13 Ed Gulski Praesentation

Stuttgarter Hochspannungssymposium 6/7 März 2012

Die Anwendung von gedämpften Weichselspannungen für Vor-Ort Prüfung und Zustandsbestimmung von

Hochspannungskabeln

Edward GULSKI, onsite hv solutions, Switzerland

Robert BACH, onsite hv technology, Germany


Die Anwendung von gedämpften Weichselspannungen für Vor-Ort Prüfung und

Zustandsbestimmung von Hochspannungskabeln

1. General aspects of modern testing of (E)HV power cables

2. Damped AC voltage 3. Monitored testing procedures 4. Field examples 5. Conclusions


New installed cables

Important issue: to exclude poor workmanship

(installation defects)

Quality / system integrity of the cable circuit

HV and EHV power cables for rated voltages up to 380 kV

More details in Cigre Brochures No. 279 and No. 358

Testing


Service aged cables

Important issue: to detect local aging and check insulation

degradation status

Availability / reliability of the cable circuit

HV and EHV power cables for rated voltages up to 380 kV

More details in Cigre Brochures No. 279 and No. 358

Diagnosis


Cable type

Test purpose DC VLF 0.1Hz AC 20-300Hz DAC 20-300Hz

Transmission networks (E)HV

XLPE Installation test / Acceptance test

No** No* Yes Yes

Maintenance test / Diagnostic test

No** No* Yes Yes

Oil-filled

Installation test / Acceptance test

Yes No* Yes Yes

Maintenance test / Diagnostic test

No No* Yes

Yes

Internationally not recommended Internationally in use

Modern On-site Testing and Diagnosis

* according to [1] IEC 60840 Power cables with extruded insulation and their accessories for rated voltages above 30 kV (Um = 36 kV) up to 150 kV (Um = 170 kV) Test methods and requirements. [2] IEC 62067, Standard Power cables with extruded insulation and their accessories for rated voltages above 150 kV (Um = 170 kV) up to 500 kV (Um ** according to [3] Recommendations for a new after laying test method for HV extruded cable systems CIGRE 1990, Paris, paper 21-105 [4] CIGRE WG 21-09; After-laying tests o HV extruded cable systems; Elektra 173, August 1997


After-laying testing of new installed HV and EHV cables

using DAC Technology

Damped AC (DAC) voltage application has been introduced end of 80’s by Cigre Study Committee 21 Insulated Cables as an effective method for on-site testing,

represents the newest technological progress in power electronics and advanced signal processing,

is characterized by

lightweight and high level of mobility, compactness versus output voltage, system assembling and voltage erecting

effort, necessary power demand for long lengths, possibility of sensitive PD detection and

dissipation factor



1. Electrical stress versus withstand destructiveness: – breakdown effectiveness for insulation defects: AC and DAC are

complementary /alternative methods, – harmless or harmful for defect free insulation: is harmless for the

dielectric, if no artificial defects are present,

2. Influences of the DAC test parameters: – DAC frequency: no significant effect – the damping rate: does not play an important role – number of excitations: appears to be an important parameter; the

breakdown voltage decreases as the number of shots increases – charging time: does not seem to have an important effect

[Ref] Aucourt, C., Boone, W., Kalkner, W., Naybour, R.D. Ombello, F. "Recommendations for a New After Laying Test Method for High Voltage Extruded Cable Systems." CIGRE Paper No. 21-105, August, 1990

What is damped AC voltage ?


[Ref]: 8th ISH Yokohama (1993)

Using damped AC voltage used was 10kHz (called oscillating voltage) and regarding other alternative voltages conformity has been found for:

- PD inception voltage for strong inhomogeneous configuration - Treeing growth in new and old XLPE cable insulation for strong inhomogeneous

configuration


On-site testing and PD measurement on a 150 kV XLPE cable at KEMA, The Netherlands, 1994 [Ref] ISBN 90-73192-5-6

On-site testing and PD measurement on a 150 kV external gas pressurized cable at a Dutch utility Nuon, The Netherlands, 2007

What is damped AC voltage ?

technological progress

Example of a continuous AC voltage source

Example of a damped AC voltage source


General purpose of using DAC voltages

[Ref] IEEE PES Insulated Conductor Committee Spring 2008 Meeting, Minutes F05D Damped AC Voltages Testing

International survey about using damped AC voltages (2007)


for dielectric losses

measurement

for DAC voltage withstand testing including partial discharge measurement

for DAC voltage withstand testing

23%

25% 52%


System in use: up to 350 kV damped sinusoidal voltages (DAC) in the frequency range of 20Hz up to 500Hz, Technology has been introduced by Lemke Diagnostics and SebaKMT in Germany and by Seitz Instruments AG in Switzerland end of 90’s, In last 12 years worldwide about 350 DAC systems are successfully implemented for testing and diagnosis of distribution and transmission power cables using different DAC solutions.

0255075

100125150175200225250275300325350375

1999 2004 2005 2006 2007 2008

Year

Max

. tes

t vol

tage

DAC Testing


Weight: 960kg Supply voltage: 5kW Output: DAC 250kVpeak (20Hz - 300Hz) Test object: power cables 220kV up to 30km

250kV DAC system for testing (E)HV power cables up to 30km length


1. After laying testing package before service operation 2. Package condition monitoring during service operation

Example: After laying testing package before service operation 380kV

Power cable circuit

OWTS HV Technology

damped AC voltage source (20Hz-300Hz)(IEC60270) PD detection at the near termination


DAC system max. 150kV DAC system max. 250kV DAC system max. 350kV

DAC systems for testing (E)HV power cables

Network voltage [kV] Type HV 150

x U0 Type HV 250

x U0 Type HV 350

x U0

50 3.7 - -

66 2.8 - -

110 1.7 2.8 -

132 1.4 2.3 3.2

150 1.2 2.0 2.9

220 0.8 1.4 1.9

230 - 1.3 1.9

330 - 0.9 1.3

380 - - 1.1


Examples of typical damped ac voltage frequencies for different lengths of two typical 230kV power cables

Length [km]

XLPE (C=200pF/m)

[Hz]

Oil filled (C=350pF/m)

[Hz] 0.25 258 195 0.5 183 138 1 129 98

2 91 69 4 65 49 8 46 35

16 32 24 20 29 22

OWTS® HV Technology

DAC 250 kV system

E.g. testing with damped AC (29Hz) of 20km 230kV XLPE Cable possible with one system of 970kg)


Applicability for HV and EHV power cables

Results of several successful comparison tests as published by Cigre (1990), TU Delft/Kema (1999), Cesi (2002), Singapore Power (2007), EuroTest (2007), TU Helsinki (2007), Prysmian Cables and Systems BV (2009), EPRI State Grid, China (2010), Twentsche Kabel Fabriek BV (2010)

All comparison tests have demonstrated the applicability of damped ac (dac) voltages !

Damped sinusoidal ac voltages in the range of 20Hz- 300Hz are

equivalent to continuous 20Hz- 300Hz ac voltages

OWTS® HV Technology


General IEC 60060-3: High Voltage test techniques Part 3: Definitions and requirements for on-

site testing; On-site testing IEEE 400: Guide for Field Testing and Evaluation of the Insulation of Shielded Power Cable

Systems Rated 5 kV and Above; HD 632 S2 (CENELEC): Power cables with extruded insulation and their accessories for

rated voltages above 36kV (Um=42kV) up to 150kV (Um= 170kV) IEC 60840: Power cables with extruded insulation and the accessories for rated voltages

above 30kV up to 150kV Test methods and requirements; IEC 62067: Power cables with extruded insulation and the accessories for rated voltages

above 150kV; IEEE 400.4: Guide for Field-Testing of Shielded Power Cable Systems Rated 5 kV and

Above with Damped Alternating Current Voltage (DAC) (draft under preparation) Standardized PD detection IEEE 400.3: Guide for PD Testing of Shielded Power Cable Systems in a Field Environment; IEC 60270: Partial discharges measurements; IEC 885-3: Test methods for partial discharges measurements on lengths of extruded

power cable; Dissipation Factor measurement IEC 60141: Tests on oil-filled and gas-pressure cables and their accessories; IEEE 1425: Guide for the Evaluating of the Remaining Life of Impregnated Paper-insulated

Transmission Cables Systems

Important international recommendations used


DAC voltage excitation

Display snapshot: 250kV damped AC with standardized PD measurement


Damped AC voltage excitation

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Energizing phase

Time scale in [s]

Switching phase

Time scale in [μs]

0……………… …………e.g. 10

U [kVpeak]

t [s] t [ms]

LC resonance phase

Time scale in [ms]


HV Inductor

HV Switch

DUT

kV

dU/dt

HV power source HV Inductor

HV Switch

DUT

(b)

(a)

HV Divider

PD Detector

PD

HV Divider

PD Detector

PD


HV Switch

DUT

kV

dU/dt


HV Switch

DUT

(b)

(a)

HV Divider

PD Detector

PD

HV Divider

PD Detector

PD

HV power source

Damped AC test circuit

Energizing phase

LC resonance phase

Test object

Test object


Important Characteristics of DAC Testing

Damped AC stress represents E-stresses similar to factory testing conditions: Energizing phase: due to AC field distribution no DC stress, due to continuous uni-polar voltage increase no steady-state condition, due to E-field (< 20kV/mm) and relatively short durations (tens of seconds) no space charge accumulation, due to immediate switching after the maximum voltage is reached, no steady state condition, Switching phase: due to low cable inductance no transient over-voltages, LC resonance phase: due to AC stresses similar condition for PD inception, PD amplitudes due to AC stresses similar behavior for breakdown condition of homogenous defects, due to bipolar AC discharging process no remaining charges


DAC test voltages levels (20 Hz..500 Hz) as recommended for DAC testing (50 DAC excitations) of new installed power cables. Power cable rated voltage

[kV]

Uo [kV] DAC test voltage level VT

[kVpeak] *

N x Uo

6 3.6 13 1.7 10 6 21 1.7 15 8.7 31 1.7 20 12 42 1.7 30 18 64 1.7

45-47 26 74 2.0 60-69 36 102 2.0

110-115 64 181 1.7 132-138 76 187 1.73 150-161 87 212 1.73 220-230 127 254 1.42 275-287 160 297 1.31 330-345 190 353 1.32

DAC Testing


DAC test voltages levels (20 Hz..500 Hz) as recommended for maintenance testing (50 DAC excitations) of repaired /refurbished power cables. Power cable rated voltage

[kV]

Uo [kV] DAC test voltage level VT

[kVpeak]

N x Uo

6 3.6 10 1.36 10 6 17 1.36 15 8.7 25 1.36 20 12 34 1.37 30 18 51 1.36

45-47 26 60 1.6 60-69 36 82 1.6

110-115 64 145 1.36 132-138 76 150 1.4 150-161 87 170 1.4 220-230 127 203 1.14 275-287 160 238 1.05 330-345 190 282 1.05 380-400 220 294 1.0

DAC Testing


Basic parameters of damped AC testing Maximum DAC test voltage level VT [kVpeak] see tables maximum

DAC test voltage levels

Test voltage steps ΔV [kVpeak] 0.2U0

Number of DAC excitations per voltage step: NDAC/ ΔV 5 DAC voltage withstand test duration NDAC 50

ΔV e.g. 0.2Uo

NDAC e.g. 5

DAC voltage withstand phase

Test duration: NDAC e.g. 50

DAC voltage withstand level

DAC volta

ge incre

ase p

hase

PD free

?

If yes

-> in

creas

e

If no -

> eva

luate

VT

ΔV e.g. 0.2Uo

NDAC e.g. 5

DAC voltage withstand phase

Test duration: NDAC e.g. 50

DAC voltage withstand level

DAC volta

ge incre

ase p

hase

PD free

?

If yes

-> in

creas

e

If no -

> eva

luate

VT

DAC Testing


New installed cables Repaired / refurbished cables

Service aged cables

Acceptance test Diagnostic test

DAC voltage

withstand test

Monitored Non-monitored Evaluation

Diagnostic parameters partial discharges (PD)

dissipation factor (tanδ)

criteria Pass/Fail

Maintenance test

Testing Procedures


1. The duration of the test is determined by a number of DAC excitations e.g. 50 which have been applied to the test object at a selected max. DAC test voltage.

2. The maximum DAC withstand voltage level is determined by the voltage peak values VDAC respectively RMS-values VDAC/√2 of the 1st DAC cycle. 1. The best-practice (IEEE D3 400.4) shows that: a) In case of after-laying testing of new cables the max. test voltage levels are used

conform the IEC standards or national regulations b) In the case of maintenance / diagnostic testing the max. test voltage levels are

reduced to 75%..80% c) The duration is based on a number of DAC excitations is fixed at 50x at maximum

test voltage level d) In the case of short cable length where the duration of 50 DAC excitations is much

shorter than 1 hour, then 1 hour of DAC excitations is recommended

Principles of DAC withstand test

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

VT [kV] VT [kV] VT [kV]


Monitored testing using DAC

End test timeStart test time

increase phase withstand phase increase phase withstand phase

Bre

akdo

wn

Bre

akdo

wn

(a) (b)

(c)

DAC

max

imum

test

vol

tage

DAC

max

imum

test

vol

tage

PD

PDPD

NDAC End test timeStart test time NDAC

DAC

max

imum

test

vol

tage increase phase withstand phase

PD background noise

End test timeStart test time NDAC

(d)

DAC

max

imum

test

vol



End test timeStart test time

increase phase withstand phase increase phase withstand phase

Bre

akdo

wn

Bre

akdo

wn

(a) (b)

(c)

DAC

max

imum

test

vol

tage

DAC

max

imum

test

vol

tage

PD

PDPD

NDAC End test timeStart test time NDAC

DAC

max

imum

test

vol


PD background noise


(d)

DAC

max

imum

test

vol




Evaluation monitored testing of (E) HV power cables using DAC

Case: inhomogeneous defects

Breakdown during DAC voltage

withstand test

No breakdown during DAC voltage

withstand test

PD present PD not present

Breakdown during DAC voltage

withstand test

PD not present

No breakdown during DAC voltage

withstand test

PD present

Case: large homogenous defect(s)

Case: no weak-spot(s)

Case: large inhomogenous defect(s)


(1) Test object and system preparation (1h)

(2) Test circuit calibration: accessories identification

(0.5h)

(4) Data analysis and report generation (1h)

(5) Cable status assessment

DAC Testing

(3) On-site testing, diagnosis (3 x 1 h)

System installation, testing and measurement 230kV (3 phases) in less 6 hours


DAC Test Evaluation

Breakdown duringDAC test

No breakdown during DAC

PD observed PD not observed

Test failed

PD analysis

Test passed

Harmful PD

Harmless PD

Breakdown duringDAC test

No breakdown during DAC

PD observed PD not observed

Test failed

PD analysis

Test passed

Harmful PD

Harmless PD


Dissipation factor

DAC excitations

DAC Testing

DAC voltage testing

During DAC withstand test continuous PD monitoring controls

the impact of the over-voltage stresses


00.20.40.60.8

11.21.41.61.8

2

0.40 0.80 1.00 1.36

x Uo

Die

l. Lo

sses

L1 L2 L3

Partial discharges

DAC Diagnosis

Dissipation factor

PD defect localization

diagnosis

The use of diagnostic parameters supports the evaluation: PD detection: localisation of weak spots Dissipation factor (tanδ): integral insulation degradation


Practical Examples

Test van for transportation of a complete 150kV or 250kV damped AC system


After-laying test 50kV XLPE (12km) Example 1:

PDD-LossesVoltage

N:\...\yellow .vw d Tuesday, October 05, 2010 1:18 AM

Time (s)3,6003,4003,2003,0002,8002,6002,4002,2002,0001,8001,6001,4001,2001,0008006004002000

PD (p

C)

180160140120100

80604020

0

Voltage (kV Peak)

180160140120100806040200

D-lo

sses

(%)

10.90.80.70.60.50.40.30.20.1

0

3,6003,4003,2003,0002,8002,6002,4002,2002,0001,8001,6001,4001,2001,0008006004002000

Testing DAC frequency:28Hz; Cable load:4.2uF; PD (IEC 60270) background noise <10pC (at 1.7Uo) Test in accordance to Dutch NEN 3630 recommendation: voltage withstands testing using AC resonance system 25-200 Hz applied at 2.5xUo: PD monitored withstand testing by using damped sinusoidal AC voltages (25-200 Hz) for 1 hour testing at 2.5Uo.


Maintenance test 110kV XLPE (8km)

PD pattern and PD mapping at 1.1Uo

Example 2:


Testing DAC frequency:52Hz; Cable load:1.69uF; PD (IEC 60270) background noise <8pC History: joint failure during 6 years after successful non-monitored installation test (IEC 60840)


Maintenance test 110kV XLPE (4km)

Testing DAC frequency:75Hz; Cable load:0.8uF; PD (IEC 60270) background noise < 5pC History: joint failure during 6 after successful non-monitored installation test (IEC 60840)

Example 3:

voltage withstand test: 50 DAC excitations at 1.3Uo

At 1.3Uo before At 1.3Uo after


Q-V

0

1000

2000

3000

4000

5000

6000

7000

8000

0 20 40 60 80 100 120 140

kVpeak

pC

Breakdown

PDIV

0.6xUo

0.73xUo

PD patterns

After-laying test 150kV XLPE (4.5km)

Testing DAC frequency:62Hz; Cable load:0.92uF; PD (IEC 60270) background noise <20pC History: non-conclusive breakdown after few minute of non-monitored AC withstand test at 2.5Uo (NEN3660)

Example 4:

0.9xUo

0.98xUo

Joint with a breakdown


Diagnostic test 220kV XLPE (0.9km)


Testing DAC frequency:183Hz; Cable load:0.14uF; PD (IEC 60270) background noise <10pC History: no failures during 17 years after successful non-monitored installation test (IEC 62067)

PDIV > Uo (180kVpeak)

Example 5:


On-site Testing and Dissipation Factor Diagnosis

For oil-impregnated cable circuits the damped AC (DAC) voltage on-site testing and dissipation factor measurements can be performed at HV conditions and at power

frequency testing range (20Hz-300Hz)

For more details see also A.8.3

Example 7:


Maintenance test 230kV HPFF (27.5km)

Testing DAC frequency:20Hz; Cable load:8.5uF; PD (IEC 60270) background noise <10pC (at 1.36Uo) History: Age 28 years (high operational load)

As a result of 50 DAC excitations at 1.36Uo of DAC over-voltage no breakdown has been observed. No PD activity has been observed At 1.33Uo the max. tan δ value was between 0.8% and 0.9% The Δtanδ was between 0.35% and 0.4%

00.20.40.60.8

11.21.41.61.8

2

0.40 0.80 1.00 1.36

x Uo

Die

l. Lo

sses

L1 L2 L3

Example 8:


1. DAC is applicable for onsite monitored testing of new and service aged MV and (E)HV power cables and accessories.

2. Standardized PD detection can be sensitively achieved under on-site conditions to detect discharging defects in accessories.

3. The best-practice shows that: a) In case of after-laying testing of new cables the max. test voltage levels are

defined in the IEC standards b) In the case of maintenance / diagnostic testing the max. test voltage levels are

reduced to 75%..80% c) The duration is based on a number of DAC excitations is fixed at 50x at

maximum test voltage level d) The DAC voltage increase is based on max 5 DAC excitations every 0.2Uo e) In the case of short cable length where the duration of 50 DAC excitations is

much shorter than 1 hour, then 1 hour of DAC excitations is recommended

4. The use of standardised PD detection and the estimation of dissipation factor to

monitor the voltage testing provides additional information about the discharging defects and insulation degradation (OF cables).

5. Application of DAC testing In combination with distributed PD Agents PD provides sensitive detection in long length power cables circuits

Conclusions


Thank you for your attention !


Why damped AC testing is more efficient and effective as compared to continuous AC on-site testing ?

Continuous AC and damped AC on-site testing

Comparison of application aspects between using continuous AC and damped AC on-site testing

Continuous AC Damped AC

After-laying testing for (E)HV power cables √ √

Diagnostic testing for (E)HV power cables X √

Ability for efficient testing long length (10km +) X √

Transportation and execution costs High Low Space required for the test set up on-site Large Small Test set-up effort/duration on-site Days Hours System mobility Large/heavy

Low portability Small/light

High portability Size versus output power Large Small Power demand per unit length of cable system Large Small


Why damped AC testing is more efficient and effective as compared to continuous AC on-site testing ?

Continuous AC and damped AC on-site testing

Comparison of technical aspects between using continuous AC and damped AC on-site testing

Continuous AC Damped AC

Necessary power demand for long lengths Large Small Possibility of standardized PD detection X √

Voltage source background noise Very High Very Low Sensitive PD detection in cable accessories X √

PD detection in cable insulation X √

Dissipation Factor (tan δ) estimation X √

Thermal stability for multiple uses a day e.g. 8 hours

X √

History of using for MV networks X 10 years

History on using for (E)HV networks 10 years 5 years


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Contacts

onsite hv technology AG Brünigstrasse 25 6055 Alpnach Phone: +41 41 500 5120 Switzerland Fax: +41 41 500 551 www.onsitehv.com

http://www.onsitehv.com/�


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Documents

13 Ed Gulski Praesentation