STARTING OF FYP 2

 STARTING OF FYP 2

WEEK 1

Activity : 
Continue study on operation of an ideal Marx Generator.

Objective : 

• To understand more about circuit diagram.

Content:

Single Stage Marx impulse Circuit

The energy storage capacitor C1 is charged from the high voltage direct current (HVDC) power supply. The output waveform is controlled by the interaction of the front resistor R1 and the tail resistor R2 with the energy storage capacitor C1 and the load C2. The sphere gap in the circuit is a voltage limiting or voltage sensitive switch. Capacitor C1 charges from a dc source until the sphere gap breaks down. The time of breaking down of sphere gap is very short.

Figure 1: Single Stage Impulse Generator Circuit.

Charging voltage in large impulse generator can be of the order of mega volt (MV). The wave shaping network in the impulse generator consists of R1, R2 and C1. Resistor R1 basically damps the circuit and regulates the front time while R2 is the discharging resistor through which C1 will discharge. C2 is the load which represents the capacitance of the load itself and capacitance of other elements parallel with the load. Capacitor C1 discharges into the circuit comprising of R1, R2 and C2, when break down of the sphere gap takes place.

Usually the impulse generator incorporates a load capacitance which is adequately large that the output waveform shape does not change considerably with changes in sample capacitance. The resistors R1, R2 and the capacitance C2 form the wave shaping network. R1 will primarily damp the circuit and control the front time T1. R2 will discharge the capacitors and therefore essentially control the wave tail. The capacitance C2 represents the full load, i.e. the object under test as well as all other capacitive elements which are in parallel to the test object.

Fast impulse or slower impulses can be generated if switching modifications are applied in the impulse generating circuits. One probable way of generating longer pulse is to add an inductance in series with R1. The difference in circuit arrangement will have different efficiency for the impulse generator. The dc voltage can be generated by the use of rectifier circuits. The smoothness of dc value is not much of concern as it has to only charge the capacitor to peak. A sphere gap is a switch and the voltage across the sphere gap builds up as a voltage building up across capacitor takes place. Normally the sphere gaps are allowed to fire naturally or for smooth operation it can be fired through control methods, for example using MOSFET as a switching device. 

CONCLUSION

The simplest building block of Marx Generator is coming from single stage.

WEEK 4

WEEK 4

Activity : 
Continue study on operation of an ideal Marx Generator.

Objective : 

• To study more on advance marx generator.

Content:

Integrated Marx Generator.

The Improved Impulse Marx generator works same as the standard Impulse Marx generator i.e. the energy storage capacitor, C1, is charged from the high voltage direct current (HVDC) power supply. The output waveform is controlled by the interaction of the front resistor R1 and the tail resistor R2 with the energy storage capacitor C1 and the load C2. The only difference is that the switch here acts as a potential divider that divides the tail resistor. The advantage of this method is that this circuit design helps in proper shaping of the impulse wave as the standard wave i.e. it helps in reducing the errors in rise time and tail time. The rise in peak voltage is not that considerable.

In multistage Marx generator circuit resistive voltage divider are used in order to minimize the level of voltage to a measureable value across each capacitor. It consists of two impedances which are connected in series and a tapping is introduced in between these resistors in order to connect the sphere gap. Usually charging resistance is chosen to limit the charging current to about 50 to 100mA, while the generator capacitance is chosen such that the product of charging resistance and generator capacitance is about to 10s to 1 minute . The discharge time constant will be too small (microseconds), compared to the charging time constant which will be few seconds.

CONCLUSION

The integrated marx geneartor configuration produce high efficiency to the circuit.

WEEK 3

WEEK 3

Activity : 
Continue study on operation of an ideal Marx Generator.

Objective : 

• To understand more about circuit diagram.

Content:

Cockcroft walton voltage multiplier

The Cockcroft–Walton (CW) generator, or multiplier, is an electric circuit that generates a high DC voltage from a low voltage AC or pulsing DC input. It was named after the British and Irish physicists John Douglas Cockcroft and Ernest Thomas Sinton Walton, who in 1932 used this circuit design to power their particle accelerator, performing the first artificial nuclear disintegration in history. They used this voltage multiplier cascade for most of their research, which in 1951 won them the Nobel Prize in Physics for "Transmutation of atomic nuclei by artificially accelerated atomic particles". Less well known is the fact that the circuit was discovered much earlier, in 1919, by Heinrich Greinacher, a Swiss physicist. For this reason, this doubler cascade is sometimes also referred to as the Greinacher multiplier. Cockcroft-Walton circuits are still used in particle accelerators, but now also in many everyday electronic devices that require high voltages, such as x-ray machines, television sets, and photocopiers.

Figure 2: Circuit Diagram of Cockcroft Walton Voltage Multiplier

CONCLUSION

Study circuit diagram of  Cockcroft Walton Voltage Multiplier.

WEEK 2

WEEK 2

Activity : 
Continue study on operation of an ideal Marx Generator.

Objective : 

• To understand more about circuit diagram.

Content:

Multi Stage Marx Impulse Circuit

Due to the difficulties faced in very high voltage switching of the spark gap, increase in circuit element size, requirement of high direct current voltage to charge capacitor and difficulties in corona discharge suppression from the structures during charging period the extension of the single stage to multistage impulse generator is made.

A multistage generator is developed by cascading smaller single stage generator to generate high magnitude of output voltage. The primary requirement is to charge capacitors through the rectifier circuit and when all the capacitor reaches to the fully charged state then spark gaps are allowed to break down causing the capacitors to add in series. As a result the nominal output voltage is equal to the input voltage multiplied by the number of stages in the impulse generator circuit. At first, n capacitors are charged in parallel to a voltage (V) by a high voltage DC power supply through the resistors. The spark gaps used as switches have the voltage V across them, but the gaps have a breakdown voltage greater than V, so they all behave as open circuits while the capacitors charge. The last gap isolates the output of the generator from the load; without that gap, the load would prevent the capacitors from charging. To create the output pulse, the first spark gap is caused to break down (triggered); the breakdown effectively shorts the gap, placing the first two capacitors in series, applying a voltage of about 2V across the second spark gap. 

Consequently, the second gap breaks down to add the third capacitor to the stack, and the process continues to sequentially break down all of the gaps. The last gap connects the output of the series stack of capacitors to the load. Ideally, the output voltage will be nV, the number of capacitors times the charging voltage, but in practice the value is less.

CONCLUSION

Looking fot the multiple stage marx generator.