219. Construction of Marx generator and simulated Impulse ...eesd.muet.edu.pk/sites/default/files/imagecache/EESD_2016_paper... · 4th International Conference on Energy, Environment

4thInternationalConferenceonEnergy,EnvironmentandSustainableDevelopment2016(EESD2016)

219. Construction of Marx generator and simulated Impulse voltage of the Marx generator

Imdad Ali Bangwar a 1,Ali Adnan Bhutto b, Mahnoor Hayat c a,b,c Mehran University of Engineering and Technology Shaheed Z.A Bhutto campus Khairpur Mir’s, Pakistan

* Corresponding author: [email protected]

Abstract

“The impulse voltage wave is a spike of voltage that suddenly rises in very short time to its peak and falls slowly to zero with respect to time axis. The standard Impulse waveform has characteristics similar to that of produced using impulse generator for that purpose we are using Marx generator circuit divided into 3 portions combinedly having 50 stages and can generate peak voltage of 200kV normal voltage neglecting losses due to atmospheric conditions. This Marx generator is of low energy level and can be used for dielectric testing of equipments practical based on Impulse voltage and the test object must lie under limit of its ratted output capacitance. This paper is used to describe the analysis of output impulse voltage using software simulation and of the circuit utilizing 10 stages with 4kV ratted per stage voltage generation” © 2016 “Imdad Ali Bangwar, Ali Adnan Bhutto, Mahnoor Hayat”Selection and/or peer-review under responsibility of Energy and Environmental Engineering Research Group (EEERG), Mehran University of Engineering and Technology, Jamshoro, Pakistan. Keywords: “Multistage marx generator; constructional principle ;operating principle.”

Introduction/Literature review

The impulse voltage is a short time transient voltage that may cause disturbance or failure of power system

equipments. The Impulse voltage is either caused by lightening or switching surges. The Impulse, name referred, is a

voltage level having high magnitude than normal power system AC voltage. Hence during the development of power

equipments their high voltage testing is mandatory against surge voltages. As per origin of transients, there should be a

distinction between lightening and switching impulse in the relevance of International Electro-technical Commission

(IEC) standard (60060-1). Measurement of the dielectric properties of nonlinear grading elements is best carried out using

an impulse generator [2].

Lightening over-voltage wave characterised as double exponential given in the following equation:

V=V0[e(-αt) - e(-βt)] (1)

Vo in equation (1) is capacitor charging voltage the equation represents the wave of unidirectional that quickly rises to


peak value and falls slowly to zero. The 1.2/50 full lightning impulse voltage as defined in IEC 60060-1 [1] is of particular

practical importance. Impulse wave can be generated by combination of RLC circuit or by RC Circuit. For specification of

impulse wave, there is front time and fall time of impulse wave. The rise time and fall time can be varied by varying

circuit parameters. The wave shape can be controlled by resistors of generator as generator capacitance and load

capacitance are considered as fix. For the production of impulse wave if single capacitor is used, its size and cost causes

problem of large size and its cost. Its solution is by connecting number of capacitors are charged parallel then discharged

in series alternatively. This ideas was proposed by E. Marx in 1923. In present time several modifications are employed on

Marx circuit generator.

As per IEC standards, the impulse generator would produce wave which can be lightening or impulse switching, with

1.2/50 micro seconds standard front and tail time ratio. The nature of lightening impulse voltage is to sudden rise in its

magnitude in small time to its peak called front time and fall to downward from peak to 50% of its peak voltage with

respect to time called tail time. As given in IEC standards, the front time and rise time constant ratio is 1.2:50 µs.

Figure 1: basic circuit of Marx generator


Figure 2: Standard Impulse voltage wave shape with specifications [5]

In this research the results of simulation of multistage impulse marx generator has been taken into account and

considered same as that of impulse voltage which may be occurs due to lightning strike or switching surges. There are 10

stages of marx generator is to be considered for the output results. The results have been considered as that of IEEE

standard with increasing and decreasing tolerance in rise and fall time as well as rise and fall voltage with respect to time.

Designing of multistage Marx generator The design principle of marx generator is that the source charges the all connected capacitors in parallel and after full

charging the gap of first stages has to be break to connect with other capacitors in series. When the N capacitors have to be

charged in parallel through charging resistors, the gas is triggered by pulse method or without pulse method.

In this research the marx generator is used having 10 stages, each stage consist capacitor and of charging resistor

and without pulse gap triggering method is used. the all capacitors charged by dc source in parallel and after complete full

charging the voltage of each stage will be added with next stage because of their series connection hence discharges in

series. The voltage across load (capacitive or test object) is equals to sum of all voltages across each stage. The per stage

voltage is 4 kv ratted, when 10 stages are added to gather, the output is considered to be 40kV, neglecting the voltage

drops and environmental conditions.


Figure 3: schematic diagram of n stage Marx generator circuit

Construction of multistage Marx generator The 10 stage practical marx generator is constructed according to the consideration of different parameters including

current, voltage, power ratting of each capacitors Co resistors, wave front resistor Rf and wave tail resistor Rt. Also the

test objects are two gap adjustable electrodes which produces spark when breakdown voltage meets.

The ratings and values of particulars are as under:

• Resistor: 470 k ohm of resistance, power rating of 2 watts.

• Capacitor: 4.7 nF/ 4kV, code 472 M, power rating of 2 watts.

• Electrodes: Diameter: 2.1 cm, gap width: 4.5-7.7 cm

The two electrodes are placed at the load side considered as test object with maximum capacitance of 75uF.

The source is adjustable dc voltage and fed into the marx generator is 4 kV.

Figure 4: Constructed 50 stages Marx generator


Figure 5(a) (5b): Adjustable Electrodes of Marx generator

Experimental measurement The measurement of voltage is utilized by using gap distance between two electrodes considering the environmental

factors such as temperature, humidity and pressure and oscilloscope connection across gap with voltage divider circuit.

The measurement results are taken according to each stage using simulation. Initially one stage is used and fed by

dc supply and output measured, and second stage output is measured and then third stage and so on. In this way the

measurement of peak voltage is measured, while front and tail time can also be measured using oscilloscope graph. The

second type of problem confronting the impulse generator user is that of determining the approximate front and tail

resistances to give the desired impulse shape with a particular value of load capacitance. Here again the exact solution is

tedious and time consuming so an approximation method has been developed [3].

The front time, tail time, α and β can be measured using equations from (3.1-3.12) in [4]

Simulation and its Results The simulation of same constructed practical circuit is considered circuit is designed and assumed to provide

output that is similar to the constructed multistage marx generator.

2nd stage marx generator simulation

Test object capacitance setting : 0.008pF

Figure 6: 2nd stage Simulation circuit


Figure 7: two stage simulated Impulse wave

Figure 8(a): 2nd, 3rd, 4th stage impulse wave figure 8(b): 5th, 6th, 7th stages impulse waves

Figure 8(c):8th, 9th and 10th stage waves


1. Table

Stage Peak Voltage

kV

2nd 6.3254

3rd 9.1213

4th 11.7460

5th 14.1447

6th 16.4379

7th 18.4647

8th 20.5239

9th 22.4088

10th 24.1154

Conclusion The simulation results and wave shows that the constructed impulse generator would have to be same output that is in

simulation, the practical experiment needs high voltage measuring instruments in regard of measurement and protection

for experimental data and must be performed in high voltage engineering lab.

Future work The multistage marx generator is consist of 50 stages. Only 10 stages are utilized in simulation. For future it’s all stages

peak voltage can be calculated by simulation as well as using high voltage measuring instruments in high voltage lab,

experimental values can also be calibrate for experimental data comparison with IEEE standards and for higher

capacitance testing objects, all stages can be utilized at same time.

Acknowledgement

I am very thankful to my friends Noman khan who helped me in the designing and construction of practical Marx


generator as well as in simulation and also thankful to our chairman sir Shakir Ali soomro who encourage us for making of

Marx generator and i can not forget my friends and classmates Ali Adnan and Mahnoor Hayat who have helped me

construction and simulation of of Marx generator

References

[1] IEC 60060-1, “High-voltage test techniques – Part 1: General definitions and test requirements”, Edition 3, 2010.

[2] S. A. Boggs and J. Y. Zhou. ‘‘Dielectric Property Measurement of Nonlinear Grading Materials’’, IEEE Conference

Electrical Insul. Di-electric Phenomena, pp. 764767, 2000.

[3] F.C. Creed and M.M.C. Collins. “SHAPING CIRCUITS FOR HIGH VOLTAGE IMPULSES”, National Research

Council of Canada Radio and Electrical Engineering Division Ottawa, Canada, pp. 2239-2243

[4] C.L. Wadhwa. “HIGH VOLTAGE ENGINEERING”, second edition, New Age International (P) Ltd., Publishers,

pp.84-89

[5] M S Naidu, V Kamaraju. “HIGH VOLTAGE ENGINEERING”, second edition, Mc Graw-Hill publishing company

limited, pp. 129, fig. 6.14

Documents

219. Construction of Marx generator and simulated Impulse ...eesd.muet.edu.pk/sites/default/files/imagecache/EESD_2016_paper... · 4th International Conference on Energy, Environment