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Paul L. Cinquemani Frank L. Kuchta Member, IEEE Member, IEEE

Pirelli Cable Corporation Lexington SC


Longitudinal water blocked cable designs have gained popularity among many electrical utility and rural cooperative users in North America. These types of cables are used for primary underground distribution which tend to operate in wet environments where the harmful effects of water, especially water tree deterioration of the insulation and corrosion of the metallic components, are of primary concern.

In the case of radial water ingress through external damage or other mechanism, the swellable agents and water blocking tape will swell upon contact with water resulting in the formation of gel and restricting longitudinal water propagation to a minimum. This paper investigates proposed test methods in determining longitudinal water penetration of water blocked cables and discusses the results of tests performed on a typical cable design. Longitudinal water penetration testing has been performed under various conditions including hydrostatic pressure applied on unconditioned cable specimens as well as cable under temperature cycling under specific durations. Investigations into the compatibility of the key water blocking components of the cable constructions have encompassed studies of the water swellable agents in both the dry and gelled state under a variety of thermal conditions.


There are many situations under which a medium voltage URD cable cross-section may be subjected to water during the cable’s life. It is well known that the life of the cable which is subjected to water ingress can deteriorate more rapidly under ac voltage stress.

0-7803-1 883-8$04.00019941EEE

To minimize the detrimental effects of water, the use of water blocking tapes and swellable agents in the design of Longitudinal Water Blocked Cables have become increasingly popular in North America. The use of water blocking components has seen widespread cable application in Europe 111. The popularity of these designs in Europe has led to the recent publication of an IEC water penetration test [21 although national standards have existed for some time. Currently, North America has addressed only the water penetration resistance of the inner conductor of medium voltage cable via ICEA Guide T-31-610 131.

In addition to the performance characteristics of the cable designs, the compatibility of the water blocking components contained within these constructions is also evaluated.

The purpose of this paper is to review new test methods in an effort to propose a reliable qualification program to evaluate the performance of Longitudinal Water Blocked (LWB) Cable designs. The continuing test program encompasses further investigations in water penetration resistance testing and compatibility of the concentric neutral water blocking components. The recently published ICEA guide for compatibility of conductor filling compounds is also reviewed.


There are two distinct LWB cable designs which are being utilized by electrical utilities and rural cooperatives in North America, i.e., Encapsulated Jacket and Sleeved Jacket Designs 141.

Both designs incorporate a water blocked conductor, extruded polymeric insulation system and water blocked concentric neutral utilizing water swellable tape or water swellable powder, and/or combinations of the two. The major difference between the two designs is that one employs an extruded jacket which encapsulates the wire neutral and the other a non-encapsulated jacket otherwise


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known as sleeved over the concentric neutral.


The ICEA Publication T-32-645 [SI published in 1993,is the only North American industry guide to address compatibility of longitudinal water blocking filling compound and stress control extrusion layers (conductor shield materials). This guide was designed to verify that the electrical properties of a conducting material used as a conductor stress control layer are not adversely affected when exposed to conductor filler material. It describes a test method of demonstrating that the volume resistivity and volume resistivity stability remain within their specified limits when the conducting material is exposed to the conductor filler material at the emergency operating temperature of the cable.

In regards to water swellable agents, to the authors’ knowledge, there are no known documented industry test procedures to determine compatibility with other cable components. While raw material testing is a pre-requisite, this paper describes a test protocol for evaluation on full scale cables.

Conductor Filling Conmound

The ICEA method was employed for testing compatibility of conductor filling compound with various conductor shields. The salient p in ts of the ICEA test are:

Molded plaque samples encompass a 5 to 1 ratio of stress control material to conductor filling compound. Test conducted at emergency operating temperature (130T). Incorporates ICEA T-25-425 for volume resistivity measurements and evaluation of stability. Qualification test only.

As per the ICEA test, a minimum of fivespecimens of each combination were prepared and subjected to the stability for volume resistivity test. At the conclusion of the test, the five specimens were removed from the oven and allowed to cool at room temperature. At least 95% of the filler compound was removed without any damage to the stress control material specimens. The final resistance between the electrodes was measured and the volume resistivity was computed.

The volume resistivity measurements at 130T are provided in Figure 1. Each test group represented an average of five test specimens. Test Group A consisted of a common medium voltage shielding material with conductor filling

compound. Test Group B consisted of a high voltage conductor shield material with the same filler compound as Test Group A. Whereby each control represented an average of 5 conductor shield material samples without any filling compound. Each test group achieved Volume Resistivity Stability within forty-two days. The final volume resistivity measurements after the filler compound was removed were well within the ICEA limit (lo00 ohm- meters).


, 0 10 20 30 4 0 50


Swellable Agents

Swellable agents may be utilized in water swellable tapes, yams and/or via direct application. The agents are available in many different types and grades of absorbency [ 6 ] . The key characteristics necessary for power cable application are as follows:

Capable of absorbing and retaining under pressure large

Good thermal resistance. Fast absorption rate (time). Compatible with other cable components.

quantities of water.

The test program described in this paper was designed to test compatibility of water swellable agents with extruded cable components which come in contact with the agents. The Longitudinal Water Blocked (LWB) Encapsulated Jacket Design was selected for the test as the swellable agents are in intimate contact with the adjacent extruded layers and copper concentric neutral. The control samples selected were identical to the LWB cable design except no


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water blocking components were present.

Aging Duration


The test program consisted of continuous thermal aging of multiple control and LWB cable samples in an air oven at 11093. The 11093 test temperature corresponds to the emergency operating temperature of the insulation shield/jacket interface in accordance with AEIC and ICEA standards. Conditioning in a controlled air oven was deemed appropriate to provide a stabilized and uniform aging environment where multiple samples could be accommodated. Aging periods consisted of 30,60,90 and 120 days.

Percent Dif ference Between Control & Ly8 Sanple

Insu la t ion Shield Jacket

Tensi le Elongation Tensi le Elongation I 1

At the end of each conditioning period, both the control and LWB specimens were subjected to the following tests:

I n i t i a l 30 60 90


Visual Inspection - Concentric Neutral Wires and Swellable Agents

0 Physical Properties - Tensile and Elongation (Insulation Shield and Jacket)

Electrical Properties - Volume Resistivity (Insulation Shield)

0 Water Propagation Testing - (LWB Cable only)

0.6 1.6 5.7 4.8 0 . 4 4.7 2.2 6.3 1.7 16.6 2.3 9.8 5.0 6.3 5.4 0.6 8.0 8.7 1.3 9.0

1. Visual Examination - During the aging process, the concentric wires exhibited sporadic blue and green discoloration. Discoloration appeared after 30 days of conditioning and remained constant without further darkening up to the 120 day aging period. Both the control and LWB samples exhibited the same amount of discoloration throughout the test period. This discoloration is considered normal for heat aging of copper.

During the aging period, the swellable agents within the LWB samples were also visually examined. The agents exhibited no visual discoloration at any interval during the 120 day aging period.

2. Physical Properties - Tensile strength and elongation of the insulation shield and jacket were measured at each test interval. At each interval, the control sample and LWB sample were compared and essentially no difference was observed as shown in Table 1. In evaluating the data, it was not deemed appropriate to compare each interval to the original value as this would be demonstrating heat aging retention of the material and not compatibility of components.


3. Electrical Properties - Volume resistivity measurements of the insulation shield were also taken at each time interval. The samples were allowed to cool to room temperature and testing was performed in accordance witb ICEA T-25-425 171. The results shown in Table 2 indicate essentially no change during the test period between the control and LWB samples.


Insu la t ion Shield Volune

4. Water Propagation Testinq- LWB samples were retained from each aging interval for subsequent longitudinal water penetration resistance testing on the full cable cross section. The procedure consisted of applying full hydraulic water pressure without any time delay to the three foot aged samples. All samples withstood 15 psi (103.4 kPa) water pressure for one hour with no sample penetration exceeding half the test length.

This test functionally combines an evaluation of two performance criteria of the swellable agents within a cable structure as follows:



The effect of heat aging on the longitudinal water blocking capability. The compatibility with adjacent components.

As it was the intent of this test program to evaluate completed cable structures, it was not possible to isolate the individual contribution of the two performance criteria.


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However, it was deemed appropriate that the study of the combined synergistic effect was more representative of actual cable operation.

It should be noted that the aging program was extended to 120 days which is approximately six times longer than the allowable emergency operating duration specified by ICEA Standards and twice the allowable continuous emergency duration as per the AEIC Standards for the life of the cable. Additionally, the water pressure which the samples withstood (15 psi) is three times more severe than the industry requirement for the conductor. This pressure level equals a 34.5 foot depth (10.5 meter water head) which exceeds the requirements of most underground cables.


Industrv Summarv

The ICEA Publication 7'-31-610 published in 1989 was the first North American guide to address longitudinal water propagation testing of filled conductor. The guide was developed to address only the conductor and included a procedure for both qualification and production testing. Qualification testing requires conditioning of samples at subambient and elevated temperatures followed by three 180" reverse bends. Samples are then subjected to the water propagation test at a recommended pressure of 5 psi (34.5 kPa) for one hour by use of the assembly shown in Figure 2. Samples for production testing are subjected to three 180" reverse bends. without temperature conditioning and are subjected to the water propagation test at the recommended 5 (34.5 kPa) psi for 15 minutes. The salient points of this testing methodology are:

conditions for 10 cycles, as shown in the test assembly of Figure 3. The salient points of the testing methodology are:

Pressure testing under cyclic loading conditions. Water pressure applied gradually (up to 5 minutes

1.4 psi (9.7 kPa) water pressure. Qualification test only. Concentric neutral water block test. Test limited to conductor surface.


Rubber Hose

Hose Clamp

Copper Reducer

, Hose Clamp

r Dyed Water

Clear Vinyl Tubing

Build-up of Rubber Tape (when required for a tight fit)

Hole Clamp

Hose Clamp

Paper Towel (for water leakage detection)

FIGURE 2: ICEA TYPICAL WATER PENETRATION TEST ASSEMBLY Water pressure applied to full cross-sectional area of

conductor. Recommended 5 psi (34.5 H a ) water pressure. Instantaneous applica.tion of full water pressure (no wet out time). Both qualification and production test are provided. Test limited to conductor only.



The IEC Publication 840 Amendment 1 dated 1991, addresses longitudinal water propagation testing at the interface of the insulation shield and the metallic sheath and the outer surface of a conductor, if applicable. The standard includes only a type (qualification) test which includes three 360"reverse bends at room temperature. A ring approximately 2 inches (50.8 mm) wide is then cut down to the layer(s) being tested in the center section of a three meter length. The sample is then subjected to the FIGUI(1.: 3 ILC 'I'YPICAL T-'TYPE WATER TICIITNESS water tightness test at 1.4 psi (9.7 kPa) under cyclic loading TEST ASSEMBLY


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I C E A 1-31-610



6 X D


5 m . 5



Previous investigations [4,8] have shown that a combination of the current testing methodologies may be necessary to fullyevaluate LWB cable designs. The modified ICEA test (Test A) provides a means to evaluate cables after exposure to environmental conditioning and bending such as would be seen under installation conditions, prior to splicing and terminating. Under these conditions, it is critical to test the total cable cross-section, including the conductor. Additionally, it provides a relatively simple routine factory production test. The modified IEC test (Test B) allows evaluation of a cable construction under cyclic loading as would be seen under normal and emergency operating conditions. The following is an outline of the qualification test methods which are under investigation in this test program.



10'/3 8 3/.9

o/ 100 6 X D







Qualification Testing

Sanple Length (ft lm) Preconditioning

Bend test- diameter Load Cycling Hours on Hours o f f No. of Load Cyc l es ~ e n p . of ~ o a d cycle cot) water Pressure (psi /kPa 1 Test ful l Cross-section Test Under Jacket

( O C )

As the ICEA T-31-610 test is intended to test only the insulated conductor, the following modifications are necessary to test a LWB cable design. This modified test is primarily intended for installation type conditions before the cable is e n e r g i d , as a cable would be incapable of operating in the field with a water pressure head on the conductor.

IEC 840


- 20 (D*d)

YES a 16 10





Water applied to full cable cross-section in lieu of insulated conductor.

0 Constructions utilizing thermoplastic jackets conditioned at 100T in lieu of 130T to avoid thermal degrading of the jacket which may affect test results.

0 Utilization of non-compressive sealing device (adhesive layer) to attach test assembly to cable specimen in lieu of hose clamps. This will eliminate any erroneous results which may have been imposed by overtightening of the clamps.

The IEC-840 test was derived from other national standards where the testing methodologies primary intent was to evaluate the longitudinal water blocking capability at the shield-jacket interface. To accommodate designs which incorporate sealed conductor, IEC provides the option of testing down to the conductor surface.

This test primarily addresses that cables can and will operate with a water pressure head exerted at the shield- jacket interface under cyclic loading conditions. After the review of national specifications and published literature the following modifications to the IEC test were deemed appropriate.

Test pressure increased to 5 psi (34.5 kPa) in lieu of 1.4 psi (9.7 kPa). Standardized on ICEA bending conditioning as bend radius is more severe. Heat/cooling cycle time changed to 4 hours current on, 4 hours current off in lieu of 8 hours current on, 16 hours off based on reported results 191 indicating a more severe condition. Addition of 4 heat/cooling cycles prior to application of water to evaluate dry conditioning. Time to obtain full test pressure reduced from 5 minutes to one minute. Heat/cooling cycling time and application of water changed from 10 cycles to 125 cycles. This value has been found to be the minimum number of cycles to ensure that the longitudinal water penetration has reached a stable plateau and no further water penetration can be expected [IO]. Heat cycling temperature has been raised to the higher emergency temperature recognized in North American standards (130°C for thermoset insulations).

The combination of the above two modified tests, Test A and Test B, provide the investigatory qualification test program carried out in this evaluation.

Table 3 provides an outline showing the basic requirement of the IEC and ICEA and the comparison to the LWB Qualification Program adopted for this investigation.

** Assuning thermosetting insulations. D= Overall diameter d= Conductor diamcter

Pressure applied to center of sanple

Oualification Samples

A review of ICEA T-31-610 and IEC 840 relative to qualification concludes that neither document particularly addresses all the elements needed to qualify a full range of cable designs used today.


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When evaluating LWB designs for qualification purposes, analysis of the cross-sectional area which must be effectively blocked by the swellable components is necessary. This is critical for determination of the number of samples necessary to qualify the broad range of constructions utilized for URD designs.

In the case of Sleeved Jacketed Designs consideration must be given to the neutral wire size and coverage as these variables influence the cross-sectional area which must be blocked. Of particular concern is the height of the area which is the distance between the insulation shield and the jacket, as when this height increases, the water blocking components become less effective. Therefore, more than one water blocking design may be necessary to qualify a full range of sizes.

Investigations are under ?way to determine what samples are necessary to qualify the tlroad range of URD constructions. In the meantime, for Sleeved Jacketed constructions, designs which exhibit the greatest cross-sectional height (larger concentric wire size) should be qualified whereas in the Encapsulated Jacketed Design, any concentric neutral wire size may be utilized. For Encapsulated Jacketed Designs, the neutral wire size and coverage are not as critical as compared to #Sleeved Jacketed Designs because the cross-sectional area which must be effectively blocked is insignificantly changed with these variables.

1. Test A (Modified IC=- Both the Sleeved Jacket and Encapsulated Jacket LWB designs have been extensively tested to the modified ICEA test program. Test samples have encompassed a range of conductor sizes including variations in concentric neutral designs (neutral size and percent coverage). This data has been reported in reference 4 and 8 and concludes that a properly designed construction can withstand at minimum the 5 psi (34.5 kPa) presented in the paper. More recent testing has confirmed these results.

2. Test B (Modified IEC) - Again, both the Sleeved Jacket and Encapsulated Jacket LWB design were included in the test program. Due to the complexity and time consuming nature of this test, results will be reported in the future. The authors’ earlier studies and the test results obtained so far, support that within 125 cycles stability can be reached as found in reference 10. However, no conclusion can be drawn at this time whether the 125 cycles is the optimum testing duration due to the increased test pressure and temperature of the combined programs.


Many water blocking components and designs are available to the power cable industry to produce water blocked cables. Currently, Longitudinal Water Blocked Cables widely available to the industry lack a recognized testing methodology to evaluate the performance characteristics of the completed cable. The methods presented in this paper have been found useful to qualify a completed LWB cable design.

Two longitudinal water propagation tests have been investigated and the combination of both testing methods may be necessary for optimum evaluation of LWB cable designs. The modified ICEA test (Test A) is a close facsimile of ICEA T-31-610 for sealed conductors and the results thus far suggest that an industry evaluation would be appropriate at this time. The modified IEC test (Test B) has been significantly upgraded, as far as testing severity, in an effort to develop a test to meet North American practices and applications for URD designs. Thus, the modified IEC test program is still under evaluation in an effort to establish the most appropriate set of parameters to test water blocking performance under cyclic loading conditions.

Methods have been outlined to evaluate the compatibility of the key water blocking components at the concentric neutral interface of LWB cables. Preliminary results on the aging of completed cable designs indicate that the investigated water swellable agents are compatible with adjacent cable components when tested at the emergency operating conditions. The test samples which were conditioned at each interval (30, 60,90 and 120 days) were subsequently subjected to the modified ICEA water pressure test at 15 psi (103.4 kPa) for one hour. All samples complied with the water propagation test. Further investigations are continuing in the area of compatibility and to determine the activated length of water penetration vs. temperature conditioning.

Relative to compatibility testing of the conductor filling compound, the efforts of ICEA Working Group 645 towards the recent publication of Guide T-32-645 has resulted in a viable method in qualifying conductor filling compounds.

Equally important in the qualification of an LWB cable is the performance of the connections in conjunction with the filled conductor strand. This subject has been presented in many papers such as references 4 and 8. Additionally, Underwriters Laboratories, Inc. offers an evaluation program for UL listing of filled conductor.


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1. The principles to evaluate Longitudinal Water Blocked Cables have been identified in this paper with an emphasis on North American practices (pressure and temperature). They are: compatibility of components; longitudinal water penetration performance; and connectability of filled conductors.

2. Presented test methods (Test A and Test B) are necessary to evaluate the water blocking performance of an URD cable in installation and operation. Further work is continuing to complement ICEA's activities.

3. meet or exceed the testing criteria presented.

Appropriate materials and properly designed cables can










W. J. Van Gelder, "Longitudinal Water Tightness Tests For Power Cable," IEEE Spring, 1991 Insulated Conductor Committee Meetings, Appendix 111-A-l .

IEC 840 Amendment 1, "Test For Power Cables With Extruded Insulation For Rated Voltages Above 30 kV Up To 150 kV, 1991.

ICEA Publication T-3 1-610, "Guide For Conducting A Longitudinal Water Penetration Resistance Test For Sealed Conductor," September, 1991.

F. Marcianb-Agostinelli, P. L Cinquemani, F. L. Kuchta, "State Of The Art Medium Voltage Longitudinal Water Blocked Cables, " 199 1 IEEE-Rural Electrical Power Conference, pp. C3-1 to C3-6.

ICEA Publication T-32-645, "Guide For Establishing Compatibility Of Sealed Conductor Filler Compounds With Conducting Stress Control Materials, " February, 1993.

R. S. deBoer and P. Vogel, "The Use Of Waterswellable Materials In The Design Of Power Cable," JICABLE 91, International Conference on Polymer Insulated Power Cable, paper A.7.1.

ICEA T-425, "Guide For Establishing Stability of Volume Resistivity For Conducting Polymeric Components Of Power Cables," February, 1981.

F. Marcianb-Agostinelli, P. L. Cinquemani, F. L. Kuchta, "Longitudinally Water Resistant Cables, " JICABLE 91, International Conference on Polymer Insulated Power Cables, paper A.6.1.

191 J. C. Chan and H. Compani, "Performance Characteristics Of Water Blocking Tapes And Their Influence On Water Treeing In XLPE Insulations," 1992 IEEE International Symposium on Electrical Insulation, pp. 99-103.

[lo] C. A. Geerts and J. R. Bury, "Longitudinal Water Blocking Of Power Cables, " IEEE Fall, 1991 Insulated Conductor Committee Meetings, Appendix 111-B-1.

Paul L. Cinquemani (M'84) received his BSEE Degree from The City College of New York in 1974and his MS in Business Management from Polytechnic Institute of New York in 1984. From 1974 to 1977, he was employed by E. I. duPont de Nemours and Company, Inc. He joined Pirelli Cable Corporation in 1978 and has held various positions in design and application engineering. He is currently Manager - Engineering Services in the Research, Development and Engineering Department.

Mr. Cinquemani is an active participant in IEEE-ICC, NEMA, CSA and ICEA. He is currently First Vice President, Power Cable Section of the Insulated Cable Engineers Association and Chairman in the development of ICEA guides for filled conductors and longitudinal water blocked cables. Via election, he presently Serves Underwriters Laboratories on their Technical Advisory Panel for Wire and Cable. He currently holds two patents in the area of water blocked cable designs.

Frank L. Kuchta (M'84) received his BSEE Degree from Fairleigh Dickinson University in 1982. Upon graduation, he joined Pirelli Cable Corporation and has held various positions in design and application engineering. He is currently Supervisor of Application Engineering in the Research, Development and Engineering Department. His work has included specialized projects in computer aided design where he developed the computer program and user guide for the EPRI sponsored project, "Maximum Safe Pulling Lengths For Solid Dielectric Insulated Cables".

Mr. Kuchta is an active participant in IEEE-ICC and the Insulated Cable Engineers Association where he is Chairman in the development of a new concentric neutral cable specification. He currently holds one patent in the area of water blocked cable designs.


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