How to calibrate digital instruments basedon IEC 61850-9-2M. Agustoni and A. Mortara

This work is partially funded by the EMRP projectFutureGrid (ENG61). The EMRP is jointly fundedby the EMRP participating countries and theEuropean Union.

Overview

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Introduction: IEC 61850-9-2 digitalinstruments

The Stand Alone Merging Unit (SAMU)Calibration setupMetrological characterization

The “Test Set” (can be used as SAMUcalibrator)

Calibration setupMetrological characterization

Scenario: Power Network Substation

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In modern power network substations, currentand voltage signal are digitized formeasurement and control purposes.

Digitized values and correspondent time-stamps are delivered through the Ethernet asSample Values (SV) as described inIEC 61850-9-2 standard.

The traceability of digital devices based onIEC 61850-9-2 must be established.

The Stand Alone Merging Unit (SAMU)

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Digital communication interface between (non-)conventionalcurrent/voltage sensors and protection devices in switchyard andsubstation control area.

It combines these signals in one device and converts them into digitalstream (IEC 61850-9-2).

SAMU SV IEC 61850-9-2

Calibration notstandardized IEC 61869-13

GPS rec.

PPS

LAN

SAMU Under Test

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Specifications

The Test Bench (Hardware)

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24 bit

The Test Bench (Software)

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LabView® and C/C++ based.

DAC ADC

SAMUSV

decoder

ReferenceGenerator

SV decoder: adapted version of open platform developed byS.M. Blair et al. at the University of Strathclyde.

[S. M. Blair, et al., IEEE Transactions on Power Delivery, vol. 28, no. 2, pp. 1103-1110, 2013]

Recorder

The Test Bench (Software, SV decoder)

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SV decoder consists basically in 2 parts:

1. A packet sniffer intercepts the desired SV stream over thenetwork (MAC destination + MAC source + Ethertype +SV ID).

2. Decoding functions extract the encapsulated digitizedvalues and time-stamps from the rest of Ethernet frame.

MACDestination

MACSource

Ethertype(0x88BA SV) Data

6 bytes 6 bytes 2 bytes Variable

SV ID

The Test Bench (Software, Main Code)

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The Test Bench (Software, Main Code)

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Build signal from file parameters

The Test Bench (Software, Main Code)

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Start SV decoder

The Test Bench (Software, Main Code)

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Generate output analog signal

The Test Bench (Software, Main Code)

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Read reacquired signal

The Test Bench (Software, Main Code)

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Record reacquired and SAMU signal

Metrological Characterization of SAMU

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The measurement bench allows formetrological characterizations in bothtime/frequency and amplitude domain.

Test example:

Frequency stability of clock oscillator.

Sine wave testing.

Frequency Stability

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Single-tone sine wavesignal 50 Hz1h recordDetermination of relativefrequency offsets

[Performed with: Quantum Wave Toolbox: https://qwtb.github.io/qwtb/]

Overlapped AllanDeviation

Relative stability of 0.5nHz/HzSAMU practically doesn’tintroduce additional jitter

Method

Result

Analysis

Sine Wave Testing (Modulo Time Plot)

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Single-tone sine wavesignal 50.0028 HzResampling of 225periods in 1 periodAll codes in consideredvoltage range swept

Sine wave fit, nlsalgorithm with 4 freeparameters

Well defined structuresin residuals

ENOB~11

Method

Result

Analysis

[F. H. Irons and D. M. Hummels, IEEE Transactions on Instrumentation and Measurement,vol. 45, no. 3, pp. 734-738, Jun 1996]

Sine Wave Testing (Residual Spectrum)

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FFT of residuals

First two harmonicsdistortion

First twocomponents of othercontribution at 4 kHz

may be related toclock feedthrough

Harmonics Clock feedthrough

The Test Set

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OMICRON CMC 356

Multifunction calibratorCan be used for SAMU calibration on the field.Provide the simultaneous generation of an analog signaland its digital version according IEC 61850-9-2

Test Set (Test Bench)

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The Test Set (Delay tests)

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Single-tone sine wavesignal 50 Hz100-200 kHz samplingrateMeasurements repeated10 times at sameconditions

Sine wave fit, nlsalgorithm with 4 freeparameters

Mean phase delaybetween -1 and -1.7mrad 3-5 µs

Method

Result

Analysis

[Uncertainties: M. Zeier et al., “Metas.UncLib —a measurement uncertainty calculator for advancedproblems,” Metrologia, vol. 49, no. 6, pp. 809–815, Dec. 2012]

Summary

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A calibration setup for IEC 61850-9-2 devices has beenpresented.

The measurement bench is designed to be robust andversatile.

Software architecture makes possible a wide range ofmeasurement types.

As an example, frequency stability and sine wave tests forSAMU as well as delay measurement for test set have beenpresented.

The forthcoming publication of IEC 61869-13 standard willallow for setting parameters for complete and accuratecalibration for SAMUs.

Acknowledgement

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This work is partially funded by the EMRP project FutureGrid(ENG61). The EMRP is jointly funded by the EMRP participatingcountries and the European Union.

Thank you very much for your attention

Additional Slides

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Why IEC 61850 Standard?

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Problem:Technological improvements in communication andmeasurement system (as non-conventional sensors)Increasing number of software-based substationautomation system

interoperability issues between suppliers of substationdevice equipment

Solution: IEC 61850

Benefits:IEC 61850 is designed to be independent of technologicalchangesIEC 61850 allows to reduce costs for: wiring, commu-nication infrastructure, installation and maintenance,…

IEC 61850-9-2

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• Describes the communication of SVover Ethernet with Multicasttransmission service.

• The standard is very general describedand can be interpreted in different ways

complication in interoperability.

• To meet the requirements of thestandard’s implementation a dedicatedguideline has been introduced.

• The UCA International Users Group’sguideline referred as IEC 61850-9-2LE“Light Edition”.

SV Decoder

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SV ID

Mean packet delay over LAN

Frequency Stability

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Input WF discretized

Relative frequency offset of oscillator

Sine Wave Tests

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Number of codes to see

Fine-scale frequency selectionp= number of periodsS= number of samples nominal freq.fS = sampling rate