Rogowski coil...

[Externet]

Hello all.

The Rogowski coil image starts its winding by near 6 of the clock and the turns continue counterclockwise to complete the circle. Then the conductor returns clockwise towards the start of winding by 6 of the clock position again.
Why is it made that way ? What if the curved returning wire continued winding turns towards the 6 of the clock start point, like doubling the turns instead ?
Would it be more efficient doubling the turns instead of wasting the route back ? Or not winding the clockwise route is mandatory construction ?


[Image borrowed from the web]

 

[stenzer]

Hi,

Then the conductor returns clockwise towards the start of winding by 6 of the clock position again.
Why is it made that way ?

this is done to provide both terminals at one side of the coil. Thus it is possible to wrap a rogowski probe around an already fixed/installed cable or around a leg/terminal of THT component in a circuitry.

BR

 

[FvM]

Return must take same path as coil, otherwise the sensor would pick up unwanted fields.

To achieve the intended characteristic a Rogowski coil should
- completely encircle the conductor
- have small coil diameter compared to the conductor distance
- constant turn distance along the coil
- return in the same path, e.g. wire in the coil center

Coaxial forward and return coils are possible but impractical, e.g. due to increased parasitic capacitance.

 

[wwfeldman]

if you make N turns around the core, you end up with N+1.
the return wire drops the turn cunt back to N.

it is a geometric effect.
if you reduce the cross sectional area of the core to 0,
N turns get zero cross sectional area, and are effectively removed.
but there is still a net single loop around the central opening.
the return wire eliminates that

 

[Externet]

Thanks. I was not clear.
Why the 'returning' wire is not made winding its way back coaxially on top of the previous turns layer instead of just routing with no turns ? Is the parasitic capacity that much detrimental at low impedances and 60 Hz for plain current sensing applications ?
Am evaluating a wound one on an iron bendable strip as added core that can be wrapped around a conductor. Will it be more sensitive than the air core one ? Can the core strip ends overlap ? What if do not touch ends leaving a gap as shown below ? Comments welcome.

Yes, both coil terminals at the same end allows wrapping around a current carrying conductor. But wires ending at both ends allows wrapping too, or then stops being a Rogowski ??

 

[FvM]

Am evaluating a wound one on an iron bendable strip as added core that can be wrapped around a conductor. Will it be more sensitive than the air core one ?

That's no Rogowski coil.

 

[wwfeldman]

if you wind the return wire on top (along side) the original windings, either you double the windings, (as they are wound in the same clockwise sense) or you zero the windings, (as they are wound in the opposite clockwise sense)

the iron core is not part of a Rogowski coil