Temperature Profile for 36 Marker Spheres on 3M 788 ACCR Conductor 3M Company

Temperature Profile for 36 Marker Spheres on 3M 788 ACCR Conductor 3M Company NEETRAC Project Number: 07-113 June 2007 A Research Center of the Georgia Institute of Technology Requested by: Dr. Colin McCullough 3M Company Principal Investigator: Paul Springer, PE Reviewed by: Elsa Harris

SUMMARY Temperature Profile for 36 Marker Spheres on 3M 788 ACCR Conductor 3M Company NEETRAC Project Number: 07-113 June 2007 3M Company requested temperature data for 788 ACCR conductor with 36 diameter marker spheres installed. Aluminum and plastic marker spheres manufactured and provided by P & R Technologies (Portland, OR) were mounted on a conductor section, and instrumented with thermocouple temperature sensors. P&R Technologies produce the aluminum marker sphere for use on conductors that are rated to temperatures of 250 C. The conductor was loaded using AC current to raise the temperature up to 300 C. Steady-state temperature data was recorded at 100 C, 210 C, 240 C and 300 C. The continuous and emergency operating temperature ratings for ACCR are 210 C and 240 C respectively. The surface of both the plastic and aluminum marker spheres remains below 54 C for conductor temperatures up to 300 C. Of particular concern is the temperature of the resin plug used to secure the formed wire rods to the marker sphere mounting flanges. Here the aluminum sphere has an aluminum casting for the resin plug, while the plastic sphere has a molded plastic mounting flange. Improved heat transfer characteristics of the aluminum sphere is apparent, because the hottest part of the resin reaches 145 C with the plastic sphere, and only 100 C with the aluminum sphere. With conductor temperatures of 210 C & 240 C, these flange temperatures dropped by 10 C. P&R Technologies testing has indicated that the resin is able to operate at 120 C with no degradation. The hottest location in the test loop is the conductor in the center of the marker sphere. With the conductor in still air running steady-state at 300 C, the wire at the center of the marker sphere was steady-state at 324 C. Back at 210 C & 240 C, the conductor at the center of the marker sphere was only 20 C hotter. KEY FINDINGS Surface temperature of the marker sphere does not exceed 54 C except at the mounting flanges, where large formed-wire rods conduct heat into a resin plug. Temperatures on the surface of the sphere and on the mounting rods are very consistent between spheres with the exception of the marker sphere mounting flange nearest the conductor. The resin temperature reaches 145 C for the plastic sphere, and 100 C for the aluminum sphere with the conductor at 300 C. These temperatures drop 10 C with the conductor at 210 C-240 C. The material used for the resin holder (plastic versus aluminum) appears to account for the temperature difference. Anomalous behavior at some locations may be due to mechanical effects (varying thermal contact) as the conductor heats up. Core temperature in the free span was 14 C hotter than the 300 C surface. Conductor temperature in the center of the sphere runs approximately 24 C warmer than the free-span conductor. Core temperature at the center of the sphere was not instrumented, but the gradient should be approximately the same as the gradient for the still-air free-span. NEETRAC Project Number 07-113, Final Report June 2007 Page 2 of 11

PROCEDURE AND RESULTS Approximately 25 feet (8 meters) of 788 ACCR conductor was connected to the NEETRAC fault current transformer. The unit is designed to deliver 30,000 amperes into a fault, and can provide up to 5000 amperes of steady-state AC current. Sheathed type-t thermocouples were used to measure conductor temperature. For the control temperature, a drill was used to make a small hole between two adjacent strands. For the core thermocouple, the hole was drilled to the surface of the core. To date, we have not found a drill capable of making a 0.033-inch diameter hole to the center of the core. The shell of the aluminum marker sphere is too thin to insert a thermocouple. Therefore, stick-on type T thermocouples were used to measure surface temperature on both types of marker sphere. Note that all temperature measurements are influenced to some degree by heat conduction into the thermocouple and the thermocouple wires. The measurement error is small for the conductor and other massive components. On the thin shell of the aluminum sphere, heat transfer effects could be significant, and test data could under-represent the actual temperature if the instrument was absent. Localized heat transfer is minimized by routing the leads along the surface (to keep them warm, and using light (lowmass) thermocouples and wires. Hand feel of the marker surface near the thermocouples did not detect any temperature difference, and therefore it is assumed that the error due to heat transfer into the sensors is within the +/- 2 C error normally accepted for thermocouple measurements. The thermocouples used for the measurements have a +/- 0.5 C error specification. The conductor was not placed under tension. The weight of the conductor loop and marker sphere was supported on the point of a fiberglass structural angle, which was in turn supported by steel stanchions. The intent was to minimize heat transfer at the support points. One problem encountered during the heat up was mechanical movement as the wire heated. This caused thermocouples to pull out, and it is apparent in the test data that the thermal contact between the conductor and the formed-wire mounting rods changed as the temperature changed. All channels behaved as expected during the cool-down phase. Figures 1-4 show the marker spheres and their thermocouple arrangements. NEETRAC Project Number 07-113, Final Report June 2007 Page 3 of 11

Figure 1: marker sphere under test (striations on top surface are reflections of overhead lights) Figure 2a: detail showing mounting flange 1 through 4, and inboard A formed wires NEETRAC Project Number 07-113, Final Report June 2007 Page 4 of 11

Ball Surface Top Ball Surface in-line 4 Ball Surface in-line 3 Ball Surface in-line 2 Ball Surface in-line 1 Mounting Flange 4 Mounting Flange 3 Mounting Flange 2 Mounting Flange 1 Figure 2b. Position and naming convention of thermocouples in-line with conductor Inboard A preform Outboard A preform Outboard B preform Ball Flange Ball Surface x conductor 4 Ball Surface x conductor 3 Ball Surface x conductor 2 Ball Surface x conductor 1 Figure 2c. Position and naming convention of thermocouples perpendicular to conductor Figures 3 and 4: detail showing ball flange and ball surface (left), and inboard A formed wire (right) NEETRAC Project Number 07-113, Final Report June 2007 Page 5 of 11

Figure 5 shows the temperature profile for the plastic marker sphere. Figure 6 shows the same information for the aluminum sphere. Figures 7 and 8 show the steady-state temperature rise above ambient for the different locations in the test loop and on the marker spheres. Figure 9 shows bonus material illustrating the steady-state ampacity for the 3M 788 ACCR conductor. A more detailed discussion of each graph is provided in the figure captions. Temperature (deg C) 340 320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 Temperature Profile for Plastic 36" Marker Sphere Anomalous heat-up may be caused by change in contact pressure. The instrument channel appears to be functioning correctly 20 0 50 100 150 200 250 300 350 400 450 500 Elapsed Time (min) Control Cntl Core Outboard A preform Inboard A preform Outboard B preform Conductor center of sphere Mounting flange 1 Mounting flange 2 Mounting flange 3 Mounting flange 4 Ball Surface in-line 1 Ball Surface in-line 2 Ball Surface in-line 3 Ball Surface in-line 4 Ball Surface Top Ball Flange Ball surface x conductor 1 Ball surface x conductor 2 Ball surface x conductor 3 Ball surface x conductor 4 Ambient Center of sphere Figure 5: Data recorded for plastic marker sphere. With the conductor at 300 C, the formed wires run at 220 C, the mounting flange near the formed wires at 130-140 C, and the ball surface at < 50 C. With the conductor at 240 C, the formed wires run at 170-180 C, the mounting flange near the formed wires at 120-130 C, and the ball surface at < 50 C. With the conductor at 210 C, the formed wires run at 150-170 C, the mounting flange near the formed wires at 110-130 C, and the ball surface at < 40 C. Figure 7 shows the corresponding data plotted in terms of temperature rise. NEETRAC Project Number 07-113, Final Report June 2007 Page 6 of 11

Temperature (deg C) 340 320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 Anomylous data is the result of safety stanchion falling against sample Temperature Profile for Aluminum 36" Marker Sphere Spurious (noisy) data was deleted where there are gaps 20 0 50 100 150 200 250 300 350 400 450 500 Elapsed Time (min) Control Cntl Core Outboard A preform Inboard A preform Outboard B preform Conductor center of sphere Mounting flange 1 Mounting flange 2 Mounting flange 3 Mounting flange 4 Ball Surface in-line 1 Ball Surface in-line 2 Ball Surface in-line 3 Ball Surface in-line 4 Ball Surface Top Ball Flange Ball surface x conductor 1 Ball surface x conductor 2 Ball surface x conductor 3 Ball surface x conductor 4 Ambient Figure 6: Data recorded for aluminum marker sphere. With the conductor at 300 C, the formed wires run at 230-240 C, the mounting flange near the formed wires at 80-100 C, and the ball surface at < 50 C. With the conductor at 250 C, the formed wires run at 200 C, the mounting flange near the formed wires at 80-90 C, and the ball surface at < 50 C. With the conductor at 210 C, the formed wires run at 160 C, the mounting flange near the formed wires at 70-80 C, and the ball surface at < 40 C. Figure 8 shows the corresponding data plotted in terms of temperature rise. NEETRAC Project Number 07-113, Final Report June 2007 Page 7 of 11

Temperature Rise Above Ambient (deg C) 280 260 240 220 200 180 160 140 120 100 80 60 Steady-State Temperature Rise Above Ambient for Plastic 36" Marker Sphere Control Outboard A preform Inboard A preform Outboard B preform Inboard B preform Mounting flange 1 Mounting flange 2 Mounting flange 3 Mounting flange 4 Ball Surface in-line 1 Ball Surface in-line 2 Ball Surface in-line 3 Ball Surface in-line 4 Ball Surface Top Ball Flange Ball surface x conductor 1 Ball surface x conductor 2 Ball surface x conductor 3 Ball surface x conductor 4 40 20 0 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 Control Surface Temperature Figure 7: Steady-state temperature rise above ambient for locations on the plastic marker sphere. Note the mounting flanges show a rise of 100-110 C, and the ball surface 20 C. Temperature Rise Above Ambient (deg C) 280 260 240 220 200 180 160 140 120 100 80 60 Steady-State Temperature Rise Above Ambient for Aluminum 36" Marker Sphere Control Outboard A preform Inboard A preform Outboard B preform Inboard B preform Mounting flange 1 Mounting flange 2 Mounting flange 3 Mounting flange 4 Ball Surface in-line 1 Ball Surface in-line 2 Ball Surface in-line 3 Ball Surface in-line 4 Ball Surface Top Ball Flange Ball surface x conductor 1 Ball surface x conductor 2 Ball surface x conductor 3 Ball surface x conductor 4 40 20 0 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 Control Surface Temperature Figure 8: Steady-state temperature rise above ambient for locations on the aluminum marker sphere. Note the mounting flanges show a rise of 50-70 C, and the ball surface 20 C. NEETRAC Project Number 07-113, Final Report June 2007 Page 8 of 11

300 Temperature vs Current (still air, indoor lab space) y = 1.738E-08x 3 + 1.940E-05x 2 + 4.622E-02x 250 Temperature (deg C) 200 150 100 Control Temperature Rise Above Ambient Ambient Temperature Poly. (Control Temperature Rise Above Ambient) 50 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Current (amperes) Figure 9: steady-state temperature versus current for 788 ACCR conductor in draft-free lab space. Data are from the heat run on the plastic marker sphere. CONCLUSION: Test results show the only significant thermal performance difference between the aluminum and plastic marker spheres is the temperature of the resin plug close to the conductor (mounting flange). Skin temperature, ball-flange temperature, and the temperature of the attachment rods track each other within the measurement error except for locations near the mounting flange. The aluminum mounting flanges conduct heat away from the conductor more effectively, and therefore maintain lower temperature. With the conductor at 300 C steady state temperature, the aluminum flange has a maximum temperature of 100 C. The plastic flange at the same location measures 145 C. The skin temperatures of both spheres are always less than 50 C. P&R Technologies testing has indicated that the resin is able to operate at 120 C with no degradation. Even if the resin material failed, the power line marker would not move or slip on the line, or cause any failure of the marker due to the fact that the wire-formed armor rods are turned nearly 90 degrees from the line, and are potted into a mounting plate that is then bolted to the power line marker surface. This creates a sandwich effect on the wireformed armor rods, being held in place mechanically by the mounting plate and power line marker surface. With the free-span conductor at steady state temperature of 300 C, the conductor in the center of the sphere is 24 C warmer. The temperature difference would be greater as wind speed increased. NEETRAC Project Number 07-113, Final Report June 2007 Page 9 of 11

Therefore, caution is in order if dynamic rating methods are used for spans with large marker spheres. The heat-up and cool-down data provided an opportunity to observe the thermal time constants of the various locations. Thermal time constants are useful for computing transient (short-time) overload ratings. The free span (control) conductor exhibits a thermal time constant of 13 minutes. All parts of the sphere and its mounting hardware have considerably longer time constants. Due to the lower temperatures of the mounting flange in the aluminum marker sphere, 3M recommends the use of the aluminum marker sphere with 3M ACCR conductors. EQUIPMENT USED: Yokagawa DC 100 temperature recorder, calibration control # CN 1098 Omega Engineering Type T sheathed thermocouples (sheath electrically isolates the thermocouple from the conductor, while still allowing thermal coupling) Omega Engineering Type T stick-on thermocouples (for thin surfaces where the sheathed thermocouples are too large). NEETRAC high-current AC power supply REFERENCES AND STANDARDS LISTING Specification sheet, 3M 788 ACCR conductor DISCLAIMERS Notice The information contained herein is, to our knowledge, accurate and reliable at the date of publication. Neither GTRC nor The Georgia Institute of Technology nor NEETRAC will be responsible for any injury to or death of persons or damage to or destruction of property or for any other loss, damage or injury of any kind whatsoever resulting from the use of the project results and/or data. GTRC, GIT and NEETRAC disclaim any and all warranties, both express and implied, with respect to analysis or research or results contained in this report. It is the user's responsibility to conduct the necessary assessments in order to satisfy themselves as to the suitability of the products or recommendations for the user's particular purpose. No statement herein shall be construed as an endorsement of any product, process or provider. TECHNICAL INFORMATION AND DATA; PRODUCT USE. Technical information and data, recommendations, and other statements provided by 3M are based on information, tests, or experience which 3M believes to be reliable, but the accuracy or completeness of such information is not guaranteed. Some of the standard industry tests conducted by 3M were originally designed for conventional conductors and were adapted by 3M for use with composite conductors; references to such tests should be considered in light of this fact. Such technical information and data are intended for persons with knowledge and technical skills sufficient to assess and apply their own informed judgment to the information. No license under any 3M or third party intellectual property rights is granted NEETRAC Project Number 07-113, Final Report June 2007 Page 10 of 11

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