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Discussion on measuring method of DC resistance of aluminum stranded conductor
Mar 19, 2018

Many companies have also made a lot of research on the measurement of DC resistance of aluminum stranded conductor. In the GB3048, the distance between the voltage end and the current end and the measurement current are stipulated in the measurement of resistance.


There are still some problems that can be discussed in the actual measurement of the line core with normal process, such as the influence of the potential end shape on the measurement result, the key point of the four-terminal method measuring resistance, and how to realize the measurement current uniformity.


One, with qualified single line and the normal skein of the wire core resistance has a certain margin The insulation of each single line in the Strand core is a helical flow along a single line, and all single lines of the core are reliably connected with the current.

 

   Calculate the length of each layer in the 1m long strand, and calculate the DC resistance formula of the stranded wire according to the calculation formula of the shunt resistance, such as: There is a certain conductivity in the single line of the actual strand core, and the conductivity is related to the surface of the filament. The presence of conductance causes the DC not to flow completely along a single helix in the core, and part of the current is axially flowing along a single wire. At this time the core DC resistance than the current completely along the filament into a spiral flow is smaller.

 

   As a result of the stranded aluminum single line resistance no significant changes in the single line, even considering the cable after the length of the cable to increase 1%, stranded core resistors or a certain margin. Two.


Causes of unqualified measurement


The failure of the stranded wire resistance is due to the fact that the measuring current in the resistance measurement is not evenly flowing through the specimen. All the filaments of the core are reliably connected with the current, and the insulating current between the wires in the core is spirally flowing along the single wire. So in the case of single filament diameter and homogeneous texture, the cross section perpendicular to the core of the specimen should be the equipotential plane, and the potential difference between the two wires on the section should be zero.

 

   In the case of equal position, the potential difference between voltage terminals is not due to the shape of the voltage fixture, the way of contacting the specimen and the change of the compressive force of the specimen. At present, the shape of the clamp is more knife-shaped and surround, and the pressure of the specimen is caused by tightening the bolts. Because of the existence of oxide film on the surface of aluminum monofilament, when the measuring current is introduced into the specimen by this form of fixture, the current distribution is often uneven, and the current density of the filament in the Strand. The phenomenon is serious with the increase of the Strand section.

 

   Although the V-type current fixture has a greater improvement than the blade shape, the annular current fixture has not yet achieved an ideal uniform state. The uneven distribution of the measurement current makes the voltage difference between the two voltage terminals at 1m apart, greater than the voltage difference between the two voltage terminals under the uniform measurement current. In this case, the voltage end fixture shape, the pressure to make a near-step improvement is often not effective.


Therefore, the key to solve the resistance measurement problem is how to measure the current uniformity and voltage end fixture requirements, so that the measurement of current evenly and down. Three.


Workaround In order to make the inner current uniformity of the core, the sample end can be treated. The treatment method is to use the end welding method, and to make the current end as close to the wire core welding place.

 

   There are still some problems in adopting this method. In addition to the welding method, and the end of the cold pressed aluminum nose method, this method can achieve the measurement of current uniformity simple and effective method. To make the current even, the contact resistance of the inlet end and the specimen must be reduced. The method of tightening bolts with compression type is small. The contact resistance of the compression type is several micro-Euclidean to more than 10 micro-Euclidean, while the contact resistance of the clamping current end and the specimen is dozens of to 100 or 200 micro-Euclidean.


By means of cold crimping method, the measurement of current directly from the aluminum nose can better overcome the uneven current distribution of the oxide film between single wires. Aluminum stranded conductor Resistance measurement method, the power cable products can be a fair assessment, the accurate resistance measurement for the enterprise to reduce the single wire diameter, saving raw materials, the process to provide an important basis for improvement, in this regard, more practical significance.


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