Line Isolation monitor for DC power line

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gaminid
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Line Isolation monitor for DC power line

Post by gaminid » Fri Apr 05, 2013 12:49 am

Hello,

I need to design a line isolation monitor for a isolated DC power line. Just wondering whether you can give me a head start as where to you begin. I am thinking of biasing a small current (wrt to GND) to +V and monitor the return via ground back to +V. If there is no leakage from +V to GND the monitoring circuitry should see any thing. However if there is a leakage from +V to GND then that leakage should show up in the monitoring circuitry as the return path for that leakage is via GND back to +V.

Your help is greatly appreciated.

Thanks

Gamini
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SemiconductorCat
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Re: Line Isolation monitor for DC power line

Post by SemiconductorCat » Fri Apr 05, 2013 7:43 pm

I'm not clear what kind of isolation that you need?Could you be more precise.
Magnetic isolation
Optical isolation or what else?

I head there are Hall effect sensors for DC current. But never used them before.

And this device is already in the markert, this is called DC earth fault monitoring right.I think we also
have a one(In our Cutting machine).

http://www.megacon.com/default.aspx?pageId=179

NOTE: if you are looking for a HVDC application , please ignore my suggestion. It's not easy as it is. HVDC design
is out of my capabilities.
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SevenZero
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Re: Line Isolation monitor for DC power line

Post by SevenZero » Sat Apr 06, 2013 7:04 pm

If you need current sensing, you can find a contact-less inductive current sensor from TRONIC.LK
gaminid
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Re: Line Isolation monitor for DC power line

Post by gaminid » Mon Apr 08, 2013 8:35 pm

Many thanks for both of you for alerting me on hall effect sensors. I will look into that. Here is more details of I want to do.

I am going to use an isolated 1600VDC supply to operate a device about 200m away from the power supply (the cable length is about 200m long). I need to know if there is a leakage to ground (or to the frame of the device) from either +1600VDC or -1600VDC leads (may be I should call it an insulation monitoring). The moment the leakage is detected the power supply should be shut off.

Thanks again,

Gamini
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SemiconductorCat
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Re: Line Isolation monitor for DC power line

Post by SemiconductorCat » Mon Apr 08, 2013 9:47 pm

>> The moment the leakage is detected the power supply should be shut off.

This is not a good idea at all. Normally you could not turn off HVDC lines as you switching on/off a
230V light bulb. You have to synchronously switch off the load softly and switch off the line systematically,
otherwise it will violently explode. Anyway 1600V is not much HVDC at all. So I think here you could. But
I need more info before I make any suggestion.

NOTE: For HVDC application ,hall effect sensors from lanaktronics are not suitable at all. Never even think
about it.

Even I have done a HVDC design I could not advise on this to you. Even need more information, what kind of
a device that you describe. What kind of power line quality that you have(harmonics etc). What kind of cabling
[underground ?]. what kind of a application? Is this is a application something like going into a tunnel?

Megacon have that device that you need.Such devices that could predict where the leakage is at even.

But I could not advise on it,because of experience. My father
have done several HVAC designs , You could simply post with more info , I'll tell him to answer.If not
you could ask this on http://electronics.stackexchange.com/


>> may be I should call it an insulation monitoring

Sounds like you describing an underground cable right? Our electricians do use a FM radio to detect it.
They took a FM radio and walk trough the line, when there are sparks ,there would be EMI and radio will
start to noise violently. But anyway these days we have computer based simulation software to simulate
and find out where is the leakage.

And also for 200m away device, you simply don't need HVDC at all.Simple 3 phase 415 line would do that.
gaminid
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Re: Line Isolation monitor for DC power line

Post by gaminid » Mon Apr 08, 2013 10:04 pm

Unfortunately Megacon devices do not support 1600VDC. Their max voltage is 1400VDC.

The power supply I use has the enable/disable feature and I can simply drive that with TTL logic. As long as I can create an alarm signal (say +5V TTL) I can disable the power supply.

Any ideas...

Thanks

Gamini
SukhdeepMankoo
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Re: Line Isolation monitor for DC power line

Post by SukhdeepMankoo » Mon Apr 15, 2013 6:02 pm

Use optical isolator and give different ground.

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