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Assessment of Harmonic Distortion and Voltage Unbalance

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  • 8/9/2019 Assessment of Harmonic Distortion and Voltage Unbalance

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    Assessment of Harmonic Distortion and

    Voltage Unbalance

    Zia Emin

    National Grid Transco

    Network DesignSystem Policy & Support

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    What is Quality of Supply? (1)

    Ideal 3-Phase Balanced Voltages

    -1

    -0.9

    -0.8

    -0.7

    -0.6

    -0.5

    -0.4

    -0.3

    -0.2

    -0.1

    0

    0.1

    0.2

    0.3

    0.4

    0.5

    0.6

    0.7

    0.8

    0.9

    1

    0 0.01 0.02 0.03 0.04

    Time(Seconds)

    V(pu)

    V(Red)

    V(Yellow)

    V(Blue)

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    What is Quality of Supply? (2)

    Actual measurement 3-phase measurement

    -1.5

    -1

    -0.5

    0

    0.5

    1

    1.5

    V(pu)

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    Todays Talk

    Will cover harmonic voltage distortion and voltage unbalanceassessment in some detail

    Will not cover voltage dips, voltage steps, flicker or transients

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    Voltage Waveform Quality: the Grid Code

    National Grid is bound by Grid Code CC6.1.5 to:Apply G5/4 planning criteria for new connections to limit harmonicemissions

    Take existing and prospective users into account

    Comply with the compatibility levels of G5/4

    To ensure, under planned conditions, a maximum continuous PhaseVoltage Unbalance of

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    ER G5/4 Stage 3 Assessment

    All new connections at 33 kV Consider voltage distortion at the connection point andother nodes(not necessarily owned by NGT)

    Detailed harmonic impedance model of the network Resonance conditions must be considered

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    Stage 3 Assessment Process

    BACKGROUND

    MEASUREMENTS

    HARMONIC

    STUDIES

    ESTIMATE

    TOTAL HARMONICVOLTAGES

    EMISSION

    LIMITS

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  • 8/9/2019 Assessment of Harmonic Distortion and Voltage Unbalance

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    Harmonic Studies (2)

    For each system condition, calculate up to the 50

    th

    harmonic: Harmonic self-impedance (ZAh) at the connection point (node A)

    Voltage gain to other nodes (GAXh)

    Harmonic voltages: At the connection point: VAh= IhZAh

    At a remote node X: VXh= VAhGAXh

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    Harmonic Study Example

    400kV

    132kV

    MV Node C

    Node A

    Node B

    Polluting Load

    Node E

    Node H

    Ih

    VAh=Ih . ZAh(ZAh)

    GAE

    GAH

    GACVHh=GAHh . VAh

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    Self-Impedance at Node A (ZAh)

    0

    0.1

    0.2

    0.3

    0.4

    0.5

    0 2 4 6 8 10 12 14 16 18 20 22 24

    harmonic number

    Zmag(p

    u)

    intact system

    system condition 1

    system condition 2

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    Voltage Gains

    Intact System Conditions

    0.0

    1.0

    2.0

    3.0

    4.0

    5.0

    6.0

    7.0

    8.0

    0 2 4 6 8 10 12 14 16 18 20 22 24

    harmonic number

    voltagegain

    GAE

    GAH

    GAB

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    Background Measurements

    Minimum period of 7 days (no bank holidays!)

    95th percentile assumed for background

    Preferably no outages

    Choose a few representative sites Not possible at some locations (no suitable transducer)

    Access can be a problem (3rd party sites)

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    Example Background Measurement

    5th

    Harmonic Voltage

    0.0%

    0.5%

    1.0%

    1.5%

    2.0%

    2.5%

    3.0%

    Wed Thu Fri Sat Sun Mon Tue Wed

    Magnitude

    95thPercentile (2.35%)

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    Estimate Total Individual Harmonic Voltages

    Combine study results and measured background: Assume 0 phase shift for the harmonic with the highest magnitude

    90 for the rest

    meashcalchtotalh VVV +=

    22

    meashcalchtotalh VVV +=

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    Estimated Total Harmonic Voltage (5th)

    0.00%

    0.50%

    1.00%

    1.50%

    2.00%

    2.50%

    3.00%

    3.50%

    A (400kV) B (132kV) E (11kV)

    Nodes

    5thharmonicvolt

    agemagnitude

    new load

    background

    G5/4 Planning Level

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    Harmonic Emission Limits

    Set to declared emission level, unless planning levels are exceeded

    Otherwise, reduce emission until Vtotalh

    is below planning level at all

    nodes

    What if background already exceeds planning level?

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    Phase Unbalance

    Under unfaulted system condition, caused by:

    Untransposed transmission lines

    Unbalanced loads (e.g. traction supplies)

    Inverse relationship to system strength eg 50 MVA phase to phase load atfault level of 5000 MVA gives approx 1% NPS voltage

    Highest risk is generator NPS relay operation

    Low NPS levels when the network is intact Unfavourable outages could lead to higher levels

    Balanced Phases Unbalanced Phases

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    Where does OHL NPS come from?

    seqseqseq IZV *= For a double-circuit one can write

    where

    if the phasings are RYB/BYR then

    =

    zps

    nps

    pps

    zps

    nps

    pps

    seq

    V

    V

    V

    V

    VV

    V

    2

    2

    2

    1

    1

    1

    =

    zps

    nps

    pps

    zps

    nps

    pps

    seq

    I

    I

    I

    I

    II

    I

    2

    2

    2

    1

    1

    1

    =

    666564636261

    565554535251

    464544434241

    363534333231

    262524232221

    161514131211

    ZZZZZZ

    ZZZZZZ

    ZZZZZZ

    ZZZZZZ

    ZZZZZZ

    ZZZZZZ

    Zseq

    zpsnpsppszpsnpsppsnps IZIZIZIZIZIZV 2262252241231221211 +++++=

    =

    82778.0161023.011025.078436.078010.0125010.0

    11025.086256.015027.043010.0101013.0151015.0

    161023.0163027.086256.0114010.031015.081013.0

    78436.0114010.043010.082778.0108025.078023.0

    125010.081013.0151015.078023.086256.043027.0

    76010.031015.0101013.0108025.0135027.0860.256

    seqZ

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    Configurations Leading to System Unbalance

    outaged

    A B

    C

    outaged

    A B

    C

    outaged

    A B

    C

    Loop in of a demand point creating mismatch in flows Loop in of a demand point creating opposite flows

    Loop in of a generation point creating opposite flows

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    NPS Voltage due to Flow Mismatch

    outaged

    A B

    C

    0

    100

    200

    300

    400

    500

    600

    700

    800

    900

    1000

    00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00

    time (hr)

    powerflow(MW)

    0.00%

    0.10%

    0.20%

    0.30%

    0.40%

    0.50%

    0.60%

    0.70%

    0.80%

    0.90%

    1.00%

    NPSvoltage(%offundam

    ental)

    outage of C - B

    line taken at this

    point flow from A to B

    flow from A to C

    flow from C to B

    NPS voltage at C

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    NPS Voltage due to Counter Flow

    Approximate NPS levels for generation connected to Quad Circuit

    Single circuit export with counter flow in the parallel circuit

    0

    1

    2

    3

    4

    5

    0 25 50 75 100

    Line Length kM

    NPS

    Volts

    %

    400 MW gen/1400 MVA flow

    400 MW gen/2400 MVAflow

    400 MW flow/3400 MVA flow

    800 MW gen/1800 MVA flow

    800 MW gen/2800 MVA flow

    800 MW gen/3800 MVA flow

    Flow

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    NPS Voltage Measurement

    0

    0.1

    0.2

    0.3

    0.4

    0.5

    Tue Wed Thu Fri Sat Sun Mon Tue

    NPSVoltage(%)

    95th percentile

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    Effects of Phasing

    NPS/ZPS

    Voltages

    Maximised

    RYB YBR BRY

    NPS/ZPS

    Currents

    MaximisedRYB

    YBR

    BRY

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    Distribution of NPS Voltage with Proper Phasing

    RYB

    BYR

    RBY

    YBR

    YRB BRY

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    Unbalanced Loads

    Optimum Phase-Pair Allocation

    -1.2

    -1

    -0.8

    -0.6

    -0.4

    -0.2

    0

    0.2

    0.4

    0.6

    0.8

    1

    1.2

    -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2

    0o

    90o

    180o

    270o

    Y-B load

    R-Y load

    B-R load

    -------- 0.9pf

    -------- 1.0pf

    -1.2

    -1

    -0.8

    -0.6

    -0.4

    -0.2

    0

    0.2

    0.4

    0.6

    0.8

    1

    1.2

    -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2

    0o

    90o

    180o

    270o

    Y-B load

    R-Y load

    B-R load

    -------- 0.9pf

    -------- 1.0pf

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    Controlling NPS Voltages

    Introduce phase transpositions

    Create parallel lines

    Install phase balancer

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    Transposition Tower (Its nothing new)


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