Selection of Conductor Cross-section of Steel Core Aluminum Stranded Wire?
The cross section of the overhead transmission line conductor is generally selected according to the economic current density, and should be verified according to the heating conditions, voltage loss, mechanical strength and corona in the event of an accident. When necessary, the corona is determined by techno-economic comparison, but the corona is often not the decisive factor in the selection of conductor cross-section for 110kv and below.
1) Select the wire cross section according to the economic current density
The transmission capacity used to select the conductor section according to the economic current density should consider the development plan of the power system 5 to 10 years after the line is put into operation. In the calculation, the maximum load that is often repeated in the normal mode must be used. However, if the system is not clear, care should be taken not to make the cross section of the conductor too small.
2) check wire cross section according to corona condition
With the increasing of operating voltage in China, the corona and discharge probability of conductors, insulators and metal tools increase, and the cross section of 220kv and above voltage, corona condition often play a major role.
Corona generated by the wire will bring two adverse consequences:
1. Increase the power loss of the transmission line;
2. Interfere with the radio communication and carrier communication.
With regard to corona loss, if the corona loss of transmission line is calculated directly, the advantage is that the concept of quantity is very clear, and the disadvantage is that the calculation is cumbersome. At present, this method is rarely used.
Now it tends to measure the ratio of the maximum working electric field strength Em (unit: KV/cm) of the wire to the total corona critical electric field strength E0, and the ratio of Em/E0 should not be greater than 80% to 85%.