JICABLE15_0001.docx Ampacity and other design considerations for medium voltage cables used in renewable energy applications Earle C. (Rusty) BASCOM, III (1), Richard W. ALLEN Jr. (2) 1 - Electrical Consulting Engineers, P.C., Schenectady, New York, USA, [email protected] 2 - Consultant, Northboro, Massachusetts, USA, [email protected] Renewable energy systems often include underground distribution cables to connect solar panels or wind turbines to collector stations where there is a step up in voltage for transmission to the nearest utility system. The general approach is to utilize medium voltage distribution cables. Many of these systems are designed and installed by developers that are seeking to minimize the project cost so that the payback period of the systems can be realized sooner, making the economics of these systems more attractive to regulators, utilities and other entities. There have been many instances of these cable systems failing after being placed in service due to issues related to thermal overload. The cause of these problems is based on applying traditional utility distribution cable system practices to the environments and operating scenarios associated with many of the renewable energy sites that have alternate characteristics. Factors to consider include: Common cable installation practices for renewable energy projects Geographic environments for renewable projects Route thermal survey and trench design and backfill characteristics Load and loss factors and circuit loading diversity as affects ratings Selection differences between utility distribution cables and renewable energy cables Economic factors Common project ownership Generating characteristics of wind and solar farms Cable system ampacity The combination of these factors and their proper consideration impacts longevity of the cable system and can result in rapid thermal degradation within a few years, affecting the availability and reliability of the renewable energy source that normally would have an expected life of decades. The paper summarizes and discusses each of these issues and shows that economic factors encourage minimizing the cable size for a given project while also seeking to reduce installation costs without fully engineering the cable ratings and design. Often, the assumed characteristics of the thermal environment are highly optimistically such that cable ratings based on the selected cable size are over stated. The paper identifies the key features of the cable system design to enhance reliability by avoiding thermal degradation of the cable system. The conclusion states that with careful selection of the cable size with proper consideration for the approach used during installation of the cable, including realistic evaluation of the extent of trench preparation and application of specialized backfill, can allow a reliable cable connection for renewable energy projects. The work is a guide to the renewable energy industry. JICABLE15_0002.docx New approach to installation of offshore wind energy cables Willem GRIFFIOEN (1), Christophe GUTBERLET (1), Jeannette MULDER-GROOTOONK (2), Lars HØJSGAARD (3), Willy GRATHWOHL (4), Håkan BRINGSELL (5), Johnny SØRENSEN (6), Niels-Jørgen BORCH-JENSEN (6) 1 - Plumettaz SA, Bex, Switzerland, [email protected], [email protected] 2 - Wavin T&I, Dedemsvaart, Netherlands, [email protected] 3 - NKT Cables AS, Brøndby, Denmark, [email protected], 4 - NKT Cables AS, Asnaes, Denmark, [email protected] 5 - NKT Cables AB, Falun, Sweden, [email protected] 6 - Siemens Windpower, Brande, Denmark, [email protected], niels.borch- [email protected] To reduce costs for subsea power cables in offshore wind applications, an alternative installation method has been developed. Instead of armoured cables HDPE pipes are laid (trenched) into the seabed. A special telescopic riser has been developed to install the pipes from the Transition Pieces (TPs), avoiding J-tubes. Specially designed bend restrictors bring the pipe into position in the seabed near the feet of the mono-piles. After that, the (non-armoured) cable can be installed into the pipe. For this the cable drum and (compact) installation equipment can be previously placed inside the TP. This system can with minor modifications be applied to other foundation types, e.g. gravity- and jacket- foundations. Cables are installed into the pipes using the water flowing technique, an alternative to traditional pulling. For cables used for offshore wind parks the technique has now been developed to work also without pig at the cable´s front-end (called floating). A high speed water flow propels the cable. Besides these propelling forces, a mechanical pusher introduces the cable into the pipe (which is under pressure), effectively pushing the cable. Because of the buoyancy of the cable in water, installation lengths are long while forces exerted on the cable are much lower than for traditional pulling, reducing wear. There is no need to first installing a winch rope. Also there is no need to place equipment at the far end of the pipe. The method can be used for installation of array cables as well as for export cables, the latter being even possible from land (current length of 3 km targeted to be increased to 5, 10, 20 km,...) Costs savings are achieved because of the lower price of non-armoured cable, reduced AC-losses and reduced risk of pipe kinking and thus eliminated risk to kink the cable (should the pipe kink, it is much easier to repair). Telescopic riser and flexible bending restrictor will allow the cable in pipe to follow the seabed in case of erosion around the mono-pile. Tests were performed which showed that non-armoured cables in pipes are better protected against mechanical impact than armoured cables, because of the free space in the pipe. Keeping the pipes in the TP-zone filled with water, hotspots will be better cooled. Trials done at Lindø, DK (onshore) and Thyborøn, DK (semi-offshore) are described. Here array cables (82 mm 3x300 mm2 Alu in 125/102 mm pipe) and export cables (60 mm 1x630 mm2 Alu in 90/80 mm pipe) were installed with ease over lengths of about 1 km, but the potential is much higher. Flexible joints were also tested to pass installation device and pipe. Using high salinity water the effective weight of the cable (in the pipe) can be tuned to zero. The same high salinity water can also be used to sink pipes. In many cases the density of the pipes with cable can even be tuned to the density of the seabed. Before the cables were installed, the pipe route was evaluated by intelligent pigging. JICABLE15_0002.docx Fig. 1: Overview alternative system Fig. 2: Overview semi-offffshore trial JICABLE15_0003.doc The design of H level thermal -conductivity composite insulation structure for explosion-proof motor with high efficiency and low voltage LIU Chen-yang (1), YIN Mo (2), CHEN Xu-feng (3), ZHENG Xiao-quan (1) 1 - State Key Laboratory of Electrical Insulation and Power Equipment， Xi’an Jiaotong University，Xi an 710049，China; 2 - Nanyang Explosion Protection Group Co., Ltd., Nanyang 473011, China; 3 -.School of Mechanical Engineering, Shanghai Jiaotong University, Shanghai 200000,China Corresponding author, email: [email protected] When the electric motor is running for a long time, due to the rise of temperature of the copper wire effect, the electric motor winding temperature can be increased, and because of winding covered with insulating paint, that can make heat dissipation hardly and reduce the service life of the electric motor. In view of the difficult insulation structure heat dissipation problem, this paper developed a new type of high efficient heat conduction insulation structure(grade H) and the new method to reduce the motor temperature, made high thermal conductive insulation test and calculation analysis of efficiency for YB2132-5.5 Kw-4P electric motor. The result shows that the H level insulation structure can make the electric motor temperature reduce significantly, and it can also achieve the purpose of improving the efficiency of the electric motor. the H-class high thermal insulation structure tests for prototype losses, efficiency testing and theoretical analysis, calculated and experimental results show that the new high thermal insulation structure used to reduce winding temperature rise of 8 , the stator copper loss and rotor copper losses have been greatly reduced accordingly, improve the efficiency of the motor to reaches 86.7%, the efficiency of the existing motor is 0.7 percentage points compared to the initial motor, and the experimental and theoretical values are similar, it demonstrated the superiority of the design of thermal structure fully. Consolidation of the economic benefits generated by the use of the H high thermal insulation structure can save energy up to 44.8 million （yuan）/year for our country, it is a important implications for environmental protection and energy saving. JICABLE15_0004.docx Permanent PD Monitoring Experiences on Shaanghai 500kV Power cable Lines JIANG yun (1)，GAO Xiaoqing (1)，QIAN Tianyu (1)，XIAO Chuanqiang (2)，DAI Hongbin (2) 1 - Shanghai Electric Power Company, Shanghai, China 2 - SINDIA Instruments, Beijing, China, [email protected] For the safety operation of a 500kV 15.6 km-length power cable line, a permaanent PD monitoring system was installed in September 2013. Thhe cable line included 2 circuits and 6 phases in total, with 147 cable joints and 12 GIS terminations. 1159 HFCTs and PDDs were installed on the grounding cable of each joint and termination. Based on installation experience and 1 year operating experience of the PD monitoring system, this paper illustrates some key factors for cable line PD monitoring. These factors include HFCT installation, calibration, alarm setting, and PD pattern recognition. Different positions to install HFCT sensors are compared in this paper, and HFCT sensor on the grounding cable is recognized as the best sensitivity for PD monitoring. For joint only with coaxial grounding cable available, it was recommended to install HFCT inside the cross bonding box and modify the box to make the signal cable out from the box.