One of the conditions of quality of service in the electricity sector is the uninterrupted power supply to consumers of different categories.
Requirements for the security of electricity supply are one of the important aspects of the consumers today. From the current level of supply reliability of consumer's electro receivers depends on the number of spoilage in production, quality of manufactured products and, consequently, the competitiveness of the company as a whole.
There are three categories of power supply reliability (Fig. 1).
Figure 1. Three categories of power supply reliability
First category of power supply reliability.
Consumers of 1 category of reliability of electricity — is power-consuming equipment, interruption of power supply which may entail danger to human life, a threat to the security of the state, significant property damage, breakdown of complex technological process, disruption of the functioning of particularly important elements of the communal services objects of communication and television. Also among consumers of 1category of power supply reliability a separate special group is allocated. Electroreceivers of special group of the first category are characterized by their uninterrupted functioning is essential for trouble-free production stop, preventing fires and other emergencies.
Second category of power supply reliability.
Second category of reliability of electricity supply of consumers include those power-consuming equipment, interruption in work of which may lead to significant reduction of issue manufactured by goods consumers, that takes place in connection with the inoccupation of staff idle time of production equipment, or it may affect the normal life of a large number of citizens.
Third category of power supply reliability.
Third category of power supply reliability includes all those power-consuming equipment, which are not included in group 1 or 2. The third category of reliability may include shops, small industrial premises, office buildings, etc. The period in which the power supply of consumers 3 category of reliability can be stopped — not more than 24 hours and not more than 72 hours per year in total
It is worth noting that every consumer is entitled to switch from the third category of safety to the 2 or 1 if necessary.
Owing to the long distances and deterioration of overhead power lines, underload of installed transformer equipment, which capacity is 5–10 times higher than the maximum power consumption, there are significant specific losses of electricity associated with underload of power system (high proportion of permanent loss component), and time-consuming to eliminate damage. Therefore, there is need to assess the effectiveness of building small power plants that use alternative energy sources, to improve the reliability of power supply.
In systems that convert alternative energy sources, also a significant role plays the process of uninterrupted supply of electricity for the needs of sectors of the national economy. Therefore, such systems often combine several subsystems converting non-traditional sources of electricity that replace one another when there is no one or the other alternative energy source, or work together. Currently, the most developed are combined wind power plants (wind turbines), i.e. systems consisting of a wind power plant, and any other source of energy (diesel, petrol, gas turbine engines, solar collectors, etc.) used as a backup or an additional source of power supply to consumers (Fig. 2).
To date, wind-diesel systems consisting of wind turbines and diesel-electric systems (DES) with optimally matched capacities got widespread.
Figure 2. Variants of hybrid wind turbines
Typically, the diesel generator is used in conjunction with wind turbines in the case where the purpose of it is to save diesel fuel, the value of which, considering costs for shipping can be very high (Fig. 3). The ratio of power system components depends on the generating circuit, load and wind resources. Using the separate operation of wind turbines and the DPP allows raising share of wind turbines up to 50–60 % or more. However, in this case the complexification of the system due to the need for a control system, inverter equipment and batteries that store energy generated by wind turbines at operating wind speeds for the load in calm weather or at low wind speeds is inevitable [1].
Figure 3. Wind-Diesel System
In areas with excessive solar radiation is possible to use wind and solar systems (Fig. 4). Electrical energy can be obtained by converting solar photovoltaic batteries (PB). Despite the rather high, at the moment FB value, their use in conjunction with wind turbines in certain cases may be effective [1]. Since the in winter there is great potential of wind, and in the summer on clear days, the maximum effect can be obtained using the FB, the combination of these resources is beneficial to the consumer.
Figure 4. Wind-solar systems
In areas with a large number of water sources is possible to use wind turbines together with micro HPP, having a water tank. In such systems, in the presence of wind, wind generator is supplying the load, and the excess of energy is used to pump water from the tailrace to the top. In periods of calm wind energy is produced by micro HPP. Such arrangements are particularly effective for small hydraulic power resource (Fig. 5).
Figure 5. Wind turbines in conjunction with micro HPP
If you look in detail at the systems operating only on alternative energy sources (e.g. wind and solar systems), it may be a situation of complete absence of both of alternative energy at the moment due to weather conditions in the area. Also, the plants comprising a diesel generator are not without drawbacks: the presence of the two generators on the installed capacity, current surges while switching the load from one generator to another, etc.
Currently, by the engineers of the chair «Electrotechnology and electrical equipment» of Orenburg State Agrarian University developed a combined (hybrid) power generation system that combines in its construction plant, using alternative sources of energy and as a backup, the system using energy of fossil fuels. It comprises a synchronous generator: one end of the shaft is connected to the heat engine and the other with a wind turbine, variator and the optimizer of loading of wind turbine.
This system has several advantages over systems of this type, namely the existence of one of the generator; instead of reducer as an intermediary between the wind turbine and the generator, variator is used here which with use of optimizer of load will exercise maximum use of wind energy.
Thus, the use of combined power generation systems for autonomous objects has an advantage over conventional systems. They are able to provide reliable transmission of electricity to consumers at varying loads and wind speed, which is especially important in areas with relatively low and unstable wind speeds that are observed in most of the Russian Federation's territory.
References:
1. Kharitonov, V. P. Autonomous wind power plants [Text] / V. P. Kharitonov. — M.: SSI ARIEA, 2006. — 280 p.
