Experimental Comparison of Multi-day Cable Loading Considering Weekly Load Factor
Objective: Reduce balance of system cost by reducing medium voltage cable size
Methods: Load factor has a significant impact on underground cable ampacity. The Neher-McGrath method includes adjustment for load factor that is inferred to be the daily load factor. This paper compares the calculated ampacity with measurements of a buried cable heated continuously for multiple days—a daily load factor of 100%.
Results: Analysis reveals that a load factor of 66% reduces the error between the calculated cable temperature and the measured temperature. It illustrates that load factor should be considered beyond a 24-hour day. This can lead to a 50% reduction in cable size, which can reduce cost for the balance of system by hundreds of thousands of dollars for large (>10MW) solar projects and can reduce installation difficulties due to large cable diameters.
Conclusion: Engineers should evaluate multi-day load factor when designing medium voltage cable. Project managers should confirm this analysis is being used to ensure costs are as low as possible.