Cable tray ampacity and cable operating environments
- Georgia Inst. of Tech., Atlanta (United States)
The problem of predicting cable tray temperatures is a complex matter, often far more difficult than predicting the operating temperature of an overhead conductor or an underground cable. The knowledge of a cable tray operating temperature is vitally important to the safe operation of a modern power plant. Ampacity models for cable trays are complicated by the large number of variables that influence the cable mass temperature. The problem is further complicated by factors such as distribution of heat generation rate across the cable mass that make it difficult to precisely quantify the temperature in the tray. While computer simulations of the heat transfer from the tray are complex, the task of experimentally measuring cable temperatures are also challenging. The temperatures must be monitored along the path of the tray at numerous locations to assure that the weak thermal link along the cable route has been uncovered. The measurement of the maximum cable mass temperature when the thermal environment changes drastically along the cable route can become a very expensive proposition. This paper examines the weaknesses in the existing cable tray ampacity model published by ICEA/NEMA. A simple experiment in which temperatures of cables in stacked trays are measured is then described. The measured temperatures are compared to those that are predicted by the ICEA/NEMA ampacity model. The model is conservative when predicting temperatures in single trays but not conservative for the case of stacked trays. Two situations, those involving non-uniform heat generation in the cable mass and the presence of fire stops, are then considered. The complexity of non-uniform heat generation is simplified by examining the pattern of heat generation which leads to extreme limits on the cable mass temperature. The case of a fire stop is considered by approximating the maximum tray temperature for various fire stop material thickness and different thermal properties of the fire stop.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (United States); Grove Engineering, Inc., Rockville, MD (United States)
- OSTI ID:
- 145508
- Report Number(s):
- EPRI-NP--7399; CONF-9004140--
- Country of Publication:
- United States
- Language:
- English
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