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How to build an electronic ground fault detector ?

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DrWhoF

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ground fault detector

How to build an electronic ground fault detector which can be used in protection of a diver working with tool and light under water.
The protection should be reliable and very fast.
Thanks
DrWhoF
 

Re: ground fault detector

If I were you I wouldn't go into this subject, as you have to remember that there will be great liability from your side to ensure that if something goes wrong, you will be able to provide funds to cover the "to be" victum(s).
You will never be able to predict which component can, hypothetically, give up, but you will be fully responsible for the final product..
So, consider this thoroughly, and if you still want to proceede .. come back ..
Regards,
IanP
 
Re: ground fault detector

I would like to try.
Any schematic will be appreciated.
Thanks
DrWhoF
 

Re: ground fault detector

Attached is a circuit of Ground Fault Monitor.
Have a look at it, if you have questions come back..
Regards,
IanP
 

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    DrWhoF

    Points: 2
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Re: ground fault detector

I have several questions about this circuit.
First of all how does it work?
What is the function of 2 SCRs?
What are the vlues of RC network at pin 5 of the first opamp?
What deos this funny configuration of the second opamp?
What is the voltage at zener diode and why this point is connected to system ground?
Thanks,
DrWhoF
 

Re: ground fault detector

Cutting story short, this circuit imposes dc voltage (≈150Vdc, depending on the Zener diode used) on AC isolated circuits, so first of all, circuit under protection has to be isolated. It basically monitors DC resistance to ground.
This "funny" (as you said) circuit is a single opamp gyrator and together with 6.8nF capacitor builds equivalent to LC filter (with high Q) and filters out AC componet (50 or 60Hz, depending to which system it is tuned).
SCRs are used because of their "latching" action in dc circuits.
The component valuse that you asked for are as follow:
top resistor is 1kΩ;
RC - R=2.2kΩ and C=56nF/630V.
I think I have answered all your questions..
Regards,
IanP
 

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    DrWhoF

    Points: 2
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Re: ground fault detector

This is 3-phase circuit, isn't it? I am confused how can you impose 150Vdc on a 380V ac system?
Thanks
DrWhoF
 

Re: ground fault detector

As I said previously, and bear it in mind, this circuit ONLY works with ISOLATED systems. This means that somewhere in that system there has to be an isolation transformer (single phase or 3-phase) in which case you can easily shift the reference from the agreed "0V" to the new 150Vdc. You can compare this to relativity: travelling on a train does not change your relationship with a bunk you are sitting on, yet you both travel at 100km/h speed..
Regards,
IanP
 

    D

    DrWhoF

    Points: 2
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