68
10/8/2004 1 MEDIUM VOLTAGE CABLE TESTING New Technologies - New Methods Michael T. Peschel High Voltage, Inc. Copake, NY. USA www.hvinc.com

2659 8 Vlf Td Epri High Voltage Inc

Embed Size (px)

DESCRIPTION

pruebas de altaion tens

Citation preview

  • 10/8/2004 1

    MEDIUM VOLTAGE CABLE TESTING

    New Technologies - New Methods

    Michael T. PeschelHigh Voltage, Inc.Copake, NY. USA

    www.hvinc.com

  • 10/8/2004 2

    This Can Be Prevented

    In-service failures cause great damage to faulted cables and adjacent cables. Not so if failed under a VLF test.

  • 10/8/2004 3

    Cable Test Methods AC Power Frequency. AC Series & Parallel Resonant. DC Hipot. Very Low Frequency (VLF) AC Hipot. Tan Delta, Partial Discharge, And Other Diagnostic

    Methods.

  • 10/8/2004 4

    Why Is DC Used DC hipots are small, portable, and economical. DC originally used with PILC, oil insulated cable,

    worked well. Same techniques used when HMW, XLPE, EPR, and

    other solid dielectric cables were installed. Years later DC was found to be damaging to

    insulation and leakage current measurements often ineffective for exposing defects. VLF work started.

    Until recently, AC field testing of cable was not practical.

  • 10/8/2004 5

    Worldwide consensus exists among engineering organizations, utilities,

    and cable manufacturers that typical DC test voltages of 4 5 Vo damage

    insulation and lead to failures.

    DC Use Discouraged

  • 10/8/2004 6

    Avoid DC Voltage On Service Aged, Solid Dielectric Insulation

    z DC Voltage Polarizes Cable. Water trees trap space charges lead to

    future failures.z Leakage current measurements mean

    little - not predictive of cable quality.

  • 10/8/2004 7

    Water Treesz Tree shaped channels found within the

    insulation of operating cables resulting from the presence of moisture and electrical fields.

    z Prevalent in solid dielectric cables.z Eventually leads to the inception of PD.z Leads to insulation failure.

    Why is DC Harmful

  • 10/8/2004 8

    Water Trees

  • 10/8/2004 9

    Why DC Is Damaging

    DC hipot input

    Negative space charges

    AC input

    DC hipot output negatively charges up water tree areas.

    These trapped space charges remain after test.

    When AC is reapplied, theres a high difference of potential across very little of the insulation. Leads to electrical trees cable fails.

  • 10/8/2004 10

    Utilities Response To DC Concerns

    z Typical DC test voltages were/are 4 - 5 times V0.z At these high voltages, damage is done.z Some reduce voltage to 15 kVDC on 15 kV cable.z 15 kV is only 30% above the peak AC stress in service.z At this voltage, leakage currents are meaningless.z Some do nothing, letting cables fail and then repair.z Many have adopted VLF AC hipoting to expose bad

    insulation and accessories. VLF is the best splice checker.

  • 10/8/2004 11

    VLF Very Low Frequency AC Advantages:

    Stress Similar to Service Conditions. Light Weight. Low Cost. Simple to Use.

    Disadvantages: Voltage Waveform in Some Designs. Destructive Cable May Fail Under Test.

    What To Do? Use AC Voltage

  • 10/8/2004 12

    WHAT IS VLF?Very Low Frequency: 0.1 Hz and lower.

    By decreasing the frequency, it is possible to test miles of cable with a small and affordable unit.

    Models range from 0.1 0.01 Hz.

    A VLF AC hipot is just an AC hipot withan output frequency lower than 60 Hz.

  • 10/8/2004 13

    VLF ExplainedXc = 1

    2 x pi x f x C

    The lower the frequency, the higher Xc (capacitive reactance).

    The higher Xc (or resistance across the power supply output),

    the lower the current/power needed to apply a desired voltage.

    At 0.1 Hz, it takes 600 times less power to test a cable, or any other high capacitance load, than at 60 Hz. At 0.01 Hz, 6000 times

    higher capacitive loads can be tested than at 60 Hz.

  • 10/8/2004 14

    60 Hz vs. 0.1 Hz

    At 60 Hz. a 1 F cable has an Xc of 2.65 kOhms. At 22 kV, it requires 8.3 amps of current to test.

    Total power supply rating must be 183 kVA.

    At 0.1 Hz, the Xc is 1.59 megohms. At 22 kV, the current needed is 14 mA. Total supply power needed is .304 kVA.

    (22 kV is the typical test voltage for 15 kV cable)

  • 10/8/2004 15

    50 kVAC @ 3 kVA

    Can test ~ 50 of cable

    60 Hertz

    40 kVAC @ 1.2 kVA

    Can test ~ 5 miles of cable

    0.1 0.02 Hertz

    60 Hz. vs. 0.1 Hz.

  • 10/8/2004 16

    Can Now AC Stress Test Cable

    z With VLF units, utilities, testing services, industrials, and others can now AC stress test cables in the field.

    z Just like with vacuum bottle or rubber glove testing, now a go/no-go test can be performed on power cable.

    z If a cable cant hold 2 3 times normal voltage, its not healthy. Find out now, make the repair, and move on.

    z At the very least, every newly installed and/or repaired cable should be VLF tested before energizing, since many failures are due to installation damage or faulty workmanship.

  • 10/8/2004 17

    The First VLF Models Original marketed designs were European. Very large, heavy, expensive. Thus, limited

    practical application. 1997 new VLF technology was introduced.

    Smaller - lighter - less expensive. Now used worldwide for cable testing.

  • 10/8/2004 18

    VLF with Sinusoidal Waveform Advantages

    z Stress Similar to Service Conditions.z Light Weight.z Low Cost.z Simple to Use.z Can Be Used For Diagnostic Testing.

    (tan-delta and partial discharge)

  • 10/8/2004 19

    VLF Applications Power Cable. Large Rotary Machines. Diagnostic Testing:

    z Tan z Partial discharge

  • 10/8/2004 20

    North American Standards For VLF Testing Of Cable

    IEEE 433-1974 covers VLF testing for rotating machinery.now being updated

    IEEE 400-2001 overall cable testing standard sanctions VLF testing of cables.

    IEEE 400.2 sub-standard specific to VLF cable testing

  • 10/8/2004 21

    Recommends test voltage of 3V0 peak(V0 equals line-to-ground voltage).Test duration is 15 60 minutes.

    Recommendation is for 30+ minutes*

    * Based on >15,000 tests by TNB Malaysia

    IEEE VLF Std 400.2/D3 (11/03)

  • 10/8/2004 22

    System Voltage

    phase to phase

    kVrms

    5

    15

    25

    35

    Installation

    phase to ground

    kVrms/kVpeak

    9/12

    18/25

    27/38

    39/55

    Acceptance

    phase to ground

    kVrms/kVpeak

    10/14

    20/28

    31/44

    44/62

    Maintenance

    phase to ground

    kVrms/kVpeak

    7/10

    16/22

    23/33

    33/47

    ---------------------- 0.1 Hz Test Voltage --------------------

    Suggested IEEE Field Test Voltages

    For Shielded Power Cable Systems

    Using Sine Wave Output VLF

    Test voltages are generally 2.5 3 time the line-to-ground system voltage.

    The above per IEEE400.2/D3 dated 11/03.

  • 10/8/2004 23

    The World View Of VLF

    IEEE 2 3Vo for 15-60 minutes30+ minutes @ 3Vo recommended.

    Germany 3Vo for 60 minutes

    Japan 3Vo for 15 minutes

    Malaysia 3Vo for 30 minutes Over 40 countries have purchased the HVI VLF

  • 10/8/2004 24

    Cable German Test Voltage

    Insulation DIN-VDE 0.1 Hz DC AC: 46-62 Hz

    Type Spec. Test Level Duration Test Level Duration Test Level Duration

    PVC0276-620

    0276-10013 x U0 30 Min. 6/10kV:34-48kV

    12/20kV:67-96kV18/30kV:76-108kV

    15-30 Min.15-30 Min.15-30 Min.

    2 x U0 30 Min.

    XLPE0276-620

    0276-10013 x U0 60 Min. DC Test was Withdrawn N/A 2 x U0 60 Min.

    Paper/Oil0276-621

    0276-10013 x U0 30 Min. 6/10kV:34-48kV

    12/20kV:67-96kV18/30kV:76-108kV

    15-30 Min.15-30 Min.15-30 Min.

    2 x U0 30 Min.

    VLF Test Duration for mixed paper/PE-XLPE insulated cables should be 60 minutes.Criterion for a successful test is no flashover.

    AC VLF test level is 3 x U0 and test duration depends on type of cable insulation.

    German Standard

  • 10/8/2004 25

    IEC 60060-3

    Standard for field testing power cable.

    Updated to add VLF Hipot testing.

    2 3 times V0 for 15 minutes.

  • 10/8/2004 26

    If cable passes the above test, there is a 97% probability that cable will last 3 or 5 years.

    2.8/3.0 Uo2.2/2.4 Uo1.8/1.9 Uo

  • 10/8/2004 27

    ANSI IEEE Std. 433-1974 (1974)z Recommended Practice For Insulation Testing of Large

    AC Rotating Machinery with High Voltage VLF.z Refers to Large AC Machines 10 MVA/6 kV & above.z Test Waveform: Sinusoidal.z Test Frequency: 0.1 Hz.

    North American Standards

  • 10/8/2004 28

    IEEE/EPRI RecommendationsVLF TEST PROCEDURE

    1. Apply 2 3Vo voltage for 30+ minutes.2. If cable holds voltage, cable is good, test is over.3. If cable fails, repair and start test over.4. If cable then holds, cable is good, test is over.5. If cable fails again, repair and resume test or stop

    test and replace cable soon, depending on nature of failures. Or, perhaps conduct a tan delta test.

  • 10/8/2004 29

    How to VLF Testz Isolate cables ends like with DC testing.z Connect HV lead to conductor ground to shield.z Apply HV to cable in several steps. Not to measure leakage

    currents but helpful in determining where cables fail.z There are no leakage currents read. Test is go/no-go z Wait the desired test time.z If cable holds, test is over. De-energize.z If cable fails, make repairs and repeat test.

  • 10/8/2004 30

    Growth rate at 0.1-Hzsinusoidal test voltage

    (mm/h)2.3

    10.9-12.658.3-64.2

    336

    Test voltage factor(V/Vo )

    2345

    XLPE Tree Growth RatePer IEEE 400-2001

    A 15kV 133% cable has an insulation thickness of 5.9 mm.In a 30 minute test, nearly all defects will grow to failure.

  • 10/8/2004 31

    The Move To VLF

    Why Utilities Worldwide Have Switched to VLF

    To Not Perform Any Cable Testing Is Unacceptable DC Testing Is Out AC Testing Is The Most Desirable

    Most Diagnostic Methods Are Inconclusive & Expensive

    A VLF Test Is Easily Performed With Results Certain

    Worldwide Standards Exist

  • 10/8/2004 32

    VLF Vendors

    High Voltage, Inc. NY, USA

    Baur Austria

    Seba/KMT (HDW) Germany

  • 10/8/2004 33

    Waveform Outputs

    High Voltage, Inc. Sine Wave

    Baur Sine Wave

    Seba/KMT (HDW) Cosine Rectangular(Trapezoidal)

    * Sine wave needed for pd and td diagnostics

  • 10/8/2004 34

    Model Sizes Available(all vendors included)

    Voltage ratings from 20 kV 200 kV

    Load ratings from 0.4 uF 50 uF

    For a 15 kV cable, 0.4 uF can test ~4000, 50 uF can test >50 miles.

  • 10/8/2004 35

    Users Of VLF

    VLF is now embraced worldwide as the most effective method of cable testing.

    Over 350 VLF units have been shipped from High Voltage, Inc. over the last four years, delivered to 30+ countries and numerous US locations. Other VLF products have shipped from other vendors

    for even more years.

  • 10/8/2004 36

    Worldwide Users of VLF

    HVI has shipped over 350 VLF products to the following:USACanadaTaiwanIndonesiaSo. KoreaAustraliaSaudi ArabiaEnglandCosta Rica

    So. AfricaSingaporeHong KongBelgiumPuerto RicoHollandNew ZealandJapanMalaysia

    Slovak RepublicCzech RepublicChinaDubai, UAEVietnamPanamaJordanGermany

  • 10/8/2004 37

    In SummaryVLF testing:z Has the virtues of DC test equipment (low cost, small size,

    light weight, easy to use) but is AC.z Does not have the negative consequences of DC.z Requires 1/600 1/6000 of the kVA of power frequency.z Can be used for breakdown tests and predictive tests such as

    Tan Delta and Partial Discharge. (sine wave VLF units)z Internationally accepted Standards exist and more are in the

    process of issuance.

  • 10/8/2004 38

    Conclusionz The surest way to verify voltage withstand capability of

    any load is perform an AC stress test.z Its easy and certain. The load holds voltage or fails.z VLF testing is easily performed with minimal training.z Worldwide standards and years of history exist.z Some VLF models are very portable and affordable.z VLF makes Tan Delta diagnostic testing possible.

  • 10/8/2004 39

    PAUSE

  • 10/8/2004 40

    Dissipation Factor or Loss Angle Measurement For Power Cables

    Non Destructive Testing To Determine Insulation Quality

    (Similar to Power Factor Testing)

    Tangent Delta or Tan

  • 41

    Tan Delta MeasurementUsing VLF @ 0.1 Hz

    z Excellent predictive tool for determining the integrity of insulation z Absolute values, variations, and trending of values are of interest for

    predicting insulation integrityz Evaluates over all condition of cable (rather than localized problems

    as with PD measurement) z Tan Delta is more easily measured at VLF (magnitude increases as

    frequency decreases)z Requires VLF sinusoidal applied test voltagez Excellent way to evaluate Water Trees

  • 42

    Simplified Cable Model and Phasor DrawingTan Delta = IR/ IC - measured in radians

    With perfect insulation, a cable is a near perfect capacitor, with a 90 phase shift between voltage and current. Less than 90 indicates insulation degradation. Cables can be rated good, marginal, or bad.

    The tangent of this angle is calculated

    I

    V

    IC

    IR

    IR IC

    = tangent of C R

    Cable insulation Cable Cross Section

  • 43

    Characteristics of Water Trees

    z Addition of a new parallel R- C component

    z Water trees increase resistive current through insulation

    z The R component is voltage dependent (nonlinear I = V/R)

    z Tan Delta becomes a function of voltage

  • 10/8/2004 44

    Are There Established TD Numbers?(Table from IEEE400-2001)

    Above numbers are at 20C. Numbers vary with temperature. Consult your cable vendor.

  • 10/8/2004 45

    What do the numbers mean?

    Absolute and differential values are meaningful.

  • 10/8/2004 46

    Tan Delta Test ProcedureMeasurements are recorded at

    numerous voltage levels. Loss angle versus voltage important.

    Recommended voltage test points are:

    0.5 Uo, .75 Uo, 1.0 Uo, 1.25 Uo,

    1.5 Uo, 1.75 Uo & 2 Uo.

  • 47

    Tan Delta vs.Voltage for New and Aged XLPE Cables

    New and Aged 15 kV XLPE Cable (Nov 2000)

    0

    0.01

    0.02

    0.03

    0.04

    0.05

    0.06

    0 2.5 5 7.5 10VLF Voltage (kV rms)

    L

    o

    s

    s

    A

    n

    g

    l

    e

    (

    T

    a

    n

    D

    e

    l

    t

    a

    )

    Aged

    New Cable

    New cablelinear tan delta #s

    versus voltage

    Aged cablenon-linear tan

    delta #s versus voltage

  • 10/8/2004 48

    0.1 Hz phase 1 phase 2 phase 3 phase 1 phase 2 phase 3x Vo tgdelta L1 tgdelta L2 tgdelta L30.5 0.0018 0.0008 0.0013 (2Uo-Uo) (2Uo-Uo) (2Uo-Uo)1.0 0.0019 0.0009 0.0014 0.0035 0.0018 0.00251.5 0.0026 0.0011 0.0019 0.0019 0.0009 0.00142.0 0.0035 0.0018 0.00252.5 0.0044 0.0026 0.0032 0.0016 0.0009 0.0011

    0.0000.0020.0040.006

    0.0 1.0 2.0 3.0Voltage x Vo

    t

    a

    n

    d

    e

    l

    t

    a

    L2: tg delta 0.1Hz L3: tg delta 0,1HzL1: tg delta 0.1Hz

  • 10/8/2004 49

    TD at 0.1 Hz vs. 60 Hz.

    Why Do We Use VLF?TD numbers higher at 0.1 Hz versus 60 Hz

    Equipment far smaller, lighter, and less expensive, VLF can test longer cable runs than 60 Hz systems.

    VLF may be more effective for TD measurements of unheated cable (most test conditions).

  • 10/8/2004 50

  • 10/8/2004 51

    Tan Delta Loss Analyzer

    HV divider Signal analyzer/controller

    60kV model

    Used with VLF as voltage source

  • 10/8/2004 52

    Loss AngleAnalyzer

    VLF Control

    VLF

    M

    e

    a

    s

    u

    r

    i

    n

    g

    U

    n

    i

    t

    Cable Under Test

    Fiber Optic Cables

    Tan Delta

    Test Set Up

  • 10/8/2004 53

    Tan Delta TestingAdvantagesz Less destructive than VLF or 60 Hz testingz Allows prioritization of cable replacementz Easier to use and interpret than other diagnostic methods

    Disadvantagesz Can be destructive if cable very degraded.z Gives overall condition of cable, not singularitiesz Not best for mixed type cable runsz More useful with historical data

  • 10/8/2004 54

    Other Diagnostic Methods

    z Partial Discharge On-Linez Partial Discharge Off-Linez Current Relaxationz Voltage Recoveryz Oscillating Wave Test (Partial Discharge)

  • 10/8/2004 55

    Explanation of Methods

    z Except Pd testing, methods are based on predictable properties of capacitance

    z Voltage/Current charging & discharging is predictable in a perfect capacitor

    z Imperfections in a cable alter this normz Measurements can determine level of cable

    insulation impuritiesz For partial discharge testing, location and

    amplitude of pd can be measured

  • 10/8/2004 56

    Advantages/Disadvantages

    Advantagesz Non destructive (although not in all cases)

    Disadvantagesz Results highly interpretive and often unrepeatablez Most methods are very expensivez Some methods unproven for accuracy in the fieldz Require skilled operatorz Insufficient data of acceptable/unacceptable Pd levels

    and other parameters to make test results conclusive

  • 10/8/2004 57

    Utilities and others need a method that is:

    Affordable

    Portable

    Easy to use

    Offers conclusive results

  • 10/8/2004 58

    Conclusion

    VLF is the most effective method of exposing cable and accessory defects. With the addition of Tan Delta and Pd testing, hipoting and diagnostics are achieved.

    VLF is suitable for use on cables and rotating machinery.

    Worldwide standards exist for both. IEEE, VDE, CEA, EPRI, other countrys engineering organizations, cable manufactures, and major utilities all recommend VLF.

    Hundreds of users worldwide have embraced VLF

  • 10/8/2004 59

    Thank You

    Mike Peschel - High Voltage, Inc.

    www.hvinc.com

  • 10/8/2004 60

  • 10/8/2004 61

  • 10/8/2004 62

    VLF Cable Check

    Model VLF-25CM

    0 - 25 kV Peak0.1 Hz @ 0.4 f Load

    ~ 4000 ft of 15 kV CableSingle Piece Design

    Weight: 69 lbs/30 kgONLY

  • 10/8/2004 63

    VLF AC Hipot

    Model VLF-4022CM

    0 - 40 kV Peak

    0.1 Hz @ 1.1 f Load0.05 Hz @ 2.2 f Load0.02 Hz @ 5.5 f Load

    Controls: 50 lbs/22 kgHV Tank: 72 lbs/31 kg

  • 10/8/2004 64

    VLF AC Hipot

    Model VLF-6022CM

    0 - 60 kV Peak

    0.1 Hz @ 1.1 f Load0.05 Hz @ 2.2 f Load0.02 Hz @ 5.5 f Load

    Controls: 55 lbs/25 kgHV Tank: 100 lbs/45 kg

  • 10/8/2004 65

    VLF AC Hipot

    Model VLF-12011CM

    0 - 120 kV Peak

    0.1 Hz @ .55 f Load0.05 Hz @ 1.1 f Load0.02 Hz @ 2.75 f Load0.01 Hz @ 5.5 f Load

    Weight: 565 lbs/257 kg

  • 10/8/2004 66

    Other VLF ModelsVLF-50CM 0 50 kV @ 50 F @ 0.01Hz 0.1 0.01 Hz

    Tests up to 50 kilometers of cable.

    VLF-65CM 0 65 kV @ 2.2 F @ 0.1Hz 0.1 0.01 Hz0 65 kV @ 22 F @ 0.01Hz

    VLF-200CM 0 200 kV @ 0.55 F @ 0.1Hz 0.1 0.01 Hz0 200 kV @ 5.5 F @ 0.1Hz

  • 10/8/2004 67

    VLF THUMPERURD Cable Care System

    Only Combination VLF AC Hipot and Thumper

    VLF Output: 30 kVAC peak

    Load Rating: 1.0 uF @ 0.1 Hz ~ 1.5 miles of 15 kV cable

    Discharge: 0 8 kV @ 500 J

    VLF Cable Burning Mode

    Radar Ready

  • 10/8/2004 68