Vande Graaff Generator


Vande Graaff Generator

Vande Graaff Generator is a device which is generate very high voltage.

The general function of generator is convert mechanical energy into the electrical energy. But by using Vande Graaff Generator we can get electrical energy as well as high potential. Vande Graaff Generator can generate electrical energy up to many 10s millions of volts. It invented by the Robert J. Vande graaff, and he is American physicist.


vande graaff generator

The generator is enclosed in an earthed metallic cylindrical vessel. It is operated under pressure oil vaccume. Belt is connected between the lower nibble to the collector nibble. Which is made of insulation material like rubber or silk. High voltage electrode is connected with the collector nibble. Excitation voltage is given to the lower nibble by using hand driven pulley or other method.

Belt is carrying the positive charge. when belt goes up, the Positive charge are transfer to the collector nibble. which is collect positive charge carrying by belt.


The potential of high voltage electrode above the earth at any instant is given by,
                                                               V = Q / C
Where, Q is charge store by belt
C is capacitance of high voltage electrode to earth.
The charging of the belt is done by the lower nibble spray point. Which are the shaft nibble and its connected to the DC source. Dc source is about 10 to 100kv. The charge from the corona point is connected by the collecting nibble by the belt.  It is transfer on to the HV electrode as the belt entire in to HV electrode. The belt returning with the charge drop and fresh charge is spread on it. As it passes through the lower corona point. The generator is normally work on high pressure gases medium. For that may be nitrogen or SF6 can used.
The potential of outer sphere would keep on rising at up to the breakdown strength of air. The breakdown strength of air is about 30 KV/cm.


  1. Used for medical purpose, to produced high beam rate to treat cancer.
  2. Used to trigger the nuclear reaction to accelerated beam particles.

There are some advantages and disadvantages are following,
1. Output is ripple free
2. Flexibility and precision of voltage control.
3. Very high voltage can be easily created.

1. Vibration is more , hence it is difficult to have accurate electric filed.
2. Output current rating is low
3. Limitations on belt velocity due to its tedancy for vibration


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