Switching a high voltage (30kV)
Thomas F, Sun Mar 22 2020, 10:51AMHello kind folks,
I need some suggestions.
I have a 30kV DC source voltage. I need to chop it into a pulsed waveform with a very low duty cycle say about 1%.
Would this be feasible with a HV switch at 30kV levels ?
Cheers
Thomas
Re: Switching a high voltage (30kV)
Sulaiman, Mon Mar 23 2020, 02:12AM
Of course it is feasible
... national grid type HVDC links are now in the 1MV range and switched electronically.
There are several considerations ;
. cost
. explosive R&D
. losses / efficiency
On the assumption that your 30kV dc source is low power (?)
you may find that balancing/biasing and switching losses are too large.
I would consider using a spark gap ... low-tech but rugged.
If by switch you just mean 'mechanical switch' then that too is possible,
arc supression (e.g. a snubber) will be critical for reliability.
For clearer advice you need to give more information;
power or current available at 30kV
repetition frequency
switching current
load type
Sulaiman, Mon Mar 23 2020, 02:12AM
Of course it is feasible
... national grid type HVDC links are now in the 1MV range and switched electronically.
There are several considerations ;
. cost
. explosive R&D
. losses / efficiency
On the assumption that your 30kV dc source is low power (?)
you may find that balancing/biasing and switching losses are too large.
I would consider using a spark gap ... low-tech but rugged.
If by switch you just mean 'mechanical switch' then that too is possible,
arc supression (e.g. a snubber) will be critical for reliability.
For clearer advice you need to give more information;
power or current available at 30kV
repetition frequency
switching current
load type
Re: Switching a high voltage (30kV)
Thomas F, Thu Mar 26 2020, 10:15PM
Hi Sulaiman,
Thanks for replying.
Your second point is unclear; it shows up here as "explosive R&D"
Yes the DC source is low power , and can be varied from about 5kV to 30kV.I took 30kV as the maximum.The current delivered would be maximum of 50mA,during the On Period which is 300uS while the total period is 25mS; i.e. very low duty cycle.
I could not understand the spark gap method;any links ? In an case it would be probably not suitable.The gizmo is used to check insulation,which may have breakages. The spark created at this blemish needs to be detected and alert the user.
Mechanical switch could be also avoided to reduce complexity and improve reliablity. I am looking for some MOSFET/IGBT which can switch 30kV and is probably less than $50.
Thanks again and good luck to all of us!
Thomas F, Thu Mar 26 2020, 10:15PM
Hi Sulaiman,
Thanks for replying.
Your second point is unclear; it shows up here as "explosive R&D"
Yes the DC source is low power , and can be varied from about 5kV to 30kV.I took 30kV as the maximum.The current delivered would be maximum of 50mA,during the On Period which is 300uS while the total period is 25mS; i.e. very low duty cycle.
I could not understand the spark gap method;any links ? In an case it would be probably not suitable.The gizmo is used to check insulation,which may have breakages. The spark created at this blemish needs to be detected and alert the user.
Mechanical switch could be also avoided to reduce complexity and improve reliablity. I am looking for some MOSFET/IGBT which can switch 30kV and is probably less than $50.
Thanks again and good luck to all of us!
Re: Switching a high voltage (30kV)
Sulaiman, Fri Mar 27 2020, 03:32AM
Google 'thyratron' and 'triggered spark gap'
I literally meant explosive ... bits of flying silicon, metal and plastic :)
I have not seen transistors (IGBT) above 2600V rated.
Sulaiman, Fri Mar 27 2020, 03:32AM
Google 'thyratron' and 'triggered spark gap'
I literally meant explosive ... bits of flying silicon, metal and plastic :)
I have not seen transistors (IGBT) above 2600V rated.
Re: Switching a high voltage (30kV)
HiVi, Fri Mar 27 2020, 07:22AM
It will be hard to get single semiconductors to switch 30 kV. As far as I know highest voltage are SiC mosfets for 15 kV which are not yet available. Than next are thyristors, but are usually made for high powers. In any way it will be hard to go under 50$.
If you want to go with semiconductor swithching, you should go stacking easy to obtain high voltage mosfets (1200 V - 1500 V). Magnetically or optically isolated gate driving. Zenner protected overvoltage of single mosfet and maybe some resistor balanced divider that passively distributes load among them.
There are also companies that produce such high voltage stacked mosfet switches (google: high voltage switches).
HiVi, Fri Mar 27 2020, 07:22AM
It will be hard to get single semiconductors to switch 30 kV. As far as I know highest voltage are SiC mosfets for 15 kV which are not yet available. Than next are thyristors, but are usually made for high powers. In any way it will be hard to go under 50$.
If you want to go with semiconductor swithching, you should go stacking easy to obtain high voltage mosfets (1200 V - 1500 V). Magnetically or optically isolated gate driving. Zenner protected overvoltage of single mosfet and maybe some resistor balanced divider that passively distributes load among them.
There are also companies that produce such high voltage stacked mosfet switches (google: high voltage switches).
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