CTC 460 kcmil ACCC Conductor Stress Strain Tests

Transcription

1 CTC 46 kcmil ACCC Conductor Stress Strain Tests NEETRAC Project Number: 8-45 March, 28 Requested by: Doug Pilling CTC Principal Investigator: Paul Springer, PE Reviewed by: Graham Price

2 CTC 46 kcmil Conductor Stress Strain Tests NEETRAC Project Number: 8-45 March, 28 SUMMARY Stress-strain tests were performed in accordance with the 1999 Aluminum Association guide to measure the elastic and short-term creep properties for 46 ACCC Stockholm conductor. Upon completion of the stress-strain test, the conductor and core samples were pulled to destruction to determine actual breaking strength. The conductor model and stress-strain coefficients are provided. The conductor made 17% of RBS during the tensile test and the core made 18% of its rating. TEST SAMPLES 1) 3.5 meters (1 ) of 46 kcmil ACCC conductor PROCEDURE I) Stress-strain: The sample was cut into 6.3 meter (2-7 ) long sections. Bolted clamps were installed on both sides of each cut to prevent any component from shifting. The composite stress-strain sample was taken from the inner part of the reel to ensure the manufacturing pre-stress is most representative. Cast-resin terminations were applied to the sample ends using a procedure designed to preserve the conductor manufacturing pre-stress and thereby ensure that test samples behave as similarly as practical to in-service conductor. The 1999 Aluminum Association guide for conductor stress-strain testing was followed. Composite conductor {RBS kn (35,115 lb)} 1) Apply load of kn (1 lb). Remove sag with a mid-span support 2) Install extensometer, and set to zero 3) Pull to 3% of RBS { kn (1,535 lb)} 4) Hold for 3 minutes 5) Relax load to kn (1 lb) 6) Pull to 5% RBS {78.1 kn (17,558 lb)} 7) Hold for one hour 8) Relax load to kn (1 lb) 9) Pull to 7% RBS { kn (24,581 lb)} 1) Hold for one hour 11) Relax load to kn (1 lb) 12) Pull to 75% RBS { kn (26,336 lb)} 13) Relax load to kn (1 lb), and remove the extensometer (for its own protection) 14) Pull sample to destruction at kn/min (15, lb/min) Core (nominal rating is kn (29,248 lb) 1) Pull to calculated initial tension {in this case, kn (492 lb)}. Remove sag with a mid-span support NEETRAC Project Number 8-45, Final Report March, 28 Page 2 of 1

3 2) Install extensometer, and set to zero 3) Pull to.273% strain (same strain as conductor at start of 3% of RBS test) 4) Hold for 3 minutes 5) Relax load to kn (492 lb) 6) Pull to.6848% strain (same strain as conductor at start of 5% of RBS test) 7) Hold for one hour 8) Relax load to kn (492 lb) 9) Pull to % strain (same strain as conductor at start of 7% of RBS test) 1) Hold for one hour 11) Relax load to kn (492 lb) 12) Pull to 75% of the core rating { kn (21,936 lb)} 13) Relax load to kn (492 lb), and remove the extensometer (for its own protection) 14) Pull sample to destruction at kn/min (15, lb/min) RESULTS Stress-strain Figure 1: Sress-strain setup. Extensometer is suspended next to the sample. Elongation in between knife-edges is measured to nearest.254 mm {.1 inch (<.5 ppm)}, using a digital sensor. NEETRAC Project Number 8-45, Final Report March, 28 Page 3 of 1

4 CTC 46 kcmil "Stockholm" ACCC Load vs. Time for Composite Stress-strain Test Tension RBS 75% RBS 12 7% RBS 5% RBS 1 3% RBS Load (kn) Elapsed Time (minutes) Figure 2: Load profile for composite stress-strain test CTC 46 kcmil "Stockholm" ACCC Stress Strain Data with Initial and Final Modulus 3 25 Stress-strain data Initial modulus data Final modulus data Poly. (Initial modulus data) Linear (Final modulus data) Initial Modulus y = x x x Final Modulus y = 615.7x Stress (MPa) Strain (%) Figure 3: Plot of composite stress-strain data with initial and final modulus. Negative strains measured were first believed to be caused by instrument slippage. The phenomenon was traced to release of compressive stress in the aluminum layer after the aluminum yielded. Therefore, the negative values are valid measurements. See core test data illustrating the instrument s repeatability. NEETRAC Project Number 8-45, Final Report March, 28 Page 4 of 1

5 Stress-strain data Initial modulus data Final modulus data Linear (Final modulus data) Linear (Initial modulus data) CTC 46 kcmil "Stockholm" ACCC Core Stress-strain data with Initial and Final Modulus Final Modulus y = x Initial Modulus y = 114.6x Stress (MPa) Strain (%) Figure 4: Plot of core stress-strain data with initial and final modulus 3 25 Translated initial modulus data Translated final modulus data Poly. (Translated initial modulus data) Linear (Translated final modulus data) CTC 46 kcmil "Stockholm" ACCC Composite Modulus Translated Along Strain Axis Initial Modulus y = x x x Final Modulus y = 615.7x Stress (MPa) Strain (%) Figure 5: Initial and final moduli data from Figure 3 translated along strain axis for correct zero intercept NEETRAC Project Number 8-45, Final Report March, 28 Page 5 of 1

6 2 18 Initial modulus data Final Modulus data CTC 46 kcmil "Stockholm" ACCC Core Modulus translated along strain axis Initial Modulus y = 114.6x Final Modulus y = x Linear (Initial modulus data) Linear (Final Modulus data) Stress (MPa) Strain (%) Figure 6: Initial and final modulus data from Figure 4 translated along strain axis for correct zero intercept NEETRAC Project Number 8-45, Final Report March, 28 Page 6 of 1

7 National Electric Energy Testing, Research & Applications Center Stress*area ratio MPa Initial Composite Final Composite Initial Core Final Core Initial Aluminum Final Aluminum Poly. (Initial Aluminum) Linear (Final Aluminum) Linear (Final Composite) Linear (Initial Core) Linear (Final Core) Poly. (Initial Composite) Ratio Core: Ratio Aluminum: kcmil ACCC "Stockholm" Conductor Combined Stress-Strain Diagram Initial Composite y = x x x Final Composite y = 615.7x Initial Core y = x Final Core y = x Initial Aluminum y = x x x Final Aluminum y = x Strain (%) Figure 7: Combined stress-strain model NEETRAC Project Number 8-45, Final Report March, 28 Page 7 of 1

8 Equations for Stress-Strain Properties. Coefficients below are with respect to actual area. Figure 7 contains the equations normalized for area ratio of core and aluminum constituents: Composite Conductor Properties, direct test values: Initial Modulus for Stress Strain Curve: Stress (mpa) = *(Strain%) *(Strain%) *(Strain%) Final Modulus for Stress Strain Curve: Stress (mpa) = 615.7*(Strain%) Tensile Test, Composite Sample: kn (36,613 lb (17% RBS)) Composite Conductor, data shifted along strain axis to provide correct zero strain reference: Initial Modulus for Stress Strain Curve: Stress (mpa) = *(Strain%) *(Strain%) *(Strain%) Final Modulus for Stress Strain Curve: Stress (mpa) = 615.7*(Strain%) Core Strand Properties, direct test values: Initial Modulus for Stress Strain Curve: Stress (mpa) = 114.6*(Strain%) Final Modulus for Stress Strain Curve: Stress (mpa) = *(Strain%) Tensile Test, Core Sample: kn (31,794 lb (18% Rating)) Core Properties, data shifted along strain axis to provide correct zero strain reference: Initial Modulus for Stress Strain Curve: Stress (mpa) = 114.6*(Strain%) Final Modulus for Stress Strain Curve: Stress (mpa) = *(Strain%) Aluminum Properties (computed, direct measurement is not possible): Initial Modulus for Stress Strain Curve: Stress (mpa) = *(Strain%) *(Strain%) *(Strain%) Final Modulus for Stress Strain Curve: Stress (mpa) = *(Strain%) NEETRAC Project Number 8-45, Final Report March, 28 Page 8 of 1

9 Tensile Tests Following stress-strain testing, both samples were tested for ultimate tensile strength. The results are summarized in the following table. Table 1 Post Stress-Strain Tensile Tests Sample RBS/Rating Failure Load %RBS/Rating Failure Mode Composite Stress- Strain kn (35,115 lb) kn (37,613 lb) 17 Core broke in gage section Core Stress-Strain kn (29,248 lb) kn (31,794 lb) 18 Core broke in gage section The composite sample and the core sample exceeded RBS. A graph of the results is shown below. 18 CTC 46 kcmil"stockholm" ACCC Post Stress-strain Tensile Tests 15 Load (kn) 12 9 Composite Core RBS Core Rating Crosshead Position (mm) Figure 8: Post stress strain tensile tests NEETRAC Project Number 8-45, Final Report March, 28 Page 9 of 1

10 DISCUSSION / CONCLUSION: Stress-strain data provides coefficients for line designs (no acceptance criteria are applicable). Tensile tests following the stress-strain tests show both the core and the composite conductor exceeded the nominal ratings EQUIPMENT 1) MTS Servo-hydraulic tensile machine, Control # CQ 195 (load and crosshead data) 2) Dynamics Research Corporation (DRC)/NEETRAC cable extensometer, Control # CQ 32 (strain data). 3) Yokogawa DC1 data acquisition system, Control # CN 322 (temperature data) 4) HBM linear position indicator for crosshead displacement (for reference only) REFERENCES AND STANDARDS LISTING 1) ASTM E4, (Calibration of Load Testing Machines) 2) Aluminum Association Guide for Stress-Strain Testing, 1999 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. NEETRAC Project Number 8-45, Final Report March, 28 Page 1 of 1