Analysis of thermo-mechanical stress in three core submarine power cables
Authors : M. A. Hamdan; J. A. Pilgrim; P. L. Lewin
Abstract : In this paper, a 2D thermal - mechanical coupled model is established using finite element modelling. Through simulation, the advantage of testing the whole cable is highlighted. It is found that the risk of creating a gap between dielectric and sheath is higher during cooling than heating especially when the sheath is plastically deformed. The deformed cable model is then studied through an electrical model. It is concluded based on the simulation results that the potential differences in the gaps created are found to be insufficient to trigger any degradation process.
Keywords : plastic deformation, thermo-mechanical stress, three core
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Thermo-mechanical analysis of solid interfaces in HVAC cable joints
Authors : M. A. Hamdan; J. A. Pilgrim; P. L. Lewin
Abstract : Mechanical stresses affect the electrical performance of solid-solid interfaces in high-voltage cable joints. This paper assesses the influence of insulation material mechanical properties and temperature on interface pressure. Based on a hyper-elastic model, the mechanical stresses inside silicone rubber joint tube were determined. Circumferential stresses can reach 50% of the silicone rubber tensile strength at normal pre-operation expansion ratios. An analytical method to determine the thermally induced mechanical stress during operation is presented and its accuracy is confirmed using finite element method. This method is modified to account for the variation of the mechanical properties with temperature. This paper shows that circumferential stresses at the interface increase as temperature drops, which may have a significant impact on the electrical performance of the interface during operation.
Keywords : cable joint, interface pressure, elastic modulus
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Effect of Short Circuit Currents on Thermo-mechanical Properties of Insulated Cables
Authors : M. A. Hamdan; J. A. Pilgrim; P. L. Lewin
Abstract : Cables are expected to have the ability to safely carry the rated short circuit current during abnormal dynamic conditions, such that a through fault does not damage the whole cable. For XLPE insulated cables, the maximum temperature during short circuits should not exceed 250 °C. This temperature must not adversely affect the conductor or the lead sheath. However, the effect of the thermo-mechanical stresses generated on the speed of degradation of the insulation system is of great importance. This paper analyses the influence of short circuit current on the interface between the cable sheath and insulation. Based on the theory of elasticity, a finite element thermomechanical model is proposed of a single core cable, incorporating temperature-dependent properties. The model demonstrates the importance of the mechanical properties of the insulation material, which plays a critical role in understanding the internal thermomechanical stresses within a cable.
Keywords : Short Circuit, Cable Joint, Interface Pressure, Elastic modulus, Thermal Expansion
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Effect of Sheath Plastic Deformation on Electric Field in Three Core Submarine Cables
Authors : M. A. Hamdan; J. A. Pilgrim; P. L. Lewin
Abstract : The integration of offshore wind farms has caused an increase in the number of submarine three core cables used. In these heavily and dynamically loaded circuits, cables face thermomechanical stresses that could affect the cable electrical performance. Existing electrical test standards test only single cores, which are highly concentric, not fully laid up cables, which may be more eccentric. It is known that Aluminium and lead are ductile materials and during high cable loading, the sheath could yield, increasing the possibility of creating gaps or voids at the interface. If the electric field within any void surpasses a critical field, a discharge will be ignited. Using FEM, a 2-D thermal-mechanical coupled analysis of a three-core cable was established in order to investigate the mechanical stresses generated in cable that would affect the shape of the insulation, and hence the electric field. The deformed cable model is then studied through an electrical model, to understand how the elastic plastic deformation of the sheath will affect the performance of the cable electrically. It was found that high intensity electric field is established in the deformed regions.
Keywords : finite element method, plastic deformation, submarine cable, elastic modulus, yield stress
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The Temperature Dependence of Insulation Mechanical Properties and its Effect on Interface Pressure in Cable Joints
Authors : M. A. Hamdan; J. A. Pilgrim; P. L. Lewin
Abstract : Contact pressure is a vital factor that controls the interfacial electrical breakdown strength. Loss of interface pressure between cable insulation and joint insulation must be avoided in practice to ensure a long-life span of power cable joints. The contact pressure depends on the temperature profile in the bulk material the thermal characteristics and the mechanical properties of the insulation materials. In this paper, a mathematical model using the thermo-elastic equations was developed to estimate the contact pressure taking into account how the mechanical properties (elastic modulus and thermal expansion) change with temperature, along with a realistic radial temperature profile. Two different approaches are compared, one using finite element analysis and the other using a set of differential equations which may be solved without the need for proprietary software.
Keywords : finite element method, Cable Joint, Interface Pressure, Elastic modulus, Thermal Expansion
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Adaptive Probabilistic Model for Energy-Efficient Distance-based Clustering in WSNs (Adapt-P): A LEACH-based Analytical Study
Authors : Husam Suleiman, Mohammad Hamdan
Abstract : Network lifetime and energy consumption of data transmission have been primary Quality of Service (QoS) obligations in Wireless Sensor Networks (WSNs). The environment of a WSN is often organized into clusters to mitigate the management complexity of such obligations. However, the distance between Sensor Nodes (SNs) and the number of clusters per round are vital factors that affect QoS performance of a WSN. The designer’s conundrum resolves around the desire to sustain a balance between the limited residual energy of SNs and the demand for prolonged network lifetime. Any imbalance in controlling conflicting objectives may result in either QoS penalties due to draining SN energies which leaves WSN’s environment unevenly covered, or an over-cost environment that is significantly difficult to distribute and operate. Low-Energy Adaptive Clustering Hierarchy (LEACH) is a well-known distributed clustering algorithm proposed to tackle such difficulties. Multiple LEACH-based algorithms have also been proposed to enhance QoS requirements. Proposed algorithms typically focus on residual energies of SNs to compute a probability function that selects cluster-heads. Some algorithms form an optimal energy-efficient path toward a destination SN. Nevertheless, these algorithms do not consider variations in network’s state at run-time. Such a state changes in an adaptive manner according to existing network structures and conditions. Thus, cluster-heads per round are not elected adaptively depending on the state and distances between SNs. To tackle such complications, this paper proposes an energy-efficient adaptive distance-based clustering called Adapt-P, in which an adaptive probability function is developed to formulate clusters. A near-optimal distance between each cluster-head and its cluster-members is formulated so that energy consumption of the network is mitigated and accordingly the network lifetime is maximized. Distances between and residual energies of SNs are employed to obtain a maximum number of cluster-heads to be elected per round. The cluster-head selection probability is adapted at the end of each round based on the maximum number of cluster-heads permitted per round found a priori and the number of existing alive SNs in the network. The Adapt-P based algorithms proposed in this paper improve the performance of LEACH algorithm in term adaptivity and network lifetime.
Keywords : Energy-Efficient Clustering, Cluster-Head Selection, LEACH, WSN
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