Effects of Thermal Cycles on Interfacial Pressure in MV Cable Joints

Abstract

The use of medium voltage cable joints is mandatory when dealing with power cable faults and the installation of new lines. However, such an accessory is among the top causes of faults among the grid. To this purpose, one of the quantities monitored to understand the causes of such faults is the interfacial pressure between the insulating layers of the cable joint. In this work, the interfacial pressure between Cross-linked polyethylene (XLPE) and silicon rubber has been evaluated when the cable joint experiences thermal cycles. From the results, the pressure variation caused by the thermal cycles is demonstrated. Such a phenomenon may be connected to the generation of voids and weak spots that accelerate cable joint ageing. Therefore, proper comments and conclusions are drawn.Sensors 2020, 20, 169 2 of 13 delta at ambient temperature. The same setup is then used to perform measurements in the 5-60 • C temperature range [25]. The experiments demonstrated a relationship between the temperature and the tangent delta, affecting the cable joint service life. In [26,27], different Tanδ extraction methods are presented.The pressure between the insulating elements and the cable joint is also believed to affect the insulation effectiveness provided by the cable joint. The selection of materials plays a relevant role in this respect [28]. A method is available in literature to calculate and simulate the surface pressure [29]. The correlation between the interfacial pressure and tangent delta has been explored in [30]. The variation of the interfacial pressure with the ambient temperature was also investigated [31].As for the PD, they are considered by several experts to be an effective method to assess the "healthy" status of the cable joints. Therefore, literature provides a high number of studies on this topic. For example, new PD extraction and analysis methods are presented in [32,33], while an on-line measurement setup is described in [34]. Based on these works [30,31], a correlation between the three physical parameters involved can be established.In light of the above mentioned, the aim of this paper is to measure and evaluate the interfacial pressure between XLPE and SR when subject to thermal cycles. Such cycles aim at reproducing the ambient temperature variations that a cable joint suffers during its working life. From the results, compared also with the current literature, it can be appreciated a typical behavior, due in this case by the thermal cycles, that is cause of ageing acceleration of cable joints (as detailed below).The paper is structured as follows. In Section 2 the measurement setup and the details of its elements are described. The experimental tests are described in Section 3, while Section 4 is dedicated to the results analysis and comparison with consistent literature. In Section 5, comments on the obtained results and conclusion are drawn.

Numerical Analysis of Electric Field Characteristics and Interfacial Pressure of HVDC XLPE Cable Joint Considering Load Cycles

“…Both graphs show common profiles, in that the radial stress increases during the heating period and decreases during the cooling period. These pressure profiles of the simulation results are similar to the measurement results of the cable joints under the thermal cycle conditions [36][37][38]. The measured pressure and simulation results at the XLPE/SiR interface of the cable joints are summarized in Table 4.…”

“…The measured pressure and simulation results at the XLPE/SiR interface of the cable joints are summarized in Table 4. Experimental results show an increase in interfacial pressure of up to 0.306 MPa and an average of 0.257 MPa as the temperature increases [38]. The results of the simulation show a pressure increase of up to 0.420 MPa.…”

Effect of Temperature and Thermal Ageing of Cable Silicone Rubber Accessories on Interface Pressure of Cable Joints

“…Abbas Ghaderi and others studied the variations in interface pressure of cable intermediate joints under simulated cyclic temperature conditions in real operating conditions. However, they did not consider the influence of cyclic temperature under different aging durations on the interface pressure [14]. At present, there are more studies at home and abroad on the effect of temperature on the partial discharge, breakdown field strength and electrical field distribution of silicone rubber fabricated parts and cable intermediate joints, while there are fewer studies on the effect of temperature on the interfacial pressure of cable intermediate joints [15][16][17].…”

A probabilistic approach for power cable cross section area selection: Most economic design by computer aided

“…Power losses induced in the cable due to metal sheaths, synchronous reluctance motor in pumping station [4] , [5] , [6] , [7] , armor, hysteresis, and conductor losses are important to be considered. These losses will cause heat to be exposed to cable failures [8] , [9] , [10] , [11] . Many literature works [12] , [13] , [14] , [15] show the construction and most influencing parameters on cable calculations; according to [15] , soil resistance is the most influencing parameter on current cable rating when compared to other parameters.…”