Rogowski coil assembly

1. A Rogowski coil assembly useful for measurement of high frequency electrical currents comprising:

(a) at least two coil segments disposed in series, wherein each coil segment includes an input and an output;

(b) retrospective impedance influence reduction coupling of said at least two coil segments;

(c) a signal decoupling circuit having an input and an output; and

(d) a non-magnetic core and a return conductor;

wherein the at least two coil segments are wound around the non-magnetic core, and the return conductor is led through the non-magnetic core,

wherein the at least two coil segments are connected to each other in series through the signal decoupling circuit, with the output of one coil segment connected to the input of the signal decoupling circuit and the input of a subsequence coil segment connected to the output of the signal decoupling circuit,

wherein the signal decoupling circuit comprises an impedance converting electrical component with high input impedance and low output impedance, and

wherein the impedance converting electrical component comprises an operational amplifier or an electrical difference amplifier with high input impedance and low output impedance.

2. A Rogowski coil assembly according to claim 1 , wherein the operational amplifier is mounted as a voltage follower.

3. A Rogowski coil assembly according to claim 1 , wherein:

the impedance converting electrical component comprises an operational amplifier and two resistances in series configured as a voltage divider, the operational amplifier having a noninverting input and the voltage divider having an input;

the operational amplifier and the voltage divider are configured as a non-inverting amplifier; and

the output of said one coil segment is connected to the non-inverting input of the operational amplifier and the input of said one coil segment is connected to the input of the voltage divider.

4. A Rogowski coil assembly according to claim 1 , wherein the signal decoupling circuit comprises a signal converter having an electrical input signal channel and an electrical output signal channel.

5. A Rogowski coil assembly according to claim 4 , wherein the signal converter comprises at least one element from the group consisting of:

an optoelectrical converter having an electrical input signal channel and an electrical output signal channel,

a high frequency converter having an electrical input signal channel and an electrical output signal channel, and

an A/D-D/A converter.

6. A Rogowski coil assembly according to claim 1 , wherein:

at least one coil segment of said at least two coil segments comprises a first coil and a second coil connected in series and wound such that induced voltages of each coil are added;

the signal decoupling circuit comprises a first operational amplifier with a gain A, a second operational amplifier with unity gain, and a fully differential amplifier with unity gain, one end of the first coil being connected to a non-inverting input of the first operational amplifier and an unconnected end of the second coil being connected to an inverting input of the first operational amplifier, an output of the first operational amplifier being connected to a noninverting input of the fully differential amplifier, outputs of said fully differential amplifier being outputs of a coil segment, an inverting input of the fully differential amplifier being connected to an output of the second operational amplifier, and non-inverting and inverting inputs of said second operational amplifier being connected to outputs of a preceding coil segment of said at least two coil segments.

7. A Rogowski coil assembly according to claim 1 , further comprising:

a low-pass filter connected between a point between an output of one of said at least two coil segments and an input of the signal decoupling circuit, and said return conductor.

8. A Rogowski coil assembly according to claim 1 , wherein the low-pass filter comprises damping resistance.

9. A Rogowski coil assembly according to claim 1 , where the non-magnetic core comprises a hollow center and a radially oriented longitudinal slit between the hollow center and an outer periphery of the non-magnetic core.

10. A Rogowski coil assembly according to claim 1 , wherein the non-magnetic core comprises built up core segments together having the same total length as the length of the coil segments.

11. A Current measurement apparatus comprising a Rogowski coil assembly according to claim 1 .

12. A shaft erosion monitoring device for at least one of monitoring and analysis of electrical machines during operation comprising a current measurement apparatus according to claim 11 configured and arranged to detect shaft currents.