WP5 -Task 5 - National Physical Laboratoryprojects.npl.co.uk/power_energy/docs/1000 Measurement of...

Noordwijk, Netherlands, 23.03.2011 111/6

WP5 -Task 5.2

Impulse current and short circuit

current measurements

Noordwijk, Netherlands, 23.03.2011 2

Task 5.2 Impulse current and short circuit current measurements

Context

High-impulse currents occur in high voltage power systems:

• Lightning strikes

• Switching operations of circuit breakers

• Switching manoeuvres in gas-insulated switchgear

• Electromagnetic pulses

The understanding of higher current events is important for the

management of power quality.



Objectives

Identify suitable sensors for impulse and fast transient currents up

to 60 kA

Characterization of the complete measurement system with a target

uncertainty of 0,1 %

Parameters of 8/20 µs signals

-2.000000

0.000000

2.000000

4.000000

6.000000

8.000000

10.000000

0 2000 4000 6000 8000 10000 12000

Upeak

0.9Upeak

0.1Upeak

0.5Upeak

T1T2

Peak value, UPeak < 60kA

Front time, T1 : 8 µs

Time to half value, T2: 20µs


Specification of existing transducers and first selection

Pearson coil

Rogowski coil

U

1I

I 2

50 Ω

Non-In

trusi

veN1I1 = N2I2

dt

dINAE ⋅= 0µ

IRC

NAVout ⋅=

01

0µ

Pearson50 000 A

0,25 Hz to 4 MHz10 mV/A

Rogowski50 000 A

0,6 Hz to 1 MHz0,1 mV/A

Selection of transducers

Rated current range

Large bandwidth

Dynamic performances to accurately

capture the short-lived events

Linearity

On-site measurements


Measurement chain: comparison method


8/20 µsImpulse

Current Generator

2 Current transducers

Different technologies

PC

Digitizer

12 Bit, 100 MS/s

I1

0.0

5.0

10.0

15.0

20.0

-500 500 1500 2500 3500 4500

Pass over the generator fluctuations and other common factors

Share the advantage of two different technologies

Rigid bar circuit with modular geometry designed


Digitizer characterization according to EN 61083-1: 2001

Internal noise level (quantization noise):

INL - Integral Non-Linearity

of FSR4108

−⋅

Limits: 41040

−⋅ of FSR

Integral Linearity Error, Yokogawa SL 1000, 12 bits

-2.00E-04

-1.50E-04

-1.00E-04

-5.00E-05

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

-12.5 -7.5 -2.5 2.5 7.5 12.5Uin (V)

ILE

of

the

ra

ng

e

4max1085.1

−⋅+=NLISε

4min1062.1

−⋅−=NLISε

FSofNLIS

41050

−⋅±=ε

Limits:

of FS

High-speed data

acquisition unit

12-Bit, 100 MS/s


DynamicStatic

DNL – Differential Non-Linearity

LSBNLDS 43.0min −=ε

LSBNLDS 37.0max +=ε

LSBNLDS 8.0±=εLimits:

LSBNLDD 27.0min −=ε

LSBNLDS 27.0max +=ε

LSBNLDS 8.0±=εLimits:




Uncertainty Budget

)1(102.34 =⋅= −

kUdigitizer

Value allowing to maintain the 10-3 targeted uncertainty for the

complete measurement system

Quantity

iX

Estimated value

ix

Probability distribution

Standard uncertainty

)( ixu

Sensitivity coefficient

ic

Uncertainty contribution

)()( iii xucyu ⋅=

Type

Quantization error, qε

0.4 Rectangular

3

4.0

2850

1

4108.0

−⋅ A

Integral linearity error

(ILE), ILEε

1 Rectangular

3

6.0

2850

1

4102.1

−⋅ A

Offset error,

offε 0 Normal

3

75.0

2850

1

4104.0

−⋅ B

Gain error,

gainε

0 Normal 3

375.0

2850

1

4104.0

−⋅ B

Sampling error, sε

0 Rectangular Neglected Since sampling

time(10ns)<<Time(µs) when

measured value is constant

2850

1

0 B

Step voltage relative error,

0

0 )(

U

Uu

- - - 1 4101

−⋅ B

Combined standard uncertainty (k=1) 4102.3

−⋅


Current step generator

Dynamic characterization of the impulse current sensors and measurement chain

High level of current (~ 100A)

Steep falling slope (tens of ns)

Low parasitic inductance and capacitance


Measurement chain step response

Rogowski coil

Settling time, ts = 5.59 µs

Pearson coilSettling time, ts = 1.87 µs

The attenuation of the step responses in few µs indicates no influence on the measure of 8/20

µs impulse currents.

Response parameters for a 50A current step


Impulse current measurements up to 60 kA (peak value)

Frequency spectra

Normalised impulse waves, Pearson, Rogowski

Site measurements


Analysis parameter for peak value, 0,5 - 60 kA

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

0 10 20 30 40 50 60 70

I [kA]

12

Results for the impulse currents up to 60 kA

Reduced dispersion between Pearson and Rogowski coils for the measurement range

Comparison method validation

∆meansensors

Analysis parameter: the mean value of the difference (absolute value) between the 2 transducers for a set of 10 measurements

Peak Value

Front Time

Time to Half Value

4102

−⋅

2102

−⋅

3105

−⋅


Link between measurements of current pulses and calibrations at 50 Hz

Gain 8/20 µs = Gain 50Hz ?

Sensors performances • Linearity up to 60 000 A • Frequency response from 50 Hz to 100 kHz

How does the digitizer influence the dynamic gain to be established?

Rogowski coil – 50Hz

Accept high power frequency currents

Low dynamic

Pearson sensor – 8/20 µs

Designed for pulse currents

Adapted dynamic

What we know

What we need to know

A

B


Frequency response of sensors and digitizer

Digitizer Errors [%], Channel 1

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.1 1 10 100

F [kHz]

Calibre 0.1V

Calibre 0.2V

Calibre 0.5V

Calibre 1V

Calibre 2V

Calibre 5V

Calibre 10V

Calibre 20V

Calibre 50V

Calibre 100V

Calibre 200V

DigitizerErrors [%], Channel 2

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

0.40

0.1 1 10 100

F [kHz]

Calibre 0.1V

Calibre 0.2V

Calibre 0.5V

Calibre 1V

Calibre 2V

Calibre 5V

Calibre 10V

Calibre 20V

Calibre 50V

Calibre 100V

Calibre 200V


Pearson gain, 200A, sinusoidal

10.020

10.030

10.040

10.050

10.060

10.070

0.01 0.1 1 10

f [kHz]

Ga

inP

[m

V/A

]

%1,0±

Rogowski gain, 200A, sinusoidal

0.0990

0.0992

0.0994

0.0996

0.0998

0.1000

0.01 0.1 1 10

f [kHz]

Ga

inR

[m

V/A

] %1,0±



RogowskicoilÎ

Û kAHzkiGainRogows 5,50

Sinusoidal regime

µs

kiGainRogows

20/8

8/20 µs impulse

RogowskisensorÎ Digitizer

Softwaretreatment

Pearsonsensor

µs

nGainPearso

20/8

kHzsCorrection10

Hz

nGainPearso

50

Approach

A

B?



[5 kA; 50 kA] the obtained gain for Pearson sensor is constant at

Î < 5 kA SNR impact

Î > 50 kA Sensors out of range specifications

%1,0±

ResultsObtain Gain for Pearson sensor

9.86

9.88

9.90

9.92

9.94

9.96

9.98

10.00

10.02

0 10 20 30 40 50 60 70I [kA]


Commercial sensors might be used for 8/20µs impulse current measurements with an uncertainty of 0,1% (k=1)

On-site measurements indicate a reproducibility of 3.10-4

Quality of the analysed sensors allows to use them as impulse current standards

Conclusions

Pearson/Rogowski output ratio

100.10

100.20

100.30

100.40

100.50

100.60

100.70

0 5 10 15 20 25 30 35 40 45

I [kA]

Sept. 2010

March 2011

Different circuit configurations

Measures at 7 months interval

Same components of the impulse measurement chain

%1,0±



Thank you for your attention.

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