correlated aging of xlpe and ep cables in the laboratory and in … · 2016. 12. 9. · one line...

Correlated Aging of XLPE and EP Cables in the Laboratory and in the Field

by CARLOS KATZ

Cable Technology Laboratories New Brunswick, NJ

Presented at ICC 2012 Spring Meeting

Seattle, WA

Project Execution

• Laboratory aging and testing – CTL

• Field aging and data collection – O&R Utilities

Project Sponsors

• EPRI and ESEERCO

Project Conception

To answer questions:

• How does accelerated aging in the laboratory relate to actual aging in the field?

• How to use laboratory aging data to estimate cable performance?

Time Perspective

• At the time, plenty of XPE studies

• Limited studies of TR-XLPE and EPR

• Various formulations of EPR in the marketplace

• Expected difference in performance of the EPRs

Issues with EPR Formulations

• Different ingredients – 10 to 20

• Different Ethylene to Propylene ratio in insulation

• Difference in fillers

• Proprietary formulations

Cables Used in Project

• 4/0 Copper Conductor

• 0.020 in. Conductor Shield

• 0.175 in. Insulation

• 0.030 in. Insulation Shield

• 20 - #10 Copper Concentric Neutrals

• Unjacketed

Cable Aging Test Sites

• CTL - 34.5/19.9 kV

• O&R - 13.2/7.62 kV Mid-Circuit

• O&R - 34.5/19.9 kV URD Development

Laboratory Aging Conditions

• Coils in water* • Water inside conductor* • 2.5 Vo applied voltage* • Adjusted water temperature (every 2

months) • Surge application (2 per month at 120 kV)

*Laboratory Accelerating Factors

Cable & Conduit Layout - 15 kV Site

EP

EP

EP

6” PVC Conduit

EP

EP TR- XLPE

6” PVC Conduit

Concrete Encasement

One Line Diagram for 15 kV Test Site

Manhole3

Manhole2

Manhole1

RiserPole

RiserPole

EP F

Monitoring TemperaturesMonitoring Temperatures

VoltagesCurrents

Pullout 19/97

380 feet

Pullout 34/01

650 feet

Pullout 27/99

340 feet

Pullout 46/02

750 feet

EP E

EP D

EP A

EP B

TR-XLPE

EP A EP A EP A

EP B

EP B

EP B

TR-XLPE TR-XLPE TR-XLPE

EP D

EP D

EP D

EP E EP E EP E

EP F EP F

EP F

Cable & Conduit Layout - 35 kV Site

EP EP TR-XL EP

EP

EP

4” PVC Conduit6” PVC Conduit 6” PVC Conduit

Direct Buried - 3 Foot Depth

BoxPad 3

BoxPad 2

BoxPad 1

SwitchPad

MeteringPad

Monitoring TemperaturesMonitoring Temperatures

VoltagesCurrents

Pullout 16/97

Pullout 211/98

Pullout 34/00

Pullout 410/01

URDLoad

SourceEP F

EP E

EP D

EP A

EP B

TR-XLPE TR-XLPE TR-XLPE TR-XLPE

EP B

EP B

EP B

EP D

EP D

EP D

EP F EP F

EP F

EP A EP A

EP A

EP E EP E EP E

One Line Diagram for 35 kV Test Site

Laboratory Aged at 2.5 Vo (Months)

Field Aged at 2.5 Vo (Months)

Field Aged at 1.0 Vo (Months)

0 0 0

3.5 23 26

7 40 48

30 64 70

55 75 84

82 -- --

Periodic Evaluations

Data Collected from Field Aging Sites

• Voltage

• Load Current

• Temperature

• Impulse Levels & Durations

Monthly Average Load Currents at 15 kV Field Site

0

5

10

15

20

25

30

35

Feb-95 Jul-96 Nov-97 Mar-99 Aug-00 Dec-01

Time (Months)

Curr

ent (

Amps

.)

Phase APhase BPhase CAve. Yearly Phase Current

Monthly Average Load Currents at 35 kV Field Site

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Feb-95 Jul-96 Nov-97 Mar-99 Aug-00 Dec-01

Time (Months)

Cur

rent

(Am

ps.)

Phase APhase BPhase CAve Phase Current

Temperature Data from the 15kV Field Site

-10-505

101520253035

12/2

6/19

96

1/26

/199

7

2/26

/199

7

3/26

/199

7

4/26

/199

7

5/26

/199

7

6/26

/199

7

7/26

/199

7

8/26

/199

7

9/26

/199

7

10/2

6/19

97

11/2

6/19

97

12/2

6/19

97

Tem

pera

ture

(C)

DuctEarthAirTR-XLPEEP HighEP Low

- 10

- 5

0

5

10

15

20

25

30

Jan-97

Apr-97

Jul-97

Oct -97

Jan-98

Apr-98

Jul-98

Oct -98

Jan-99

Apr-99

Jul-99

Oct -99

Jan-00

Apr-00

Jul-00

Oct -00

Jan-01

T ime ( Months)

Te

mp

era

ture

s (

oC

)

EP H ighTR- XLPEEP L owDuctAir

Temperature Data from the 35kV Field Site

- 5

0

5

10

15

20

25

30

35

40

45

Oct-95

Jul- 96 Mar-97

Nov-97

Jul- 98 Mar-99

Dec-99

Aug-00

Apr-01

Dec-01

Mont hs

Tem

pera

ture

(o C)

Air at O&REP CableEP CableEP Cable

Lab. Tank Temp. vs. Field Ambient Temp.

Cable Aging Results

Evaluation Tests

• Cable Characterization Shield Strippability Moisture Content of Insulation Water Tree Analysis Dissipation Factor

Partial Discharge Shield Resistivity • A.C. Breakdown

• Impulse Breakdown

Data Analysis

• Multiple samples used for each evaluation

• Characterization tests performed as per AEIC Specifications

• AC and Impulse breakdown strength tests on 6 samples

• Weibull plots used to obtain the most likely probability (63%)

GENERAL

• One of the EP cables had 6 failures during laboratory aging.

• No failures during the 7 years of field aging at 1.0V0 or 2.5V0 on any of the cables.

Cable D Failure Timeline

Failures of Cable "D" During Laboratory Aging

Time from Start of Aging - months0 10 20 30 40 50 60 70 80 90

Aging End

Stripping Strength

Insulation Shields had negligible change in:

• Minimum bond strength

• Maximum bond strength

Moisture Content of Insulation Close to Insulation Shield

Cable Identif.

Water Content (weight/weight, %)

New Cable

Aged in Lab. 82 Months at 2.5 Vo

Aged in Field 75 Months at 2.5 Vo


EP A

0.09

0.21

0.17

0.16

EP B

0.11

0.20

0.17

0.17

TR-XLPE

0.04

0.61

0.23

0.33

EP D

0.06

0.20

0.14

0.15

EP E

0.13

1.04

0.30

0.46

EP F

0.10

0.23

0.19

0.18

Moisture Content of Insulation Close to Conductor Shield

Cable Identif.

Water Content (weight/weight, %)

New Cable

Aged in Lab. 82 Months at 2.5 Vo



EP A

0.10

0.19

0.15

0.15

EP B

0.10

0.19

0.15

0.16

TR-XLPE

0.04

0.60

0.14

0.30

EP D

0.07

0.17

0.14

0.15

EP E

0.15

0.94

0.32

0.42

EP F

0.11

0.24

0.18

0.18

Vented Trees Cable

EP A

EP B

TR-XLPE

EP D

EP E

EP F

Range (mm)

CS

IS

CS

IS

CS

IS

CS

IS

CS

IS

CS

IS

Aged in Lab. 82 Months at 2.5 Vo – Number Of Trees

0.05 to 0.13

1

--

2

3 2

8

7 2 -- -- 2 1

0.14 to 0.25

--

2

--

-- 1

6 5

-- -- -- 2 --

0.26 to 0.50

-- -- -- -- 1

1

3

-- -- -- 2

--

0.51 to 0.76

-- -- -- -- -- -- --

-- -- -- 1 --

Aged in Field 75 Months at 2.5 Vo – Number of Trees

0.05 to 0.13

-- 1

-- -- -- -- 1

1 -- -- -- 2

0.14 to 0.25

-- 2 -- -- -- -- 2 --

-- -- -- --

0.26 to 0.50

-- -- -- -- -- -- -- -- -- -- -- --

0.51 to 0.76

-- -- -- -- -- -- -- -- -- -- -- --

Aged in Field 84 Months at 1.0 Vo – Number of Trees

0.05 to 0.13

-- 1 1 -- -- 3 3

-- -- -- 2 1

0.14 to 0.25

1

-- -- 1 2 1 -- -- -- -- -- 1

0.26 to 0.50

-- -- -- -- -- -- -- -- -- -- -- --

0.51 to 0.76

-- -- -- -- -- -- -- -- -- -- -- --

Bow Tie Trees

Cable EP A EP B TR-XLPE EP D EP E EP F

Range (mm) Number of Trees Aged in Lab. 82 Months at 2.5 Vo

0.05 to 0.13 63 92 330 98 -- 40 0.14 to 0.25 30 42 36 64 -- 82 0.26 to 0.50 9 15 4 43 -- 65 0.51 to 0.76 -- 17 -- 34 -- 22 0.77 to 1.00 -- 5 -- 9 -- 2 1.01 to 1.30 -- 1 -- 3 -- -- 1.31 to 1.80 -- -- -- 2 -- --

Aged in Field 75 Months at 2.5 Vo 0.05 to 0.13 4 7 136 34 -- 5 0.14 to 0.25 2 3 2 21 -- -- 0.26 to 0.50 -- -- -- 6 -- 2 0.51 to 0.76 -- -- -- 2 -- 1

Aged in Field 84 Months at 1.0 Vo 0.05 to 0.13 10 15 28 33 -- 11 0.14 to 0.25 8 9 9 15 -- 3 0.26 to 0.50 4 -- 2 2 -- -- 0.51 to 0.76 -- -- -- -- -- --

Dissipation Factor

With the exception of one EP cable that had a very significant change, all

others had negligible change.

Partial Discharge

• When aged in the laboratory, under water, except for one of the EP cables, the others tested below 5 pC.

• In the field, in addition to the above exception, another of the EP cables developed partial discharge.

Volume Resistivity of Conductor Shields Cables Aged at 2.5 Vo in Field

Volume Resistivity, ohm-m

Aged at 2.5 Vo in Field

Cable New Cable 23 months 40 months 64 months 75 months

At 90°C A

B

C

D

E

F

70

7.4

20

19

7.8 x 106

0.31

62

4.3

31

7.2

6.2 x 106

0.34

70

6.8

37

9.4

12.7 x 106

0.47

79

5.7

44

4.7

50 x 106

0.56

130

9.7

46

5.5

26 x 106

0.62

AEIC Requirement: 1000 ohm-m maximum

Volume Resistivity of Conductor Shields

• One of the cables had a conductor shield

with significantly higher Volume Resistivity

than the other five.

• During the aging program, all cables had

negligible change in Volume Resistivity

of the conductor shield at 90° and 130°C.

Volume Resistivity of Insulation Shields Cables Aged at 2.5 Vo in Field

Volume Resistivity, ohm-m

Aged at 2.5 Vo in FieldCable NewCable 23 months 40 months 64 months 75 months

At 90°CA

B

C

D

E

F

3.2

210

3.6

2.3

1.7

1.6

1.6

290

10

5.9

1.3

7.2

1.7

350

11

9.2

1.8

2.4

0.48

220

4.2

8.1

0.45

0.82

0.73

130

5.2

6.3

0.66

1.1

AEIC Requirement: 500 ohm-m maximum

Volume Resistivity of Insulation Shields

• One of the cables had an insulation shield with

significantly higher volume resistivity than the other five.

• During the aging program, all cables had negligible change in their insulation shield volume resistivity.

• The cable having higher volume resistivity of the insulation shield developed partial discharge between the neutral wires and the extruded insulation shield.

AC Breakdown Data

Typical 63% Weibull Plot - AC Breakdown

05

101520253035404550

0 10 20 30 40 50 60 70 80 90Aging Time (Months)

A.C

. Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)

A.C. Voltage Breakdown Stress of EP Cables

LAB AGED

Normal Operating Stress

05

101520253035404550


A.C

. Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)


LAB AGED


15kV AGED

05

101520253035404550


A.C

. Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)


LAB AGED


15kV AGED 35kV AGED

05

101520253035404550


A.C

. Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)



TR-XLPE LAB EP LAB

TR-XLPE 15kV EP 15kV

TR-XLPE 35kV EP 35kV

A.C. Voltage Breakdown Retentions for Laboratory Aged Cables at 2.5 Vo

0%

20%

40%

60%

80%

100%

120%

CableA

CableB

CableC

CableD

CableE

CableF

3.5 Months7 Months30 Months55 Months82 Months

A.C. Voltage Breakdown Retentions for Field Aged Cables at 1.0 Vo

0%

20%

40%

60%

80%

100%

120%

CableA

CableB

CableC

CableD

CableE

CableF

26 Months48 Months70 Months84 Months

A.C. Voltage Breakdown Retentions for Field Aged Cables at 2.5 Vo

0%

20%

40%

60%

80%

100%

120%

CableA

CableB

CableC

CableD

CableE

CableF


35 kV Field Cable Aging Test Site

Impulse Breakdown Data

020406080

100120140160


Impu

lse

Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)

Impulse Voltage Breakdown Stress of EP Cables

LAB AGED

Design BIL Stress

020406080

100120140160


Impu

lse

Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)


LAB AGED Design BIL Stress

15kV AGED

020406080

100120140160


Impu

lse

Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)


LAB AGED Design BIL Stress

15kV AGED 35kV AGED

020406080

100120140160


Impu

lse

Vol

tage

Bre

akdo

wn

Stre

ss (

kV/m

m)

Impulse Voltage Breakdown Stress of All Cables

Design BIL Stress

TR-XLPE LAB

TR-XLPE 15kV

TR-XLPE 35kV

EP LAB

EP 15kV

EP 35kV

Impulse Voltage Breakdown Retentions for Laboratory Aged Cables at 2.5 Vo

0%

20%

40%

60%

80%

100%

120%

CableA

CableB

CableC

CableD

CableE

CableF

3.5 Months7 Months30 Months55 Months82 Months

Impulse Voltage Breakdown Retentions for Field Aged Cables at 1.0 Vo

0%

20%

40%

60%

80%

100%

120%

CableA

CableB

CableC

CableD

CableE

CableF


Impulse Voltage Breakdown Retentions for Field Aged Cables at 2.5 Vo

0%

20%

40%

60%

80%

100%

120%

CableA

CableB

CableC

CableD

CableE

CableF


Conclusions

General

• The aging in the laboratory is significantly more accelerated than in the field.

• No failures took place during seven years of field aging of any of the cables.

• Cables had negligible change in stripping tension and shield resistivities.

• Most water trees are of the bow-tie type. Vented trees are less frequent.

Conclusions (continued)

EP Cables

• Six failures took place on one of the five EP cables during laboratory aging. V-t curves confirm the shorter expected life for this cable.

• The above cable had a greater number of water trees, especially, vented trees from the conductor shield.

• Another EP cable having high insulation shield volume resistivity developed PD during accelerated field aging.

• The performance of each EP cable is different.


AC Breakdown

• All EP cables show an initial drop during aging; after which they remain more or less stable.

Impulse Breakdown

• With the exception of one EP, which did not change, all other EP’s remained stable after initial drop of about 30-40%.

• There does not appear to be a significant difference in impulse strength of cables aged at Vo or 2.5 Vo under all aging conditions.


TR-XLPE Cables

• AC Breakdown

• Remains extremely stable during all aging conditions.

• Impulse Breakdown

• Stabilizes after an initial drop of about 40-50%.

• There are no major differences between laboratory and field breakdown strengths.

correlated aging of xlpe and ep cables in the laboratory and in … · 2016. 12. 9. · one line...

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