Ampacity of Three-Phase, Low Voltage, Single-Conductor Cable Systems under Non-Sinusoidal Currents

This paper investigates the ampacity of PVC insulated, low voltage (0.6/1.0 kV) single conductor cables made according to CENELEC standard HD603 in the presence of harmonics. The cables are considered to be laid in free air or over metallic trays. The investigation is made with a validated finite element model for the fundamental and higher harmonic frequencies. The calculation results are compared to relevant results corresponding to respective multi conductor cables examined by papers under the same examination conditions. An ampacity derating factor for single conductor cable bundles is proposed. It is shown that the cables effective resistance and as a result the cables ampacity depends greatly on the cable arrangement and the loads current harmonic content. The presence of zero sequence harmonics reduces the cables ampacity. When zero sequence harmonics are present the ampacity derating factor of the single-conductor cable bundles is reduced in respect to the multi-conductor cables. With only non-zero sequence harmonics present the ampacity derating factor of multi-conductor cables and single-conductor cable bundles in free air is approximately the same. The influence of the tray on the ampacity derating factor is more significant for single-conductor cable bundles in respect to multi-conductor cables.