477 kcmil, 3M Brand Composite Conductor
Core High-temperature Creep Tests
3M Company
Purchase Order 0000572787
NEETRAC Project Number: 02-179
February, 2003
A Center of
The Georgia Institute of Technology
Requested by:
Mr. Colin McCullough
3M
Principal Investigator:
Paul Springer III, P.E.
Reviewed by:
Dale Callaway
477 kcmil, 3M Brand Composite Conductor
Core High-temperature Creep Tests
3M Company
Purchase Order 0000572787
NEETRAC Project Number: 02-179
February, 2003
Summary:
3M contracted with NEETRAC for high-temperature creep tests on the metal matrix composite
(MMC) core strand from 3M’s 477 kcmil ACCR conductor. The Aluminum Association’s 1999 guide on
creep testing was used as a reference, with the exception that samples were tested at 150o C and 250o C.
The test results demonstrate extremely low creep at both temperatures.
Samples:
1) Sixteen (16) meters of 477 kcmil, type 16, 3M Composite conductor, from reel received
8/16/02.
References:
1) “Proprietary Information Agreement ….” Dated 3/27/01
2) “A Method for Creep testing of Aluminum and ACSR Conductors”, Aluminum Association,
1999.
3) 3M Purchase Order 0000572787.
4) PRJ 02-179, NEETRAC Project Plan
Equipment Used:
1)
2)
3)
4)
5)
6)
7)
Limitorque creep actuator
Mitutoyo creep frame extensometer, Control # CN 3041.
Creep system LabView data acquisition system, Control # CN 3040
National Instruments AT-MIO-16XE-50 computer interface
HBM 10,000 lb load cell, Model USB-XX108, Control # CN 3018.
Omega Engineering DMD load cell conditioner, used to condition HBM load cell
High current AC test set, Control # CN 3007
Procedure and Results:
Testing was conducted in accordance with a NEETRAC procedure entitled “PRJ02179,
CONFIDENTIAL – MMC Conductor Evaluation, 477 kcmil ACCR Core High-temperature Creep Test,
150o C and 250o C”. The procedure controls all technical and quality management details for the project.
For each sample, an 8-meter section was cut from the reel. All aluminum strands were removed,
leaving a naked core. Two complete sets of aluminum strands each approximately 3 feet long, were
NEETRAC 02179, 477 ACCR core high-temperature creep testing
Page 2 of 7
wrapped over the sample ends to provide connections for electrical terminations. Cast-resin terminations
were then fitted to each end of the sample. The aluminum strands were connected to tubular-to flat
NEMA four-bolt connectors. This arrangement allows for application of mechanical tension (resin
termination), and loading current (NEMA connector).
Each sample was installed in the creep frame, which has a computer interface for load control and
automatic logging of test data. Nominal tension of 400 lbs was applied during the set up phase. Supports
are provided in three locations along the sample to minimize sag. The Mitutoyo cable extensometer is an
aluminum box beam, which hangs from springs. The springs hold the beam in a neutral position next to
the sample, and senses elongation without applying significant loads. The instrument is shielded from the
hot sample by a four-inch air gap and a thick rubber blanket. The gage beam and the sample are
instrumented for temperature. Photographs 1 through 4 show the test in progress.
Photograph 1, sample temperature sensor
Photograph 2, Mitutoyo digital indicator,
electrical connection, and rubber heat shield
for gage rod
Photograph 3, tension actuator
Photograph 4, Railroad spring used to buffer
the actuator.
Room temperature was controlled, although the data show a daily temperature cycle due to solar
heating of the room, and cycling of the heating equipment. Both tests ran over 1000 hours with no
interruption in temperature or tension. Creep at the applied loads is very small – near the level of
instrument noise and extraneous effects. Extraneous effects include thermal and time-dependent drift of
NEETRAC 02179, 477 ACCR core high-temperature creep testing
Page 3 of 7
the load cell conditioners, and temperature effects on the load frame and the gage-reference rod. The
sample and the gage rod are instrumented for temperature. Raw elongation data was corrected for
temperature effects, but the correction does not result in smooth data. Factors contributing to non-smooth
data are believed to be the following:
1)
2)
3)
4)
5)
Instrument noise
Instrument temperature drift
Sample temperature gradients (the hot sample reacts to room drafts)
Gage rod temperature gradients (the rod will bow if it is warmer on one side, and
that will introduce measurement errors
Discrepancy in the thermal time constant of the sample (short TC) versus the gage
rod (long TC).
The creep measured during the test is small relative to extraneous effects on the instruments and
test equipment. For temperature compensation, values of 0.00006% per degree C is used for the sample,
and 0.00023% per degree C is used for the aluminum gage rod. For load compensation a coefficient of
0.000055% per pound was used for load compensation. Figures 1 and 2 show a summary of the data
collected, along with the logarithmic fit to the compensated creep data.
In spite of the ragged appearance of the data, the logarithmic fit to the corrected creep data
appears to be reasonable:
Creep150C@15%RBS (%)= 0.00036*Ln(hours) + 0.0009
Creep250C@15%RBS (%)= 0.00050*Ln(hours) + 0.0029
477 ACCR Core Creep at 150 C
300.0
0.010
y = 0.000361Ln(x) + 0.000946
0.008
250.0
0.006
0.004
Creep (%)
0.002
0.000
0
100
200
300
400
500
600
700
800
900
150.0
1000
-0.002
Raw Creep (%)
-0.004
Compensated Creep
lbs/10, degrees C
200.0
100.0
Tension (Y2 axis)
Gage Temp. (Y2 axis)
-0.006
Sample Temp. (Y2 axis)
Log. (Compensated Creep)
50.0
-0.008
0.0
-0.010
Time (hours)
Figure 1, tension, temperatures, creep, and the fit curve for the 150o C core creep test
NEETRAC 02179, 477 ACCR core high-temperature creep testing
Page 4 of 7
0.025
350
0.020
300
0.015
250
200
0.010
y = 0.000503Ln(x) + 0.002864
150
0.005
0.000
0
100
200
300
400
500
-0.005
Raw Creep (%)
Compensated Creep
600
700
Tension
(Y2 axis)
Gage Temp. (Y2 axis)
Sample Temp. (Y2 axis)
Log. (Compensated Creep)
800
900
lbs/10, degrees C
Creep (%)
477 ACCR Core Creep at 250 C
100
1000
50
0
-0.010
Time (hours)
Figure 2, tension, temperatures, creep, and the fit curve for the 250o C core creep test
Bonus Data:
At the end of the 1000-hour creep test, it was possible to control the load and temperature to
provide data on the properties of the core strand in the “fully aged” condition. Figures 3 and 4 show the
cool-down curves, and the linear and polynomial fits to the cool-down data.
NEETRAC 02179, 477 ACCR core high-temperature creep testing
Page 5 of 7
Cool-down Curve after 1000 Hours at 150C
4000
0.10
3800
0.09
2
y = 8.02E-07x + 4.58E-04x + 4.84E-03
3600
0.08
Strain
Tension
Linear (Strain)
Poly. (Strain)
Strain (%)
0.06
3400
y = 5.90E-04x - 1.14E-07
3200
0.05
3000
0.04
2800
0.03
2600
0.02
2400
0.01
2200
0.00
0.0
20.0
40.0
60.0
80.0
100.0
120.0
Temperature (deg C)
Figure 3, Cool-down data following the 150o C Creep Test
NEETRAC 02179, 477 ACCR core high-temperature creep testing
Page 6 of 7
140.0
2000
160.0
Tension (lbs)
0.07
Cool-down Curve after 1000 hours and 250 C Creep test
0.20000
4000
0.18000
3800
3600
0.16000
2
Strain (%)
y = 5.65E-07x + 5.39E-04x + 6.03E-03
0.14000
3400
0.12000
3200
0.10000
3000
0.08000
2800
0.06000
2600
0.04000
2400
Cool down after 1000-hour creep
Tension
Linear (Cool down after 1000-hour creep)
Poly. (Cool down after 1000-hour creep)
0.02000
2200
0.00000
0.0
50.0
100.0
150.0
200.0
Temperature (deg C)
Figure 4, Cool-down data following the 250o C Creep Test
NEETRAC 02179, 477 ACCR core high-temperature creep testing
Page 7 of 7
250.0
2000
300.0
Tension (lbs)
y = 0.000678x + 0.000000