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.