ACHIEVEMENTS
Thermal calculation of a cable for a variator (case of a study in the oil & gas field)
Requirement
One of our industrial customers needs to determine the ampacity of HV cables for the power supply of an air compressor through a variator.
In the case of calculations regarding cables between a variator and its motor, the corresponding current spectrum contains elements at very high frequencies leading to a significant rise of skin effect and eddy current losses.
The consideration of these phenomena implies that a more detailed calculation of cable ampacity must be done in accordance with the IEC 60287 standard. The standards usually provide cable ampacities for frequencies of 50Hz or 60Hz.
The thermal calculations must also take into account the harmonic distortion, the method of connection to earth of the shield and the practice of the cable laying.
Realization
CAPSIM designs the cables along with their laying practices with a software enabling thermal calculations of cables in accordance with IEC 60 287 standards.
The model considers the following:
- The various materials consisting of different cable layers and the laying practice,
- The frequency spectrum of currents due to the presence of a speed variator.
The various losses are also calculated for every studied harmonic order and the ampacity for the thermal resistance of the insulating is calculated with a cable thermal calculation.
Results
The model built by CAPSIM, according to the IEC 60287 standard, helped to put forward an under-sizing issue regarding the initially chosen cables. In order to solve the cable ampacity issue, CAPSIM recommended to change the cables’ burial depth. This solution makes the cables to be exposed to a colder environment (the earth’s surface being cold) and therefore increases their respective ampacities.
