This circuit is connected to and uses lethal mains voltages and must not be used by any non-qualified persons.
There are often times when a superimposed impulse is required on a supply to either test the effectiveness of a suppressor circuit, or the capturing ability of a power quality recoder etc. The following circuit provides an economical means to generate a 5/30µS impulse which is superimposed on a normal 230VAC waveform. Two impulse voltage levels are available, 50V and 500V.
When C3 charges sufficiently and the voltage across G1 reaches firing voltage (230V) the low voltage end of C4 is "pulled" toward the high voltage end of C3. This in turn significantly raises the high voltage end of C4 and effectively places C3 and C4 in series making the total voltage approximately 500V. As this is beyond the firing voltage of G2, it now conducts placing the full charge of C3 and C4 across R9 and R10. R11 and L1 serve to indicate when a strike has happened. R12 is an inrush resistor.
For those concerned about the energy levels dissapated in this circuit, we use the formula J=½CV2. The capacitance is taken as 0.235µF (2 x 0.47µF in series). For the sake of argument we assume it possible that the voltage on G2 could be at 350V without it firing, and then G1 reaches 230V, this makes the total voltage 580V. The total energy dissapated = ±40mJ. This can give you a serious whollop but the danger lies in the fact the output is always delivering mains voltage, not the energy during an impulse.
If operating the impulse generator at 115VAC (used extensively in the mining industry around the world as well as being the mains voltage in the USA) then use a simple auto transformer arrangement as shown alongside. This could comprise of the two input windings on a small mains transformer (as shown).
PARTS LIST D1, D2 - 1N4008 diode R1-R4 - 1Meg R5-R8 - 240k R9 - 30 ohms R10 - 270 ohms, 2 watts, 1kV working R11 - 100k R12 - 10k all resistors 1 watt, 350 volts working unless otherwise stated C1, C2 - 1µF C3, C4 - 470nF all capacitors 400 volts working, polycarbonate. G1 - 230 volts, 20A/20kA gas discharge tube G2 - 350 volts, 20A/20kA gas discharge tube L1 - Neon indicator lamp S1, S2 - suitable high working voltage push buttons