Introduction to the Selection Rules of Cross-Section

1 The temperature of the cable conductor under the maximum working current shall not exceed the allowable value of the service life of the cable. 

The working temperature of the cable conductor of the continuous working circuit shall comply with the following table.

2 The cable conductor temperature under the action of maximum short-circuit current and short-circuit time shall comply with the above table.

3 The voltage drop of the connecting circuit under the maximum working current shall not exceed the allowable value of the circuit.

4 In addition to the requirements of paragraphs 1 to 3 above, the power cable cross-section of 10kV and below should be selected according to the principle of comprehensive economic of the initial investment of the cable and the operating cost during the service life.

The general cable design selection step is to first determine the cable type according to the laying conditions. 

The cable conductor cross-section should be selected in combination with the local laying environment. 

For the 66kV and above cables, refer to the current industry standard cable current carrying capacity calculation JB/T 10181. 

Common cables of 35kV and below can be calculated according to the correction factor according to the current carrying capacity provided by the manufacturer and the local laying environment.

The cable cross section should meet the requirements of continuous allowable current, short-circuit thermal stability, and allowable voltage drop. 

Check the voltage drop of the voltage class of 10kV and below, because when the voltage is below 6, 10kV, and the wire cross section is below 70~95mm2.

The voltage check is performed because the wire with the cross section is larger than 70~95mm2.

The effect of the cross-section method to reduce the voltage loss is not very significant, and it will cause more investment and non-ferrous metals. 

For example, transformers with electrostatic capacitor compensation or load regulation and other measures are more suitable, but technology should be applied. 

The economy is relatively certain. For 10kV and above cables, verify the thermal stability of the short circuit.

The conductor cross section shall be selected from the nominal cross sections listed in the relevant cable product standard.