epecentre pq workshop report 2009

8/3/2019 EPECentre PQ Workshop Report 2009

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Outcomes from the EPECentre Workshop on

Power Quality in Future Electrical Networks

June 2009

www.epecentre.ac.nz


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DISCLAIMER

This document was prepared by the Electric Power Engineering Centre (EPECentre) at the University ofCanterbury in Christchurch, New Zealand. The content included in this document is based on a Power Qualityworkshop held in April 2009. The EPECentre takes no responsibility for damages or other liability whatsoever fromthe use of this document. This includes any consequential damages resulting from interpretation of material.

Electric Power Engineering Centre, University of Canterbury, New Zealand

Published by Electric Power Engineering Centre (EPECentre), University of Canterbury, New Zealand.

First edition, June 2009

Authors and Editors:

Assoc. Prof. Neville Watson, BE(Hons), PhD, CPEng, Int PE, SMIEEE, MIPENZ,EPECentre, University of Canterbury, New Zealand

Prof. Vic Gosbell, BSc, BE(Hons), PhD, CPEng, MIEEE, FIEAustIntegral Energy Power Quality and Reliability Centre, University of Wollongong, Australia

Dr Stewart Hardie, BE(Hons), PhD, MIEEEEPECentre, University of Canterbury, New Zealand

Acknowledgements:

Joseph Lawrence, EPECentre, University of Canterbury

Tas Scott, Orion NZ Ltd

Assoc. Prof. Sarath Perera, Integral Energy Power Quality and Reliability Centre, University of Wollongong,

Australia

Bill Heffernan, EPECentre, University of Canterbury

Peter Berry, Executive Director, EEA

Ken Smart, University of Canterbury

Dudley Smart, EPECentre, University of Canterbury

Sponsors and participants of the EPECentre Power Quality Conference and Workshop, 23-24 April 2009,University of Canterbury, Christchurch, New Zealand.

Electric Power Engineering CentreUniversity of CanterburyPrivate Bag 4800ChristchurchNew ZealandT: +64 3 366 7001E: [email protected]

2009 Electric Power Engineering Centre, University of Canterbury, Christchurch, New Zealand. All rights

reserved, no part of this publication may be reproduced or circulated without written permission from the Publisher.


Power Quality in Future Electrical Networks 2
mailto:[email protected]://www.epecentre.ac.nz/http://www.epecentre.ac.nz/mailto:[email protected]


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Electric Power Engineering Centre


Power Quality in Future Electrical Networks

Contents

Preface............................................................................................................................................................61 Introduction to Power Quality....................................................................................................................7

1.1 What is Power Quality?......................................................................................................................71.2 Power Quality issues..........................................................................................................................7

1.2.1 Steady-state voltage..................................................................................................................101.2.2 Voltage dips (sags)...................................................................................................................101.2.3 Voltage imbalance....................................................................................................................101.2.4 Harmonics.................................................................................................................................10

1.2.5 Interharmonics..........................................................................................................................111.2.6 Transients..................................................................................................................................111.2.7 Light flicker due to voltage fluctuations...................................................................................11

1.3 Power Quality standards...................................................................................................................131.3.1 IEEE Standards ........................................................................................................................131.3.2 IEC 61000 series of Standards and Technical Reports.............................................................151.3.3 New Zealand standards.............................................................................................................18

1.4 Emission from existing equipment...................................................................................................191.4.1 Residential equipment..............................................................................................................191.4.2 Industrial equipment.................................................................................................................271.4.3 Distributed generation and inverters.........................................................................................29

1.4.4 Future equipment......................................................................................................................301.5 Immunity of equipment....................................................................................................................31

2 Summary of Power Quality Workshop....................................................................................................332.1 Question 1: Identification of significant Power Quality issues .......................................................332.2 Question 2: Data acquisition and use ..............................................................................................352.3 Question 3: Responsibility for Power Quality issues ......................................................................382.4 Wrap-up............................................................................................................................................402.5 Future challenges..............................................................................................................................41

3 Conclusions and future work...................................................................................................................424 Bibliography............................................................................................................................................43




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Preface

First of all, thank you to all those who attended the Power Quality in Future Electrical Networksworkshop. Your presence and participation made it the successful event that it was. It was a great time oflearning from each other, as well as making useful contacts.

Power Quality issues have been around for a long time. However, most of the time it does not feature in

peoples thinking until problems are experienced. Prevention is far better than curing problems after theyoccur, hence the focus of this workshop. This document contains a summary of the workshop groupdiscussions, which we hope you will find informative. As a primer to the Power Quality area, a summaryof the international standards and the concepts underpinning them is included. Moreover, the measuredcharacteristics of existing and up-and-coming electrical equipment is given, so that you can be aware ofthe likely impact equipment will have if widespread use is made of it. Finally, a comprehensive list ofbooks on Power Quality is given for further reading on this subject.

Assoc. Prof. Neville Watson

Associate, Electric Power Engineering Centre, University of Canterbury




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1 Introduction to Power Quality

1.1 What is Power Quality?

The geometry of synchronous generation results in a sinusoidal EMF being generated. This allowstransformation to higher voltages for efficient transmission of power. All equipment connected to the

electrical network is designed to operate with a sinusoidal voltage at rated value, as shown in Figure 1.Power Quality, or more accurately Voltage Quality, is essential for electrical equipment to operatecorrectly. Power Quality is the degree to which the supply voltage waveform conforms to the idealsinusoidal waveform (including magnitude and timing). Any deviation from this is a Power Quality issue.

Power Quality is a subset of ElectroMagnetic Compatibility (EMC), as depicted in Figure 2. The principalphenomena causing ElectroMagnetic Compatibility issues are listed in Table 1. ElectroMagneticCompatibility refers to the ability of electrical and electronic equipment or systems to functionsatisfactorily in the environment, without introducing intolerable disturbance to that environment. Thus itimplies that a limitation of emissions from equipment or systems is required, as well as a certain level ofimmunity to interference which must be expected from other equipment and systems in that environment.

Emissions can be in the radiated or conducted form. Although power systems can be sources of radiatedemissions, radiated emissions from outside sources rarely affect the voltage waveform. Therefore inPower Quality only conducted interference is of concern. Traditionally, Continuity of Supply (Reliability)is considered as a separate class from Power Quality, however many would argue that the ultimate poorPower Quality is having no voltage, hence Continuity of Supply is shown on the boundary in Figure 2.

1.2 Power Quality issues

Power Quality events can be classified into those that are discrete events (such as voltage dips/sags) andthose that are continuous (e.g. harmonics, steady-state voltage, flicker etc). Each of the more commonPower Quality problems will be introduced in the following sections.

One suggested classification of voltage magnitude events is shown in Figure 3. Note that the boundariesare somewhat arbitrary, for example the threshold between under-voltage and interruption is 1% ofnominal for IEC and 10% for IEEE. The classification according to IEEE standard 1159 is displayed inFigure 4. Note that Voltage Dips and Voltage Sags are synonymous, the former term being used inEurope and the latter in North America.



Figure 1: Ideal voltage waveform (also showing RMS value).

325.27

Phase-to-neutralVoltage

(Volts)

230 V


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HarmonicsInter-Harmonics

Sub-Harmonics

Power Qualityor more accurately

Voltage Quality

ElectroMagneticCompatibility (EMC)

Flicker due to Voltage

fluctuationsElectric

Fields

Magnetic FieldsRF Radiation

Unbalanced

3-phase

Voltages

Frequency

Deviations

Waveshape

Faults

High

Frequency

Noise

Continuity of Supply

(Reliability)Surges/

SwellsImpulse and

Switching

Transients

Steady-state voltage

Figure 2: Power Quality as a subset of ElectroMagnetic Compatibility (EMC).

Table 1: Principal phenomena causing electromagnetic disturbances.

Conducted low-frequency phenomena

Harmonics, Inter-harmonics Signalling voltages

Voltage fluctuations Steady state voltage Voltage swells Voltage dips and interruptions Voltage unbalance Power frequency variations Induced low frequency voltages DC in AC networks

Radiated low-frequency phenomena

Magnetic fields Electric fields

Conducted high-frequency phenomena

Induced CW (continuous wave) voltages or currents Unidirectional transients Oscillatory transients

Radiated high-frequency phenomena

Magnetic fields Electric fields Electromagnetic fields Continuous waves Transients

Electrostatic discharge phenomena (ESD)

Nuclear electromagnetic pulse (NEMP)


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Figure 3: Suggested definition of voltage magnitude events. (Source: M. Bollen.)

Very short

under-voltage

Notch/transient

90%

100%

110%

120%

0.5cycle

1 to 3hours

Event Duration

Transient

1 to 3min.

Very shortinterruption

1 to10%

Short interruption Long interruption

Short

under-voltage

1 to 3cycles

Long

under-voltage

Very long

under-voltage

Very short

over-voltage

Short

over-voltage

Long

over-voltage

Very long

over-voltage

Normal operating Voltage range

Very long interruption

Figure 4: Definition of voltage magnitude events according to IEEE Std. 1159 (1995).

Voltage Dip/Sag

Notch/transient

90%

100%

110%

Under-voltage

Swell

120%

Over-voltage

0.5cycle

3 s 1-3 hours

Event Duration

Normal operating Voltage range

Transient

1

min.

Momentary10%

Temporary Sustained Interruption


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1.2.1 Steady-state voltage

Long term over-voltage or under-voltage is a major problem in many electrical networks around theworld. In New Zealand, the supply voltage is required to be 230 6%.

1.2.2 Voltage dips (sags)

A voltage dip is typically caused by a fault on the system or a large motor starting. The large current

flowing through the system impedance causes a depressed voltage until the fault is cleared or the motorgets up to speed. If the retained voltage is very low (


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There are numerous Power Quality indices derived from the harmonic components of a waveform, but themost widely used is the Total Harmonic Distortion (THD), i.e. :

THDV=

h=2

n

Vh2

V1

THDI=

h=2

n

Ih2

I1

The THD does not represent the ability to distort as it is a normalised index (normalised by fundamentallevel), hence Total Demand Distortion (TDD) has been proposed as an alternative, i.e. :

TDDI=

h=2

50

Ih2

Irated

For calculating the interference on telecommunication systems caused by harmonics and interharmonics,two weighting systems are used, i.e.:

1. Psophometric weighting system proposed by the International Consultation Commission onTelephone and Telegraph Systems (CCITT), used in Europe.

2. C-message weighting system proposed jointly by Bell Telephone System (BTS) and EdisonElectric Institute (EEI), used in the United States and Canada.

1.2.5 Interharmonics

With the introduction of Integral cycle controlled load and cyclo-converters, the waveform is not periodicover the period of the fundamental and hence inter-harmonics and sub-harmonics are present. This isdemonstrated in Figure 6. Interharmonics can be also induced by some types of control signals.

1.2.6 Transients

Transient phenomena is also classified into impulsive transients (e.g. due to lightning) or oscillatorytransient (e.g. capacitor bank switching). Two examples are shown in Figures 7 and 8.

1.2.7 Light flicker due to voltage fluctuations

Voltage fluctuation that causes the fluctuations in the magnitude of the voltage envelope to have afrequency component in the visual perception range (< 35 Hz), as shown in Figure 9, will cause light bulbflicker. Voltage fluctuations due to amplitude modulation can be mathematically described by:

v t=2V 1m t cos t

Consider for example the fundamental modulated by a purely sinusoidal voltage fluctuation i.e.:

mt=Mcosm

m

The voltage waveform can then be seen to be made of three sine waves, a carrier and two sidebands:

v t=2V1Mcosmm cos t

=2Vcos tMcosmmcos t

=2Vcos t1

22VMcos m tm

1

22VMcos m tm




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Figure 6: Cyclo-converter waveform which contains inter- and sub-harmonics.

Impulsive Oscillatory

Figure 7: Voltage transients as defined in IEEE 1159.

Figure 8: A recorded voltage transient.


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1.3 Power Quality standards

The development of standards and guidelines is centred around the following:

1. Description and characterisation of the phenomena.

2. Major sources of power quality problems.

3. Impact on other equipment and on the power system.

4. Mathematical description of the phenomena using indices or statistical analysis to provide aquantitative assessment of its significance.

5. Measurement techniques and guidelines.

6. Emission limits for different types and classes of equipment.

7. Immunity or tolerance level of different types of equipment.

8. Testing methods and procedures for compliance with the limits.

9. Mitigation guidelines.

1.3.1 IEEE Standards

The United States (ANSI and IEEE) do not have such a comprehensive and complete set of PowerQuality standards as the IEC. IEEE 1159 (1995), as shown in Table 2, contains recommended practice onmonitoring electric power quality and categories of power system electromagnetic phenomena. The IEEEStandard 519 is more specialised and is the IEEE recommended practice and requirement for harmoniccontrol in electric power systems, as shown in Tables 3 and 4.



Figure 9: Sinusoidal modulation of the voltage waveform.


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Table 2: Overview of IEEE Standard 1159.

Description Spectral Content Typical Duration MagnitudeTransient

ImpulsiveNanoseconds 5 ns rise < 50 nsMicroseconds 1 s rise 50 ns 1 ms

Milliseconds 0.1 ms rise >1 ms

OscillatoryLow frequency 1 min. 0.1 to 0.9 puUnder-voltage > 1 min. 0.8 to 0.9 puOver-voltage > 1 min. 1.1 to 1.2 puVoltage imbalance Steady-stateWaveform distortion

DC offset Steady-state 0 to 0.1 %Harmonics 1-100th Order Steady-state 0 to 20%Interharmonics 1-6 kHz Steady-state 0 to 2%Notching Steady-state

Noise Broad-band Steady-state 0 to 1%Voltage fluctuations


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1.3.2 IEC 61000 series of Standards and Technical Reports

ElectroMagnetic Compatibility (EMC) is the ability of equipment or system to function in itselectromagnetic environment without introducing intolerable disturbances to anything in that environment(IEC 61000-1-1). The compatibility level is the specified disturbance level at which an acceptably highprobability of electromagnetic compatibility should exist. Each utility is to decide what emission marginis appropriate for their system, based on the characteristics of their system and set a planning level whichis lower to give an emission margin. Likewise an appropriate immunity margin is needed to give animmunity level which is larger than the compatibility level, for equipment manufacturers to design theirequipment to meet. This is illustrated in Figure 10 where the compatibility level is set to give a highprobability of electromagnetic compatibility. The rectangles show a range of possible planning levels andimmunity testing levels that may be chosen. These are at the discretion of the utilities andregulatory/standard setting bodies. Compatibility levels are often set as a level to be achieved at least acertain percentage of time, as demonstrated in Figures 11 and 12.

The IEC 61000 series of standards and technical reports are very comprehensive and the majorsubdivisions are:

General (IEC 61000-1-x): The general section introduces and provides fundamental principles on

EMC issues and describes the various definitions and terminologies used in the standards. Environment (IEC 61000-2-x): This part describes and classifies the characteristics of the

environment or surrounding where equipment will be used. It also provides guidelines oncompatibility levels for various disturbances.

Harmonic compatibility levels of residential low voltage (LV) systems (IEC 61000-2-2)

Industrial plants (IEC 61000-24)

Residential medium voltage (MV) systems (IEC 61000-2-12).

Limits (IEC 61000-3-x): This section defines the maximum levels of disturbances caused byequipment or appliances that can be tolerated within the power system. It also defines theimmunity limits for equipment sensitive to EMC disturbances.

Harmonic current emission limits for equipment connected at LV with input current 16 A perphase (IEC 61000-3-2).

Flicker (IEC 61000-3-3): Limitation of voltage change equipment connected at LV with low(< 16 A per phase) current.

Harmonic current emission limits for equipment connected at LV with high (> 16 A per phase)current (IEC 61000-3-4)

Assessment of emission limits for distorting loads in MV and HV power systems (IEC 61000-

3-6). Assessment of emission limits for voltage fluctuations in MV and HV power systems (IEC

61000-3-7).

Assessment of emission limits for voltage fluctuations and flicker in LV power systems Equipment rated current < 75 A and subject to conditional connection (IEC 61000-3-11).

Harmonic current emission limits for equipment connected at LV with input current >16A and75 A per phase (IEC 61000-3-12)

Testing and Measurement Techniques (IEC 61000-4-x): These provide guidelines on the design ofequipment for measuring and monitoring Power Quality disturbances. They also outline the

equipment testing procedures to ensure compliance with other parts of the standards.




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Figure 10: Relationships between attributes of ElectroMagnetic Compatibility.

Figure 11: Example of calculation of disturbance level time percentage.

Time

x

Disturbance Level

t1

t2

tTotal

Percentage Time = 100*(t1+

t2)/t

Total


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Harmonic and interharmonic measurements and instrumentation (IEC 61000-4-7)

Dips and interruptions (61000-4-11)

Interharmonics (61000-4-13) Testing and measurement techniques: Flickermeter Functional and design specifications

(IEC 61000-4-15)

Power Quality measurement methods (IEC 61000-4-30)

Installation and Mitigation Guidelines (IEC 61000-5-x): This section provides guidelines on theinstallation techniques to minimise emission as well as to strengthen immunity against EMCdisturbances. It also describes the use of various devices for solving Power Quality problems.

Generic Standards (IEC 61000-6-x): These include the standards specific to certain category ofequipment or for certain environments. They contain both emission limits and immunity levels

standards.

IEC 61000-3-2 introduces Power Quality limits for four classes of equipment:

Class A: Balanced three-phase equipment and all other equipment, except those listed in otherclasses.

Class B: Portable tools.

Class C: Lighting equipment, including dimming devices.

Class D: Equipment with a "special wave shape" and an input power of 75 to 600 W.

It is not widely appreciated that some of these publications are International Standards while others areTechnical Reports and hence do not have the same standing.



Figure 12: Two case studies that demonstrate percentage compatibility. Case 1 meets thestandard at least 95% of the time, while Case 2 meets the standard only 75% of the time. This

is irrespective of Case 2 levels often being much lower than Case 1 levels for much of the time.


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1.3.3 New Zealand standards

New Zealand was one of the first countries to pass regulations in 1981 to limit the harmonic levels in theelectrical network ( Limitation of Harmonic Levels Notice 1981, issued by the Office of the ChiefElectrical Inspector, Ministry of Commerce). This was due to the early installation of large rectificationequipment in the form of a HVDC link between the North and South Islands and aluminium smelter atTiwai point. This Limitation of Harmonics Notice 1981 now forms the basis of NZ Electrical Code of

Practice 36, which is cited in the Electricity Regulations 1997, making it a mandatory requirement. Thiscovers only allowable harmonic voltages and also indices covering telephone interference (EDV & EDI).The code is split into requirements for when the Point of Common Coupling has a nominal voltage of lessthan 66 kV, or 66 kV and above. All these limits are absolute, not statistical, however there is anexception for control signals (i.e. ripple control).

Nominal voltage less than 66 kV

1. The phase-to-neutral harmonic voltage at any Point of Common Coupling with a nominal voltageof less than 66 kV shall not exceed 4% for any odd numbered harmonic order, or 2% for any evennumbered harmonic order.

2. The Total Harmonic Voltage Distortion (THDV) at any Point of Common Coupling with a

nominal voltage of less than 66 kV shall not exceed 5%.Nominal voltage of 66 kV or above

If the nominal voltage is above 66kV, the limits in Table 5 apply.

The equivalent disturbing voltage (EDV) shall not exceed 1% on any phase.

EDV=6.25x105n=2

50

nPn Vn2

wherePn is the weighting given to each frequency (from Psophometric weighting table).

Section 3 of this code of practice does give harmonic current limits, but only for 66kV, 110kV and

220kV.

New Zealand also has joint AS/NZS standards and these are clones of the IEC standard of the samenumber. These at present are volunteering standards and some requirements (i.e. harmonic levels,frequency deviation) conflict with the existing regulations.



Table 5: Harmonic voltage limits for nominal voltages of 66 kV or above.

Harmonic order Harmonic voltage levels(percentage phase-to-neutral values)

3 2.3

5 1.4

7 1.0

9 0.8

11 0.7

13 0.6

15 0.5

17 to 21 0.4

23 to 29 0.3

2 1.2

4 0.6

6 0.4

8 to 10 0.3

12 to 50 0.2


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1.4 Emission from existing equipment

The rectification process by which AC is converted to DC is a common source of harmonics. This processis widely used in household appliances such as TVs, stereos, PCs, microwave ovens, compactfluorescent lamps, fluorescent lamps with electronic ballasts, LED lighting, and all types chargers (forcell phones, cameras etc). The level of harmonic distortion is very much a function of the design of therectifier. The problem is that market forces put pressure on to cut costs, which results in a poorer rectifier.

1.4.1 Residential equipment

1.4.1.1 Compact fluorescent lamps (CFLs)

Figure 13: Block diagram of a CFL



Figure 14: Various CFL filtering options presently in use.

No filtering

Passive filtering Improved Valley-Fill

Active filtering

Power-Factor

Control Drive

PTC

DIAC

Block 1

Filtering and Protection

Block 2

Rectifier

Block 3

DC Filter

Block 4

Inverter and tube

Fuse


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Figure 15: Current waveforms resulting from use of different CFL filtering options shown in Figure 14.

0 0.005 0.01 0.015 0.02-400

-300

-200

-100

0

100

200

300

400

Current(mA)

Time (s)

0 0.005 0.01 0.015 0.02

-600

-400

-200

0

200

400

600

Time (s)

Current(mA)

0 0.005 0.01 0.015 0.02

-600

-400

-200

0

200

400

600

Time (s)

Current(mA)

0 0.005 0.01 0.015 0.02

-600

-400

-200

0

200

400

600

Time (s)

Current(mA)

Active Power-Factor

ControlBasic, no filtering

Basic, with filtering Valley-fill or Equivalent

Figure 16: Current harmonics resulting from use of different CFL filtering options shown in Figure 14.

0 5 10 15 20 25 30 350

50

100

150

200

250

Current(mA)

Harmonic order0 5 10 15 20 25 30

0

10

20

30

40

50

60

70

80

90

Harmonic Oder

RMSCurrent(mA)

0 5 10 15 20 25 300

10

20

30

40

50

60

70

80

90

Harmonic Oder

RMSCurrent(mA)

0 5 10 15 20 25 300

10

20

30

40

50

60

70

80

90

Harmonic Oder

RMSCurrent(mA)

Active Power-Factor

ControlBasic, no filtering

Basic, with filtering Valley-fill or Equivalent


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1.4.1.2 Personal computers

The current THD for a PC is typically between 70% to 120%. Below is a measurement on a PC with awaveform with a THDI of 119%.

Figure 18: Example current waveform and harmonics of personal computer components.



Current

mSec

Amps 05

10

-5

-10

. 2.5 5. 7.5 10.01 12.51 15.01 17.51

Current

Harmonic

Amps

0.0

0.5

1.0

1.5

2.0

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 17: Example current waveform and harmonics of a personal computer.


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Figure 19: Example current harmonics of personal computer components.

1.4.1.3 Microwave ovens



Current

mSec

Amps 0

25

50

-25

-50

. 2.51 5.02 7.53 10.04 12.55 15.06 17.57

Current

Harmonic

Amps

0

5

10

15

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 20: Example current waveform and harmonics of a microwave oven.


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1.4.1.4 Stereos

A current THD of 38.8% was measured and this is typical of stereos.

1.4.1.5 Heat-pumps

Figure 22: Example current waveforms of six different models of residential heat-pump.



Current

mSec

Amps 1 0

250

500

-250

-500

. 2.5 5. 7.5 10.01 12.51 15.01 17.51

Current

Harmonic

Amps rms 1

0

50

100

150

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 21: Example current waveform and harmonics of a stereo.


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1.4.1.6 Battery chargers

1.4.1.7 Digital camera



Current

mSec

Amps 1 0

50

100

-50

-100

. 2.5 5. 7.5 10.01 12.51 15.01 17.51

Current

Harmonic

Amps rms 1

0

2

4

6

8

10

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 24: Example current waveform and harmonics of a digital camera.

Current

mSec

Amps 1 0

25

50

-25

-50

. 2.5 5. 7.5 10.01 12.51 15.01 17.51

Current

Harmonic

Amps rms 1

0

5

10

15

20

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 23: Example current waveform and harmonics of a battery charger.


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1.4.1.8 Mobile phone charger

1.4.1.9 Cordless phone charger



Current

mSec

Amps 0

25

50

-25

-50

. 2.51 5.02 7.53 10.04 12.55 15.06 17.57

Current

Harmonic

Amps

0

5

10

15

20

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 25: Example current waveform and harmonics of a mobile phone charger.

Current

mSec

Amps 1 0

25

50

-25

-50

. 2.5 5. 7.5 10.01 12.51 15.01 17.51

Current

Harmonic

Amps rms 1

0

5

10

15

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 26: Example current waveform and harmonics of a cordless phone charger.


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1.4.1.10 Electronic photo-frame

1.4.1.11 Television

Figure 28: Example current waveform and harmonics of a television and video tape player.



Current

mSec

Amps 1 0

250

500

-250

-500

. 2.5 5. 7.5 10.01 12.51 15.01 17.51

Current

Harmonic

Amps rms 1

0

5

10

15

20

25

30

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Figure 27: Example current waveform and harmonics of an electronic photo-frame.


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1.4.2 Industrial equipment

Another major source of harmonic distortion is equipment used in industry and on dairy farms,particularly the use of Variable Speed Drives (VSD). On dairy farms, VSDs for driving irrigation pumpsare a major harmonic source in rural networks with the 5 th harmonic current often approximately 30% ofthe fundamental current.

1.4.2.1 Irrigation pumps

Figure 29: Schematic of a Variable Speed Drive.



Current

Time mS

Amps 0

250

500

-250

-500

. 2.5 5. 7.5 10.01 12.51 15.01 17.51

Figure 30: Example current waveform and harmonics of a Variable Speed Drive.

Current

Harmonic number

Amps rms

0

50

100

150

200

DC 2 4 6 8 10 12 14 16 18 20 22 24 26 28 301 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

33.2%

8.5% 8.0%

3.7%

AC

DC AC

DC33

IM


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1.4.2.2 DC Drive

Because of the simplicity and precise motion control capability of DC Drives, as shown in Figure 31, theyfind applications in printing presses, gondolas, and traction applications.

Figure 31: Schematic of a DC Drive system.

1.4.2.3 Metallurgical applications

Many metallurgical processes have a large impact on Power Quality: arc furnaces (AC, DC and inductionfurnaces) as well as electroplating and refining processes.

1.4.2.4 Manufacturing

In manufacturing, conversion from AC to DC is often used. For example, one case that arose was in

making a product out of plastics. To ensure accurate control of the constituent compounds, thyristorcontrolled heating elements were used, as shown in Figure 32. The machine had five three-phase thyristorbridges driving a purely resistive element and the 5th harmonic current was 40% of the fundamental. TheAC side harmonic currents are a function of the DC side ripple and the 5th harmonic increases as theripple increases.

Figure 32: Schematic of a thyristor controlled heating element.



1

2

53

4 6

3

R

1

2

53

4 6

3

M


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1.4.3 Distributed generation and inverters

Inverters are an essential component to allow the energy from renewable sources to feed into an ACelectrical network. Many papers have been written about the harmonics introduced by photovoltaicsystems and this would be of great concern if the use of photovoltaic systems became widespread. Somewind energy systems rectify the generator output and use an inverter to feed the energy into the ACsystem. The design of the inverter that interfaces the DC source of energy determines the impact thedistributed generation will have on Power Quality. Figure 33 shows measured waveforms and spectrumof two commercial inverters. It is clear that these waveforms are rich in harmonics and can detrimentallyaffect cables (due to extra I2R losses) and voltage waveform.

Inverters are often used to reclaim energy that might otherwise be lost. In some applications, a processcan be used to generate DC, and this energy can be fed back to the AC system. One example would be incombined heat and power systems, such as Whispergen, and similar schemes. These systems use energysources such as natural gas to provide heat. Electricity is generated from the waste heat and is fed backinto the AC system via an inverter.

Another Power Quality issue with distributed generation (particularly wind) is its intermittent nature andhow it fluctuates. These give rise to frequency stability issues and voltage fluctuations which cause lightsto flicker.



(a) (b)

Figure 33: Example current waveform and harmonics of two commercial inverters.


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1.4.4 Future equipment

There are several major future trends that could considerably impact on the Power Quality of theelectrical network. One of these is the widespread use of electric vehicles, such as the 2009 sample inFigure 34. Various prototypes are already in service and full scale production will be within one year.Although the initial uptake of electric vehicles is expected to be low, when the cost reduces and peoples'confidence increases, they may well gain wide acceptance, particularly if they are heavily promoted. Thecharging circuit again requires rectification and the same issues regarding the design of the rectifier andits performance in terms of Power Quality is an issue. The charging requires a higher current thanavailable from the domestic 10A outlet and hence at present an electrician is required to wire in an outletwith greater capacity in order to charge these vehicles.

LED lighting has the promise of giving higher efficiencies. A prototype LED system, shown in Figure35(a), gives 30% more light for the same electrical consumption. They are also very flexible, with theability to colour correct and automatically adjust for lighting levels. There are also advantages forspecialist applications such as in hydroponics. The main barrier is cost. Again they run on DC and hencerequire rectification.

Hot-water cylinders that use a heat-pump rather than a resistive element, as shown in Figure 35(b), arealready a commercial reality with most manufacturers offering this alternative. The Power Quality issuesassociated with heat-pumps also apply to this, and if widely adopted would mean conversion of asignificant amount of the resistive loading of the system to a non-linear load. This has implications forharmonics, voltage dips and voltage stability of the system.

Figure 34: Mitsubishi Innovative Electric Vehicle.




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1.5 Immunity of equipment

Immunity of equipment is an important aspect and changing the design to improve immunity of asensitive device (termed device hardening) is often more practical that reducing the disturbance level.Over the years a number of bodies have developed standards for equipment immunity. The most well-known is probably the 'CBEMA curve' (Computer Business Equipment Manufacturer Association),shown in Figure 36. It was used to evaluate the voltage quality of a power system with respect to voltageinterruptions, dips or under-voltages and swells or over-voltages. This curve was originally produced as aguideline to help CBEMA members in the design of the power supply for their computer and electronicequipment.

CBEMA has been renamed as ITIC (Information Technology Industry Council) and a new curve, knownas the ITIC curve (shown in Figure 37) has been developed to replace the CBEMA curve. The maindifference between them is that the ITIC version is piecewise, and hence easier to digitise than the

continuous CBEMA curve. The tolerance limits at different durations are very similar in both cases.

Other curves have been developed such as SEMI47 which is designed for the semiconductor industryrequirements.

Testing the immunity of equipment, particular computer equipment for voltage dips has been reported inthe literature. Also work on what is known as 'device hardening'has been performed. The development ofsuper (ultra) capacitors now allows a level of energy storage on the DC busbar that was previouslyunobtainable, and at a low price. This can give substantial improvement in immunity of equipmentrelatively cheaply.

Market forces however cause manufacturers to trim their costs to compete with their competitors and this

usually reduces, rather than enhances, the equipment immunity (as well as device emissions).



(a) (b)

Figure 35: (a) Prototype LED lighting system and (b) hot-water cylinder that uses a heat pump (Source:Quantum Energy Technologies).


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Figure 36: CBEMA curve.

0.001 0.01 1 c 10 c 100 c

0

30

80

100

200

300

400

Voltage ToleranceEnvelo e

106

87

1000 c0.1 0.5

0.1s 0.5s 2s8.33ms1ms0.1ms

Time in cycles & seconds

Percent of Nominal Voltage

(RMS of Peak Equivalent)

Figure 37: ITIC curve.

1 us

0.001 0.01

1 ms

1 c 10 c 100 c

3 ms 20 ms 0.5 s 10 s

Steady

State

0

40

80

100

120

140

200

300

400

500

Voltage ToleranceEnvelope

110

90

Percent of Nominal Voltage

(RMS of Peak Equivalent)

Time in cycles & seconds

Prohibited Region

No Damage Region


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2 Summary of Power Quality Workshop

This section presents a summary of the individual workgroup responses to three sets of questionspresented to them during the workshop, and a end-of-day 'wrap-up'.

2.1 Question 1: Identification of significant Power Quality issues

What are the most significant Power Quality issues YOU are facing NOW? Mark and describethose issues that have the most negative economic impact, and issues that receive the most customercomplaints.

NEI = Negative economic impact, CC = customer complaints

Harmonics Non linear loads, irrigation drives, HVDC, trains, DC inverters, thermal failure,amplification due to capacitor banks

Voltage Dips Motor starting, network faults, loss of production

Steady State Voltages Low voltage and high load stressing networks (NEI, CC), high voltage Voltage Unbalance High voltages (NEI)

Flicker Industrial loads (NEI, CC), wind farms, single phase loads RF Insulator design/sensitivity of equipment

DC components in/by transformers Oversizing of transformers Safety, future proofing, harmonics

Transmission Unbalance (one phase loads, lack of transposition with high loads, harmonics) Distribution Flicker (short term soln CFLs), voltage variation (CC), sags not so bad,

proliferation of VSD motors, protection relay response to harmonics, quantifying in $$ cost ofpoor PQ

Regulation influences Compliance with regulations

Lack of equipment standards Lack of consumer understanding

For UTILITIES, what are the most likely significant Power Quality issues to be faced in theFUTURE? Why? Provide details of Power Quality issues, also considering excessive emissions,immunity, and present or future regulator requirements.

Harmonics Increasing levels More distorting loads VSD, CFLs, TVs

Less equipment immunity Stricter regulations

Standards Different application thereof, are they correct, complex, developing and enforcingnew standards

Distributed generation Wind farms voltage control Create awareness in community (education)

Derated equipment (Transformers/cables) Uncertainty Political, environmental Future loads What are they? D.G and despatch rules

Economy Traditional network design vs future design

Non compliance enforcement




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Customer responsibility Evolving standards

For each of the following CUSTOMERS (a) to (c), what are the most likely significant PowerQuality issues to be faced in the FUTURE? Why?

(a) Industrial/commercial

Voltage sags Compliance/standards

Poor design and installation practices leads to production losses Education/good advice for customers Short interruptions Harden PLC

Spending more on quality Increased penetration of sensitive equipment and import of PQ

Upgrade requirements due to changing PQ levels (allocation) Embedded generation issues

(b) Rural

Voltage sags Customer expectation

Increased use of electronics etc in low fault level areas Education/good advice for customers

Drive failure due to PF cap switching and voltage dips No filtering required on pumps and drives Designed to urban standard?

Insurance stance? Expectation doesnt match the supplier capabilities Disturbances die to interaction of different loads

Differential PQ Standards

(c) Residential

Voltage sags Infill housing and steady state voltages Increased non linear load (heat pumps, air con)

Education/good advice for customers More rubbish on the market Need a star rating for PQ?

High Voltage causing appliance failures and short life Shifting load profile (night time charging) Use of ripple control? Expectation doesnt match the supplier capabilities More sensitive equipment Voltage control with DG penetration, uptake of the Greenie

effect




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2.2 Question 2: Data acquisition and use

At each of the following points of the network (a) to (g), how much data acquisition equipmentshould be installed by a UTILITY in the next 10 years? What should it record? If only a percentageof multiple sites of the same class should have equipment installed, indicate what that percentageshould be. Weight the acquisition equipment/records as compulsory, highly recommended, oruseful.

A = compulsory, B = highly recommended, C = useful

(a) Grid exit point

Workgroup % sitesmeasured

V I Steadystate value

Unbalance Harm Fluct Sags Transients Anotherquantity

1 100% Y Y A B B B A C

2 100% -20%

Y Y A A A A A A

3 80% A A A A A B A C

4 100% Y Y Y Y Y Y Y Y CB Status Time Stamp

5 100% Y Y A A A A A A

(b) Town substation




1 100% Y Y A B B B A C

2 10-20% Y Y A A A A A A

3 5-10% A A A A A B A B

4 30% Y Y Y Y Y Y Y Y CB Status Time Stamp

5 50% Y Y A A C B A C

(c) Rural substation




1 100% Y Y A B B B A C

2 30-50% Y Y A A A B A B

3 5% A A A A A B-C B B

4 100% Y Y Y Y Y Y Y Y

5 20% Y Y A A B A A B

(d) Industrial site




1 0-10% Y Y A A A B A B

2 1% Y Y A A A B A B

3 50%+critical

A A A A A A A B

4 Roaming Y Y Y Y Y Y Y Y

5 5% Y Y A A A A A A




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(e) Residential transformer




1


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(b) Voltage unbalance

Graph monthly/quarterly/yearly

(c) Harmonics

THD and 5th

(d) Voltage fluctuations (flicker)

Continuous PST < 1?

(e) Events (sags, transients)

Continuous

Other comments

Exceedances to be reported Data used if network issues arise Perhaps trend PQ issue Project, other signals, circuit breaker status, time stamping Standardisation of sampling/presenting

According to standards 10 min to 1 week period Lack of consistency

So that effective technical mitigation options may be studied, what are the barriers and good andpoor approaches to obtain Power Quality data (and system network information) from OTHERUTILITIES or CUSTOMERS? Any specific experiences that have been witnessed that stand out?Consider high-level political/commercial/personal relationships and agreements for data access oracquisition. Consider low-level formatting of data, data standards and universal protocols.

Barrier to sharing Commercial, closed mentality, utilities can lose access to data, revenue metersowned by retailers

Different devices - Instruments hold data in different forms Low level formatting can be an issue 10 min cycles Resourcing Is there a cost benefit? Need utilities to take responsibility

No litigation data distribution and data sharing International data format agreement

International standards agreement

Standardisation of sampling/presenting Regulator issues Planning Working together with customers and regulators

Who pays?




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2.3 Question 3: Responsibility for Power Quality issues

For each of the following equipment scenarios (a) to (e), what CRITERIA and WEIGHTING forresponsibility/costs should the UTILITY, EQUIPMENT MANUFACTURER/RETAILER andCUSTOMER have for meeting future Power Quality conditions. Why?

(a) Rural customer's equipment that generate significant harmonic current injections.Consider how harmonics should be allocated (device/site level, first come first served,

divided by expected number of connections, IEC declared customers)? Consider howallocations should be enforced? What problems are there with present standards? Shouldmodifications be made to harmonic allocation levels in NZECP?

Equipment Harmonic current limits (with inf. bus) Utility Harmonic voltage, perhaps connection charges? Manufacturer, by agreement with utility Use allocated share

Ratio of S/C capacity allocation Rural/Urban User pays Utility = Standard, Equip/Mnf = Standard, Customer = Ongoing

Monitoring = IEC stds, utility. Costs = User.

(b) Residential heat pumps causing voltage sag and generating harmonic currents. Shouldmodified standards be introduced? What should they be?

Forced drop out and soft start Manufacturer (not DOL)

Quality over price Standard driven production Quality driven by refined standards

Import guidelines CF type tests? Utility = Min standard of network required, Equip/Mnf = Standard Monitoring = Stds, manufacturer. Costs = Manufacturer.

(c) Compact Fluorescent Lights generating harmonic currents. Should modified standardsbe introduced? What should they be?

Enforce import standards for Ih Manufacturer (not DOL)

Quality over price

Standard driven production Quality driven by refined standards Import guidelines Tests? Utility = Min standard of network required, Equip/Mnf = Standard Monitoring = Stds, manufacturer. Costs = Manufacturer.

(d) Wind farms: system frequency stability, voltage sag and flicker. Consider large windfarms and small DG wind farms. What about sub-20kW grid connected wind turbines,especially in remote network sections?

IEC61400 21

Utility to require AS4777




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Large farms Keep on line voltage regulation Small farms Safety Responsibility Grid operation, ensures compliance Utility = Min level, Equip/Mnf = Network code, Customer = Ongoing

Monitoring = IEC stds, utility. Costs = Owner.

(e) Distributed Generation inverters at residential premises. Should modified standards beintroduced? What should they be?

A standard of some sort DG more on safety, same as d) Utility = Min level, Equip/Mnf = Network code, Customer = Ongoing

Networks not designed for embedded DG at local level Ongoing monitoring/policing/teeth

Monitoring = Manufacturer. Costs = Owner.

(f) Another scenario of your choice (if time is available).

Utility should be ultimate policeman to protect other and all users

What sort of information would be the most useful in a Power Quality guidelines booklet that helpsplan and mitigate present and future Power Quality issues? Eg. Case studies, bench marking,calculation methods, other? Please update later if further suggestions arise in the future.

Practical examples Examples with typical solutions Possible side effects Review of standards/summary

Clarification and agreement of standards Publicly available book

Increased awareness Communication to end users Equipment emission levels Assessment criteria

Need to modify standards to suit NZ conditions Education to local Electricians

Product standards heat pumps - realistic Process flowcharts Complaint, new installation, preventative 5 year review




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2.4 Wrap-up

This section contains the Power Quality workshop end-of-day 'wrap-up'. It consists of whiteboard notesand floor comments about what were considered to be the important issues.

ECP36

Consensus to change it

Requirement to update standards, but do not want NZ only standards (too costly for manufacturersto meet), therefore need international standards. Except if there is good grounds to vary eg. faultlevels reference impedance, current limits.

Emerging issues

DG Political drive, subsidies, grid code to handle intermittent power injection, smart metering Electric vehicles Opportunities as well as threats, where is the generation, charging currents and

load management, smart metering could help, road tax issues

VSDs also pumps in general, sag issues for big loads on long lines, general agreement onharmonic issues.

Heat pumps Load management, lobby standards committees for reasonable standards, the horsehas bolted??, hot water heat pumps, loss of load control through ripple control, use solar waterheating

Windfarms Need grid code to handle intermittent power injection

Routine monitoring levels

GXPs (high need to monitor) LV consumers (more statistical approach, need for utility smartmetering?)

PQ monitoring in smart metering, accuracy issues, who pays for more accurate meters?

Guidelines

Target audience Customers, electricians (ENA guide, no techy talk), internal (HB264 startingpoint, recommended practices, calc methods)

Application Case studies, language, straight forward

Installation standards

Connections Factories, farming, residential

Appliance standards

Extra categories in CEC star ratings, merge with efficiency in the future? ANZS 61000 already available, are the numbers suitable for a compliance regime?




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2.5 Future challenges

What is the role of standards/regulations in Power Quality, or should a market approach be used?

If standards:

How is the permissible level set?

Should there be requirements on an installation or on each individual device?

Should the standard be absolute or 95% value?

Who has the responsibility for policing the Power Quality level?

How are interactions and resonances resolved?

Which customers should have priority on allocation?

Figure 38: Simple model of customers on a 11 kV feeder for Power Quality allocation purposes.



Customer

A

Customer

B

Customer

C

Customer

D

Customer

E

Customer

F

Customer

G

Customer

H

33 kV11 kV


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3 Conclusions and future work

It is clear that Power Quality is an issue and will be more of an issue in the future with the uptake of newtechnology. A few people prefer a market approach to Power Quality arguing that one limit does notnecessarily fit all. There was common consensus that standards and regulations are required to ensure theaddition of new equipment can be accommodated without any detrimental effects. This is because it is a

more practical way to deal with Power Quality issues, and there are pitfalls with a market approach. At anindustrial or commercial level it was felt that any standards should be on installations rather than onindividual items of equipment. This is because application to each item of equipment would restrictavailability or increase the equipment price, while a more cost effective solution may to deploy tomitigation equipment in one place in the installation. On a domestic level, standards for individual itemsof equipment were deemed more appropriate due to the impracticability of expecting each installation toinstall mitigation equipment appropriate to the loading and the variability of the loading. Also theincremental cost is very low to dramatically improve the device performance in low power domesticappliances, hence minimum performance standards are required.

There are two sides to Power Quality: the emission levels and the immunity levels of equipment.Coupling these is the network characteristics, as it controls for a given emission level, how high the

disturbance level generated is, and the next question is whether it is above or below the equipmentsimmunity level? New Zealands electrical network is a weak Island system due to our geographicalisolation from other electrical networks. Our system peak is approximately 6000 MW. This is very smallconsidering Europe, which is interconnected, United Kingdom, North America and our nearest neighbour,Australia. This means that for a given emission level, it would be expected that a higher disturbance levelwould result with a smaller system (ignoring the possibility of resonances). Much of the future workrevolves around investigating what a typical New Zealand electrical system can withstand in terms ofsteady-state and transient disturbance. Normally the voltage quality is the key quantity and the measure ofthe disturbance level, while current specification characterises the emission level. To allocate emissionlimits to installations and equipment while ensuring the disturbance level does not exceed the planninglevel requires knowledge of the system impedance.

The relevant IEC publication is IEC/TR 60725, entitled Consideration of reference impedances and public supply network impedances for use in determining disturbance characteristics of electrical

equipment having a rated current 75 A per phase. Tables 6 and 7 show data from this technical report,some of which is measured and the rest based on calculations.



Table 6: Single-phase service capacities


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4 Bibliography

Arrillaga J., Chen S. and Watson N.R.Power System Quality AssessmentJohn Wiley & Sons 2000

Arrillaga J. and Watson N.R.Power System Harmonics 2nd EditionJohn Wiley & Sons 2003

B. KennedyPower Quality PrimerMcGraw-Hill 2000

R.S. Vedam & M.S. SarmaPower Quality: VAR Compensation in Power SystemsCRC Press 2009

M.H.J. BollenUnderstanding Power Quality ProblemsIEEE 2000

E.F. Fuchs & M.A.S. Masoum,Power Quality in Power systems and Electrical MachinesElsevier 2008

G.T. HeydtElectric Power Quality2nd EditionStars in a Circle Publications 1991

C. SankaranPower QualityCRC Press 2002

F. C. De La RosaHarmonics and Power SystemsCRC Press 2006

R.C. Dugan, M.F. McGranaghan and H.W. BeatyElectrical Power Systems QualityMcGraw-Hill 1996




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Antonio Moreno-Muoz (Ed.)Power quality : mitigation technologies in a distributed environmentSpringer 2007

By A. Kusko and M. T. ThompsonPower quality in electrical systems

McGraw-Hill Professional, 2007

Angelo BagginiHandbook of Power QualityJohn Wiley & Sons Inc. 2008

G.J. WakilehPower Systems Harmonics: Fundamentals, Analysis and Filter Design (Hardcover)Springer 2001

W. Mielczarski, G.J. Anders, M.F. Conlon, W.B. Lawrence, H. Khalsa and G. MichalikQuality of Electricity Supply & Management of Network LossesPuma Press, Melbourne, 1997

T.A. ShortDistribution Reliability and Power QualityCRC Press 2006

A. Ghosh and G. LedwichPower Quality Enhancement using CUSTOM Power DevicesKluwer Academic Publishers, 2002

Mohammed S. S. Al-MandhariImproving Voltage Dip Ride-through Using Super/Ultra Capacitors, 2008 Third Professional YearProject, Electrical & Computer Engineering Department, University of Canterbury, 2008

epecentre pq workshop report 2009

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