Abstract
The calculation of the continuous allowable current of an underground cable is determined by various characteristics. To calculate the allowable current in cables with alternating magnetic fields such as AC, special phenomena such as the proximity effect and skin effect must be applied. However, there are no standards or research related to the calculation of the continuous allowable current of a DC power cable that does not have an alternating magnetic field. In this paper, a quantitative DC cable continuous allowable current calculation formula of direct burial laying was derived by applying the existing AC cable continuous allowable current calculation method to the DC system. We developed a calculation tool that can calculate the continuous allowable current of DC cables using the derived formula. Assuming the cable conditions (cable specification, laying conditions, soil characteristics, arrangement, and number of strands, etc.), a continuous allowable current simulation of DC cables was performed. In addition, the level of contribution to the continuous allowable current value was analyzed by classifying the parameter categories into major and minor factors in the order of influence on the allowable current among the determined calculated parameters. As a result, the effectiveness of the DC cable continuous allowable current calculation tool derived by performing the allowable current calculation simulation was evaluated, and the allowable current calculation method of the HVDC cable was established.
Highlights
Allowable current is defined as the maximum value of current that can be passed through a wire or cable and is evaluated as the most important factor in cable design along with insulation performance
The continuous allowable current calculation tool was established by classifying and formulating the key factors for calculating the allowable current of a direct burial laying HVDC underground cable based on the existing AC cable allowable current calculation formula
(1) Core factors affecting the continuous allowable current value of direct burial laying HVDC underground cables can be divided into internal factors (cable specifications) and external factors (T4)
Summary
Allowable current is defined as the maximum value of current that can be passed through a wire or cable and is evaluated as the most important factor in cable design along with insulation performance. In the conductor of the cable, the proximity effect and the skin effect are generated by the alternating magnetic field, and due to these effects, the resistance of the conductor itself increases and heat is generated when current flows This effect continuously occurs on the conductor and on the insulator, and circulating current is generated in the metal sheath along with the dielectric loss caused by the polarity change according to the frequency, which is applied as an additional heat-generating element. Equation (1) is a formula for calculating allowable current in AC cables with an alternating magnetic field, dielectric loss due to an alternating magnetic field, AC conductor resistance due to the proximity effect and skin effect, metal sheath loss rate due to sheath circulation current, and thermal resistance according to temperature gradient These formulas can be summarized as follows, and the presence or absence of the influence of the frequency containing the largest difference in AC and DC characteristics in each element was confirmed. On the other hand, when there is no frequency-like DC, the heat-generating element exists only in the conductor, and the loss caused by the frequency component can be ignored
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