high voltage cable testing using ac voltage.pdf
TRANSCRIPT
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การเปลี�ยนวธิีการทดสอบสายใตด้ินแรงสูงจาก DC เป็น AC
ตามมาตรฐาน IEC 60840 (2004)ตามมาตรฐาน IEC 60840 (2004)
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IEC 60840 (2004)
No DC voltage is No DC voltage is No DC voltage is No DC voltage is No DC voltage is No DC voltage is No DC voltage is No DC voltage is
specified for specified for specified for specified for
Insulation test Insulation test Insulation test Insulation test
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Defects in Cable & Accessories
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Defects in Cable & Accessories
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Why Not DC ?
� Stress created by DC field (resistivity) is different from 50 Hz AC field (permittivity).
� Even massive insulation defects massive insulation defects massive insulation defects massive insulation defects in extruded dielectric insulation cannot be detected with DC at the recommended voltage levelsdielectric insulation cannot be detected with DC at the recommended voltage levels
� Space (trapped) charge Space (trapped) charge Space (trapped) charge Space (trapped) charge development at the sites of water trees or other defect sites
� Only finds conductive type gross workmanship conductive type gross workmanship conductive type gross workmanship conductive type gross workmanship errorserrorserrorserrors in extruded dielectric cable systems
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Example of Failure
สายส่งสถานีย่อยทววีฒันา
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Example of Failure
สายส่งสถานีย่อยเสาระหง
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Example of Failure
สายส่งสถานีย่อยแสนแสบ
24/02/588888
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Example of Failure
สายส่งวภิาวด ี– สามย่าน MH 76
24/02/589999
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Example of Failure
สายส่งวภิาวด ี– สามย่าน MH 8
24/02/5810101010
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Conductive Type Defect Revealed by DC Test
สายส่งแจ้งวฒันะ – เมอืงทอง
24/02/5811111111
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Space Charge
DC hipot output negatively charge up void. These trapped space charges remain after test. When AC is reapplied,
there’s a high difference of potential across very little insulation. Leads to electrical trees – cable fails.
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Partial Discharge
� Localized electrical breakdown taking place in the electrical insulation system under voltage stress that only partially bridged the insulation between conductors and which may or may not occur adjacent to a conductorbetween conductors and which may or may not occur adjacent to a conductor
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Partial Discharge
Electric Stress Distribution With No Void
( 12.7 kV rms on the cable conductor )
Electric Stress Distribution With a Void
( 12.7 kV rms on the cable conductor )
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Partial Discharge
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Partial Discharge
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What Choices Do We Have ?
� AC voltage at power frequency
� AC resonance voltage
� ACRL test voltage
� ACRF test voltage� ACRF test voltage
� AC oscillating wave voltage (OWTS)
� Very Low Frequency voltage (VLF)
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IEC 60840 Test Voltage
Rated voltageHighest voltage for equipment
Value of U0 for Determination of test voltages
Voltage test after
installation
U (kV) U (kV) U (kV) (kV)U (kV) Um (kV) U0(kV) (kV)
45 to 47 52 26 52
60 to 69 72.5 36 72
110 to 115 123 64 128
132 to 138 145 76 132
150 to 161 170 87 150
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Power Frequency Test Voltage
� A voltage of U0 applied for 24 h (IEC 60840-2004)
� The cable to be tested is connected to the
network in normal operation by means of a
power transformer of which the neutral point
network in normal operation by means of a
power transformer of which the neutral point
of the secondary wye is not grounded. Upon
connecting one phase of the cable to ground
during a previously determined period, the
other two phases will be exposed to √3 times the nominal voltage with respect to earth (from
IEEE Transaction 1992).
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AC Resonant Voltage
�AC voltage testing uses alternating current at
frequencies between 20Hz and 300Hz is an
effective method to energize onsite all types of
cable systems. As compared to AC voltage
stresses during factory testing and service stresses during factory testing and service
operation it is recommended for withstand testing.
�HVAC withstand test: HVAC withstand test: HVAC withstand test: HVAC withstand test: The cable section can be
accepted if after application of a selected HVAC
voltage stress for a recommended duration no
breakdown has occurred.
�DiagnosisDiagnosisDiagnosisDiagnosis: At certain voltage levels partial
discharges, dielectric losses can be measured in
function of time/voltage and used for diagnostic
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AC Resonant Voltage
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AC Resonant Voltage
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AC Resonant Voltage
On-site test of a 245 KV cable system on Los Angeles Water
and Power Administration /USA
Testing of the 400 kV cable system of London with a
length of more than 20 km
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Damped AC Voltage
� Damped AC voltage testing uses damped alternating
current at frequencies between 20Hz and 500Hz. In
combination with partial discharge measurement it is an
effective method in testing on-site all types of cable
systems. Due to similarity in partial discharges
occurrence at AC voltage stresses during factory testing
systems. Due to similarity in partial discharges
occurrence at AC voltage stresses during factory testing
and service operation it is recommended for on-site
testing and PD measurements.
� DAC withstand testDAC withstand testDAC withstand testDAC withstand test: The cable section can be stressed
with a selected DAC voltage stress for selected time
duration and the cable section can be rejected if a
breakdown has occurred.
� DiagnosisDiagnosisDiagnosisDiagnosis: At certain voltage levels partial discharges,
dielectric losses can be measured in function of
time/voltage and used for diagnostic purposes.
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Damped AC Voltage
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Damped AC Voltage
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Damped AC Voltage
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Damped AC Voltage
PD diagnosis of a service aged 150kV XLPE cable
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Damped AC Voltage
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Very Low Frequency Voltage
�Very low frequency (VLF) voltage testing uses
frequencies down to 0.01Hz to test on-site the all
types of cable insulation. Due to much lower
frequency range as compared to AC voltage
stresses, VLF testing is based on the fact that stresses, VLF testing is based on the fact that
insulation defects have to breakdown during time
of testing.
�VLF withstand testVLF withstand testVLF withstand testVLF withstand test: The cable section can be
rejected if after application of a selected VLF
voltage stress for a recommended duration
breakdown has occurred.
�DiagnosisDiagnosisDiagnosisDiagnosis: At certain voltage levels partial
discharges, dielectric losses can be measured in
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Very Low Frequency Voltage
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Programmable voltage waveforms
Sinewave test voltage at 0,1 Hz:
Squarewave voltage at 0,1 Hz with defined slew -rate:
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Very Low Frequency Voltage
VLF HV test and diagnosis (DF&PD) system up to VLF HV test and diagnosis (DF&PD) system up to VLF HV test and diagnosis (DF&PD) system up to VLF HV test and diagnosis (DF&PD) system up to 400400400400kVrms, kVrms, kVrms, kVrms,
600600600600kV DC up to kV DC up to kV DC up to kV DC up to 7777µFFFF
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Utility Practice
� KOREAKOREAKOREAKOREA: 24 hours working AC voltage test or VLF with PD measurement. � VLF for lower voltage cable (distribution cables 22.9
kV).
� Working voltage for 154kV and above.
In future, OWTS may be applied for distribution � In future, OWTS may be applied for distribution cables. AC withstand voltage test will be applied for transmission cable.
� JAPANJAPANJAPANJAPAN:10 mins working AC voltage test with construction check for 154kV class or less, 24-hours AC withstand test (about 1.7 U0) with PD measurement for 220KV and above
From IERE technical meeting in 2007
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Utility Practice
� EDFEDFEDFEDF high voltage insulation testing policy (2010):
� The cable shall withstand an ac test voltage applied between a conductor and sheath or all conductors with the sheath earthed. Where applied between a conductor and sheath or all conductors with the sheath earthed. Where possible a Partial Discharge (PD) test shall be carried out during the ac test.
� The test will normally be provided by a series resonant test set operating close to power frequency.
Rated Line Rated Line Rated Line Rated Line
VoltageVoltageVoltageVoltage
(kV)(kV)(kV)(kV)
Ac Test Voltage for Ac Test Voltage for Ac Test Voltage for Ac Test Voltage for
New Cable SystemsNew Cable SystemsNew Cable SystemsNew Cable Systems
(kV)(kV)(kV)(kV)
FrequencyFrequencyFrequencyFrequency
(Hz)(Hz)(Hz)(Hz)
DurationDurationDurationDuration
(min)(min)(min)(min)
66 7220-300 60
132 132
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Utility Practice
� Energy AustraliaEnergy AustraliaEnergy AustraliaEnergy Australia: Network Standard – Specification for Testing of Underground Cable (2004) � High Voltage DC Tests shall not be applied routinely to XLPE
insulated sub-transmission cables (123 kV) and/or accessories.
� Prior to commissioning, sub-transmission XLPE insulated cables shall be subject to VLF test voltages (preferred), or alternatively energized only at power frequency system voltages for a period of 24 hours before carrying load current.energized only at power frequency system voltages for a period of 24 hours before carrying load current.
� The test duration may be reduced at the discretion of the System Operator
� A VLF test, if available, is preferred to a system voltage test.
� For XLPE cables, it is accepted that for the present, unipolarpulsed test voltages shall be required for fault location.
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Which Direction Shall MEA Go ?
Shall MEA continue with DC Shall MEA continue with DC Shall MEA continue with DC Shall MEA continue with DC
Test ?Test ?Test ?Test ?Test ?Test ?Test ?Test ?
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Which Direction Shall MEA Go ?
30 30 30 30 MBMBMBMB
25252525 MBMBMBMB
> > > > 30303030 MBMBMBMB
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