Measuring High voltage

Other Hardware General Electronics
1

Dear all.

Here i am attaching old and new schematic for reference.While designing the old board i have made mistake keeping HV- (j14) as common ground reference .

J14 and j12 are connected with high voltage 0-700V dc. Using voltage devider network i am dropping to 0-5v output and feeding analog A3 pin.

I am taking connection of A&B from (J7 connector ) and connected to A & B of the communication SPD**(data sheet attached)** . and earth of communication connected to ground/earth terminal.

Problem statement:

with communication ground connected , When i measure voltage across the j12 . found voltage around 700V.

with communication ground removed,When i measure voltage across the j12 . found voltage around 5V.also when i removed HV+ & HV- wire it operated normally.

So when i tested out i found due to common ground sharing i found 700V .

My question is

How can i separate J12,J14 , i.e HV - ground seprate.

Method1:

Use Voltage transducer ; LM20-P or RTVSM10/25A.I have made setup like this as shown in Capture.

input voltage 260V DC r1=20Kohm and Rm=150ohm supply voltage + or -15v

With this setup. I am getting smoke at input HVside. Can someone suggest what mistake i have done

Method2:

Refer New schematic, I found when voltage measured across A,B w.r.t HV- or earth plate i am getting 700V. So planned to separate the ground for communication side. SO i used isolated 5vDC to 5vDC out put .

When i try with same setup still problem exist.

If i removed communication earth , boards starts working normally. I also replace with communication SPD from other vendor. Issue remains same.

Can someone suggest me How can i measure High resistance , keeping ground isolated.Like HV- (high voltage ground potential)should be separated from Arduino Ground(or controller ground).

old schematic.jpg
old schematic.jpg3508×2481 468 KB

New Schemaic.jpg
New Schemaic.jpg3508×2481 495 KB

0001.jpg
0001.jpg2480×3509 247 KB

Capture.JPG

2

A 20kΩ resistor connecter across a 260V supply is going to dissipate 2602/20000 = 3.38W.

What rating is R1? This might explain the smoke.

3

can suggest appropriate resistor need to be used to make it work.
In future i am going to provide 700V-800V max.

http://rongtech88.en.ec21.com/RTVSM025A_Hall_Voltage_Sensor--4540851_4556075.html

3695783-2013041109071351667d41c4a77.pdf (167 KB)

4

Can someone suggest me How can i measure High resistance , keeping ground isolated?

Normally, you don't isolate the meter from the high voltage... The meter normally shares a ground with the high-voltage, but the meter's ground is isolated from the outside world.

With a battery powered multimeter that's easy. You put it in a plastic case. There is a black or minus lead which may, or may not be, internal ground. It might be the minus input to a differential amplifier. (But, a differential amplifier doesn't isolate.)

The internal circuitry, and probe connections, of an AC powered multimeter are isolated from the power line (and from power-line neutral) by the power supply's transformer. The chassis normally goes to power-line ground, but there's no connection between the chassis or external ground and the internal circuitry.

If there is any digital communication between the meter and the outside, it needs to be optically isolated. Of course, the Arduino's USB port is not isolated and it provides a ground connection to the outside world. It could be dangerous (to you, your Arduino, and your computer) to connect USB and high voltage at the same time, even if the power supply is fully-isolated.

5

My application user for string monitoring . i have totally 24 current sensor which measuring using hall sensor. To measure voltage we are giving 700-800 v from strings of panel.which connected I'm parallel and goes to switch.since its my applixa application how can keep HV ground and low voltage ground separate

6

How frequently is that voltage changing.
I'm experimenting currently with a "flying cap" cell-voltage measuring system for a high-voltage battery stack.
This is fully isolated from he Arduino, and done with relays.

Imagine a voltage divider on the high-voltage side, to lower the voltage to <=5volt.
And a cap across the lower resistor, e.g. 10uF/6.3volt.
The cap is also connected to a DPDT relay.
When the relay is activated, the cap is disconnected (both pins) from the HV side, and connected to Arduino's A/D and ground, measured, and returned.
Sampling can't be done that often with a mechanical relay, but the relay could last years if you sample a few times per minute.
Leo..

http://forum.arduino.cc/index.php?topic=383818.0
Post#8 has a picture.

7

Here strings are connected to solar panel. Almost series. The voltage fluctuations depend on radiation of sun.the fluctuations are in range 700-1000v . currently I have given 750v with + or - 5v w.r.t solar panel.
Main intention is to measure the 1000v in range of 5v analog with separate from HV ground and Lv grounds. Kindly reference schematic. Since the ground are same for both. Lower ground or signal ground carry the leakage current or whatever voltage fed to system. In my schematic if remove -ve voltage it operating normally

8

If we using dpdt relay or spdt relay we are just sepating ground. My intentions are with separating ground I should capable of reading. HV voltage given at input. For example if I m given hv+ 1000v output must be 5v w.r.t low voltage ground . similarly 500v approximately 2.5 v w.r.t low voltage.

In order to measure sensor value. We need to common ground. My question is how can read this value in this case.if it low voltage we could measure directly . since it 700v +1000v DC . how could we measure

9

Do you really need a common ground ?

Could you use an opto isolator ?

They are sometimes used in regulated HV supplies.

10

Could you use a voltage to frequency converter on the high voltage sensor side (expendable of course) and send the frequency signal via opto coupler to Arduino then do a frequency to voltage conversion?

11

Can you suggest me model and relevant schematic so I can try out on board

12

Boardburner2:
Do you really need a common ground ?

Could you use an opto isolator ?

They are sometimes used in regulated HV supplies.

I havent tried this before.can you suggest me model and schematic so I can tryout here

13

I havent tried this before

Me either ;D But I've seen the method used in industrial equipment. Here's one link that might help, also google "V to F converter".
ww1.microchip.com/downloads/en/AppNotes/00795a.pdf
Check "Fig. 8".

14

Something like this:

HVIso2.png

NOTE: Just an idea, NOT a real circuit.

15

AMPS-N:
Can you suggest me model and relevant schematic so I can try out on board

Need to know a little more.

My knowledge is not so much as a designer but a fixer and i cannot share actual diagrams.

With the high voltage side current is fairly important.
The sensing circuit requires current.

If this is power solar this may not be a problem.

If it is something like charging a flash tube it is a big problem.
Low power solar can have similar problems if you are considering mppt systems.