This paper introduces a new mathematical procedure for the calculation of power cable ampacities in the case of water-cooled circuits. Both, internal and external cooling installations are ...considered. The algorithm permits a non-iterative calculation of the water temperature and the temperature-dependent losses along the cooling length of the cables, evaluation of the heat absorbed and emitted by the cooling pipes as well as the effect of the water flow on the cable conductor temperature. Numerical examples show the effect of the direct and the indirect cooling on the ampacity of a 230 kV XLPE cable circuit.
This paper introduces a new analytical method for the analysis of unsymmetrical, three-dimensional cable arrangements thus allowing ampacity calculations for complex underground cable systems. Up to ...now, the analysis of such systems required application of numerical methods, which require high level of expertise and are generally difficult to use. The resulting computational algorithm is developed from basic principles and is applicable for cables directly buried in a uniform soil. An extension of the method to the situations when the soil drying out occurs in the vicinity of loaded power cables is also presented. The method is illustrated by several numerical examples. Some of them involve crossing of two circuits, which can also be studies using the methods covered in the literature. These examples are used for comparison with the existing standard approach.
This paper discusses the possibilities of optimizing layout underground power cable lines considering environmental requirements. It presents the basic mechanisms of the occurrence of the physical ...phenomenon of a magnetic field. The permissible levels of magnetic field emissions around the world are discussed. Case studies analyze the impact of cable laying conditions on the magnitude of the magnetic field. A discussion is offered on the possibility of a reasonable reduction of the negative environmental impact of underground cable lines, namely, through the proper selection of the arrangement of the phases and distances between the cables.
This paper discusses the effects of short cable runs at the terminations on the current carrying capacity of the transmission circuit. Standard ampacity calculations assume an infinite length of the ...cable circuit, usually with a fixed laying configuration and unchanging environmental conditions. Even though this may be true for a majority of the cable lengths, the conditions at substations where the cable circuits terminate may dictate laying arrangements different from the one in the rest of the route. In this paper, the effect of changing cable arrangements at the circuit ends are discussed and the impact on cable rating is illustrated with numerical examples.
This paper addresses procedures for power cable time-dependent rating calculations. Such calculations are required to obtain cable emergency ratings and also to observe the conductor temperature ...variations with time when subjected to variable loading. The calculation procedure is described in the IEC Standards 60853-1 and 2. A real difficulty in applying those procedures lies in an ability to take into account variation of the electrical resistances of the cable metallic components with temperature. The standard gives an approximate equation, developed by Goldenberg. However, this equation is applicable to a single current step applied to the cable. The paper shows that it cannot be easily applied to multiple current steps and proposes a new approximate algorithm providing an analytical solution to this problem. A comparison with a complex iterative procedure is also offered.
The Neher/McGrath paper and the IEC Standard 60287-2-1 contain the formulae for the calculation of the external thermal resistance of cables installed in backfills or duct banks. These models are ...based on several assumptions, which often are not valid for practical installations. This paper examines the applicability of the Neher/McGrath model and proposes a new solution for the calculation of the external thermal resistance for such installations. Numerical examples illustrate the difference between the two methods.
This paper addresses time-dependent rating calculations for groups of power cables with temperature-dependent losses. It is a continuation of a recent publication 1 - the presentation of a new ...transient calculation method for one cable - and offers an extension of the algorithm presented there to the problem of multiple cables subjected to variable loading. Whereas the standards offer simplified solutions for one load step and for equally loaded cables only, the new approximate algorithm is providing a complete analytical solution to this problem. In the following, this will be explained in detail and demonstrated by practical numerical examples.
This paper presents the results of ampacity studies and proposed remedial actions for the situation where a steam pipe and several distribution circuits cross a duct bank with HV transmission cables. ...The studies involved application of a novel solution using a gravitational water cooling system. The system and the corresponding mathematical model are described in detail in the paper. The system was implemented in the BC Hydro network in downtown Vancouver. Practical concerns of BC Hydro engineers involving safety and public utility regulations as well as the measurement results obtained before and after installation are also discussed in the paper.
This paper discusses rating calculations of underground power cables when the temperature limit is imposed on a location other than the cable conductor. The issue becomes important for installations ...where the environmental conditions do not allow excessive heating. An example can be a requirement that the cable surface temperature is such that the drying out of the surrounding soil is avoided. Another example is a requirement imposed on submarine cable installations when the temperature rise caused by cable heating at the specified depth below the sea bottom does not exceed 2 K. Such requirements form rating restrictions in several countries; for example, the Netherlands, Germany, France, and others. This paper proposes new solutions to such problems including calculation of the dynamic ratings.
The IEC Standard 60287-1-1 provides the procedure for modelling of soil dryout in the vicinity of current currying power cables. Two important assumptions limit the application of the formula to the ...cases with uniform burial conditions and a uniform current with 100% load factor. Another standard in this series, 60287-2-1, contains the formula for the calculations of the external thermal resistance of cables laid in thermal backfills. It is based on the pioneering work of Neher and McGrath published in 1957. The Neher/McGrath paper provides also a modification of the external thermal resistance of buried power cables with a non-unity load factor with an assumption of the uniform burial conditions. This paper develops new formulae for the calculation of cable current ratings taking into account all three factors; that is, consideration of the soil dryout for cables laid in a thermal backfill and loaded with a variable current with known load factor. The results obtained with the proposed approach are compared with detailed finite element studies.
