J Electr Eng Technol.2018; 13(3): 1346-1354 ISSN(Print) 1975-0102 http://doi.org/10.5370/JEET.2018.13.3.1346 ISSN(Online) 2093-7423 Cost Effective Design of High Voltage Impulse Generator and Modeling in Matlab Zahid Javid*, Ke-Jun Li†, Kaiqi Sun* and Arooj Unbreen** Abstract – Quality of the power system depends upon the reliability of its components such as transformer, transmission lines, insulators, circuit breakers and isolators. The transient voltage due to internal or external reasons may affect the insulation level of the components. The insulation level of these components must be tested against these conditions. Different studies, testing of different electrical components against high voltage impulses and different industrial applications rely on the international manufactures for pulsed power generation and testing, that is quite expensive and large in size. In this paper a model of impulse voltage generator with capacitive load of pin type insulator is studied by simulation method and by an experimental setup. A ten stage high voltage impulse generator (HVIG) is designed and implemented for different applications. In this proposed model, the cost has been reduced by using small and cheap capacitors as an alternative for large and expensive ones while achieving the same effectiveness. Effect of the distributed capacitance in each stage is analyzed to prove the effectiveness of the model. Different values of front and tail resistances have been used to get IEC standard waveforms. Results reveal the effectiveness at reduced cost of the proposed model. Keywords: Capacitive energy storage, Dielectric breakdown, Impulse testing, Insulation testing, Voltage multiplier. 1. Introduction redirect the lightning strokes, to shield the system from insulation failure. These protection devices must be tested High voltage impulse generator has many applications in to make sure their reliable operation against these conditions. industrial, biological, environmental and defense related To test these devices, artificial testing equipment is needed fields, such as pollution control, electrostatic precipitation, which can generate the same conditions in the laboratory. high power microwave, flashed X-ray in industry, eye Many researchers discussed different approaches [4-7] to surgery and bone repair in medicine. This paper focuses generate these artificial conditions for testing purpose. on the applications of high voltage impulse generator in There are different types of high voltage impulse the field of electrical power industry. Both overhead generators that can generate high-voltage pulses, such as transmission and distribution lines are exposed to different Tesla-type SOS-type (semiconductor opening switch), LTD environmental conditions during their life span, including lightning strokes, which represent one of the severe stresses on electrical equipment[1]. The second cause of impulse generation in power system is load switching. The core distinctiveness of lightning strikes is over voltages with high amplitudes and rapid rates of rising, as shown in Fig. 1. It is classified as rapid front over voltages with front times varying from 0.1 to 20 μs & tail time of 50 µs(1.2/50 µs standard lightning waveform) [2]. While for the switching impulse it is 250/2500 μs [2, 3]. The insulation level of the power system components should be tested against these conditions. Lightening protection devices are developed to † Corresponding Author: School of Electrical Engineering, Shandong University, China. ([email protected]) * School of Electrical Engineering, Shandong University, China. ([email protected], [email protected]) ** Dept. of Electrical Engineering NFC IE&FR Faisalabad, Pakistan, Fig. 1. IEC standard lightening impulse wave form [front ([email protected]) time: T1=1.67 x T=1.2 µs ±30 %, tail time: T2=50 Received: August 2, 2017; Accepted: January 10, 2018 µs ± 20 %] 1346 Copyright ⓒ The Korean Institute of Electrical Engineers This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Zahid Javid, Ke-Jun Li, Kaiqi Sun and Arooj Unbreen (linear transformer driver) & Marx generator [8]. Tesla- type impulse generator cannot generate impulses with the rapid rate of rising and falling edges. SOS-type impulse generator can generate impulses with rapid rate but their efficiency is very low. LTD generators have low efficiency Fig. 2. Capacitor bank arrangement and big sizes. In comparison with these generators, Marx generators is the best choice because it can generate very high voltage (>100 KV) impulses at high efficiency and with a rapid rate [9]. Nowadays generalized Marx topology is proposed and proved to be feasible [10]. Measurement of the dielectric properties of nonlinear grading elements is best carried out using an impulse generator The simplicity of the circuit configuration and feat of the Marx impulse generator, enable its usage in a wide range of application such as science, military, insulation testing etc. Its topology Fig. 3. Block diagram of the system is simple which includes capacitors, resistors and sphere gaps as switches. Haitao Li [11] developed a pulsed power supply consisting cost calculation and the factors that affect the cost of the of several superconducting pulsed power transformers Marx impulse generator. Joe Y. Zhou[18] discussed in his with Marx generator methodology. His experimental and paper about very low energy laboratory impulse generators simulation results shows that proposed design can meet the which can be used to test laboratory scale samples. requirements of basic experimental study for a small rail In under discussion system insulation problems of the gun but not enough for real testing. Yuan Xuelin [12] structure, controllability, observability, stability and proposed a solid state pulser based on avalanche transistor efficiency of the system are also discussed in addition to Marx circuit. In which avalanche transistor is used as a its cost and size. High voltage capacitors are the most switch, it can generate high-repetition and stable short- expensive components of the Marx impulse voltage pulses, but its power is not enough for testing purpose, in generator. order to increase the power of the circuit he introduced Fig. 2 shows that how capacitor arrangements were charged capacitors in the Marx circuit which is very used to make the system cheaper. Instead of using one high inconvenient in terms of practical circuit. voltage capacitor small capacitors were coupled in a string The Marx impulse generator was introduced in 1923[2, to get the same effect with lower cost. 13]. It`s working principle is to charge the capacitors in Fig. 3 represents block diagram of the system. The system parallel and discharge them in series that produces an high is divided into five main parts; 1-High Voltage Direct voltage impulse of short duration by adding up the voltages Current (HVDC) supply 2-Impuse Voltage Generator of all the capacitors [2, 14]. The rising and falling time of (IVG) 3-Wave shaping circuit 4-Test object (11KV pin type the output impulse can be controlled by using different insulator) 5- Display. values of front and tail resistors. Various attempts were Rest of the paper is organized as follows. The detailed made to improve the performance and extend the topology design of the system is described in section II, while of the Marx circuit but the main problem was the cost and section III is about the analysis of the system. Section IV size of the generator [15, 16]. reflects the experimental and simulation results finally The current efforts are focused to transform it into section V is comprises of conclusions based on the portable and small in size and also cost effective. However, simulation and practical results. the main mechanism of this circuit remains the same. Contingent upon the purpose it is essential to understand more about the Marx basic circuit, relationship between 2. Design energy stored, input voltage, capacitor values, the number of stages and their effects on the cost. Although, 2.1 High voltage DC supply hypo-thetically any output voltage and energy for a Marx impulse generator can be expected. Various techniques were studied in the first phase to The standard values of capacitors, breakdown voltages, generate HVDC up to 10KV. Prototype hardware was size and their cost limits the viability of the desired output developed using Cockcroft-Walton voltage multiplier and design. Based on above-cited factors this paper (CWVM) technic. This technique was used because the focused on the design of impulse voltage generator which designed set was intended to be applied for the charging of is cost efficient and compact in size. IVG. The key components for the erection of high Voltage Arash Toudeshki [17] has presented the algorithm for DC power supply are; transformer, power diodes, inverter http://www.jeet.or.kr │ 1347 Cost Effective Design of High Voltage Impulse Generator and Modeling in Matlab Fig. 5. Arrangement of a 10 kV high voltage capacitor Fig. 4. High Voltage DC supply (CWVM technique) and capacitors. Eq. (1) shows the inverse relation between frequency and voltage drop so high-frequency transformer (9 kHz) was used to decrease the losses [2] Here ∆V: voltage drops, f: supply frequency, C: capacitance and n: no of stages. I æ 2 3 n ö Fig. 6. Sphere gap DV = ç n - ÷ (1) fC è 3 6 ø Joseph, M.B [19] has presented the fundamental process of multiplier circuit and discussed the guidelines for the selection of capacitors and diodes. Spencer[20] have designed a prototype of surface mounted Cockcroft-Walton board. The advantage of this set is low cost, high reliability, Fig. 7. Schematic diagram portability and simple control. The proposed model of HVDC is shown in Fig. 4. This model consist of; 28 no of stages (each capacitor is 0.68uF, 600V), diode (DGP-30 to regulate the breakdown voltage of the gaps, as the with 6 ampere current rating).