Impulse Current Generator
- Protective gear like surge diverters have to discharge the lightning circuits without damage.
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| Figure A |
- Therefore, generation of impulse current waveforms of high magnitude (100 KA peak) find application in test work as well as basic research on non-linear resistors, electric arc studies, and studies relating to electric plasmas in high current discharges.
- The waveshapes used in testing surge diverters are 4/10 and 8/20 μs ( See Figure A). The tolerances allowed on these are ±10 % only.
- For producing impulse currents of large value, a bank of capacitors connected in parallel are charged to a specified voltage and are discharged through a series RL circuit as shown in Figure B.
- C represents a bank of capacitors connected in parallel which are charged from de source to a voltage upto 200 kV. R represents the dynamic resistance of the test object and the resistance of the circuit and the shunt. L is an air cored high current inductor, usually a spiral.
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| Figure B |
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| Figure C |
- For producing large values of impulse currents, a number of capacitors are charged in parallel and discharged in parallel into the circuit. The arrangement of capacitors is shown in Figure C.
- If the capacitor is charged to a voltage V and discharged when the spark gap is triggered, the current im will be given by the equation
The essential parts of an impulse current generator are :
- A dc charging unit giving a variable voltage to the capacitor bank.
- Capacitors of high value (0.5 – 5 1F) each with very low self-inductance, capable of giving high short circuit currents.
- An additional air cored inductor of high current value.
- Proper shunts and oscillographs for measurement purpose and
- A triggering unit and spark gap for initiation of current generator.
