Transformers and substations
standard off-the-shelf varieties. Copper conductor was bare 19-strand
2/0 AWG, and aluminium conductor was Alcan NUAL 18-strand com-
pact 4/0 AWG. Conductor sizes were selected to be approximately
the same ampacity. Connectors were a combination of compression
and mechanical bolted type one-hole lug connectors. All aluminium
compression connectors were tin-plated and supplied pre-filled with
an oxide inhibitor.
Connector installation procedures
Connectors were installed onto 50 cm long conductor segments ac-
cording to the manufacturer’s recommendations, using the following
procedures:
• All conductors were wire-brushed immediately before installing
the connectors
• Thomas & Betts Contax CTB8 oxide inhibitor was applied to the
aluminium conductor for installation of mechanical connectors
• No oxide inhibitor was applied to any of the copper-to-copper
connections
• Compression connectors were crimped using a Thomas & Betts
(Blackburn) model TBM5 crimping tool
• Mechanical connectors were installed using torque levels as
shown in Table 1
• A brazed or welded equaliser was installed on the other end of
each conductor segment to provide good current distribution to
the conductor for current testing and resistance measurements
Conductor size
Screw size
Torque
AWG
In
In lb
N m
2/0
7/16
120
13,6
2/0 – 4/0
11/16
275
31,1
2/0 – 4/0
3/4
375
42,4
Table 1: Mechanical connector torque levels for installation.
Test procedures
The testing consisted of periods of corrosive environmental exposure,
followed by the application of high current. This was intended to
produce conditions in which connectors that are susceptible t corro-
sion show an increase in contact resistance as the testing progresses.
The cyclic testing was conducted in the following sequence:
• Salt fog corrosion cycling – carried out for 500-blocks of time
• Current burst tests – carried out following each 500-hour salt fog
period
• Dc resistance readings of each connector were made approxi-
mately every 170 hours during the corrosion testing, and before
and after each set of current burst tests
• A total of four sets of salt fog and current burst tests were con-
ducted for a total of approximately 2 000 hours of salt fog testing
Corrosion cycling
Connector sample groups were arranged on a three-tier PVC rack
in an environmental chamber with the conductors and connectors
oriented horizontally and the connectors suspended in clean air. The
positions of the connector sets were exchanged periodically so that
more consistent environmental exposure from sample to sample was
achieved over the testing period. Each four-hour corrosion testing
cycle consisted of the following steps:
• Salt fog spray for a period of one hour and 45 minutes, consisting
of a fine mist of aerated 3% NaC1 solution, buffered to apH of 5,5
using nitric acid
• Dry heat for a period of two hours, reaching a maximum of 70°C
during the two hour period
• Clear water rinse for a period of 15 minutes
The cycle was repeated continuously during the corrosion testing.
Current burst testing
The reason for conducting current burst testing was to encourage
accelerated degradation at the connector contact with the conductor.
For the test, current levels of 1,750 Arms for 4/0 aluminium conduc-
tor and 1,800 Arms for 2/0 copper conductor were determined to be
sufficient to produce the desired effect. For each test, the current
was held at these levels long enough to raise the temperature of
the control conductor to 250°C, as determined by the thermocouple
measurement at the centre of the control conductor span. Typically,
this required an application of current for approximately 50 seconds,
starting with a conductor at near room temperature. Samples were
subjected to current burst testing as follows:
• Each set of ten connectors, which were joined together in series,
were subjected to current burst testing simultaneously
• The control conductor was placed in series with the connector
assembly; a thermocouple was attached to the centre of the length
T
ake note
A
bbreviations
AWG – American Wired Gauge
PVC – Polyvinyl Chloride
• Many concerns in the copper versus aluminium conductor debate are
based on outdated and incorrect information.
• A study conducted by the Canadian Copper and Brass Development
Association compared the connector performance under equivalent,
harsh environmental conditions.
• The configurations used were copper connectors on copper conductor;
aluminium connectors on copper conductor; aluminium connectors on
aluminium conductor.
29
December ‘13
Electricity+Control
