FORD WESTON PHILIPS CHAPIN (US)
STEELE JAMES (US)
BUSBY DAVID C (US)
CHATTERTON WAYNE J (US)
LAURIE NATHANAEL (US)
US20050192708A1 | 2005-09-01 | |||
US5049593A | 1991-09-17 | |||
US20080173467A1 | 2008-07-24 | |||
US20100122453A1 | 2010-05-20 | |||
US20210280341A1 | 2021-09-09 |
CLAIMS What is claimed is: 1. A method for rejuvenating a strand-blocked cable having a conductor comprised of a plurality of conductor strands with interstitial volume therebetween blocked by a PIB-based strand-block mastic, the conductor being surrounded by a polymeric cable insulation, comprising: a. installing injection adapters that seal the cable ends of the cable and are usable to inject fluid into the interstitial volume between the conductor strands of the cable; b. elastically expanding the polymeric cable insulation through the application of pressure to the interstitial volume between the conductor strands of the cable; and c. injecting at least one injection fluid into the interstitial volume between the conductor strands of the cable in which the PIB based mastic is mostly insoluble. 2. The method of claim 1, where strand-block mastic has a solubility of under 10% in the injection fluid at 55°C. 3. The method of claim 1, where strand-block mastic has a solubility of under 5% in the injection fluid at 55°C. 4. The method of claim 1, where the injection fluid maintains a viscosity of under 10 cSt throughout the course of injection through the cable. 5. The method of claim 1, where the injection fluid has a diffusion coefficient of greater than 1.0 x 10-8 cm2/sec at 55°C. 6. The method of claim 1, where the injection fluid is comprised primarily from a mixture containing Phenylmethyldimethoxysilane or Cyanobutylmethyldimethoxysilane. 7. The method of claim 6, where the injection fluid further contains a hydrolysis-condensation catalyst. 8. The method of claim 7, where the hydrolysis-condensation catalyst is dodecylbenzene sulfonic acid (DDBSA) or tetra-isopropyl titanate (TiPT). 9. The method of claim 1, where the conductor temperature is increased above ambient during injection. 10. The method of claim 9, where the conductor temperature is increased by about 40°C above ambient during injection. 11. A method for rejuvenating a strand-blocked cable having a conductor comprised of a plurality of conductor strands with interstitial volume therebetween blocked by a PIB-based strand-block mastic, the conductor being surrounded by a polymeric cable insulation, comprising: injecting at least one injection fluid into the interstitial volume between the conductor strands of the cable in which the PIB based mastic is mostly insoluble. 12. The method of claim 11, where strand-block mastic has a solubility of under 10% in the injection fluid at 55°C. 13. The method of claim 11, where strand-block mastic has a solubility of under 5% in the injection fluid at 55°C. 14. The method of claim 11, where the injection fluid maintains a viscosity of under 10 cSt throughout the course of injection through the cable. 15. The method of claim 11, where the injection fluid has a diffusion coefficient of greater than 1.0 x 10-8 cm2/sec at 55°C. 16. The method of claim 11, where the injection fluid is comprised primarily from a mixture containing Phenylmethyldimethoxysilane or Cyanobutylmethyldimethoxysilane. 17. The method of claim 16, where the injection fluid further contains a hydrolysis-condensation catalyst. 18. The method of claim 17, where the hydrolysis-condensation catalyst is dodecylbenzene sulfonic acid (DDBSA) or tetra-isopropyl titanate (TiPT). 19. The method of claim 11, where the conductor temperature is increased above ambient during injection. 20. The method of claim 19, where the conductor temperature is increased by about 40°C above ambient during injection. |
Fill percentage is found to range from under 20% to over 60%. As not all cable makes and vintages were quantified, the actual range could be appreciably more. Variation is noted between manufacturers, vintages, between spools from the same apparent manufacturing run and along the length of the same cable. The measurements reveal that on average, about 44% of the conductor’s interstitial volume is filled by strand block material. If fluid were to be injected and fill the remaining 56% void space that would leave most medium voltage cables undertreated. As an example, an average non-strand filled 1/0 AWG cable with light compression has an interstitial volume of 3.2 cc/ft. For a non-strand filled cable, the fluid target would be a complete fill of the interstitial volume. However, in a strand block cable, a maximum free volume to receive treatment would typically be at best 56% of 3.2 cc/ft or 1.8 cc/ft and leave the cable under the fluid target. However, as strand block mastic is not uniformly distributed within the conductor and the free volume is actually a distribution of small voids, a complete fill of the free volume is unlikely. Carbon Black Content: In addition to molecular weight of the PIB, carbon black is known to have influence on the physical properties of mastics. A weighed portion of mastic (16.3579 g) was added to about 3 times as much weight of toluene, and the mixture was dissolved by shaking and heating in a 55°C oven. The black suspension in yellow liquid was filtered through a weighed medium fritted filter funnel to trap the carbon black. The carbon black was washed on the filter frit with additional toluene to remove any remaining PIB. The carbon black was then washed with acetone and dried by pulling air through the frit for 1 hour. The frit was then placed in a 55°C oven to remove any remaining solvent, and then the frit plus carbon black was weighed. The weight of the carbon black recovered was 7.9444 g or 48.6 wt% of the initial weight of mastic. This value is significantly higher than the 39.6 wt% documented by industry. This variation likely explains some of the differences observed between strand block materials of various cable manufacturers and vintages. Glass Transition Temperature (Tg): Differential Scanning Calorimetry (DSC) was performed on strand block (SB) mastic samples collected from five cable manufacturers including Southwire 2017, Pirelli 1987, Hendrix 2012, Prysmian 2009 and Okonite 2018. All cables were XLPE insulated with the exception of the Okonite sample which was EPR insulated. Samples were tested using a Mettler Toledo model DSC 3+. The parameters for testing began at -90°C. That temperature was held for 2 minutes to ensure the sample had thermally equalized. At a rate of 10°C per minute, the chamber was heated to 90°C, held for 1 minute then cooled at the same rate back to -90°C. This temperature cycle was performed twice for each sample. The first temperature cycle of a polymer sample often contains the thermal history of the material which is then erased in subsequent cycles. The four mastic samples show similar features especially in the second cycle when thermal history has been erased. All mastic samples show a characteristic endothermic peak near -70°C. This peak corresponds to the glass- transition temperature (Tg) for polyisobutylene rubber (PIB). The onset temperature and peak temperature were recorded and can be seen in Table 3. Table 3: Glass Transition Temperature for various strand block mastics Viscosity: An Anton Paar MCR302 rheometer was used to measure flow characteristics of various strand block samples collected from new and field-aged cables. The rheometer used the parallel plate method at a constant torque of 0.01Nm and measured the resistance to flow, or viscosity, of the mastic. Measurements were taken in 5°C increments from 100°C down to 40°C. The data are shown in Figure 2 with the rheometer platen temperature on the X-axis and the log of viscosity on the Y-axis. Exponential fitted lines with R- squared values and equations are shown for each sample. Fitted lines were extrapolated to 25°C to show the viscosity near room temperature. From 40°C to 70°C all samples follow the same exponential decrease in viscosity as the temperature increases. The same is also true up to 100°C for all samples except the Prysmian 2019, which showed some instability at higher temperatures. During the collection process it was noted that strand-block materials varied in adhesion, notably the Nexans 2019 mastic was the stickiest. The data reveals that for a given temperature, the viscosity difference between samples can vary by more than one order of magnitude. This variation is attributed to the difference in molecular weight of the PIB and specific concentration of carbon black. The data also reveals that mastics tend to experience about an order of magnitude change in viscosity for every 40°C change in temperature. The understanding of the PIB-based strand block mastic’s physical properties can be applied to create an injection protocol tailored to strand block cables. The thermally enhanced rejuvenation (TER) process disclosed by US Patent No.8,572,842 can be optimized for strand block cable by seeing an increase in conductor temperature that is sufficient to reduce the viscosity of the strand block mastic by at least an order of magnitude to encourage flow. In one embodiment, the cable temperature is increased by about 40°C above ambient. Further, the cable temperature is increased so that the viscosity of the strand-block mastic is decreased by about 1 order of magnitude or greater. Injection Fluid Viscosity An important property of an injection fluid ideally suited for strand-blocked cable injection, is its viscosity. The injection fluid must be able traverse the length of strand-blocked cable conductor by connecting the network of voids within the mastic that make of the free volume. Viscosity is however dynamic and it is well known to change with temperature and in the case of the dialkoxysilanes, the degree of polymerization upon hydrolysis with water. For reference, the viscosity of several injection fluids cited as preferred embodiments in prior art are provided in Table 4. The viscosity values below are collected from readily available manufacturer data sheets on the monomer or measured in the laboratory and are representative of the monomer. Table 4: Viscosities for Common Injection Fluids However, the injection of cable manufactured with a strand blocked mastic- filled conductor poses a further challenge as PIB mastic dissolves into the fluid. The higher molecular weight PIB will increase the rejuvenation fluids viscosity and will slow the rate of injection into the cable. In the extreme, the fluid viscosity may increase to a point that the flow of rejuvenation fluid into the cable stops altogether leaving the cable partly treated. This phenomena was well documented in the example below. Example 1 (SBT11-phase 1) In Figure 3, test setup 300 is comprised of a cable sample 302 arranged in a U shape. The cable sample is terminated at both ends with electrical connectors 308 and 310 and injection adapters 304 and 306, respectively, to make the fluid seal. A DC current supply 321 is connected to each end of the cable sample through interconnect cables 326 and 328 to complete the circuit. The DC current supply is connected to a temperature controller 322 through interconnect 330 to provide on/off control of the current. The temperature controller is joined to the cable sample through test lead 324 to monitor temperature. Injection tools 312 and 314 are used to provide fluid access to the injection adapters on the feed side and receiving side of the cable sample, respectively. The feed side of the cable is connected to a feed assembly 340 through a ball valve 346. The feed assembly is comprised of a fluid flow meter 342, a fluid injection tank 344 and a compressed gas cylinder 348. The receiving side of the cable is connected to a catch tank 450 through a ball valve 352. For the purpose of the example, a rejuvenation fluid consisting primarily of dimethyl-dibutoxysilane (DMDB) as disclosed in US patent No.7,777,131 was selected. It was mixed with <1.0 wt% hydrolysis condensation catalyst DDBSA (dodecylbenzene sulfonic acid). While DDBS was used, other hydrolysis condensation catalysts liked tetra-isopropyl titanate (TiPT) could be used. Injections were performed at 250psi and 50°C to elastically expand the cable. A 10-foot dummy cable instrumented with a thermocouple in a hole drilled to the conductor was used to control temperature. The thermally enhanced rejuvenation (TER) system was set to a current of 250 Amps. Ambient temperature was 16.5°C near the floor. Both ends of the cable were closed as soon as enough sample was collected. There was at least an hour between the start of heating and injection start for the 50 feet and 100 feet samples to be sure the test cable had stabilized at temperature. The results are shown in Tables 5 and 6. Table 5: Results The flush samples were analyzed by FTIR to determine their PIB concentration and referenced against a known calibration curve to estimate viscosity. The results for the 3 cables are shown in Table 6. Weight percent of PIB in the first flush sample (Bottle #1) is observed to increase fairly linearly with length of cable. Referring to Figure 4A, viscosity of the flush sample was plotted against cable length and found to increase following an exponential fit. Referring to Figure 4B, viscosity was also plotted against the injection duration as described in Table 5. The injection duration ranged from just over 2 minutes for the 20-foot sample to over 114 minutes for the 100-foot sample where viscosity followed a linear fit. Figure 4C plots cable length as a function of injection duration. Extrapolation of the data demonstrates that a practical limit on the length of cable that can be injected using this methodology is achieved, in this case about 140 ft and well short of the typical 300 to 400 ft lengths of URD cable installed in the field. While this experiment only looked at one particular cable and followed one protocol, it can be appreciated that a maximum could similarly be calculated for other cable. Table 6: Results Injection Fluid in which PIB is Mostly Insoluble To minimize the effect highlighted above, cables with PIB-based strand- blocked mastic filled conductor should be injected with a silicone-based rejuvenation fluid in which PIB is mostly insoluble. In addition to restoring the dielectric strength of the cable insulation, the right injection fluid should be capable of maintaining a low viscosity despite coming into contact with the PIB-based mastic solute to keep injection times low. This is of particular importance as the length of cable increases. For reference, the average URD cable in field installation is approximately 350ft and injection times longer than 1 day may be undesirable. The ability of various injection fluids to form solutions with PIB-based strand block mastic is demonstrated through the screening test outlined below. While many injection fluids were evaluated, the test is by no means fully exhaustive and it should be appreciated that a similar screening method could be applied to other injection fluid candidates. The solubility characteristics of carbon black filled PIB strand block mastic were tested in a range of solvents to determine the most efficacious material for strand block injection. The mastic was obtained from Southwire 2019 strand blocked cable by opening the cable and scraping the sticky mastic material from the conductors. Spheres of the strand block mastic were placed in glass vials, the test liquid was added, and the vial was shaken at room temperature to qualitatively determine solubility. In most cases, the vials were then placed in a 55°C oven for varying periods of time. The vials were removed periodically for brief shaking. The results can be seen in Table 7. Table 7: Results from Solubility Testing of Rejuvenation Fluids & Solvents.
The PIB based strand block mastic was first tested without a solvent at elevated temperature to assess its “melting” behavior. A sphere of PIB was placed in a glass vial, and the vial was placed in an oven. The temperature was increased from 40°C to 100°C over a period of 3 hours. There appeared to be a slight softening above 50°C, but the material did not flow even at 100°C. When spheres of the PIB-based mastic were mixed in a 1:2 weight ratio with xylenes and agitated at room temperature, the PIB began dissolving immediately. The liquid portion became black colored, and fine, carbon black particles were evident. Most of the mastic dissolved at room temperature, and the remainder dissolved within 6 hours at 55°C. This produced a yellow solution with very fine black powder suspended in it. PIB-based mastic was then tested with Novinium CableCure® 732/30 rejuvenation fluid at 1:1, 1:2, and 1:4 weight ratios at 55°C with occasional agitation over a period of 144 hours. Cablecure 732/30 is a fluid mixture primarily consisting of tolylethylmethyldimethoxysilane (TEM) and Cyanobutylmethyldimethoxysilane (CBM). No dissolution of the PIB was observed in any of the samples. PIB-based mastic with tolylethylmethyldimethoxysilane (TEM) in a 1:5 ratio did not appreciably dissolve at room temperature, so it was aged at 55°C. After about 1 hour with occasional shaking, the large spheres of PIB began to break into smaller particles, and eventually all the large spheres were reduced to small particles, but the fluffy carbon black particles resulting in the case of xylene were not seen. The experiment was repeated with a PIB:TEM ratio of 1:2.5 with the same result. PIB-based mastic with phenylmethyldimethoxysilane (PhMDM) in a 1:5.3 weight ratio did not dissolve at 55°C even after 72 hours. PIB-based mastic in dimethyldimethoxysilane (DMDM) at a 1:3.3 ratio produced no dissolution at room temperature, and after 48 hours at 55°C, the spheres of PIB were reduced to small granules with no free carbon black. A similar experiment using dimethyldiethoxysilane (DMDE) gave the same result, but the granules formed were finer than in the case of dimethyldimethoxysilane. In contrast, when the strand-block mastic was mixed at room temperature in a 1:5.3 ratio with dimethyldi-n-butoxysilane (DMDB), about half the PIB dissolved in 5 minutes. The rest dissolved in a 55°C oven in less than 30 minutes with occasional shaking. The particles formed were small and fluffy like those seen with xylenes. A mixture of PIB based mastic and tolylethylmethyldi-n-butoxysilane (TEMDB) in a 1:3.2 weight ratio was heated in a 55°C oven with occasional agitation. After 47 hours, the PIB was completely dissolved, and the mixture was filtered to remove the carbon black. The resulting yellow liquid was found to have a viscosity at room temperature of 43 cSt while the pure TEMDB has a viscosity of 4.74 cSt. This indicates TEMDB dissolves less PIB than DMDB. Two other materials with structures similar to DMDB were also tested at a weight ratio of 3.3. Di-i-propyldimethoxysilane dissolved most of the strand-block mastic at room temperature, but visually better than DMDB. Di-n- butyldimethoxysilane, which has a molecular weight identical to DMDB dissolved only part of the PIB at room temperature and clearly better than DMDB. Additional screening tests were performed on candidate fluids that showed minimal solubility to PIB-based mastics. Samples were prepared and placed in a 55°C oven and removed periodically for shaking and observations. The results are summarized below in Table 8. Based on testing, CBM and PhMDM appear to be mostly insoluble with PIB mastic. However, TEM appears to be slightly soluble up to about 5%. While only CBM, TEM and PhMDM were analyzed in this study, it is appreciated that the methodology could be applied to other candidate fluids and this list is by no means exhaustive. Table 8: Detailed screening of low solubility fluids Preferred embodiments Of the fluids evaluated in the screening tests above, cyanobutylmethyldimethoxysilane (CBM) and phenylmethyldimethoxysilane (PhMDM) were found to be poor solvents for dissolving PIB based strand-block mastic. In other words, PIB based strand-block mastic is mostly insoluble in CBM and PhMDM, which makes them ideal fluids for treating cables with PIB-based strand block mastic between the conductor strands. Tolylethylmethyldimethoxysilane (TEM) and dimethyldimethoxysilane (DMDM), were found to be moderate solvents with PIB based strand block mastic. Dimethyldi-n-butoxysilane (DMDB), tolylethylmethyldi-n-butoxysilane (TEMDB), Di- i-propyldimethoxysilane (DPrDM), and di-n-butyldimethoxysilane (DBDM) were found to be strong solvents for PIB based strand-blocked mastic. However, it should be appreciated that this list is purely demonstrative and other fluids not tested may exhibit similar behavior. Example 2 (SBT11-phase 2) The following example demonstrates the advantages of injection fluids where PIB-based strand block mastic is less soluble. A test apparatus similar to that shown in Figure 3 was prepared. For this test, 2020 vintage Prysmain Doublseal 1/0 AWG, 15kV cable was selected. This make and vintage was found to be particularly challenging to inject based on the measured fill % and physical properties of its particular strand block mastic. Three samples measuring 100ft each were prepared for injection in accordance to Table 9 and the procedure below. All fluids were prepared with approximately 1% DDBSA catalyst. Table 9: Test setup The terminations of the cable were prepared with injection adapters installed over 2-hole lugs to seal the ends of the cable. Injection tools were connected to the injection adapters to allow for the injection of fluid into the cable conductor. The terminated cables were installed into the test setup and a temperature sensor was used to monitor cable temperature and relay the reading back to a temperature control switch. For the purpose of this example, a conductor temperature of 50°C was maintained with a warming current of 250 amps. (Typical cable insulations are rated to run at 90°C, with emergency operation up to 130°C on certain cables.) When the set temperature was achieved in the cable, the temperature controller would switch current off until the cable temperature dropped back below the lower set point. The tests were performed with an ambient temperature that ranged from between 15 to 17°C. The results are summarized in Table 10. The injections of the low and medium-solubility fluids were run to completion in 2 hours and 33 minutes and 3 hours and 57 minutes respectively while the high-solubility sample failed to complete in nearly 7 hours as the viscosity of the fluid increased. During the first several minutes of the injections, the flow rate for the high-solubility fluid was fastest due to its relatively low viscosity compared to the other fluid mixtures. However, the flow rate for the high-solubility fluid dropped off quickly after the few tens of minutes and the injection was ultimately stopped after approximately 6 hours and 53 minutes. The cable sample was dissected and it was determined that the fluid front was at 66% of the total length. During the course of injection, the low-solubilty fluid’s flow rate was significantly more stable hovering near 20 mm/min on the flow meter. Table 10: Results A similar study looked at the total volume of fluid injected over the course of the first 3 hours and is shown in Figure 5. In this graph, the injected volume into cables treated by the low-solubility fluid and a medium-solubility fluid described in Table 5 are directly compared. The rate of injection begins proportionally to the starting viscosity of the two fluids. However, at approximately ¼ hour the total volume injected into each cables cross as the injection rate of the medium-solubility fluid slows relatively with the dissolution of the high-molecular weight PIB resulting dissolved into fluid resulting in an increased viscosity. By the end of the 3 hour injection, the low-solubility fluid has injected about 50% more fluid. The benefit of a low-solubility of PIB in the injection fluid is a particular benefit on long lengths of cable representative of cables installed common in field applications that may average 350 feet or more. Fast Diffusing – T15 Results The diffusion coefficients for many common injection fluids into polyethylene have been previously reported in literature and are summarized below in Table 11. When injecting cables at elevated temperatures, the diffusion coefficient can range by more than 10 times between the commonly used fluids at 55 °C and even more at 24 °C. The diffusion coefficient at 55 °C is particularly interesting when injecting cable using thermally enhanced rejuvenation process. As a preferred embodiment for strand blocked cable injection phenylmethyldimethoxysilane, dimethyldimethoxysilane and cyanobutylmethyldimethoxysilane may be of particular interest as they offer relatively fast diffusion and both were found to be poor solvents for dissolving PIB- based mastic during the screening tests described earlier. Further, fluids that see a relatively large jump in diffusion rates between 24 °C and 55 °C may be particularly advantaged when the thermally enhanced rejuvenation process is employed for injection and/or soaking supplemental fluid into a cable to adequately treat the insulation. For example, cyanobutylmethyldimethoxysilane sees its diffusion rate increase 46 fold compared to other fluids that increase roughly by only one order of magnitude. While the table below lists only four common injection fluids, it is appreciated that the same method of selection could be applied to other fludis. Table 11: Diffusion Coefficient for Common Injection Fluids The foregoing described embodiments depict different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected,” or "operably coupled,” to each other to achieve the desired functionality. While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Accordingly, the invention is not limited except as by the appended claims.