Protection systems for High Voltage Systems

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sabu31

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Hi all,

I am developing a HV voltage pulsing system which has output of 12kV, 60A , pulse duration of 10us and frequency of 250Hz. The input is 500V pulse which I am generating from DC-link using H-bridge IGBT inverter system. As there may be possibility of arcing and other faults. WHat all safety mechanisms need to be included.

The primary current is around 500A in each H-Bridge. Will current shunt using shunt of 100 A will be useful for protection.
Also over-voltage protection and any other protection mechanisms reference would be helpful
 

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Hi,

Safety in which regard?

To protect humans against electric shock?

Klaus
 

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Both aspect. But initially its in prototype stage so need safety of system from faults, arcing etc
 

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Hi,

I guess you need to tell us more details.

"Safety", "system", "fault" are rather vague descriptions. A lot of room for guessing.

Klaus
 

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a) What is the method for arcing protection in a HV system. The pulse width is 10us frequency 250 Hz and peak current under normal condition is 500A-600A. is there any current sensor for such application or current shunt with opamp
b)Will semiconductor fuses be of use
 

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For sensing the current you have to use hall effect transducer. For example the manufacturer LEM has different current transdicers.
To protect against hv arc...you need to keep enought distance between the tracks and make some cuts on the PCb if it needed
 

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Hi,

a shunt based current measurement may be used as well, there are shunts available in the low µOhm range. To achieve an galvanic isolation between this "conductive" measurement between HV and LV this measurement on the HV side has to be isolated by means of an isolated communication bus e.g. [1], if the current measurement result is digitized by an ADC. Further, you have to povide a power supply for this measurment residing on the HV e.g. by a flyback converter or push-pull converter, to deliver power from the LV side. The electronic may also be powered directly by a portion of the HV.

There are also hall-sensor based ICs available e.g. [2], but be aware of the susceptibility of this sensors against EME/EMI. Further, you need some kind of FEM based model of your system to match the measurement result with the actual current, and/or you have to calibrate it with a current of known amplitude.

One of the most important thing, as already mentioned by @flote21, is to maintain the required creepage and clearance distance to achive your required isolation.

[1] https://www.ti.com/isolation/digital-isolators/products.html
[2] https://www.melexis.com/en/products/current-sensors

BR
 

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Hi all,

Thankyou for the reply. I need to clarify that the high current is in the primary side typically 500 -600 A pulse. I am thinking of putting measurements in primary side assuming the secondary (HV Side) is a reflection of primary. The LEM sensors, I could not find any which is having a Bandwidth of more than 1Mhz. As my pulse is 10us, i am thinking will need atleast 1Mhz bandwidth.

The TI current sense amplifier with a 100A 50mV shunt looks feasible .. But still max bandwidth is only 400khz...Any workaround for bandwidth.
--- Updated ---

Is

LMP8640MK-T/NOPB​

Current Sense Amplifier, 1 Amplifier, 13 µA, TSOT-23, 6 Pins, -40 °C, 125 °C along with High Current Shunt 100A 50mV a good option. Also they are mentioning common mode voltage of -2 to 42 V , will this affect as my primary pulse is 500V and bipolar.​

 
Last edited:

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Hi,

the shown current sense amplifier is performing a high-side based measurement. By implementing the measurement at the low-side gives a higher degree of freedom by means of more components to chose e.g. by using a differential amplifier.

BR
 

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Before getting lost in details, the current measurement purpose should be clearly specified. I believe that an AC measurement (CT or Rogowski coil) is the most simple way to implement high bandwidth. If you are however not sure about correct operation of the H bridge or want to detect possible imbalance, you need a DC capable measurement. Overcurrent protection doesn't require MHz bandwidth, 100 or 200 kHz gives sufficient accuracy. I'd prefer an isolated magnetic sensor.
 

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KlausST said:
Hi,

Safety in which regard?

To protect humans against electric shock?

Klaus
Click to expand...
In case KlausST wasn't clear, this is a hugely important distinction to make (protecting the hardware itself vs protecting the operator).

For protecting the operator, that requires details about what the load is (I don't recall you ever mentioning the purpose of this project) and how it is connected. Current sensors likely won't help at all since the normal operating currents are going to be far higher than safe limits for human contact. Without knowing more, I'm betting your best bet on human safety is to put all the power circuitry inside a safety enclosure and have an interlock such that the system cannot apply power unless the enclosure is closed.

For protecting the hardware itself, a peak current limit may be useful. For measuring current, a simple current transformer ought to be fine, especially since the pulse is already transformer coupled. A rogowski coil would also work well, if you have one. Just make sure the insulation is appropriate for the voltages involved. Maybe add some layers of fiberglass or teflon sleeves.
 

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Hi
I would like to clear your purpose as I am often design.
  1. Protect primary side - H bridge 500A peak.
  2. Protect output arcing when turn off or current keep flowing after 10us.
  3. Protect output voltage is over range 12kV.

For [1] high current sensing, you can use low-side shunt current sens method. But make high lost/ dissipation power. If only for switching cycle protection, use self/body current sense by Vce of IGBT. It basese on Vce rise when Ice increase. This is no need Shunt, hall-sensor and un-expensive. Low-side sensing don't care so much high-side voltage as 500V.
For [2] when Arc happen, it make output is not really turn off. You can limit operation time when driving primary IGBT < 10uS. This even, arc voltage quite low. You can protect under voltage mode. Or use current sensor to measure output current. If output current keep flowing, you turn off primary side and/or short output to strongly protect. Or use design an EFT detect circuit (open gate mosfet/ open base transistor circuit), when arc happen it will trigger all controller off .
For [3] Use multiple resistor in serial and sense voltage over a reference...
 

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    sabu31

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stenzer said:
Hi,

the shown current sense amplifier is performing a high-side based measurement. By implementing the measurement at the low-side gives a higher degree of freedom by means of more components to chose e.g. by using a differential amplifier.

BR
Click to expand...
Can we use OPAMP such as MCP 6022 along with shunt if used in high side or AC side
 

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sabu31 said:
Can we use OPAMP such as MCP 6022 along with shunt if used in high side or AC side
Click to expand...
Yes, if supplemented by a floating power supply and isolation amplifier for the output signal. Better follow the current sense suggestions made in this thread.
 

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Hi,

Can I use bus #23 to visit my mother?


There is so much information missing, thus it's impossible to answer.
What do you want to achieve?
What circuit do you use? (From shunt ... to the destination of the signal)
What power supply do you use?
What are your precision and timing requirements?

Klaus
 

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to protect equipment and humans:

put entire thing inside steel box, fill it with transformer oil for insulation and cooling
ground (earth) the box

only connections to the outside are large, well separated, high voltage terminals for high voltage output
another smaller set for the input supply

and whatever sensing information you need to know, such as voltages and currents at appropriate locations in circuit
including fault detection. these should all be isolated
 

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Hi,

FvM said:
Yes, if supplemented by a floating power supply and isolation amplifier for the output signal. Better follow the current sense suggestions made in this thread.
Click to expand...

some kind of digital isolator in combination with an ADC with a SPI interface, residing on the HV side migth do the job. E.g. [1], but to be hornest, I'm not aware of one which can widthstand a repetitive peak voltage of 12 kV, nor one with a working voltage of 12 kV.

KlausST said:
There is so much information missing, thus it's impossible to answer.
Click to expand...
I agree on this point, so we only can make assumptions. Please explain your setup and requirements with respect to safety goals in more detail.

BR

[1] https://www.ti.com/lit/ds/symlink/i...https%3A%2F%2Fwww.ti.com%2Fproduct%2FISOW7741
 

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