science, Bangalore, India, prior to his
retirement in July 2004. He was Chairman of the Department from 1989
to 1996 and again from 1999 to July 2004. Presently, he is an Emeritus Fellow of the All India Council of Technical Education in the
Department. Currently he is working as visiting professor at school of
Engineering & technology, Jain University. His main areas of interest have been vacuum insulation, pollution performance of the transmission
line insulation, and laboratory simulation of NEMP and lightning. He has been responsible for setting up several high-voltage laboratories in
India.
Dr. Archana Sharma is an electrical engineer with Ph.D, in High Voltage
Engineering from Indian Institute of Science,
Bangalore. Presently she is head, Pulse Power Systems Section, APPD, BARC. She is the
recipient of Homi Bhabha Science and
Technology Award-2011. She is working in the design and development of intense pulsed
power system for high power microwaves and
flash X-rays radiography applications. She is currently involved in the developmental activities of compact, repetitive
and mobile. She is also part of Intentional Electromagnetic Interference
(IEMI) studies using HPM and UWB sources for various electronics circuitry and their shielding techniques.
International Journal of Electronics and Electrical Engineering Vol. 4, No. 6, December 2016
©2016 Int. J. Electron. Electr. Eng. 509
