Array of Thyristors Connected in Series

Inductive pulse triggering of the gates using a multi winding transformer.

Make all the wires from the signal source be the same length?

There is a lot of info on opto coupled triac switching, typically using a MOC3023.

Your big problem will be getting an even spread of voltage across each triac, each one will behave slightly differently, so one will die, go short circuit, another will die etc.

This uses the empirical rule that says "Semiconductors always fail to the mode that does the most damage".

I'm using on each thytistor a snubber circuit in parallel and a high ohmic resistance, 10 Mohm, to ensure equal charging of every thyristor.

This MOC3023 will be used to trigger every one thyristor or all of them?

Each one would have its own individual trigger.

But you're probably best getting a single triac rated for this voltage instead. By the time you add extra snubbers and voltage spreading resisters it'll be cheaper. Good luck.

Of cource a single hi voltage device is recommended as I pointed out not in your words but mentioned all the complications.

Regards A good point clearly mentioned.

A Marx impulse generator in which capacitors are charged in parallel and discharged through sphere gaps in series across the thyristors.

Use a triode capable of switching those voltages. Siemens makes them. But at $10,000 a piece they aren't cheap.

Regards

In DC Switching either IGBTs are used but I think of very low wkg voltage & if the technology is not faded out.

For using Thyristors for the purpose you need ''Forced Commutation''.

To connect in series is a big problem of reverse break-down in series connected semiconductors, diodes or SCRs. Special networks are connected to ensure equal voltage across all devices; otherwise breakdown of one starts damage to all.

Gate Signals to all should have a good isolation. Each Gate-driver should be isolated fully i.e. input and output side.

All the devices should be tested for equal [within some tight limits] turn-off & turn-on times; means switch on & off very closely in time.

Delay in signal path should closely be maintained.

Study thoroughly before trying in HVDC Switching systems.

Hope of any help.

Hello to all!

I' bringing this up to make another question.

The thyristor in use is SGT Thomson TYN 1225 (rated voltage 1200V).

I'm using 12 thyristors connected in series, a 33 MOhm balancing resistor connected in paraller to each thyristor and a snubber circuit with 1μF capacitor, 1200 V diode and 50 Ohm resistor to each stage of the thyristor.

For the triggering of thyristors 6 Murata 1002 transformers are used.This is a 2:1:1 pulse transformer that is triggering 2 thyristors.

The circuit seems to work, but only for input voltages of 7-7.5 kV even if it is rated for 12 kV.

I think that the problem is the snubber circuit and that the capacitor and resistor are too high valued.Another thought is that the balancing resistor 33 MOhmis too small (doubt about it though...)

Would someone please suggest a way to evaluate the exact value of the aforementioned C and R for this circuit?