Steel Core Aluminum Stranded Wire Cross Section Selection

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. If necessary, it is determined by technical and economic comparison; but for 110KV and below, corona often does not become the decisive factor for selecting the conductor cross section.

1) Select the wire cross section according to the economic current density

In order to select the transmission capacity of conductor section according to the economic current density, the development plan of power system from 5 to 10 years after the line is put into operation should be considered, and the maximum load which often occurs repeatedly in the normal mode must be adopted in the calculation. However, when the system is not clear, attention should be taken not to make the wire section too small.

2) Verify the wire cross section according to corona conditions

As the operating voltage in China continues to increase, the probability of corona and discharge of wires, insulators and fittings increases, the wire section and corona condition of 220kv and above voltage lines 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. Regarding the corona loss, if the corona loss of the transmission line is directly calculated, the advantage is that the quantity concept is clear, and the disadvantage is that the calculation is cumbersome. This method has rarely been adopted so far. Now it tends to be measured by the ratio of the maximum working electric field intensity em (kv/cm) to the total corona critical electric field intensity e0, and the ratio of em/ e0 should not be more than 80% ≤ 85%.