Cable Analysis
About Cable Analysis
PSE2 works with clients to carry out cable thermal analysis to evaluate if the cables have been correctly sized for specific installation conditions. We ensure the cables are capable of delivering the required demand, following the IEC 60287 or Neher-McGrath methodologies, which account for mutual heating from adjacent circuits and additional heat sources. These assessments are usually done at the design stage, supporting clients to select cables in a cost-effective way that are suitable for the application.
The presented case study is a little bit different:
After a visual inspection, the client noticed that the cable’s screen on his installation had turned yellowish, which led him to suspect that the cables were overheating. The client came to PSE2 for a cable sizing assessment to verify if the installed cables were suitable for the application.
Customer Challenge
Our assessment showed that the cables were undersized, reaching temperatures above 140°C, confirming the client’s suspicion. The cables were poorly selected for that application. Weeks later, the overheating issue escalated to a short circuit causing the generating plant to be interrupted until new cables were installed.
Aiming for a cost and time-effective solution, cables with greater cable ampacity could be installed in the ducts from the existing installation. After further investigation, PSE2 was informed that the ducts when installed, were laid in arrangements that deviated from the desirable trefoil formation, adding more complexity to the study.
Solution
We used Cableizer Software to carry out optimization tests for different scenarios to see which cable models and dimensions would work best, taking into consideration the constraints left from the previous installation, such as duct arrangement.
The original installation had six ducts (3 ducts per circuit, each with one 630 mm2 single-core aluminium). These cables could no longer be used after the short circuit and needed to be replaced. Copper cables, which can provide a higher ampacity with the same cross-sectional area were selected. Each one of the newly proposed 11 kV circuits is composed of 2 × 3 × 1c 300 mm2 (triplex), meaning that only four out of the six ducts are required, leaving two empty ducts.
As the ducts were not perfectly arranged in a trefoil layout throughout the cable routes, thermal analysis for different configurations was carried out to make sure the cables would meet the requirements without overheating.
PSE2 has initially proven that the original 630mm2 Aluminium cables were suitable for the application and cables capable with higher rated ampacity were required. In order to utilize the existing ducts, copper conductors (3×1c 300 mm2 triplex, two per circuit) were proposed. Using the IEC 60287 method, it was shown that the proposed circuits were capable of carrying the required ampacity without overheating.
