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Cost Effective Solution for Impulse Voltage Generator
1Amir Haider, 1Zahid Javid, 1Umer Ijaz*, 2Badar ul Islam, 1Abubaker Ijaz 1Department of Electrical Engineering, NFC-IEFR, Faisalabad, Pakistan
2Electrical & Electronics Engineering Department, University Technology, PETRONAS, Toronoh, Perak, Malaysia
*Corresponding author: drui.nfc@gmail.com
Abstract: Studies and experiments performed on high voltage system, which is required to depend on the worldwide manufacturers for its high impulse generator, which is somewhat costly and extensive in size. Because of that, this paper is centered on impulse generator with a sensible expense and exertion. Additionally, it is expected to accomplish a little in size of the test circuit, which is compact and appropriate for any tests or studies. Visualization condition of energy can disentangle understating the execution of the Marx impulse generator is ascertained and imagine for calculating of DC voltages of 10 kV. An Impulse Generator having ten stages is outlined and executed for testing of 11 kV electrical hardware. Simulation & practical results are evaluated. The experiment was performed with software & then compared with actual practical values of the system. First Test is performed at 8.5 kV gap setting then on 9 kV& 9.5 kV. Overall objectives, which are to outline and assemble a High Voltage Generator at a sensib le cost, exertion, and little in size, are accomplished.
Keywords— Energy, Impulse generator, Marx impulse generator, high voltage, Impulse testing, cost effect
I. INTRODUCTION
The ease of circuit design and its execution of a Marx impulse generator, empowering its use in an extensive variety of utilization, for example science, arm forces and industries. Its method is very easy in which capacitors; resistors and sphere gapes are included as switches. In 19231 the Marxiimpulse generator was introduced. The working principle of the generator was to generate the impulses by making the capacitors charge in parallel and discharge in series [1, 2]. The Marx generator is labor intensive and time consuming in replacing the output waveform, and its multiple spark air gap switches are sometimes triggered out of synchrony, especially when the preset voltage is not very high. In addition, electromagnetic interference that arises from the spark discharge makes partial discharge detection difficult [12].
From that point numerous endeavors are made to enhance the execution and build up the method of the Marx circuit [3]. Recent efforts were focused to transform it for portable and small size applications [4]. Contingent upon the purpose of a Marx impulse generator, it is essential to look in more detail the relationship among energy put away, number of stages, capacitor values, input voltage and their consequences for expense impulse generators. Albeit, hypothetically it may be envisioned in out coming voltage and energy of generator, Now the typical qualities of charging capacitors, most extreme descriptive breakdown of insulation voltage, the extent sizing and their consequences effect for the expense. These variables constrain the possibility of wanted output.
Fig.1. Marx Generator during charging
Taking into account the over, this paper is concentrating
on ascertaining and exhibiting the liaison between
selected values of the capacitor and piled up energy,
voltage which is to be given, number of phase and their
impacts on the expense of a Marx impulse generator. To
compute these parameters, it is accepted whole capacitors
must be completely charged. Besides, it is additionally
expected that prize value of the DC feeding voltage hasn’t
impact on a aggregate expense of the Impulse voltage
generator. Section I is about the basic introduction,
section II is about literature survey. Section describes the
Methodology & V is about System Evaluation.
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64
DOI: 10.24081/nijesr.2016.1.0012
Fig. 2. DischargingMarx Generator
II. LITERATURE SURVEY
A. Energy Calculation:
The idea of a Marx impulse generator [3] is
appeared in Figure 1 and Figure 2 and the charge and
release charge are additionally improved and appeared in
Figure 3 and Figure 4. Taking into account the
fundamental suspicion, the energy E in Figure 3, when
every in parallel capacitor energized to most extreme
voltage, (10 kV) [5]. The impulse energy transformed
during a discharge [6] is given by equation (i);
Where Cs equivalent capacitance of each stage, Vl is
basically the magnitude of Direct Current voltage of
above mention system, in our system charging voltage is
10 kV DC values of all capacitors& resistors of each stage
are equal.
In Figure 2, when Impulse generator is triggered and the
beak-down of sphere gapes takes place exactly at the ɛ
momentibeforeithe storing energy releasing to the
electric load, The capacitors are already coupled in series
and with total capacitance [6] during this situation is vary
to equation (ii);
Where n is the quantity of stages. By computing equation
(ii) the comparable capacitance [6] yields as equation (iii);
This new system has energy which is basedion
emancipation mechanism [2], [6], equation (i) and
equation (ii) can be calculated as Equation (iv);
Equation (iv) can also simplify to equation (v);
By solving equation (v) we have yields [6] as equation (vi);
By looking at equation (i) and equation (vi) it can be seen
that aggregate or overall energy of the developed system
[6], at the ɛ minute sooner than the put away energy starts
to release to the heap.
B. DC Power Supply
For High Voltage DC power supply cro ck roft
Walton voltage multiplier technique is used [8]. At low
frequency AC the losses are much more so 240 V, 9 K -
Hertz AC is used to develop high voltage power supply of
10 kV. Twenty -Eight numbers of stages are used, all
capacitors of power supply are rated at 0.68 µF and 630
V. Diodes used in Power Supply are DGP -30 power diode
having maximum peak reverse voltage of 1500 V.
C. Impulse Generator Parameters:
In given system 12 capacitors are used in one stage value
of 220 nF, 1 kV each. The purpose of connecting 12
number of 1 kV capacitors instead of a single 10 kV
capacitor for each stage is to make the system small in
size and cost effective. So each stage is rated at 18.33 nF,
12 kV. The purpose of connecting 2 extra capacitors in
each stage is to avoid any capacitor from over stressing. In
proposed system no of stages of impulse generator are ten
so the equivalent capacitance during discharge condition
is 1.833 nF. The output impulse is applied on the test
object through wave shaping circuits, which define the tail
& front time of the impulse shape.
D. Trigger Pulse:
The breakdown setting of first sphere gap is most critical.
There are three different ways to cause the breakdown of
first sphere gap. One is uncontrolled method & other two
are controlled methods. In under discussion system one of
control method is used. When stages are charged in
parallel up to rated voltage then circuit is ready to trigger
to cause breakdown the first sphere gap. When the first
sphere gap is breakdown remaining sphere gapes breaks
down simultaneously. To cause a breakdown at first gap a
trigger pulse is applied which create the extra stress at
first sphere gap and it breaks down. First setting of first
sphere gap must be slightly above the charging voltage for
this method to avoid from uncontrolled operation.
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65
(1)
(2)
(3)
(4)
(5)
(6)
E. Test Object:
11 kV Pin type insulator is used as a test object.
For 11 kV Pin type insulator the lightening impulse
standard is 95 kV impulse with rise time of 1.2 µsec and
front time of 50 µsec. Pin type insulator have a
capacitance of 25 pF.
F. Capacitor Banks Design:
To make the system cost effective & small in
size banks of small capacitors are used to develop the
system [9]. This makes the system cheaper as well as
small in size. Twelve Capacitors of 1 kV, 220 nF are
connected in series to develop a single stage. All
capacitors are placed inside the Polyvinyl Chloride (PVC)
conduit and the filled with magic epoxy & then covered
with polythene & finally covered with Bakelite sheet. This
type of construction provides the insurance of insulation
and protects the capacitor banks from environmental
effects. The whole mechanical structure of the system is
made with PVC and Bakelite material [10].
III. METHODOLOGY
This paper shows, each of the qualities are valuable for a
Marx impulse generator delivering the release pulses, not
exactly a couple of microseconds, the greatest voltage
peak of 96 kV in 10 phases and release Energy is 10
Joule.
Keeping in mind the end goal to imagine the relationship
between simulated results and practical results circuit is
recreated in Circuit programming by simulation.
Simulated results are compared with practical results for
different gap settings.
The circuit is simulated in Circuit Software, which
provides the complete provision for gap setting.
Gap setting available in software, which is used to
develop this system. It includes
1. Its ON resistance at the time of breakdown
2. It’s OFF resistance during charging before
breakdown
3. It’s holding current i.e. the amount of
currentrequired tohold the spark between
contacts of the gap.
4. And finally breakdown setting of the gap.
In practical situation increasing or decreasing the distance
between the contacts of the sphere gap can do this all [7].
Figure 5 shows the flow diagram of the complete system.
High voltage (HVDC) source charges all ten stages in
parallel [11]. When all stages are charged up to rated
value a trigger pulse is applied and which causes the
breakdown at first stage & ultimately all the stages
connect in series by the breakdown of all stages. The
output is applied on the test object, which is 11 kV pin
type insulator in the system under discussion.
Fig. 5. Flow diagram of the system
The output is applied on the test object which is 11 kV pin
type insulator in the system under discussion. For display
16 x 2 Liquid Crystal Display (LCD) is used which shows
the HVDC supply voltage, Stage Voltage, final impulse
output & leakage current of the test object. Figure 6 shows
the algorithm of the system.
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Fig. 6. Algorithm
When the stage voltage is greater than 9.5 kV System is
ready to trigger & if the stage voltage is less than 9.5 kV
then keep continue the charging of the stages until this
condition is fulfilled.
IV. SYSTEM EVALUATION
The experiment was performed with software & then
compared with actual practical values of the system. First
Test is performed at 8 kV gap setting; results are shown in
Figure 7. It is obvious from the Figure 7 that actual output
is less than expected output. The reason of this difference
is that the first gap is set at 8 kV so it breakdown at 8 kV
that’s why remaining stages have not enough time to
charge up to 8kV so ultimately the actual output is less
than expected output.
Fig. 7. Output at 8 KV gap setting
Second Test is performed at 9 kV results are shown in
Figure 8. So it is clear up to now that the setting of first
which really matters others gap have no effect they can be
adjusted exact equal to the charging voltage are slightly
above charging voltage which is more advisable to
compensate temperature & humidity effects.
Fig. 8. Output at 9 KV gap setting
So what is concluded up to now from gap setting is that if
set the first gap near the charging voltage will get near to
expected output because this setting provides all stages
enough time to charge to their rated values (9 kV). What
if the first gap exactly equal to the charging voltage?
Answer is clear that the breakdown is uncertain so it has
to be set below the charging voltage as near as possible.
Third Test is performed at 9.5 kV results are shown in
Figure 9.
Fig. 9. Output at 9.5 KV gap setting
The experimental and resultant parameters are depicted by
Table 1.
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67
TABLE 1: FINAL RESULT COMPARISON
Parameters
Values taken on following
voltages
8KV 9KV 9.5KV
Break Down Voltage 30V 10V 12V
Expected Output 80V 91V 93V
Simulation Output 70V 89V 85V
Practical Output 65V 87V 97V
V. CONCLUSIONS AND FUTURE WORK
General goals, which are to plan and assemble a High
Voltage Generator at a sensible cost, exertion, and little in
size, are accomplished. A10 stage, 100 kV, 1.2 µsec rise
time, 70-µsec-pulse duration, 9.165-Joule which gives
impulse of 95 kV at +10 kV. The reproduced outcome of
the pragmatic circuit result are near the IEC standard
wave shape for lightning drive. So it is concluded that if
this proposed type of construction is used an impulse
generator can be developed at very low cost & small in
size. This research effort can be more stretched out by
doing enhancements in the circuit with the help of altered
Marx circuits which won't just make the outline more
conservative and versatile additionally wave shapes will
also be controlled and increment as the resistances are
more disseminated all through the circuit.
ACKNOWLEDGEMENT
The authors are thankful to Department of Electrical
Engineering NFC-IEFR for providing necessary
assistance to conduct this research work.
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