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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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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(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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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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