Aluminum alloy cable aluminum stranded conductor DC resistance measurement method

Aluminum alloy cable is in full swing in China, and its application is becoming more and more extensive, and an increasing number of users plan to choose aluminum alloy cable
.
However, due to the lag in regulation and supervision, it is difficult to distinguish
between good and bad in the market.
Many companies that do not have the production skills and equipment of aluminum alloy cables are also promoting aluminum alloy cables, which brings great confusion
to the user's selection.
Choose a real high-quality aluminum alloy cable
.
First of all, we must try to be able to choose a company specializing in the production of aluminum alloy cables, such a company only focuses on research and do alloy cables, skills are more professional, production skills and skills are more mature, production equipment and so on are more perfect, skill service is also very good, professional, focused, focused, can be better
.

Aluminum alloy cable is first composed of conductor, insulation and armor (sheath), starting from the fundamental three elements of aluminum alloy cable analysis, the quality of aluminum alloy cable can be seen
.
At present, the stranded conductors produced by the domestic manufacturers usually stranded the production line usually have aluminum chips and burrs, which endanger the insulation, seriously affect the insulation effect, form safety hazards and shorten the insulation life
.
At present, the most advanced conductor stranding production line in China is a nano-level stranding machine production line controlled by sub-motor type and PLC program, and the aluminum alloy conductor surface produced by nano skills is free of aluminum chips, burrs, oil, high and low, scratches, scratches, scratches, and scratches, which can most effectively ensure that the cable insulation has no harm and damage, and ensures that the service life of the goods is much higher than that of similar products
.

For the measurement of DC resistance of aluminum stranded conductor, in GB3048, the distance between the voltage terminal and the current end and the measurement current during resistance measurement are stipulated
.
For the qualified single wire stranded by the normal process, there are still problems that can be discussed in the actual measurement, such as the influence of potential terminal shape on the measurement results, the key point of the four-terminal method to measure the resistance, and how to achieve uniform measurement current.

In this regard, I would like to make the following comments
.

The insulation between the single wires in the stranded core is that the current flows in a spiral along the single wire, and all the single wires of the core are reliably connected
to the current inlet terminal.
Calculate the length of each layer unfolded in a 1m long stranded wire, according to the parallel resistance calculation formula, calculate the DC resistance formula of the stranded wire as follows:

There is also a certain conductance between the single wires of the actual stranded core, and the size of the conductance is related to
the surface of the monofilament.
The presence of conductance makes the direct current in the core flow incompletely along the single line spiral, and part of the current flows axially along the monofilament
.
At this point
, the DC resistance of the core is smaller than when the current flows completely in a spiral along the monofilament.
Since the resistance of the aluminum single wire does not change significantly after stranding, under the qualification of the single wire, even if the length of the wire core increases by 1% after the cable is formed, the resistance of the stranded core still has a certain margin
.

The failure of stranded wire resistance occurs because the measured current in the resistance measurement does not flow evenly through the specimen
.
All the monofilaments of the core are reliably connected to the current inlet terminal, and the insulation current between the monofilaments in the core flows
spirally along the monofilament.
Then in the case of the same diameter of the monofilament and uniform texture, the section perpendicular to the core on the specimen should be an isotope, and the potential difference between the monofilaments on this section is zero
.
In the case of isolocation, the potential difference between voltage terminals does not change
due to the shape of the voltage fixture, the way it contacts the specimen and its changing surface of the compression force on the specimen.

At present, the shape of the fixture for measuring the resistance of stranded wire is mostly knife-shaped and circumferential, and the pressure on the specimen is generated by tightening the bolt
.
Due to the presence of an oxide film on the surface of the aluminum monofilament, when the measurement current is introduced into the specimen through this form of fixture, its current distribution is often uneven, and the current density
of the outer layer of the stranded wire monofilament.
This phenomenon becomes serious
with the increase of the stranded cross-section.
Although the V-shaped current fixture has a great improvement over the knife-shaped and toroidal current clamp, it cannot make the current reach the ideal uniform state
.
The unevenly distributed measurement current makes the voltage difference between the two voltage terminals 1m apart greater than the voltage difference
between the two voltage terminals under the uniform measurement current.
In this case, further improvement in the shape and pressure of the voltage terminal fixture is often not effective
.
Therefore, the key to solving the problem of resistance measurement is how to measure the uniform current and the requirements of the voltage end fixture, which can make the measurement current uniform and drop the bottom
.

In order to uniformize the current inside the core, the specimen end can be treated
.
The treatment method is to use the end welding method, and try to make the current end close
to the wire core welding.
There are still some problems
with the application of this method.
In addition to the welding method, there is also the end cold crimping aluminum nose method, which can achieve a simple and effective way
to measure the current uniformly.
To uniformize the current, the contact resistance
between the inlet and the specimen must be reduced.
The method of tightening the bolt with the compression type is small
.
The contact resistance of the compression type is a few microohms to a dozen microohms, while the contact resistance between the clamped current terminal and the specimen is tens to one or two hundred microohms
.
Using the cold crimping method, the measurement current is directly introduced from the aluminum nose, which can better overcome the uneven
current distribution due to the monofilament oxide film.

The solution of aluminum stranded conductor resistance measurement method, the aluminum alloy cable products can make a fair evaluation, the accurate measurement of resistance for enterprises to reduce the diameter of monofilament, save raw materials, process improvement to provide an important basis, from this aspect, more practical significance
.