IEEE and IEC Harmonics

Sezione di Roma

SEMINARI SULLA QUALITA’ E SULLA SICUREZZA ELETTRICA

Il Dipartimento di Ingegneria Elettrica dell’Università di Roma “La Sapienza”, nell’ambito del corso di Distribuzione ed Utilizzazione dell’Energia Elettrica, l’AEIT – Sezione di Roma, la Commissione Elettrica dell’Ordine degli Ingegneri di Roma e l’IEEE-IAS Chapter del Centro-Sud Italia hanno organizzato presso l’Aula 40 della Sapienza – Università di Roma Dipartimento di Ingegneria Elettrica, Facoltà di Ingegneria, il seminario

Harmonics in electrical power systemsProf. Ing. Mark Halpin,

professore di Electrical Power Systems dell’Auburn University - Alabama USA presidente dell’IEEE/IAS, fellow IEEE

Coordinatore : Prof. Ing. Giuseppe Parise

IEEE and IEC Harmonic Limits

Mark HalpinAuburn University

21 May 2007

Limits on Harmonics in Power Systems

• IEEE Standard 519 “Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems” suggests limitations for voltage and current harmonic contamination

– individual harmonic limits– total harmonic distortion limits

• Other standards are different and should be consulted for systems and equipment manufactured or applied outside the U.S.

– IEC 61000-3-2, 3-12 (and others): LV equipment standards– IEC 61000-3-6: MV/HV/EHV “system” standard– IEC 61000-4-7 and 4-30: Harmonic measurement standards

• IEEE 519 and IEC 61000-3-6 have the same goal but utilize different conceptual approaches

IEEE vs. IEC Harmonic Standards

• IEEE does not have equipment standards• Fundamental IEEE philosophy is “shared responsibility”

– Limit users to an equitable current emission level• Users may not create undesirable resonance conditions

– Utility companies must control system resonances to limit voltage distortion

• Fundamental IEC philosophy is “voltage quality maintenance”– Users may not inject harmonic currents that lead to excessive

voltage harmonic production– Utility (supply) system characteristics are defined by system

requirements and are not manipulated to allow greater user harmonic currents

519 Limits on Harmonics in Power Systems

• IEEE 519 considers the “point of common coupling”(PCC) as the customer-utility interface point– Harmonic current limitations for end-users apply at this point– Harmonic voltage limits apply throughout the utility network and

are suggested at the PCC to insure quality in the voltage supplied

• “Shared Responsibility” requires compromise from owner/operators and users– Voltage limits set to avoid problems– Current limits chosen based on equity between

• Owners/operators and users• Users and users

IEEE 519: Limits on Voltage Harmonics

• Voltage harmonic limits are suggested for both individual harmonics and total harmonic distortion. Different limits apply for different voltage levels

Voltage HarmonicsVoltage at PCC Individual Limit THD

<69 kV 3.0 5.069-161 kV 1.5 2.5>161 kV 1.0 1.5

IEEE 519: Limits on Current Harmonics

• Limits are provided for individual harmonics and THD (TDD) for general distribution systems. All values are in percent and based on a 15 or 30 minute demand interval

Harmonic Current Limits: 120-69000 V SystemsCurrentRatio

h<11 11≤h<17 17≤h<23 23≤h<35 35≤h TDD

<20 4.0 2.0 1.5 0.6 0.3 5.020-50 7.0 3.5 2.5 1.0 0.5 8.050-100 10.0 4.5 4.0 1.5 0.7 12.0

100-1000 12.0 5.5 5.0 2.0 1.0 15.0>1000 15.0 7.0 6.0 2.5 1.4 20.0

Current ratio: Short-circuit current divided by maximum load demand current, ISC/IL


• For higher voltage levels, lower percentages of harmonic contamination are permitted

Harmonic Current Limits: 69-161 kV SystemsCurrentRatio

h<11 11≤h<17 17≤h<23 23≤h<35 35≤h TDD

<20 2.0 1.0 0.75 0.3 0.15 2.520-50 3.5 1.75 1.25 0.5 0.25 4.050-100 5.0 2.25 2.0 0.75 0.35 6.0

100-1000 6.0 2.75 2.5 1.0 0.5 7.5>1000 7.0 3.5 3.0 1.25 0.7 10.0



• Limits for loads connected directly to the transmission system are the most stringent

Harmonic Current Limits: >161 kV SystemsCurrentRatio

h<11 11≤h<17 17≤h<23 23≤h<35 35≤h THD

<50 2.0 1.0 0.75 0.3 0.15 2.5≥50 3.0 1.5 1.15 0.45 0.22 3.75


Does IEEE 519 Over-Specify The Problem?

• Voltage and current are obviously related by impedance– Ohm’s Law applies at each frequency of interest

• IEEE 519 recommends both voltage and current limits– Does this indirectly recommend a frequency-dependent

equivalent impedance at the PCC?– Yes, but

• The relationship is not exact due to allowances for diversity and resonance

• Treating ranges of harmonics the same leads to atypical impedance characteristics

IEEE 519 Impedance Specification

Per-Unit Harmonic Impedance

0.00

1.00

2.00

3.00

4.00

5.00

6.00

3 5 7 9 11 13 15 17 19 21 23 25

Harmonic Number

Impe

danc

e (p

u) <2020<5050<100100<1000>1000

Isc/IL ratio

maximum demand current IL used as base

A More Typical Impedance

• Series and parallel resonances likely exist!

Positive Sequence Driving Point Impedance

0 6 12 18 24 0

10

20

30

40

Frequency (H pu)

Impe

danc

e (o

hms)

IEC 61000-3-6 (Ed. 1) Impedance

• Based on typical U.K. MV urban distribution without major resonance-causing capacitors

H arm onic num ber

Im pedance (Ω )

Short-circuit impedance could be used to establish y-axis values

slope=1

slope=2

IEEE “Impedance” Allows for Resonance

Limit-Based Impedance vs. Linear Short-Circuit Impedance

0.00

1.00

2.00

3.00

4.00

5.00

6.00

3 5 7 9 11 13 15 17 19 21 23 25

Harmonic Number

Impe

danc

e (p

u)

LimitSC

Based on a Short-Circuit to Load Current Ratio of 20

Impedance Summary

• IEEE 519 and IEC 61000-3-6 (Ed. 1) show increasing impedance with frequency

• More realistic systems (with resonance) may show increases or decreases with frequency

• If IEEE 519 “impedance” is greater than the system impedance, what does this mean?– IEEE 519 current limits could be increased or other

customers served– System impedance could be higher (resonance)– IEEE 519 voltage limits could be reduced

IEEE 519: Consideration of Additional Service

# Of Customers That Can Be Connected For Different SCR Levels

123456789

3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39Harmonic # (h)

# of

Cus

tom

ers

(SCR=19.999) (SCR=49.999)

IEEE 519 relies on this diversity to allow approach to be widely applied

The IEC Approach

• IEC utilizes equipment limits for disturbances (harmonics, voltage fluctuations, etc.) to promote low-voltage system electromagnetic compatibility

• A voltage quality approach is used to coordinate disturbance emissions from MV, HV, and EHV loads and installations

• The entire IEC approach is based on compatibility levels and statistics—EMC can not be guaranteed, but compatibility can be “maximized”

Disturbance level

Probabilitydensity

disturbance level

compatibility level

immunity level

planning level

assessed level

10 ≤ h ≤ 500.20.221< h ≤ 4517≤ h ≤ 49

0.40.580.20.2211.52.513

0.40.560.30.3151.5311

0.81411.29247

1.41.82243255

HV-EHVMVHV-EHVMVHV-EHVMV

Harmonic Voltage%Harmonic

Orderh


Orderh


Orderh

Even harmonicsOdd harmonicsmultiple of 3

Odd harmonicsnon-multiple of 3

IEC 61000-3-6 Planning Levels

2.0h

179.1 −⋅h

172.1 ⋅ 22.0h

1025.0 +⋅ 16.0h

1019.0 +⋅

IEC MV-HV-EHV EMC Coordination

• The IEC approach is based on maintaining adequate voltage quality with respect to compatibility levels

• Coordination is performed at each voltage level and from one level to another considering– Summation laws for cancellation/diversity– Transfer coefficients between voltage levels

TUM

(LUS)

(LMV)

GMV

SMV = St-SLV

SLV

GMV+LV MV

LV

HV upstream system

St

IEC 61000-3-6 Emission Allocation

• Voltage emissions are allocated to users according to the general concept formulae

– G denotes global emission level for a particular voltage level at harmonic h– E denotes emission limit for ith user– L denotes planning level at harmonic h– T denotes a transfer coefficient between voltage levels– α is a summation exponent to account for cancellation, etc.– S is load (or total system) power

( )

htotal

ih

hushhh

GS

SE

LTLG

=

−= α ααα

IEC 61000-3-6 Current Emissions• Current emission limits are obtained, when necessary, using

– The apportioned voltage limits– The system impedance characteristics

• Important points regarding this particular table– Table applies only to MV users– User must be less than 1 MVA– Short-circuit to (agreed power) load ratio must be > 100– User should not have power factor correction capacitors

500/h23355Ih/IL

>13131175HarmonicNumber, h

IEEE 519 “V/I” vs IEC 61000-3-6 “V/I”How Many Distorting Loads Can Be Served?

Allowable Distorting Loads For Various Current and Voltage Limits From IEEE 519-1992 and IEC 61000-3-6 For An

Assumed Short-Circuit Ratio of 100

0

10

20

30

40

50

60

70

80

90

5 7 11 13 17 19 23 25

Harmonic #

# of

Loa

ds

51961K-3-6

Technical Comparison of IEEE and IEC

• System characteristics (impedances) are only an issue if both voltage and current limits are recommended– IEEE does this for all customers

• Easier to use

– IEC does this ONLY for small customers• Less likely to encounter inconsistencies


• Diversity and harmonic cancellation are addressed in both approaches– The inconsistent impedance specification in IEEE can

be interpreted as a diversity/cancellation/resonance allowance

– IEC uses a frequency-dependent exponent to account for diversity/resonance and actual system impedance to account for resonance


• Both approaches provide some allowance for background harmonic distortion– The inconsistencies in the IEEE impedance

specification can be interpreted as an allowance for background distortion

• The background plus the customer under evaluation should not exceed the limiting values

– IEC specifically provides for transferring harmonic distortion from an upstream (source) system to a downstream (load) point

IEC 61000-3-6 or IEEE 519

• Compliance with IEC emission limits would be based on harmonic voltages produced at the PCC– IEEE 519 compliance (for the user) is based only on current

harmonics• The two approaches may or may not result in the same

conclusions regarding mitigation requirements and procedures– Cost of compliance could be substantially different

• The harmonic problem is the same, so why must the standards be different?– Globalization is driving us toward harmonization

Towards Harmonization

• Key members of 519 are active in the revision of 61000-3-6• Harmonious changes in 519 include

– Adoption of measurement protocols– Consideration of time variations through statistical methods– Treatment of interharmonics– Consideration of LV (<1kV) systems

• IEC current limits, where they exist, are similar to corresponding 519 current limits for lower frequencies– 519 has diversity assumptions whereas IEC uses summation exponent

• 519 “current limits” vs. IEC “voltage apportioning” is not likely to be resolved in the near future– Each approach has advantages and disadvantages

Harmonization: IEEE Measurement Procedure

• Recommended to use IEC 61000-4-7 and 61000-4-30 specifications

0

0.2

0.4

0.6

0.8

1

1.2

1.4

X-6

0

X-5

5

X-5

0

X-4

5

X-4

0

X-3

5

X-3

0

X-2

5

X-2

0

X-1

5

X-1

0

X-5 X

X+5

X+1

0

X+1

5

X+2

0

X+2

5

X+3

0

X+3

5

X+4

0

X+4

5

X+5

0

X+5

5

X+6

0

Interharmonics @ 5 Hz

Harmonics @ 60 Hz

Harmonization: Indices and Statistical Analysis

• From IEC 61000-4-30– 3 s “very short” value

– 10 min “short” value 0

2

4

6

8

10

12

14

16

18

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69

Time (h)

TD

D (%

)

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

TDD (%)

Freq

uenc

y

.0%

20.0%

40.0%

60.0%

80.0%

100.0%

215

1

2,, 15

1 ∑=

=i

invsn FF

2200

1

2),,(, 200

1 ∑=

=i

ivsnshn FF

95th percentile should be less than limit99th percentile should be less than X*limit

Changes to the Limits

• New voltage limit provision for low voltage (<1 kV)– 5% individual harmonic, 8% total harmonic distortion

• Revised current limits for general transmission systems (> 161 kV)

3.750.220.451.151.53.0≥50

2.50.150.30.751.02.025<50

1.50.10.150.380.51.0<25*

TDD35≤h23≤h< 3517≤h< 2311≤h< 17<11Isc/IL

Individual Harmonic Order (Odd Harmonics)

Maximum Harmonic Current Distortion in Percent of IL

Interharmonic Limits• Voltage-only 0-120 Hz limits based on (single-frequency) lamp flicker

– Similar work ongoing in IEC TC77/SC77A WG1 and IEEE Task Force on Interharmonics with several joint members

0

1

2

3

4

5

6

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

105

110

115

120

Frequency (Hz)

Vol

tage

(% o

f Nom

inal

)

V≤1kV

1 kV<V≤69 kV

69 kV<V≤161 kV

V>161 kV

V≤1kV

1 kV<V≤69 kV

69 kV<V≤161 kV

V>161 kV

allvoltages

allvoltages

Reality of Today

• Utility company users of IEEE harmonic limit standards are finding an increasing need to make system improvements

– Pressure on standards-making groups to decrease user current harmonic limits

• Utility company users of IEC harmonic limit standards are finding an increasing need to design systems differently

– Pressure on standards making groups to increase compatibility levels• Customers are relatively accepting of existing limits• Equipment emission limits (IEC only) are being strongly debated

between manufacturers and utility companies

The Legalities of the Limit Standards

• IEEE 519 is a Recommended Practice– Is not binding until directly or indirectly incorporated in power

contracts or adopted by regulators

• IEC 61000-3-6 is a Technical Report– Many European national standards and norms adopt 3-6 or variants

of it

• Engineering judgment is always necessary– Neither standard applies to all situations

Standardization Conclusions

• The global economy pushes us toward harmonization of standards

• IEEE and IEC recognize the needs and issues at technical and administrative levels

• Tangible progress is being made– Technical harmonization through joint membership– Administrative support through procedures to directly

adopt standards (IEEE has adopted IEC 61000-4-15 for flicker, for example) and jointly develop standards

Case Study Examples

• Purpose: To demonstrate typical harmonic analysis procedures and IEEE 519 applications

• Two case studies are included– proposed twelve-pulse rectifier (dc drive) load addition– effects of six-pulse operation

• Applications of IEEE 519 harmonic limits also considered

System Diagram for Examples

UtilitySupply

M SL C HF

Transformer 1

220 kV

33 kV

Transformer 2

HFCSLM

6.6 kV

Notation: M--motor load, SL--static load, C--static capacitors, HF--harmonic filters

Required Information

Table 1. Utility Supply DataParameter Value

Supply Voltage 220 kVShort-Circuit Capacity 4000-10000 MVA

X/R 10.0

Table 2. Transformer DataParameter

(transformer 1)Value Parameter

(transformer 2)Value

Power Rating 100 MVA Power Rating 30 MVAVoltage Rating 220-33 kV Voltage Rating 33-6.6 kVImpedance 14% Impedance 10%X/R 10.0 X/R 10.0

Table 3. Static Load and Capacitor Data33 kV Bus Load 25 [email protected] lag.

Capacitor 8.4 Mvar6.6 kV Bus Load 15 [email protected] lag.

Capacitor 5 Mvar

Case Study 1: DC Drive at 6.6 kV Bus

• This example demonstrates the potential impacts of adding a twelve-pulse 5000 hp dc drive load at the 6.6 kV bus

• The questions to be addressed:– Does the addition of the drive lead to significant

voltage distortion in the plant?• A study for IEEE 519 “customer compliance” would not

consider internal plant conditions

– Is IEEE 519 limit compliance attainable?• Customer is responsible for current distortion at the PCC• Utility is responsible for voltage distortion at the PCC


• The magnitude of the impedance seen “looking into” the rest of the system from the 6.6 kV bus indicates multiple resonance conditions exist

0.0

0.5

1.0

1.5

0 10 20 30 40 50 60

6.6 kV Bus Driving Point Impedance

Impe

danc

e (O

hms)

Frequency (H pu)

Case Study 1: Rectifier at 6.6 kV Bus

• Under normal conditions, the 6.6 kV bus voltage is slightly distorted by the drive current.

0

1000

2000

3000

4000

0 10 20 30 40 50 60

6.6 kV Bus Voltage (LN) SpectrumTHD=0.636%

Vol

tage

(V)

Frequency (H pu)

0

100

200

300

400

500

0 10 20 30 40 50 60

Twelve-Pulse Drive Current SpectrumTHD=11.13%

Cur

rent

(A)

Frequency (H pu)


• In some cases, waveforms provide greater information than spectral plots

-6000

-4000

-2000

0

2000

4000

6000

-1000

-500

0

500

1000

0 10 20 30 40 50

6.6 kV Bus LN Voltage and Drive Load Current

bus6

k (V

)

dcdrive-bus6k (A)

Time (ms)

6.6 kV Bus LN Voltage Twelve-Pulse Drive Current

Case Study 2: Six-Pulse Operation

• It is important to consider possible changes in multi-pulse equipment when evaluating harmonic impacts

• For critical drive loads, operation with a reduced pulse order is a common “backup” plan

0

1000

2000

3000

4000

0 10 20 30 40 50 60

6.6 kV Bus Voltage (LN) SpectrumTHD=3.63%

Vol

tage

(V)

Frequency (H pu)

0

100

200

300

400

500

0 10 20 30 40 50 60

Six-Pulse Drive SpectrumTHD=35.8%

Cur

rent

(A)

Frequency (H pu)

Case Study 2: Six-Pulse Operation

• The 6.6 kV bus voltage remains only slightly distorted

-6000

-4000

-2000

0

2000

4000

6000

-1000

-500

0

500

1000

0 10 20 30 40 50

6.6 kV Bus Voltage (LN) and Drive Current Waveforms

bus6

k (V

)

dcdrive-bus6k (A)

Time (ms)

6.6 kV Bus Volltage (LN) Six-Pulse Drive Current

Case Studies 1&2: Conclusions So Far

• Twelve-pulse drive operation will not create a harmonic voltage problem at the load (6.6 kV) bus.

• Six-pulse drive operation will not create a harmonic voltage problem at the load (6.6 kV) bus.

• What about compliance with IEEE 519 limits at the PCC?– The PCC is the 220 kV high-side bus in this case– Twelve and six-pulse operation must be considered– Primary question involves customer compliance with

current limits

Case Studies 1&2: 519 Current Limits

• To apply 519, we must know the maximum demand current and the available fault current. For this case, let use assume the following:– SL=45 MVA– SSC=10000 MVA– ISC/IL= SSC/SL=222.2

• We use the second (bottom) row in the HV (>161 kV) current limit table. All currents must be expressed as a percentage of IL!

Case Studies 1&2: 519 Current Limits

• The results for h<20 clearly indicate a limit violation at the 5th harmonic during six-pulse operation. Twelve-pulse operation is not a problem.

Harmonic 5 7 11 13 17 19Harmonic Current, % of IL 6.77 0.44 0.81 0.09 0.33 0.09

519 Limit Value 3 3 1.5 1.5 1.2 1.2

For Additional Information

• My coordinates are:Mark Halpin200 Broun HallDepartment of Electrical & Computer EngineeringAuburn University, AL 36849 (USA)[email protected]

Thank you for your attention!

Documents

IEEE and IEC Harmonics