Combisensors (Rogowsky Coils)

[FernandoCFE]

Question:
I would like to receive some feedback about your experience using
Rogowsky Coils instead of CT's.
Currently, we are participating in a project where Rogowsky Coils are
used with a ratio of 80 A / 150 mV.
My main interes is knowing:
Which is the ratio that the current is converted in secondary amperes?
I mean 150 mV are equal to X Amperes?

This is our "key point" in order to do the protection settings.

Any assistance will be welcome!

 

[Skogsgurra]

The only uses for Rogowski coils that I have any experience with is high ampere semi-DC measurement (current measured in series with diodes where it goes to zero periodically so that you always know what your reference is) and for HF current measurements (up to about 10 MHz) in motor shafts. Never seen them used normal protection applications.

Is it for high current measurements where an ordinary iron core would saturate? Or in applications with higher order harmonics? In that case I can understand your choice, but for standard protection I think that I would prefer normal CTs.

What does the manufacturer say?

 

[alehman]

Rogowski coils are fundamentally a current to voltage transducer, not to be confused with a current transformer. The output current depends on what you connect to it.

http://www.rocoil.cwc.net/principle.htm

Flexible coils are commonly used for portable instrumentation.

http://www.amprobe.com/cgi-bin/pdc/viewprod.cgi?pid=543&tid=1&type=elec

 

[manmadhan04]

Hi fernandoCFE,

For a sinusoidal current,under steady state conditions the voltage is:

Uout= M*j*ohmega.Ip

The signal is a sinusoidal voltage, proportional to the
current, with 90º phase shift (lead).

rgds

 

[FernandoCFE]

I thank you all for your kind replies.
I know that Rogowsky sensors are transducers and their secondary side
has a voltage signal. However, my main concern is related to the
settings of the protection devices that are receiving signal from the
Rogowsky coils.

In order to setting the protection relays the reference is usually In,
that could be 5 or 1 A (secondary rated of the CT's)and in this case, we
do not have secondary amperes, then:
Which is our new reference to perform the settings?
Shall we take into account the current rating of the Rogowsky coil? (in
this case 80 A)


Best Regards

 

[buzzp]

Sounds like a different relay will have to be used. At the very least contact the relay mfg and ask them.

 

[Skogsgurra]

You cannot expect a current output from a standard Rogowski. No way. Do as buzzp told you.

 

[scottf]

There are specific relays for Rog Coils, as referenced above.

You would normally expect a ratio of 1000A:5V.