31-1-2011

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Power Quality measurements near DER and disturbing loads

Ir. M. van Lumig (Laborelec NL)

1/31/2011

Table of contents

31/01/2011

Background of the research project

Technical details of the measurements

Measurement results near:

PV

Wind turbines

Disturbing loads

Households

Conclusion from measurements

General conclusion

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Background of the research project

31/01/2011

EOS-LT KTI is a research project funded by the Dutch

government investigating PQ related issues like:

New probable boundary conditions technical (EN50160)

+ society

Interaction of load and generators with the grid

New developments of power electronic mitigation

devices

Research should result into most economical

optimum structures and solutions

Technical details of the measurements

31/01/2011

Part of the research is measuring PQ parameters at

specific locations in the Dutch LV, MV and HV grid

20 locations with specific loads or DER

Equipment used: Alptec 2444d (IEC-61000-4-30)

Using GSM data channel (9600 baud)

Measuring > 100 parameters per location, most

important:

- Voltage level, Plt, Pst, THD, individual harmonics,

unbalance, frequency, events, power

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Technical details of the measurements

31/01/2011

20 specific measurement locations with expected high

levels of certain PQ parameters

Technical details of the measurements

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Data is daily downloaded to a central server

10-minute average RMS data for comparison with EN50160

During events 6 seconds of samples (10,24 kHz) are stored

Automatic reporting every week OK or NOK

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Measurement results near PV

31/01/2011

One PQ measurement in an area with 2 MWp installed

PV power (‘Stad van de zon’)

Measurement at the LV side of one of the 1 MVA

transformers in this area

Measurement results near PV

31/01/2011

During high PV production and low demand

Sunny week

THDu (%) should be ≤ 8%, 5th ≤ 6%, 7th ≤5% (95% values)

Measured THDu (%): 1-3%, mainly 5th harmonic, 3rd harmonic low

PVPVPV PV Less PV PV PV

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Measurement results near PV

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During no PV production and high demand

Clouded week with snowed PV panels

THDu (%): 1-2%, mainly 5th harmonic, same 3rd harmonic

No PVNo PVNo PV No PV No PV No PV No PV

Measurement results near PV

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Semi-cloudy days and flicker

Semi-Cloudy days clearly more flicker but still low

Plt 95% should be ≤1

Summer Plt 95% <0,3, winter Plt 95%<0,2

PVPVPV PV PV PV PV

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Measurement results near wind turbines

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One measurement in area with 33 wind turbines

Measurement at MV- side at beginning MV cable with

many connected (small) wind turbines

One measurement at the wind turbine terminals (600

kW)

Measurement at LV- side of the 630 kVA transformer

connecting the wind turbine to the grid

Measurement results near wind turbines

31/01/2011

Wind turbines use power electronics

Measured harmonic current spectrum at the terminals

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Measurement results near wind turbines

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Voltage distortion at the LV terminals

THDu (%) should be ≤ 8%, 5th ≤ 6%, 7th ≤5% (95% values)

Measurement results near wind turbines

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Flicker at the LV terminals

Plt 95% should be ≤1

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Measurement results near wind turbines

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Harmonic distortion at MV level at beginning of the MV

cable with many connected wind turbines

THDu (%) should be ≤ 8%, 5th ≤ 6%, 7th ≤5% (95% values)

Measurement results near wind turbines

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Yearly average THDu (%) at MV in function of produced

power

THDu (%) should be ≤ 8% for 95% of the 10-minute values in a week

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Measurement results near wind turbines

31/01/2011

Flicker at MV level shows very small Plt increase

during production fluctuations

Plt 95% should be ≤1

Measurement results near a stone factory

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Heavy flicker at LV- side transformer

Plt 95% should be ≤1

Clear relation with processes in the stone factory, breaking and crushing

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Measurement results near a plastics factory

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Many processes running with VSD’s, MV measurement

THDu (%) should be ≤ 8%, 5th ≤ 6%, 7th ≤ 5%, 11th ≤ 3,5%, 13th ≤ 3%(95% values)

Measurement results near a plastics factory

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Average harmonic voltage spectrum of the MV

measurement near a plastics factory

THDu (%) should be ≤ 8%, 5th ≤ 6%, 7th ≤ 5%, 11th ≤ 3,5%, 13th ≤ 3%(95% values)

Weekend Weekend

Measured voltage harmonics

Theoretical current harmonics

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Measurement results in household area

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LV measurement at a feeder of a 630kVA transformer in

area with households + small stores

THDu (%) should be ≤ 8%, 3rd ≤ 5%, 5th ≤ 6%, 7th ≤ 5% (95% values)

Measurement results in household area

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LV flicker level near households

Plt 95% should be ≤1

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Conclusion from measurements

31/01/2011

There are no PQ problems shown at the measured

locations

Measurements near DG are located in grids which are

designed for it (‘low impedance, enough capacity’)

Very low Plt rise near PV, clearly visible rise in

harmonics but still low

Low Plt rise near wind turbines, Pst can be high

Clear rise in voltage distortion near wind turbines

Measurement at ‘problem’ locations show direct

relation PQ processes

Conclusion from measurements

31/01/2011

Measurements in household area’s show no problems

and change in the 4- year measurement campaign

THDu (%) 95% between 2-3% (limit is 8%)

Plt 95% between 0,05 – 0,25 (limit is 1)

Because there is found extra distortion due to power

electronics, there is a chance that in grids with a

higher impedance compared with the measurement

locations, PQ problems can occur

Decreasing harmonic current at the POC is therefore

an important topic

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General conclusion

31/01/2011

The measurements showed a small decrease of the

PQ due to power electronics, in ‘strong’ grids the

influence is therefore low

DER at the end of long cables can cause higher

voltages than measured

Connecting power electronics in grids with higher

impedance compared to the measurement locations

can have more influence on the power quality level

It’s recommended to do measurements in existing

grids were DG/power electronics is integrated

afterwards, the majority of the LV grids has higher

impedance than at the measurement locations

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