Development of a Model Wind and Solar Power Installation Comprising High Temperature Superconductors
2014-03-21 02:35:26 《Energy Science and Technology》 2013年4期
L. I. Chubraeva; V. F. Shyshlakov; M. A. Turubanov; S. S. Tymofeyev; D. A. Volkov
The investigation of main performance properties of the hybrid wind and solar power installation with application superconductive elements was carried out. In the frames of the study， both mathematical simulations and experimental testing were performed. The study shows some difficulties to be solved during mutual operation of the various high-temperature superconductivity （HTSC） devices， especially if they operate with semi-conductive systems.
Key words： Hybrid wind； Solar power installation； High-temperature superconductivity （HTSC）； Renewable energy； Simulation； SMES； Fault current limiter； Physical modeling
L. I. Chubraeva， V. F. Shyshlakov， M. A. Turubanov， S. S. Tymofeyev， D. A. Volkov （2013）. Development of a Model Wind and Solar Power Installation Comprising High-Temperature Superconductors. Energy Science and Technology， 6（2）， 64-70. Available from： URL： http：//www.cscanada.net/index. php/est/article/view/10.3968/j.est.1923847920130602.2374 DOI： http：//dx.doi.org/10.3968/j.est.1923847920130602.2374
Hybrid wind and solar power installations are drawing increasing attention due to high prices of conventional fossil resources and ecological problems of different regions of the world. The main aim of the researches in this field is focused on the improving of the overall efficiency of such installations. The objective can be obtained by： improvement of the solar panels power output， improvement of wind generator efficiency and improvement of control methods and algorithms for entire installation.
Solar and wind are intermittent energy sources as they vary over time and do not usually meet load demands at all periods. Among these two types of renewable energy， wind is a more affective source compared to photovoltaic due to its variability. Similarly， the photovoltaic system also depends on the weather conditions and can operate only at day-time. These two unpredictable energy sources standalone system will produce fluctuated output energy and thus cannot ensure the minimum level of power continuity required by the load.
There exist numerous combined wind and solar power installation developed by different companies， but most of them are based of application of conventional materials. Until the present moment superconductors find only limited application in such types of power installations， for example， American Superconductors （AMSC） offers a design of a similar combined system involving wind generator with HTSC. 1
One of the ways of increasing wind generators efficiency is to use new types of materials， such as high temperature superconductors （HTSC）. Application of HTSC allows increasing the unit rating up to 10 MW and more at the same time reducing the units mass and dimensions parameters. Superconductors allow setting up of efficient， robust， and compact wind power plants at reduced building， operating， and maintenance costs.
Superconductor based magnetic energy storage units（SMES） can be successfully used in combined wind and solar power installation for storing generated energy and for smoothing load power peaks. Fault current limiters protect the load from abnormal modes of operation.
The advantage of application hybrid systems is in the increased reliability of energy supply because it is based on more than one generation source. Moreover， the hybrid system is suitable to use in remote areas with no access to utility grid. However， the disadvantage of these systems lies in the fact， that in most cases they are over-sized because they contain different types of power generation system.
1. GENERAL REMARKS
As a continuation of mutual researches carried out in 2009-2010 by the team uniting specialists of both SUAI（Russia） and Ben-Gurion University （Israel） （Chubraeva， Sokolovsky， & Meerovich， 2010， pp.23-40； Chubraeva， Sokolovsky， & Meerovich， 2010）， there is being developed in SUAI a model installation of independent local network comprising photovoltaic batteries and a wind generator. The model is to be equipped as well with power current controllers： SMES and a fault current limiter （FCL）. The generator， SMES and FCL utilize high-temperature superconductors， and liquid nitrogen is used as a cooling media. There is also under development a computer based control system intended for the wind power installation， providing complex control on operation of both main and peripheral equipment， including：
？ Stabilization of output electrical parameters；
？ Alarm and warning indication and emergency protection system；
？ Remote and automatic control on all of the processes in a wind power installation during the period of 240 hours （non-attended operation）.
The above control system is designed on the base of a programmable logical controller Mitsubishi Electric（FX3U series）， that is one of most flexible and costeffective process control platform for technical systems.
The main aim of the investigation is to evaluate the efficiency and aspects of a synchronous alternator with permanent magnets on the rotor and HTSC armature winding. The design seems to be advantageous as compared to the alternator with HTSC rotor winding. Moreover it is necessary to investigate mutual operation of a complex system with several HTSC devices.
The electrical scheme of the installation is presented in Figure 1.
Presented below are results of experimental and theoretical investigations of two HTSC elements： synchronous alternator with permanent magnets on the rotor and HTSC armature winding and SMES with HTSC winding and magnetic cores of amorphous alloy.
2. HTSC MODEL SYNCHRONOUS ALTERNATOR
The wind turbines are generally manufactured in a wide range of vertical and horizontal axis types. Vertical axis turbines have several advantages over the typical horizontal axis turbines， namely：
？ They can accept changes of wind direction with no problem；
？ The alternator can be fixed on the ground for easier access， rather than up in the air；
？ Generally they start rotation at lower velocity；
？ They produce less noise.
The general view of HTSC electrical generator with a wind turbine is shown in Figure 2.
Synchronous machines with axial magnetic flux and permanent magnets excitation possess the increased performance characteristics and the lower overall dimensions in comparison with conventional electric machines （Yi， Agelidis， & Shrivastava， 2009）. Application of the rare-earth permanent magnets as an excitation element of electric machines allows canceling the excitation losses and permits to exclude the exciter. Axial magnetic flux is perpendicular to narrow edge of HTSC tape， resulting in reduction of losses. Moreover armature coils of a simple circular form may be used. This fact is substantial for HTSC. The coils form one or two layers， providing a reliable， simple and more cost-effective winding （Ahmed， & Miyatake， 2006）. The rotor has 8 magnetic poles， each pole comprises two magnets on both rotor sides （Figure 3， b）. The magnets are rare-earth NdFe-B. The rotor body is made of aluminum. The alternator rating is 5kW.
The armature of the generator is of a slotless design with a stator core made of amorphous alloy tape. The stator winding consist of 12 pancake single-layer HTSC coils divided into two layers （upper and lower）， each stator layer is mounted on a separate stator disk （Figure 3， a）. It is worth nothing that the alternator may be of a multi-disc design with a multiphase armature winding. The entire alternator is emerged in liquid nitrogen.
The armature and the rotor are mounted in a hermetically sealed vessel， which acts as a cryostat （Figure 3， c）， the outer surface of the vessel is covered with a layer of a thermal insulation made of cellular rubber substance （Figure 3， d）. The generator was tested at liquid nitrogen temperature， it took 2 hours to cool down the generator to the temperature of 77K. The cooling process was controlled manually and the dynamics of the process is shown in Figure 4.
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