Can Rogowski Coils Be Used Without an Integrator for HOKA Applications?

[Glenn Emmers]

Dear all,

I'm currently working on an open core PCB rogowski coil and came up with the following design:

I concluded that the asymmetry wouldn't be a problem if the coil is centered precisely around the conductor and cause it's mainly supposed to operate around 50 Hz. Is this a good assumption?
The coil has 152 windings with the following approximated properties:
- Mutual inductance (M) = 40nH
- Resistance = 10.141 Ω
- Inductance = 8.019 μH
- Capacitance = 40.7nF
I'm supposed to measure currents up to 100A under normal conditions (higher in extraordinary cases)

For a HOKA, the integrator is replaced by a low pass filter and a gain is added afterwards. (Here is link with a bit of explanation).

So I have a couple of questions:
I thought the sensitivity of the Rogowski was also determined by the integration constant, with the sensitivity being: M/τ. But since I won't have an integrator, how will I be able to determine the sensitivity?
Also what is the best way to determine the parameters of this low pass filter and amplifier?
Can I put 2 rogowski coils in parallel to have less relative noise disturbance?
What Hall-sensors would be useful in this application?

I thank you in advance,

Glenn

 

[berkeman]

Welcome to the PF.

So HOKA is a new term? I wasn't able to find it via Google, but do see it mentioned in the paper you linked. What does HOKA stand for?

 

[Glenn Emmers]

Welcome to the PF.

So HOKA is a new term? I wasn't able to find it via Google, but do see it mentioned in the paper you linked. What does HOKA stand for?

Thank you!

HOKA stands for the names of the two people who came up with it: Verkoppelungsschaltung nach Hofer-Noser und Karrer (Source: Hudoffsky, Boris, (2014),Berührungslose Messung schnell veränderlicher Ströme)

 

[jim hardy]

Your HOKA link describes not a low pass but a Hall effect sensor element to extend frequency response down to DC. That device is inherently low pass.

Also what is the best way to determine the parameters of this low pass filter and amplifier?

I'd say from the datasheet of your Hall sensor.

here's the instruction manual for an early Tektronix combination Hall efect/Faraday effect current probe that describes how they did it in mid 1960's. Its bandwidth was DC to 50mhz. . While their Faraday element had a core the working principle is identical to your HOKA paper.
http://materias.fi.uba.ar/6644/info/puntas/manuales/p6042 current probe.pdf
I used one of those in early 1970's . It was a Godsend for non-intrusively checking AC relay drivers, which as you can imagine is REALLY handy in a nuke plant.

old jim

 

[Baluncore]

I concluded that the asymmetry wouldn't be a problem if the coil is centered precisely around the conductor and cause it's mainly supposed to operate around 50 Hz. Is this a good assumption?

Define precise.
If you remove the turns component below as you have in the rectangular area above then symmetry will be restored. Sensitivity to current will fall slightly, but eccentricity of mounting about the current conductor will no longer be a problem. The undefined precision will not be required.