Harmonics - Application of Standardshome.iitk.ac.in/~spdas/rao2.pdf · • Industrial Customers • Commercial Customers ... IEEE C57.110 “Recommended Practice ... • SDw is weighted

1

Rao S. ThallamFellow, IEEE

Salt River ProjectPhoenix, AZ, USA

Presented at:National Workshop on Electric Power Quality

Nov 10, 2004Indian Institute of Technology, Kanpur

Kanpur, UP, India

Harmonics -Application of Standards

�������• Introduction• THD and TDD• Displacement and True Power Factor• K-Factor and Transformer Derating• When should you be concerned?• Application of IEEE 519 Standard• Harmonics Measurements• Industrial Customers• Commercial Customers• IEC Standards• Conclusions

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"This alternating current thing is just a fad. It is much too dangerous for general use"

Thomas Alva Edison

What Are Harmonics ?�Harmonics are due to distortion of the voltage or

current waveform�The distortion comes from nonlinear devices,

principally loads

V(t)

I(t)

V

I

Nonlinear Resistor

3

Decomposition into Harmonic Components

·

+

+

+

+

+

+

··

+

60 Hz(h = 1)

300 Hz(h = 5)

420 Hz(h = 7)

540 Hz(h = 9)

660 Hz(h = 11)

780 Hz(h = 13)

180 Hz(h = 3)

Current vs. Voltage Harmonics

PureSinusoid Distorted Load

Current

Distorted Voltage

+ -(Voltage Drop)

Harmonic currents flowing through the system impedance results in harmonic voltages at the load

4

Why bother about Harmonics?

�Important aspect of power quality�Damaging Effects to Consumer Loads

and Power System�Problems may be incipient�Non-Linear Loads are Increasing�Power Factor Correction Capacitors

Total Harmonic Distortion

�Defines the total harmonic content of current or voltage

�Ratio of the RMS of the harmonic content to the RMS of the Fundamental, as % of Fundamental

5

THD = sum of squares of amplitudes of all harmonics

square of amplitude of fundamental x 100 .

Mathematically, THD of a voltage wave form can be defined as,

THD = V

V

100 .x h

h

h 2

122=

= ∞�

Total Harmonic Distortion

THD for Current Waveform

THD = I

I

100 x h

h

h 2

1

22=

=∞�

6

Total Demand Distortion Factor (TDD)

�Applies for current distortion only.�The total rms harmonic current

distortion, in % of the maximum demand load current (15 or 30 min demand)

Displacement Power Factor

�When V and I are not distorted, PF is:�“Ratio of the active power of the

fundamental, in watts, to the apparent power of the fundamental wave, in volt-amperes”

�P = V1rms I1rms Cos ��PF = Cos �

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Power and Power Factor�When significant distortion is present

PF = Cos θθθθ

“Displacement Power Factor”

True Power Factor

�Ratio of the total power, in watts, to the total volt-amperes. This includes fundamental and all harmonic components.

�This is also called “Distortion Power Factor”

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True Power Factor

PFPS

=

S Vrms Irms=

PT

v t i t dtT

= �1

0( ) ( )

Where:

Engineering Speak

“We are looking at a number of approaches”

Translation:We are guessing.

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Engineering Speak

“We are making modifications to address minor difficulties”

Translation:We are starting over.

Engineering Speak

“Test results are gratifying”

Translation:It worked and boy are we surprised!

10

Engineering Speak

“We are trying some new approaches”

Translation:We threw some new guys on it.

K-Factor�K-Factor is ratio of eddy current losses

due to distorted current compared to the losses for the same rms fundamental frequency current

�Example: �Eddy Current Losses with 100 A rms with harmonics =

270 Watts�Eddy Current Losses with 100 A rms 60 Hz sine wave =

27 Watts

�K - Factor = 270/27 = 10

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K-Factor

K = I ( ) 2pu

= h

h

hh

=

∞�

1

2

K-Factor�Assumes eddy current losses are

proportional to f 2 - OK for small conductor sizes and low harmonics

�At higher frequencies, eddy current loses are proportional to f

�Transition frequency depends on winding configuration, material

�Al - 2200 Hz, Cu - 700 Hz �K-factor over estimates harmonics effect

at higher frequencies

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THD and K-Factor(Example Calculation)

�Harmonics for 3-ph PWM type ASD�Fund. = 100 A rms�5th : 60 A rms = 0.6 pu�7th : 40 A rms = 0.4 pu�11th : 30 A rms = 0.3 pu�13th : 20 A rms = 0.2 pu�THD = Sqrt (0.62 + 0.42 + 0.32 +0.22)* 100 = 81 %�K = 12 + 0.62 * 52 + 0.42 * 72 + 0.32 *112+0.22*132

� = 1 + 9 + 7.84 + 10.89 + 6.76 = 35.49

Transformer Derating

�Non K-rated transformers have to be derated when load current has harmonics

�IEEE C57.110 “Recommended Practice for Establishing Transformer Capability When Supplying Nonsinusoidal Load Currents”

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K-rating

�K-rated transformers can handle non-sinusoidal load current up to the full load rating with k-factor up to the k-rating of the transformer

�K-rated transformers are designed to have lower eddy current losses

Type of Load Typical WaveformCurrent

DistortionWeightingFactor (Wi)

Single PhasePower Supply

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current 80%

(high 3rd)2.5

Semiconverter

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

high 2nd,3rd,4th at partial

loads2.5

6 Pulse Converter,capacitive smoothing,no series inductance

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current 80% 2.0

6 Pulse Converter,capacitive smoothing

with series inductance > 3%,or dc drive

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current 40% 1.0

6 Pulse Converterwith large inductor

for current smoothing

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current 28% 0.8

12 Pulse Converter

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current 15% 0.5

ac VoltageRegulator

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

varies withfiring angle 0.7

Sources of Harmonics

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Example 1 - dc drive

Example 2 - PWM drive, no choke

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Example 3 - PWM drive with choke

Example 4 - Switched mode power supply currents

Phase A (50 Amps)

Phase B (50 Amps)

Phase C (57 Amps)

Neutral (82 Amps)

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Example 5 - electronic ballast

Line to Neutral Voltage for Electronic Ballast

0 10 20 30 40 50-200

-150

-100

-50

0

50

100

150

200

Time (mS)

Voltage (V)

Max:Min:Avg:Abs:RMS:CF :FF :

170 -170 109.055 170 120.727 1.40814 1.10703

Line Current for Electronic Ballast

0 10 20 30 40 50-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

Time (mS)

Current (Amps)

Max:Min:Avg:Abs:RMS:CF :FF :

0.784 -0.792 0.305828 0.792 0.334094 2.37059 1.09242

When Should You be Concerned About Harmonics

� 20 % of total load is power electronic load

� If service transformer is loaded near rating

� When PF correction capacitors are planned

�Neutral to ground voltage in 120 V supply exceeds 1 to 2 volts

�

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Harmonic Standards

�Several Countries have developed Standards to limit harmonics

�IEEE 519-1992�IEEE 519A-2004?�IEC 61000-3-2, 61000-3-4, 61000-3-12

IEEE 519�IEEE 519 “Recommended Practices and

Requirements for Harmonic Control in Electric Power Systems”

�Specifies load current harmonic limits at PCC

�Specifies supply voltage harmonic limits at PCC

�IEEE 519A “Guide for Applying Harmonic Limits on Power Systems”

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HARMONIC CURRENT DISTORTION LIMITS IN % OF IL

V < 69 kV

ISC / IL 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

IEEE 519 Standard Limits

Application Concerns

• Selecting PCC• Calculating ISC and IL• What is TDD ? • Measurement Problems• Time Varying Harmonics• General Procedure for Applying Harmonic

Limits• Cost of Problems vs. Cost of Solutions• Distributed Generation Limits

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What is PCC ?

�“Point in the public network which is closest to the consumer concerned and to which other customers are or may be connected” IEC 61000-3-4:1998

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HARMONIC VOLTAGE DISTORTION LIMITS (in % of Nominal Fundamental Frequency Voltage)

Bus Voltage at PCC Individual Harmonic Voltage

Distortion Total Voltage Harmonic

Distortion (THDV) V <<<< 69 kV

3.0 5.0

69 kV <<<< V <<<< 161 kV

1.5 2.5

V >>>> 161 kV 1.0 1.5

IEEE 519 Standard Limits(Utility)

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IEEE 519 Standard

�Limits apply for the “worst case” for normal operation (lasting longer than one hour)

�For shorter periods, during start-ups limits may be exceeded by 50%

�Even harmonics are limited to 25% of odd harmonic limits

�Co-gen - use Isc / IL < 20, irrespective of actual value

Harmonic Current Measurements

• Calculate harmonics as % of a fixed (average max. demand) current, not as % of fundamental

• Limits in the Table Apply only to Odd harmonics – Even Harmonics are limited to 25% of those limits

• CT Characteristics are important – usually good (should be less than 3 dB)

• How long to monitor?– Very stable, One day may be adequate– one week – for most cases– Permanent monitoring in some cases

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Presentation of Results –snap shots

Presentation of Results –Time Trends

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Harmonic Voltage Measurements

• Measure at PCC• Low Voltage – measure with direct

connection• Higher Voltages – Connect with PT –

frequency response is good to 3 k Hz (50th

harmonic)• Avoid CCVTs – frequency response is not

good

Evaluation Procedure

• Non-linear load is less than 10 - 20% of total plant load – No harmonic evaluation necessary

• Weighted Disturbing Power

S S WDw Di ii

= � ( )

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Type of Load

Typical W aveform

Current Distortion

W eighting Factor (W i)

Single Phase

Power Supply

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

80%

(high 3rd)

2.5

Semiconverter

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

high 2nd,3rd, 4th at partial

loads

2.5

6 Pulse Converter,

capacitive smoothing, no series inductance

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

80%

2.0

6 Pulse Converter,

capacitive smoothing with series inductance > 3% ,

or dc drive

0 10 20 30 40-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

40%

1.0

6 Pulse Converter with large inductor

for current smoothing

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

28%

0.8

12 Pulse Converter

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

15%

0.5

ac Voltage Regulator

0 10 20 30 40

-1.0

-0.5

0.0

0.5

1.0

Time (mS)

Current

varies with firing angle

0.7

Fluorescent

Lighting

17%

0.5

Evaluation Procedure

• If SDw / Ssc < 0.1%, then automatic acceptance

• SDw is weighted disturbing power• Ssc is short circuit capacity at PCC• If customer has or considering PF

Correction Capacitors, harmonic evaluation is always necessary

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Choose PCC

Calculate Short CircuitCapacity (ISC)

Stage 1:Is Detailed Evaluation

Necessary?

Estimate Weighted DisturbingPower (SDW ) or % Nonlinear

Load

Is Power FactorCorrection Existing or

Planned?

No

Calculate Short Circuit Ratio(SCR=ISC/IL)

Yes

Characterize Harmonic Levels(Measurements, Analysis)

Stage 2:Does facility

meet harmoniclimits?

Calculate Average MaximumDemand Load Current (IL)

Yes

No

Design Power FactorCorrection and/or HarmonicControl Equipment (includeresonance and interaction

concerns)

Verification Measurementsand Calculations

(if necessary)

Yes

No

UTILITY CUSTOMER

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Applying Harmonic Limits For Industrial Facilities

1. Usually supplied by dedicated transformer2. Several nonliner loads – ASDs, Rectifiers, DC

drives, Induction furnaces 3. Loads are relatively low PF - Power factor

correction capacitors are installed4. Industrial loads like motors do not provide

much damping for resonance conditions5. Problems inside the facility before causing

problems in utility system6. Limit Voltage distortion to 5% at PCC – provide

some margin for distortion within facility

Applying Harmonic Limits For Industrial Facilities

1. Choose PCC2. Characterize Harmonic Loads3. Determine if PF Correction Needed4. Calculate Expected Current Harmonics

at PCC5. Design Harmonic Control Equipment, if

necessary6. Verify performance with measurements

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Applying Harmonic Limits For Commercial Customers

• Significant percentage of Load is Electronic Equipment and Switch mode Power Supplies

• High Efficiency Fluorescent Lighting• HVAC Load is ASD drives• Significant harmonic cancellation -Meeting

IEEE 519 at SES is rarely a problem• Internal Harmonic Problems – neutral

overheating, transformer overloading, communication interference

Overview of Proposed Revisions to IEEE 519

• Immediate– Increased voltage limits for buses < 1 kV– Limits for time-varying harmonics– Revised notch and ringing limits and

definitions• Near-term

– Measurements• Limits for Single-Phase Equipment

– Dropped

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Voltage Distortion Limits(% of nominal fundamental frequency

voltage)

Bus Voltage at PCC (Vn) Individual Harmonic

Voltage Distortion (%) Total Voltage

Distortion - THDVn (%)

V kVn ≤ 69 3.0 5.0

69 161kV V kVn< ≤ 1.5 2.5

V kVn > 161 1.0 1.5

Harmonic Voltage Limits

• Add a new voltage limit category for buses less than 1 kV– 5% limit for individual harmonics– 8% limit for voltage THD

• Main concern is associated with multiple zero crossings– Research has shown that concern has

merit

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Time-Varying Harmonics

• Limits must be based on factual cause/effect– Thermal effects occur over time– Burst distortion effects can be instantaneous– Startup/abnormal conditions should be tolerated

• The facts suggest providing– Significant limit increases for short periods– Some limit increases for intermediate periods– No increases for the majority of the time

• Some statistical techniques may be needed

Time Varying Harmonics

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Time Varying Harmonics –Total Duration Limits

Total Duration of Harmonic Bursts (Ttotal)

Total Duration of Harmonic Bursts

(Ttotal in%)

Acceptable harmonic distortion

level

Ttotal ≤15 min. Ttotal ≤ 1% 3.0×(design limits)

15 min.< Ttotal ≤1.2 hr. 1% < Ttotal ≤ 5% 2.0×(design limits)

1.2 hours < Ttotal 5% < Ttotal 1.0×(design limits)

Time Varying Harmonics – Single Burst Limits

Maximum Duration of

Single Harmonic Bursts (Tmax)

Max. Duration of Single Harmonic Bursts (Tmax in %)

Acceptable harmonic

distortion level

Tmax ≤ 15 sec. Tmax ≤ 0.02% 3.0×(design limits)

15 sec.< Tmax ≤ 30 min.

0.02% < Tmax ≤ 2% 2.0×(design limits)

30 min. < Tmax 2% < Tmax 1.0×(design limits)

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Time Varying Harmonics(24 hour period)

Total Duration of Harmonic Bursts

Maximum Duration of a Single Harmonic Burst

Acceptable Harmonic Distortion Level

<15 minutes < 15 seconds 3.0 x design limit

>15 minutes and < 1.2 hours

>15 sec and < 30 minutes and

2.0 x design limit

>1.2 hours and > 30 minutes design limit

Measurements• Define measurement specification

– Many commercial meters exist• 8, 12, and 16 cycle windows• 128 and 256 samples/cycle• Filtering

– IEC 61000-4-30 offers potential• Specific requirements• Captures 3s, 10m, and 2hr values

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IEC Standards�Apply at equipment level, 240 V or less, 1-ph,

690 V or less, 3-ph, 50 or 60 Hz� 61000-3-2: loads with input current < 16 A� 61000-3-12: loads with input current >16A and

<75A (published in 2004)� 61000-3-4: loads with input current > 75 A�Use varies from country to country, mandatory

in EC�UL certification available in US

IEC 61000-3-2

�Class A - General Purpose loads, 3-ph balanced equipment (plus any eqpt not in B,C,D)

�Class B - Portable tools�Class C - Lighting equipment�Class D - Equipment with “special wave

shape” (conduction angle < 600), P < 600W

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Class A (Balanced 3-ph Equipment)Harmonic Max. Permissible HarmonicOrder Current (Amps)

3 2.35 1.147 0.779 0.411 0.3313 0.2115-39 0.15 x 15/n

2 1.084 0.436 0.30

8-40 0.23 x 8/n

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Class C Equipment (Lighting >25W)

Harmonic Max. HarmonicOrder Current (% of Fund.)

2 2 3 30 x PF5 107 79 5

11-39 3(odd harmonics only)

Class D Equipment (Special Waveshape)

Harmonic Relative Limit Max. Harmonic Order (mA/W) Current (Amps)

3 3.4 2.305 1.9 1.147 1.0 0.779 0.5 0.4011 0.35 0.3313-39 3.85/n 0.15 x 15/n

(odd harmonics only)

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IEC 61000-3-4

� Loads with rated current > 75 A� Stage 1: SC KVA/EQ. KVA > 33� Stage 2: SC KVA/EQ. KVA 66, 120,

175, 250, 350, 450, 600� Stage 3: Local Utility Requirements

apply.

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IEC Standards� IEC Standards are based on European

distribution system� 3 ph, 3-wire feeder, and 3-ph, 3-wire

branches, 11 or 12 kV� 3-ph (delta-star), large (500 kVA - 1000

kVA) distribution transformers� 400/230V, 3-ph long secondary� USNC - IEC standards in US

US distribution systems are different

�3-ph, 4-wire Feeder, 1-ph, 2-wire branches, most 15 kV class

�Small (50 - 100 kVA) transformers serving 6 to 8 residents

�120/240 V, 1-ph, short secondaries�No consensus between manufacturers,

utilities and users

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Comparison of European and North American Systems

European North AmericanFeeder 3-ph, 3-wire 3-ph, 4-wireBranch 3-ph, 3-wire 1-ph, 2-wireTransformer 500 kVA-1MVA 50 kVA-100kVA

Connection Y / ∇∇∇∇ Gr Y / Gr YSecondary 400/230V, 3-ph 120/240V, 1-ph

Length Long short

���������

• Harmonics are important aspect of power quality

• Application of power electronics is causing increased level of harmonics

• Survey the loads and make preliminary evaluation

• IEEE and IEC Standards reviewed