Essay: LOW TO HIGH DC VOLTAGE GENERATING DEVICE

CHAPTER 1 : INTRODUCTION
1.1 Basic Theory Of Generator:
The term High Voltage usually means electrical energy at voltages high enough inflict harm or death upon living things. In certain industries voltage means voltage above a particular threshold. High voltage is used in electrical power distribution, in cathode ray tubes, to generate X-RAYs and particle beams, to demonstrate arcing, for ignition, in photo multiplier tubes, and high power amplifier vacuum tubes and other industrial and scientific applications.
IEC Voltage Range AC DC Defining Risk
High voltage
(Supply System) > 1000 Vrms > 1500 Voltage Electrical arcing
Low Voltage Supply system 50- 1000 Vrms 120 — 1500 Voltage Electrical shock
Extra low Voltage (Supply System) < 50 Vrms < 120 Voltage Low Risk
Table: 1.1 voltage rating
Two factors considered in classifying a voltage as “high voltage” are the possibility of spark in air, and the danger of electric shock by contact or proximity. The definition refer to the voltage between two conductor of a system boor between any conductor and ground.
High voltage is usually considered any voltage over approximately 35,000 volts. The general public may consider house hold main circuit which carry the highest voltage they normally encounter to be high voltage.
Voltage over approximately 50 volts can usually dangerous amount of current to flow through human being who touch two point of circuit so safety standard in general, are more restrictive around such circuit.
EHV is define as electrical power transmission engineering refer to equipment the carry more than 345000 volt between conductors.In electronic system a power supply that power supply provides that greater than 275000 volt is called EHV power supply.
1.2 Types Of Generator
Ø Homopolar Generator
Ø Magneto Hydrodynamic Generator
Ø Induction Generator
Ø Linear Electric Generator
Ø Variable speed constant frequency Generator
Vg= generator open circuit voltage,
Rg= generator internal resistance
Vi= generator on load voltage,
Ri= load resistance
1.3 Problem Identification and Proposed Solution
To generate High voltage is not easy task; it can damage the circuit or operating human body very badly. High voltage can also damage the circuit that is made of electronic devices that also cause.the problem of harmonics as well as the devices also can get damage.
Ø Selected Methods
1 Half wave Rectifier circuit
2 Full wave Rectifier Circuit
3 Voltage Doubler Circuit
4 Voltage Multiplier Circuit
5 Van-de Graff Generator
6 Marx Circuit
1.4 Project Planning:-
• Project planning and scheduling.
• Project costing.
• Project monitoring and reviews.
• Report writing and presentations.
• The initial plan should be the best possible plan given the available information. It must be regularly revised as new information becomes available.
• Establish the project constraints.
• Revise estimates of project parameters.
Chapter-2: Literature Review
Nader Barsoum* , Glenn Isaiah Stanley [1] have been presented high voltage low power supply. The objectives of this paper are to investigate and develop a device that will produce high voltage low power supply. Generation of high voltage low power supply can be determined by using Flyback converter as an optimum method which can improve the design of the device to make it smaller in size, simpler and cost effective. In this paper, the device circuits are simulated using PSPICE software to determine the characteristics of the output voltage of the circuits.Fundamental of Flyback converter, design of the circuit, simulation and construction of the device are conducted. The Flyback converter principle is analyzed to find the suitable design of the device in this paper. The chosen circuit components are simulated and their values are calculated. The device circuit is implemented and its output variables are compared with the simulation result.
Amol R. Thakare, Senha B. Urkude, Rahul P. Argelwar [2] have been represented Cockcroft-Walton cascade rectifier, without using transformer. The purpose of this paper is to get an output of a high dc voltage by applying input as an low dc voltage. It provides continuous input current to load with low ripple voltage and current. Moreover, based on the n-stage CW voltage multiplier, the proposed converter can provide a suitable dc source for an n + 1-level multilevel inverter. In this paper, control strategy employs two independent frequencies, one of which operates at high frequency while the other one operates at relatively low frequency
Nikhil M. Waghamare, Rahul P. Argelwar [3] have been present High Voltage DC generation by using Cockcroft-Walton Multiplier are purpose. This section is providing continues input current, with a low ripple cascading of diode and capacitor. Cockcroft-Walton multiplier provide suitable high DC voltage source from a low input voltage i.e, 230V AC supply which is rectified by using half wave rectifier circuit. Cockcroft-Walton multiplier constructed by ladder network of capacitor and diode for generation of high voltage. When number of stages of multiplier are increase output of the Cockcroft-Walton Multiplier is also increasing. In this paper 8 stages Cockcroft-Walton multiplier are use to generated high voltage. In this paper transformer method are eliminated therefore cost and size of Cockcroft-Walton multiplier are reduce. Other specifications considered carefully while designing multiplier and components must be used based on size consideration for expected load current and expected output voltage. A prototype was designed and experimental result was tested and demonstrate was purpose.
C. K. Dwivedi and M. B. Daigavane[4] have been repreasent their work in describes the details of high voltage D.C. power supply whose output is 60 kV, whereas its input voltage is 1-Φ 50 Hz 5 kV of sinusoidal waveform. This test set to be suitable for field testing of high voltage cables, as a prime D.C source for very low frequency high voltage test, oscillating wave technique and impulse voltage charging unit due to its light weight and portability and in this study, they constructed a prototype high voltage power supply based on design, simulation and implementation of hardware work in laboratory. The simulation work has been done by using Mat. Lab. Version 7.0 software.
K.J Anoop, Sapam Roshini Devi, Dr. V.Rajini [5] have been represent the design of a DC-DC converter to produce high voltage from a low input DC voltage by using multiplier cells instead of a transformer. The low input DC voltage is converted to AC with the help of four switches operating in two different frequencies. Further, this AC voltage is given to the voltage multiplier cells for desired high output DC voltage. The output DC voltage produced has high efficiency, high voltage gain, low ripple, low switching losses and less noise. Two independent frequencies operate in this system, one is known as modulating frequency and the other is alternating frequency which work in high level and low level respectively. A prototype of the proposed model is constructed and the output is compared with the simulated model. The model is again reconstructed by a feedback control for constant output with variable input voltages.
Chapter-3
Theoretical Background
3.1 Generator:-
Ø What is Generator?
In electricity generation, a generator is a device that converts mechanical energy to electrical energy for use in an external circuit.
Generators provide nearly all of the power for electric power grids. The source of mechanical energy may vary widely from a hand crack to an internal combustion engine.
• Types of Generators
1. AC Generator
2. DC generator
3.2 DIFFERENT METHODS TO GENERATE HIGH DC VOLTAGE:
3.2.1. Half and full wave rectifier circuits.
3.2.2Voltage doubler circuits.
3.2.3 Cascade voltage doubler circuits.
3.2.4Voltage multiplier circuits.
3.2.5Van de Graff generator.
3.2.1 HALF AND FULL WAVE RECTIFIER CIRCUITS
n This method can be used to produce DC voltage up to 20 kV.
n For high voltages several units can be connected in series.
n For the first half cycle of the given AC input voltage, capacitor is charged to Vmax and for the next half cycle the capacitor is discharged to the load.The capacitor C is chosen such that the time constant CR1is 10 times that of ACsupply.
· Disadvantages
1. The size of circuit is very large if high and pure dc output voltages are desired.
2. The H.T transformer magnitude gets saturated if amplitude of dc is comparable with the nominal a.c. of the transformer.
3. All the above circuits are able to supply relatively low currents and therefore not suitable for high current applications such as HVDC transmission.
3.2.2 Voltage Doubler Circuit
A voltage doubler circuit which has voltage multiplication factor of two. The circuit consist of only two diode and two capacitor and oscillating ac input voltage this simple diode – capacitor pump circuit give a dc output voltage equal to peak-to-peak value of the sinusoidal input. In other word, the peak voltage value because the diodes and capacitor work together to effectively double the voltage.
The voltage doubler circuits make use of the positive and the negative half cycles to charge two different capacitors. These are connected in series aiding to obtain double the direct voltage. In this case, transformer has a small rating equals the direct voltage rating with only simple rectification. Furthermore, for the same direct voltage output the peak inverse voltage of the diodes will be halved.
Each voltage doubler takes a DC input and then outputs a doubled DC voltage. By cascading n voltage doublers the output voltage increases up to 2n times.Generally, the dc output voltage of rectifier circuit is limited by the peak value of its sinusoidal input voltage,but by using combination of rectifier diode and capacitor together we can effectively multiply this input peak voltage to give a dc output equal to some odd or even multiple of the Value of ac input voltage. Consider the basic voltage multiplier circuit below.
Figure:3.2.2 Voltage doubler circuit
.
3.2.2.1 Operation of voltage doubler circuit
The circuit shows a half wave voltage doubler. During the negative half cycle of the sinusoidal input wave form diode D1 is forward bias and conduct charging up the pump capacitor, C1 to the peak value of the input voltage. Because there is no partfor capacitor C1 to discharge into, it remains fully charge and act as a storage device in series with the voltage supply. At the same time , diode D2 conduct via D1 charging up capacitor, C2.
During the positive half cycle diode D1 is reverse bias blocking the discharging of C1 while diode D2 is forward bias charging of capacitor C2. But because there is a voltage across capacitor C1 already equal to the peak input voltage, capacitor C2 chargesto twice the peak voltage value of the input signal.
In other word, V (positive peak)+V(negative peak) as on the negative half cycle, D1 charges C1 to Vp and on the positive half cycle D2 add the ac peak voltage to Vp on C1 and transfers it all to C2.The voltage across capacitor, C2 discharge through the load ready for the next half cycle.
Then the voltage across capacitor C2 can be calculated as : Voutput= 2Vp, where Vp is peak value of the input voltage.
Disadvantage:
1. It requires too many supply and isolating transformer.
3.2.3 Cascaded Voltage Doubler Circuit
Cascaded voltage doublers can be used for producing larger output voltage. In Cascade Voltage Doubler circuit, the capacitors and diodes are connected in ladder network. So the voltage produced is of high value.
Figure: 3.2.4. Cascaded Voltage Doubler Circuit
3.2.4 Voltage Multiplier Circuit
Generally, the dc output voltage of rectifier circuit is limited by the peak value of its sinusoidal input voltage, but by using combination of rectifier diode and capacitor together we can effectively multiply this input peak voltage to give a dc output equal to some odd or even multiple of the Value of ac input voltage. Consider the basic voltage multiplier circuit below.
The voltage produced by a voltage multiplier circuit is in theory unlimited, but due to their relatively poor voltage regulation and low current capability there are generally designed to increase the voltage by a factor less than ten. However, if designed correctly around a suitable transformer, voltage multiplier circuits are capable of producing output voltages in the range of a few 100’s to ten’s of 1000’s of volts, depending upon their original input voltage value but all with low currents in the mill amperes range.
Figure: 3.2.4 voltage multiplier circuit
The above circuit shows a basic symmetrical voltage multiplier circuit made up from two half-wave rectifier circuits. By adding a second diode and capacitor to the output of a standard half-wave rectifier, we can increase its output voltage by a set amount. This type of voltage multiplier configuration is known as a Full Wave Series Multiplier because one of the diodes is conducting in each half cycle, the same as for a full wave rectifier circuit.
3.2.4.1 Operation of circuit
When the sinusoidal voltage is positive, capacitor C1 charge up through diode D1 and When the sinusoidal voltage is negative, capacitor C2 charge up through diode D2.The output voltage 2Vp is taken across the two series connected capacitors.
· Advantages:-
 The advantage of “Voltage Multiplier Circuits” is allows higher voltages to be created from a low voltage power source without a need for an expensive high voltage transformer as the voltage doubler circuit makes it possible to use a transformer with a lower step up ratio than would be need if an ordinary full wave supply were used.
 However, while voltage multipliers can boost the voltage, they can only supply low currents to a high-resistance (+100kΩ) load because the generated output voltage quickly drops-off as load current increases.
 The lowest capacitors are responsible for most ripples and it is therefore most ripples and it is therefore desirable to increase the capacitance in lower stages.
 However it is objectionable from the view point of high voltage circuit where if the load is large and the load voltage goes down, the smaller capacitors would be overstressed.
3.2.5 Van-de Graff Generator
The Van de Graaff generator was developed as a particle accelerator in physics research, its high potential is used to accelerate subatomic particles to high speeds in an evacuated tube. A Van de Graaff generator is a device for making lots of static electricity. Static electricity is made from extra charges stored some place so that they can’t move. Normally charges don’t like to collect in one place. They like to find opposite charges as partners and run away from particles with the same charge.
§ In electrostatic machines charged bodies are moved in an electrostatic field
§ If an insulated belt with a charge density δ moves in an electric field between two electrodes with separation ‘s’
§ If the belt moves with a velocity v then mechanical power require to move the belt is P=F.v=V.I
Figure: 3.2.5 van de graff generator
· Advantages:-
1. Very high voltages can be easily generated.
2. Ripple free output.
3. Precision and flexibility of control.
· Disadvantages:-
1. Low current output.
2. Limitations on belt velocity due to its tendency for vibration. The vibrations may make it difficult to have an accurate grading of electric fields.
· Applications:-
1. The beam of these charged accelerated particles is to trigger the nuclear reaction.
2. Accelerated particle beams are used to break atoms for various experiments in physics.
3. In medicine, such beams are used to treat cancer.
3.3 MARX Circuit
The purpose of this generator is to generate a high-voltage pulse from a low-voltage DC supply. Marx generators are probably the most common way of generating high voltage impulses for testing when the voltage level required is higher than available charging supply voltages.
The basic principle involved is to charge a set of capacitors in parallel and then discharge them inseries. A typical Marx generator consists of an N number of modules. Each module consists of two resistor a capacitor and a switch in the form of a spark gap. Marx generator for repetitive applications is the same as conventional Marx generator but with only in compact size.
The Marx generator has several stages. Each of the stage was constructed using 4 door knob ceramic capacitors and a ball spark gap switch. It is designed as compact and repetitive as possible. Inductor charging method is used for higher repetitive operation.
3.3.1 Operation of circuit
 Charging resistance Rs is liming the charging current from 50 to 100 mA. CRs is about 10s to 1 min. The gap spacing G is greater than the charging voltage V.
 All the capacitances are charged to the voltage V in 1 min.
 The spark gap G is made spark over, then all the capacitor C get connected in series and discharge into the load.
 In Marx circuit, R1is divided into n parts equal to R1/n and put in series with the gap G, R2is divided into n parts equal to R2/n and connected across each capacitor unit after the gap G.The nominal output is the number of stages multiplied by the charging voltage
Marx Circuit
Figure: 3.3 Marx circuit
3.4 Multi-stage Impulse Generator
An impulse generator is an electrical apparatus which produces very short high-voltage or high-current surges. High impulse voltages are used to test the strength of electric power equipment against lightning and switching surges. High impulse currents are needed not only for tests on equipment such as lightning arresters and fuses but also for many other technical applications such as lasers, thermonuclear fusion, and plasma devices.
3.4.1 Operation of circuit
n A single capacitor C1 is to be charged first and then discharged into wave shaping circuits and it is limited to 200 kV
n For producing very high voltages a bank of capacitors are charged in parallel and then discharged in series.
Figure:3.4 Multi-stage Impulse Generator
3.4.2 Components Of Multistage Impulse Generator
n DC Charging set
n Charging resistors
n Generator capacitors and spark gaps
n Wave shaping resistors and capacitors
n Triggering system
n Voltage dividers
3.5 Why Voltage Multiplier Circuit?
• Easy to generate high voltages from single supply transformers by extending the voltage doubler circuit.
• This is simple and compact when load current requirement is less than 1mA.
• Electrical and electronic circuit applications such as in microwave ovens, cathode-ray tubes.
• Electrostatic and high voltage test equipment.
Chapter-4
BLOCK DIAGRAM OF MODEL
Block diagram:
Chapter-5
REFERENCES
1. Nader Barsoum* , Glenn Isaiah Stanley,”Design of High Voltage Low Power Supply Device”
Universal Journal of Electrical and Electronic Engineering 3(1): 6-12, 2015 DOI: 10.13189/ujeee.2015.030102 .
2. Amol R. Thakare, Senha B. Urkude, Rahul P. Argelwar,” Analysis of Cockcroft-Walton Voltage Multiplier” International Journal of Scientific and Research Publications, Volume 5, Issue 3, March 2015 1 ISSN 2250-3153.
3. Nikhil M. Waghamare, Rahul P. Argelwar,” High Voltage Generation by using Cockcroft-Walton Multiplier”. International Journal of Science, Engineering and Technology Research (IJSETR), Volume 4, Issue 2, February 2015.
4. C. K. Dwivedi and M. B. Daigavane,” Multi-purpose low cost DC high voltage generator (60
kV output), using Cockcroft-Walton voltage multiplier circuit” International Journal of Science and Technology Education Research Vol. 2(7), pp. 109 – 119, July 2011.
5. K.J Anoop, Sapam Roshini Devi, Dr. V.Rajini,” Analysis Of Dc-Dc Converter With Multiplier
Cells For High Voltage Generation” JATT 10th November 2014. Vol. 69 No.1