WP2: Improvements for current measurement with Rogowski coil

Prototype of a Magnetic Shielded Rogowski Coil

Final Dissemination Workshop of Future Grid Project19-20 April 2017, Haarlem

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Ø Design and Construction (TÜBİTAK UME)

Ø Temperature Compensation

Ø Characterization (VTT MIKES)

• Mutual inductance calibration

• Temperature dependence

• Current Linearity

• Position dependence

• Frequency Response

Ø Demonstration on Medium Voltage (TÜBİTAK UME)

Ø Impact

Ø Summary

Overview

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Unshielded RC:

ROCOIL SX-170

M: 3.604 µH

Design and Construction

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Design and Construction

http://www.enpay.com/en/product.php?id=59#c1

Magnetic shield was constructed by

Mumetal cores and flat rings.

DimensionsCore 1 (Outer) : 260 x 240 x 54.5 mm / 0.1 mm band thickness (µ at 4mA/cm ~ 60000)

Core 2 (Inner) : 154 x 134 x 54.5 mm / 0.1 mm band thickness (µ at 4mA/cm ~ 100000)

Core 3-4 (Top and Bottom) : 260 x 134 x 5 mm / 0.1 mm band thickness (µ at 4mA/cm ~ 100000)

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Design and Construction

Inner Protection BoxInner Winding

400 Turns with f0,9 mm enameled copper wire

Insulation of Top and Bottom Parts Applying of Magnetic Shield

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Design and Construction

Flat Rings

Outer Winding Protection box with PSP material Final Isolation

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Temperature Compensation

Ø Two main factors are changing with rising temperature:

§ The coil former expands, thus increasing the effective area of the

winding and sensitivity of the coil

§ The resistance of the copper wire increases

Ø A resistor RCOMP in parallel with the output forms a resistive voltage

divider with the resistance of the coil wire.

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Characterization - Mutual Inductance Calibration

VTT MIKES Calibration System

U1

U2

DMM

DMM Signalgenerator

GPIB

Trigger

Frequency[Hz]

Mutual inductance[nH]

Phase displacementDifference from π/2

[crad]50 3563.23 ± 0.06 0.035 ± 0.00253 3563.22 ± 0.04 0.037 ± 0.00255 3563.21 ± 0.04 0.038 ± 0.00260 3563.21 ± 0.04 0.041 ± 0.002

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Characterization - Temperature Compensation

15

20

25

30

35

40

45

-0.0005 %

0.0000 %

0.0005 %

0.0010 %

0.0015 %

0.0020 %

0.0025 %

0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 6:30 7:00 7:30 8:00

Rogowski coil with R=9500 ohm

R=9.5k

Temperature

0

5

10

15

20

25

30

35

40

-0.0400 %

-0.0300 %

-0.0200 %

-0.0100 %

0.0000 %

0.0100 %

0.0200 %

0.0300 %

0.0400 %

0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 6:30 7:00 7:30 8:00 8:30

Rogowski coil

R>10Gohm

Temperature

Before temperature compensation

41 ppm/K

After temperature compensation

9500-Ω resistor

in parallel with the coil

3 ppm/K

16°C to 36°C

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Characterization - Current Linearity

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 100 200 300 400 500 600 700

dM/M

[x10

-6]

Increasing currentDecreasing current

Selected as a

Linearity of Rogowski coilMeasured againts VTT MIKES Rogowski coil

Applied Current [A] @60 Hz

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Measurement results the influence of the conductor position

d

1

2

3

4 0

Mutual inductance Phase displacementPosition

No: [µH/H] St.dev.[µH/H] [µrad] St.dev.

[µrad]0 0.0 0.4 0.0 0.3

1 2.6 0.6 -0.2 0.5

2 1.6 0.5 -1.2 0.7

3 -0.8 0.4 -1.3 0.8

4 -1.2 0.6 -0.3 0.6

Mutual inductance Phase displacement

Distance d[cm] [µH/H]

St.dev.[µH/H]

[µrad]St.dev.[µrad]

21 -5.5 4.4 -1.6 8.3

40 -1.2 2.9 -1.9 4.9

60 0.1 2.4 -1.2 3.1

80 0.0 2.6 0.0 4.0

98 -1.9 0.9 0.6 10.3

127 -0.6 0.9 -1.2 4.7

Characterization – Position Dependence

Measurement results to determine the effect of nearby current conductor

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NI PXIe-1071 Digitizer Based Bridge was used.No integrator was used.

Method:Appropriate currents are applied both the magnetic shielded RC and similar RC withoutshielded, the secondary signals of them are compared with the Digitizer Based Bridge.

Characterization – Frequency Response

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Demonstration on Medium Voltage

Ø applying appropriate primary currents to the RC and the CT to be calibrated

Ø measuring the ratio error and phase displacement of the CT with the Bridge

Current Generator

CT calibrated

Rogowski Coil

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Declaration

Manufacturer declares for influence of position dependence:§ If the conductor is moved from the central position by a distance equal to 0.5

x the inner coil radius the output will change by less than 0.1%.§ the pick-up for any orientation of the coil is less than 0.1% compared with the

output of the coil if it was mounted round the conductor.

Our Objectiveto reduce the immunity of a Rogowski coil against coupling magnetic fields bymore than factor of 10.

After magnetic shield:§ Effect of current conductor position < 10 ppm§ Effect of nearby current conductor < 10 ppm

The effects were reduced by factor of 100

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Summary

Effect of current conductor position < 10 ppmEffect of nearby current conductor < 10 ppmCurrent linearity < 5 ppmTemperature dependence < 25 ppm

Ø Maximum primary current : 1000A

Ø Mutual Inductance : 3563.23 ± 0.06 nH

Ø OD : 265 mm, ID : 125 mm, H : 75 mm, Weight: 12 kg

Ø Shielded RC is much heavier

Ø More expensive than the conventional RC

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Impact

Ø Outcomes have been disseminated via two stakeholder workshops

Ø Presentations are publicly available on the project website

Ø CT under MV level was calibrated on-site using the shielded Rogowski coil

Ø Knowledge obtained this work is transferred to the industry

Ø Scientific impact: The project outcomes were/will be presented to;

§ 5th International Istanbul Smart Grid and Cities Congress

§ 20th International Symposium on High Voltage Engineering (Conf. paper)

Thanks for your concern