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Thermal Characteristics of Reeled Trailing Cables for Shuttle Cars

The U.S. Bureau of Mines conducted research to determine acceptable derating factors for reeled coal mine trailing cables. Four cable-reel combinations, representative of industry usage, were used in this project. Cables were continuously and intermittently loaded at six different duty cycles with direct currents of five different magnitudes. Temperatures rises within the cables were measured with thermocouples and the data recorded on a computer. Thermal time constants were calculated from the steady-state results, which fixed the periods of the duty cycles of the intermittent load tests. The relationships between the average temperature rise and current load were established for each layer of each cable. Two models were constructed; one used empirical data, from the continuous and intermittent load tests and the other was based on thermodynamic theory. Results obtained from the theoretical model were compared to those from the empirical model for the rated temperature rise of the cable. It was found that both models can be used to simulate a variety of test conditions including those that normally cannot be conducted in the lab. This information was then used to determine acceptable derating factors for each layer of these cable-reel combinations.