The efficiency of using electrical equipment is assessed by the total costs per unit of operating time and depends on many factors. The load power of electrical equipment has a great influence. The relevance of correct load selection increases due to widespread use automated electric drives in production.
For electric drives, the dependence of the efficiency criterion on the load has a complex nonlinear character. At low load, i.e. when using, for example, an overpowered engine, the electric drive has low efficiency values And . An increase in load leads to an improvement in energy performance, but at the same time there are negative consequences - overheating and decreased engine reliability. Only with optimal load power will the total costs reach the lowest value, and the operating efficiency of the electric drive will be the highest. In accordance with the widespread use of engines, even minor errors in the choice of their load lead to great economic damage.
The task of justifying the optimal load of electrical equipment is to identify and compare positive and negative consequences, i.e., competing effects that arise when the load increases, and select the load power at which best value operational efficiency criterion. In a particular case, this criterion is the total engine losses.
Optimization of engine load based on total losses. In the theory of electrical machines, it is established that the total motor losses are least significant at a load factor of equal to the root square of the engine loss ratio:
where , – no-load (constant) and short-circuit (variable) losses, o. e.
The result obtained from (4.2) is the result of solving a particular problem in which losses in the power supply system are not taken into account. In order to more accurately take into account real factors, the object of study when optimizing the load should be not only the engine, but also the system. A comprehensive accounting of the characteristics of the engine and power supply system is performed by expressing the optimal load:
where is the coefficient of increase in losses due to the power supply system (=1.1...1.2); – reactive power equivalent, showing the value of active losses in networks from each kVAr of engine reactive power (=0.12...0.18 kW/kVAr); , – reactive powers of no-load (magnetization) and short-circuit (dissipation), p.u.
The reactive magnetizing power of the motor is greater than its dissipation power and therefore is always >– The optimal load according to the criterion of minimum losses in the system is always greater than the load that optimizes only the efficiency of the motor. Calculations reveal a noticeable difference in optimization results according to different criteria (=0.7...0.8; =0.80...0.95) and confirm that full consideration of real operating factors makes it possible to clarify the optimization results.
At the same time, it should be noted that the energy properties of asynchronous motors are highly stable when their load changes. Deviations from the optimum within ±30% lead to an increase in losses by no more than 7% from the minimum level. Only when the load decreases below 40% is an intensive decrease in efficiency observed. To radically reduce energy losses caused by electric drives, it is important not only to correctly select the load when operating the engines, but also to increase the rated efficiency at the stage of their development and introduce reactive power compensation. Methods for reducing losses are effective for low-voltage drives due to the low efficiency of the power supply system due to its large length and four to sixfold transformation of electricity.
Relevance of the topic. Illuminate the operating modes of the electric motor at the compressor station (emergency, normal, self-start), etc. This problem is reflected in the works of many authors: D.P. Petelina, I.D. Syromyatnikova, B.N. Abramovich, I.D. Lishchenko, V.A. Venikova, F.G. Guseinova, N.I. Voropai and other scientists. In the works of N.D. Abdullaeva, V.F. Shumilova, G.R. Schwartz et al. considered the issues of synthesizing suitable ARV systems for overloads. However, the mission of optimizing ARV SD systems and synthesizing suitable actions remain open. In addition, the construction of digital exciters for SD GPA is considered important.
The main goal of the work is to optimize the operating modes of electric motors in networks with distributed generation.
The operation of electric motors is based on the principle of electromagnetic induction. An electric motor includes a stator (fixed part) and a rotor (armature, if we are dealing with a DC machine) (moving part). With the help electric current(or permanent magnets) stationary and/or rotating magnetic fields arise in the electric motor.
A distinctive feature of electric motors is the property of reversibility: any electric generator is capable of performing the tasks of the engine and vice versa, and in any transformer and electrical machine converter electrical energy The direction of energy conversion can be reversed. Despite this, each rotating machine is usually designed for only one mode of operation (for example, as a motor or generator). In the same way, one of the transformer windings plays the role of a receiver of electrical energy (primary winding), and the second is responsible for releasing energy (secondary winding). This makes it possible in the best possible way adapt the electric motor to the given operating conditions and use materials as efficiently as possible, i.e. achieve the greatest power per unit weight of the electric motor.
Electric motors are so common in production and everyday life that experienced designers or maintenance personnel of enterprises are well versed in the principles and modes of their operation. But the average consumer and even some non-specialized engineers are a little mistaken in their knowledge of the principle of operation and operation of electrical machines and make classic mistakes that can significantly harm the electric machine. Let's look at five main mistakes when choosing and operating electrical machines.
Slight overheating will not have a significant effect on the electric motor.
This is one of the most popular misconceptions. For those who have been involved in the selection and calculation of electric motors, it is known that electric motors are divided according to winding insulation classes. These classes normalize the maximum values of winding temperatures during operation of the electric motor. When the permissible temperature is exceeded, the insulation begins to deteriorate faster than during normal operation, thereby reducing the service life of the machine. Sometimes such overheating can reduce the service life by more than half, without leading to immediate failure of the machine.
Frequent starts will not damage the electric motor
Electric motors have such a concept as the permissible number of starts per hour. If this value is exceeded, this will also not add service life to the electric machine. During direct starting, peak (starting) currents generate additional heat, which is dissipated during operation of the electrical machine. But if the time the electric drive is parked or operating in nominal mode is not enough to return the temperature of the windings to normal, this will also cause additional overheating.
Improved power factor allows for big savings
Yes, improving the power factor (cos φ) allows you to save some energy, but not very much (depending on the power). If the electric motor low power or you don’t pay for reactive power consumption, then you won’t get any savings. The amount of reactive energy saved depends on several factors, such as the length and type of connection cables, the number of transformers, and the amount of load connected in parallel with the motor, as well as where the compensating device is located.
Electric motors have become widespread due to a number of their advantages, such as: high energy performance, ease of supply and output of energy, the ability to produce electric motors of a wide variety of powers, rotation speeds and, to top it all, ease of maintenance and ease of handling.
The energy lost in electric motors leads to heating of their individual parts. In order for the electric motor to last as long as possible, heating must be limited. Electrical insulating materials are most susceptible to heating, and depending on their quality, permissible heating levels for electric motors are set. You also need to take care of creating good conditions heat removal and cooling of electric motors.
As the load of an electric machine increases, energy losses increase and the heating level of the machine increases. In this regard, the maximum load power of the machine is determined depending on the permissible amount of its heating, as well as on the mechanical strength of its individual parts, current collection conditions on the sliding contacts, etc.
The intensity of the operating mode of AC electric motors in relation to electromagnetic loads (the magnitude of magnetic induction, current density, etc.), energy losses and heating is determined not by active, but by total power, since The magnitude of the magnetic flux in a machine depends on the total voltage, and not on its active part. The useful power provided for an electric machine is called rated power. The remaining quantities, which also characterize the operation of the electric motor at a given power, are also called nominal. Among them are rated current, voltage, rotation speed, efficiency and other values (for an AC machine - rated frequency and power factor).
The following operating modes of motors under overload are distinguished depending on its duration: long, temporary and intermittent.
During long-term operation, the motor operates without interruption; in addition, the operating period is so active that the heating of the motor reaches a steady temperature.
Long-term overload can be constant or changing. In the first case, the temperature does not change, in the 2nd case it changes along with the change in overload. The engines of conveyors, sawmill frames, etc. operate in this mode with slightly varying overload; the engines of all kinds of metalworking and woodworking machines operate with variable long-term overload.
During a short period of operation, the motor does not have time to heat up to the established temperature, but during the pause it cools down to the temperature environment. The duration of short-term operation of GOST for electric machines is set to the same 10, 30, 60 and 90 minutes.
In intermittent mode, the engine does not have time to heat up to the established temperature during the period of operation, and during the pause it does not have time to cool to ambient temperature. In this mode, the engine operates with constantly alternating periods of operation under overload and idle, or pauses.
Since the main consumers of electricity in enterprises are considered to be DC and AC electric drives, let us briefly consider the origin of power losses in steady-state and transient operating modes of adjustable electric drives. It is known that the choice of one or another method of adjusting the speed of engines is ultimately guided by its efficiency. At the present time, speed control using the UP-D (controlled converter-motor) system is considered more economical. With this method, according to the required mechanical power, the source releases the required electrical power. UP-D systems include systems with DC motors and frequency control systems with asynchronous AC motors. For DC motors with independent excitation, fixed costs consist of costs in the excitation circuit, mechanical costs and additional losses in steel. 1 PSTU, Doctor of Engineering. sciences, prof. 2 PSTU, st. teacher
Transient processes (acceleration and deceleration) are carried out by smoothly changing the supply voltage for DC motors. For motors, when receiving frequency control, the frequency also changes with the voltage. The main aspect for choosing a method for controlling high-speed modes of the main drive motor is financial judgment. In the event that financial result Since the implementation of rational control systems is higher than the result from saving electricity, it will be natural to make decisions in favor of increasing the productivity of the device, including by increasing electricity consumption. However, even in these conditions there are significant reserves for saving electricity. The solution to the difficulties lies in the study and introduction of adaptive control systems for students to control the operating modes of electric drives of rolling mills.
For productive and smooth operation of any industrial equipment, a powerful electric motor is required, which takes care of the entire production part. It is the motors that set the rated power, which ensures the rotation of the fan or the functioning of the pump. Engine models vary in application and type. In any online store you can find a list of many models of single-phase motors, three-phase motors, as well as explosion-proof motors.
Each such power unit is responsible for a number special functions and is designed to provide a certain level of power. In addition, all engines are made according to similar technical specifications, therefore, even regardless of the brand or date of development, they will have similar design features appearance and shape, which allows them to be installed in any place, even where there are problems with a lack of free space.
So, it is worth noting that the main reserves for saving electricity are contained in the study and improvement of the energy-power characteristics of industrial electrical equipment and control of the operating modes of this equipment based on the implementation of adaptive control systems. Depending on the mode of the robot engines, the amount of energy consumed changes.
References:
- Karasevich A.M., Sennova E.V., Fedyaev A.V., Fedyaeva O.N. Efficiency of development of small thermal power plants based on gas turbine and diesel power plants during gasification of regions // Thermal power engineering, 2000, No. 12, pp. 35-39.
- Energy of the XXI century: Conditions of development, technologies, forecasts / L.S. Belyaev, A.V. Lagerev, V.V. Posekalin; Rep. ed. N.I. Voropai. Novosibirsk: Nauka, 2004, 386 p.
- Bayegan M.A. Vision of the Future Grid // IEEE Power Engineering Review, 2001, Vol.21, No. 12, p. 10-12.
Optimization of operating modes of heating networks refers to organizational and technical measures that do not require significant financial costs for implementation, but leading to significant economic results and reduced costs of fuel and energy resources.
Almost everyone is involved in the management and adjustment of operating modes of heating networks. structural divisions“Heat networks”, which develop optimal thermal-hydraulic modes and measures for their organization, analyze actual modes, carry out the developed measures and set up automatic control systems (ACS), and also quickly manage the modes and control the consumption of thermal energy, etc.
The development of modes (during the heating and inter-heating periods) is carried out annually, taking into account the analysis of the operating modes of heating networks in previous periods, clarification of the characteristics of heating networks and heat consumption systems, the expected connection of new loads, plans overhaul, reconstruction and technical re-equipment. Using this information, thermal-hydraulic calculations are carried out with the compilation of a list of adjustment activities, including the calculation of throttle devices (throttle diaphragms and elevator nozzles). The calculation of throttling devices is carried out for each thermal unit, taking into account the decrease in coolant temperature due to losses of thermal energy through pipelines from the source to the thermal unit. Calculations for the heating period are carried out in 3 modes: adjustment (the ratio of the shares of hot water supply in an open circuit from the supply and return pipelines is 60 and 40%, respectively), as a result of which the diameters of the throttling devices are determined, winter (with design temperature outdoor air and 100% open circuit DHW from the return pipeline) and transitional (at the outdoor air temperature corresponding to the beginning/end of the heating period and 100% open circuit DHW from the supply pipeline). When carrying out calculations in the last two years, increasing or decreasing coefficients are applied to the calculated (contractual) loads, determined based on the actual consumption of thermal energy. Taking into account actual thermal loads allows you to more accurately calculate modes, carry out adjustments and, ultimately, minimize deviations from design modes.
The development of operating modes for heating networks over the past 10 years has been carried out using software"SKF-TS". By system district heating city of Omsk formed detailed diagram heating networks and a database containing characteristics of all elements of the circuit (sections of main and intra-block pipelines, pumping equipment, shut-off and control valves, PNS, central heating substations and transformer pump stations, connection diagrams and loads of thermal units (consumers). Currently, the database contains characteristics more than 130 thousand elements (figure).
In addition to calculating optimal modes and developing commissioning measures, SKF-TS also allows operational and engineering personnel to perform in a single information space:
1) analysis of the technical condition of the heat supply system, the actual condition of networks, modes, damageability of pipelines;
2) modeling of emergency situations, including emergencies;
3) optimization of pipeline replacement planning with replacement priorities;
4) design and modernization of heat supply systems, including optimizing planning for the modernization and development of heating networks.
The main criterion for the optimization task when developing modes and redistributing heat loads is to reduce the costs of production and transport of thermal energy (in particular, loading the most economical heat sources of CHPP-5 and CHPP-3, unloading the pumping station) with existing technological limitations (available capacities and equipment characteristics thermal sources, throughput heating networks and equipment characteristics of pumping stations, permissible operating parameters of heat consumption systems, etc.).
The developed operating modes of heating networks are coordinated with heat sources, approved and sent for management and planning of operating modes of equipment at heat sources and operational units. When developing regimes, the necessary measures for organizing regimes for main heating networks and heat consumption systems are also developed and approved, which are issued to operational areas and consumers for implementation before the start of the heating period. For heat consumption systems, the installation of throttling devices is carried out by housing management companies and other owners under the control of the personnel of the subscriber departments of heating districts upon acceptance for re-use. In addition, specialists monitor the implementation of these measures, including selectively for heat consumption systems. After the start of the heating period, adjustment work is carried out on control units, regulators are adjusted, and adjustment work is carried out on heat consumption systems.
During the heating season, multi-level control and analysis of the supply and consumption of thermal energy is carried out.
1) Operational control is carried out by the dispatch service using remotely transmitted data from heat source metering devices, as well as periodically transmitted data from control points.
2) Daily monitoring of the parameters of the coolant, the supply of thermal energy and coolant for each heating main and in general for the heat source is transferred to the server (flow rates of network, make-up and source water, temperature and pressure of the coolant) with prompt adjustments being made to the dispatch schedule of heat loads.
3) Control over the consumption of thermal energy by consumers is carried out by inspectors and specialists of subscription departments once a month. Also, based on printouts from metering devices, an analysis is made of the consumption modes of consumers with metering devices to identify violations of thermal energy consumption (increased consumption, excess temperature of return network water, etc.).
4) Monitoring the temperature of the return network water along the boundaries and along the branches (carried out weekly by personnel of the heating district to identify branches with an increased temperature of the return network water and carry out adjustments).
On the issues of regulation of heat supply and adjustment modes, weekly working meetings are held, in which managers and specialists from management, inspection, customer departments, and operational and repair personnel of thermal districts participate. In addition, weekly meetings are held at the Heating Networks joint venture on the issue of the heating period, with consideration of all problematic issues regarding heat supply and hot water supply of the city. These meetings are attended by representatives of the housing management companies, the transport organization MP “Thermal Company”, OJSC “Omskvodokanal”, and the City Administration.
Adjusting hydraulic modes is inextricably linked with regulating temperature conditions from heat sources. The main task of regulation in heat supply systems is to maintain the air temperature inside heated premises within specified acceptable limits when external and internal disturbing factors change.
In accordance with the "Rules technical operation» the water temperature in the supply line of the water heating network in accordance with the schedule is set according to the average outside air temperature over a period of time within 12-24 hours, determined by the heating network manager depending on the length of the networks, climatic conditions and other factors. Due to the lack of developed methods and recommendations, the determination of the specified parameters of the coolant (temperature, pressure) and the task time, as a rule, was carried out on the basis of the experience and intuition of the dispatcher.
The increasing share of automation of heat consumption systems and the transition to quantitative and qualitative regulation with low hydraulic stability of the system leads to significant variability in hydraulic modes, therefore the requirements for the organization and operational management of thermal and hydraulic modes of central heating systems are increasing significantly.
Analysis of the dynamics of changes in the average daily outside air temperature in Omsk in heating periods shows that the temperature change is random, while in individual periods There are significant amplitudes of changes in daily temperatures (up to 15÷17 O C), which, with high-quality regulation, implies a change in temperature in the supply pipelines of more than 30 O C.
Constant changes in external disturbing factors lead to the need to change the thermal load, modes and composition of the operating equipment of thermal power plants, as well as to the occurrence of alternating voltages in the pipelines of heating networks, which increases the likelihood of their damage and reduces reliability.
In order to eliminate negative aspects in the operational regulation of heat loads in the heat networks of the Omsk branch of OJSC "TGC-11" and to simplify the process of developing a dispatch schedule for heat loads, "Instructions for the assignment" have been developed temperature regime operation of heat sources" and a form for calculating temperature parameters for the next day. The main provisions of this instruction are based on a model that takes into account the dynamic characteristics of the heat supply system, the storage capacity of buildings, as well as the dynamics of change and the influence of the main disturbing influences (outside air temperature) over several days (actual and predicted) on the thermal regime of heated buildings.
When forming a dispatch schedule, adjustments to the task are also provided, which can be introduced on an external initiative, or in the event of a significant deviation of actual temperatures from the forecast ones. This temperature can be set for a regulation period or, subject to adjustment, for several regulation periods.
Since 2009, regulation has been applied in the heating networks of the Omsk branch of OJSC TGC-11, taking into account the dynamic characteristics of the heat supply system. As practice has shown, within certain limits of change external factors make it possible to increase the regulation periods to 24-72 hours or more, while the increase in the period has virtually no effect on the quality of heat supply to consumers, which makes it possible to operate the equipment of heat sources and heating networks in a more “gentle” mode.
In the district heating system from heat sources of the Omsk branch of OJSC "TGC-11", as a result of systematically carried out work to optimize and adjust the operating modes of heating networks over the past 6-7 years, the quality of heat supply to consumers has radically improved and the efficiency of the entire centralized heat supply system from heat sources of OJSC has been increased "TGK-11", namely:
1) the issues of heat supply and hot water supply have been resolved in entire microdistricts of the city (village 40 let Oktyabrya, village Sibzavoda, village Sverdlova, microdistricts No. 5, No. 6, No. 10, No. 11 of the Left Bank, the Central part of the city, residential areas on the street . Poselkovaya, Tyulenina St., Truda St.), as well as individual consumers;
2) the operation of heat consumption systems “for discharge” due to insufficient available pressures is completely excluded;
3) excessive fuel consumption is reduced due to overheating of consumers during transition periods;
4) electricity costs for pumping coolant were reduced by 14% (from 53 to 46 million kWh) by reducing coolant circulation costs while simultaneously connecting new consumers;
5) fuel consumption for electricity generation has been reduced by reducing and normalizing the temperature of the return network water;
6) make-up water consumption was reduced by 21% (from 40.2 to 31.9 million m3);
7) new consumers are connected;
8) damage to pipelines is reduced. Thus, with an integrated approach to the process of managing operating modes, modes can be optimized and the efficiency of the central heating system can be significantly increased.
Literature
1. Rules for the technical operation of power plants and networks of the Russian Federation. - M.: NC ENAS, 2008. - 264 p.
2. Zhukov D.V., Dmitriev V.Z. Increasing the efficiency of centralized heating systems by optimizing thermal-hydraulic modes. - On Sat. “Proceedings of VNPK “Increasing the reliability and efficiency of operation of power plants and energy systems” - Energo - 2010. In 2 volumes. - M.: MPEI Publishing House, 2010. - T. 1. 304 p. ill. pp. 229-232.
Content
Introduction……………………………………………………………………….3
1. Selection of the optimal composition of units……………………………………4
2. Optimal distribution of heat load between units of thermal power plant...7
3. Optimization of turbine operating modes when passing through dips in electrical loads……………………………………………………………… ..9
4. Efficiency of using variable frequency drives in heat supply systems………………………………………………………………………13
Conclusions……………………………………………………………………….23
References
Introduction
In conditions of restructuring and transition to market mechanisms in the Russian energy sector, priority areas in the development of energy science are those related to reducing the cost of supplied thermal and electrical energy based on increasing the efficiency of their operation. It should be noted that we're talking about not about introducing additional capacity by building new energy sources, but about increasing the competitiveness of existing ones.
To date, the developed methods for optimizing operating modes and controlling CHP equipment do not sufficiently take into account the actual state associated with obsolescence and obsolescence of main and auxiliary equipment, and the regulatory framework for the energy characteristics of equipment requires constant adjustment during operation. Existing methods for planning optimal control of operating modes of power equipment are labor-intensive and time-consuming, which reduces the efficiency of decision-making by CHP personnel not only in matters of effective distribution of loads between units, but also in the preparation and submission of high-quality reports and price applications for the participation of CHP plants in the sale of electricity on the Wholesale Electric Power Market .
Let's consider some methods for optimizing operating modes of power equipment.
- Selecting the optimal composition of units
The inclusion of individual units in operation affects the size and location of reserves, the mode of the electrical network, the flows along intersystem power lines, the fuel consumption of the system, etc. Therefore, the task of choosing the optimal composition of units is one of
the most important.
In general, for a system, k thermal stations, the task is to determine for each calculated time interval:
1) composition of aggregates;
2) moments of starting and stopping units;
3) load distribution between them, ensuring a minimum of operating costs and meeting all reliability requirements.
When formulating a mathematical description of the problem, it is necessary to take into account:
1) energy characteristics;
2) starting costs of the units (boilers or turbines cool down when they are stopped, so they require heat when starting again. These costs depend on the duration of the unit shutdown, if it is less than a day, if more, they do not depend);
3) type, grade, cost of fuel at thermal power plants;
4) power losses, restrictions in electrical networks;
5) restrictions on combinations of operating units; etc.
In accordance with the above, the task of choosing the composition of units is:
– nonlinear,
– integer,
– multi-extreme,
– has a high dimension (2n, n-number of aggregates).
It is impossible to directly solve the problem using the method of indefinite Lagrange multipliers, because the change in the number of operating units is discrete, while the characteristics of the station change abruptly. You can use the dynamic programming method, but only for the number of units up to 20-30. There are no sufficiently general methods for organizing variant analysis of various compositions. All existing methodological techniques are approximate.
Let there be a power system with only thermal power plants, i.e. All units are installed at thermal power plants. We will assume the load on the power system remains constant and will not initially take into account start-up costs. Next, we assume that all active powers are distributed between the switched-on units optimally according to the criterion.
? = b i /(1- ? i ) =idem(1)
Let us determine the criterion for the profitability of stopping one of the operating units, for example, the unit j. Let us denote the specific costs of expenses?, then:
? j= Bj/Pj (2)
Let the unit j, which we are talking about stopping, works until it stops with power P j 0 and with specific cost consumption? j 0 . Then the cost savings from stopping the unit will be:
E j 0 =? j 0 P j 0 (3)
When the unit stops j will have power P j 0 to be assigned to other units of the power system according to the principles of optimal power distribution.
Here? 0 and? k – initial and final value of the specific increase in costs in the system when the unit is stopped j ; ? j 0 and? j k – initial and final value of the specific increase in power losses in the network.
Based on this criterion, the following algorithm for selecting the optimal composition of aggregates can be adopted. For each period under consideration, for example a day, optimal units are selected. First, they assume that everyone is working and find the optimal distribution of active power under this condition. Then the savings from shutdown are found for each unit separately, as well as the specific savings per unit of rated power:
E 0 = E R j nom (6).
When stopping, the unit that gives the greatest specific savings is selected first. Accounting is carried out according to specific savings because at any hour it is possible to stop units with a rated power of no more than? P=P?nom? R? ?R wholesale,
Where P?nom is the rated power of all units, opt is the specified value of the optimal power reserve in the system. After stopping the first unit, which gives the greatest specific savings, the optimal distribution of power among the operating units is again carried out, then the specific savings from stopping additional units are calculated. Again, the unit that gives the greatest specific savings is selected for shutdown, etc. until either there are no units at all, or the shutdown of the next one does not lead to an unacceptable reduction in the power reserve.
In this way, it becomes clear which units should remain idle during certain hours of the day.
To approximate the starting costs of units, we consider that it is profitable to stop them only for a certain number of hours per day? Then, for the remaining hours of the day, the specific costs of the unit are increased by adding to the actual costs? jPj startup costs for? hours divided by the number of working hours. Corrected specific consumption costs for load Pj. Will:
= ( 4)
Where T ud – starting costs per hour of parking. Then a new selection of optimal units is made without taking into account starting costs and the specific costs are again adjusted. Due to the complexity of calculations, it is recommended to solve the problem of choosing the optimal composition of units using a computer.
- Optimal distribution of heat load between CHP units
The maximum combined generation of electrical energy determines the highest thermal efficiency of the CHP plant as a whole only in the case when the initial and final parameters (condensation temperature) of all turbines are the same. If turbines with different initial parameters are installed at a thermal power plant, then the maximum combined production of electrical energy does not always determine the highest thermal efficiency of the thermal power plant as a whole, since transferring the entire thermal load to heating turbines with the highest initial parameters in order to increase the combined energy production leads to under the conditions under consideration to an increase in low-economic condensation generation on turbines with lower initial parameters.
The condition for the highest efficiency of a thermal power plant with any set of equipment is the minimum consumption of equivalent fuel to supply a given quantity and quality (parameters) of electrical energy and heat. With the same efficiency of all operating boilers, as well as the same internal relative efficiency of the turbine compartments below the extraction pipes, the condition for the optimal thermal regime of the CHP is the minimum exergy consumption to satisfy the given heat load;
(5)
where is the performance coefficient of waste heat removed to the heat supply system; T T - average temperature of waste heat, K; T 0.C is the average temperature of heat removal to the environment, in this case from the turbine unit’s condenser, K.
In the case when all turbine units of thermal power plants T 0 c = idem and only steam from turbine exhausts is used for heat supply, the condition of maximum thermal efficiency corresponds to the minimum average temperature of saturated steam or, which is the same, the minimum average pressure in the exhaust.
At T 0 c = idem and the same pressure in the extractions of all turbine units of the thermal power plant, but at different temperatures When superheating steam in extractions, the condition of maximum thermal efficiency corresponds to the minimum temperature of the steam used for heat supply.
For the same values T T all turbo units, but with different values T 0 s, i.e. at different temperatures of heat removal from the condenser, the minimum value occurs in the turbine unit with the highest condensation temperature. First of all, it is advisable to use in this case selections of turbines that have the highest condensation temperature.
- Optimization of turbine operating modes during electrical load dips
Particular difficulties in operation are caused by deep load reductions, mainly at night, while the entire burden of regulation falls on high-pressure equipment (units with a capacity of 100, 150, 200 MW).
Regulation of night failures until 1970 was carried out by unloading some of these units up to 60% and unloading up to 5-10 MW of units with a capacity of 100 MW.
The operation of turbogenerators at low loads leads to large excess fuel consumption, and their excessively frequent shutdown leads to increased equipment wear. All this led to the need to find more economical and reliable ways to overcome daily dips in electrical load schedules in combination with high maneuverability.
One of possible ways reservation of turbine units after a set of tests and research is the transfer of the turbogenerator to the synchronous compensator mode. In this case, the generator remains connected to the network and, due to the consumption of active power, rotates together with the turbine at the rated speed.
The supply of live steam to the turbine is stopped, and cooling steam is supplied to the flow part of the turbine to ensure and maintain the required temperature state. In this case, the generator can operate as a compensating device (synchronous compensator) or in purely motor mode (without reactive power).
Figure 1. Diagram of additional pipelines for transferring a 100 MW turbogenerator to synchronous compensator mode.
I – live steam; II – from the third selection reservoir; III – from the equalizing line of deaerators.
For K-100-90 turbines (Figure 1), cooling steam is supplied to the high-pressure cylinder - HPC into the 3rd extraction from the general station manifold of 3 extractions (t=240°C p=0.4 MPa). This steam first passes through the XI and XII stages of the HPC, and then through the bypass pipes enters the low pressure cylinder (LPC) and is discharged into the condenser. To make it possible to operate the turbine in a deteriorated vacuum (summer period), an additional steam supply pipeline is provided to the LPC steam inlet from the steam equalizing line of the deaerators.
In order to avoid cooling of the sleeve in front of the seal during operation of the turbogenerator in the RD, when the sealing steam (deaeration) has a temperature of 130-150°C, as well as its rapid heating during the transition to the active load, a scheme for supplying live steam to the first suction of the front HPC seals and a valve is installed connecting this suction with the 3rd HPC extraction. To cool the pipes, the principle of pickup of reverse steam flows from the condenser into the flowing part of water in the form of fine moisture is used. To supply condensate, a recirculation line is used with reconstruction of the collector.
Figure 2. Diagram of additional pipelines for transferring a 200 MW turbogenerator to synchronous compensator mode.
I – from hot reheat; II – from cold reheat; III – from the equalizing line of deaerators; IV – discharge to the capacitor.
Operation of the K-200-130 turbine in motor mode (Figure 2) is ensured by supplying medium and low pressure steam to the flow path of the cylinders from an external source to maintain the required temperature state of the cylinder metal. For this purpose, the turbine unit is equipped with the following additional pipelines:
a) supplying steam from the hot reheating steam lines of adjacent operating units into the chambers of the front end seals of the high pressure pump and central pressure pump;
b) supplying steam to the IV turbine outlet (TSU) from the cold reheating steam lines of adjacent operating units;
c) supplying deaeration steam to the LPC bypass pipes.
To cool the exhaust pipes of the low-pressure cylinder when the turbine is operating in engine mode or at idle, special manifolds with nozzles are installed in the turbine condenser with the main condensate supplied from the recirculation line.
etc.............
Mathematician. Graduated from Ural State University in 1961 state university majoring in applied mathematics, candidate of technical sciences.
Since 1967, he has been dealing with the problems of optimizing the operating modes of power plants and energy systems.
He defended his PhD thesis on the topic “Methods for determining economical modes of hydrothermal power systems and thermal power plants with complex thermal circuits.”
A doctoral dissertation has been prepared - “Optimization of the operating mode of power plants and energy systems - the basis of the wholesale electricity market model.”
Author of more than 50 articles.
Developer of the software and hardware complex “Multifunctional mathematical model of a thermal power plant”, which is part of a project aimed at energy saving and increasing energy efficiency. Laureate of the competition of the Russian Association for Innovative Development.
The complexity of designing models of the wholesale electricity market is largely determined by the peculiarity energy industry, the product of which (electricity) cannot be produced for future use. The volume of electricity production is closely related to the volume of its consumption. Electricity is produced exactly as much as the consumer requires, so in principle there can be no excess. This feature significantly influences and determines the structure of the wholesale electricity market. Therefore, when designing a model of such a wholesale market, a difficult question arises: “What should be the architecture of the electricity market model?”
Here it is appropriate to recall one of the main goals of the transition to market relations - increasing economic efficiency electricity production. Therefore, the competition mechanism embedded in the model of the wholesale electricity market must inevitably lead to the set goal in each case.
Electricity is a socially significant and highly liquid product, so society is interested in producing it at the lowest possible cost. This, in turn, will improve the environmental situation and create favorable conditions to reduce tariffs. This approach must be considered as an important component common problem energy efficiency and energy saving implemented at the stage of electricity production. The degree of effectiveness of energy saving measures at this stage is comparable to the same indicator at the energy consumption stage. This circumstance dictates the need integrated approach to solving the problem.
The urgency of solving the problem of energy saving has increased sharply due to the transition of energy to a market economy in the electricity production sector.
An analysis of the results of the functioning of the existing model of the wholesale electricity market gives grounds to assert that the proposed mechanism is far from perfect. It does not meet the requirements for minimizing fuel costs when producing electricity (this is easy to show) and therefore, in principle, cannot be energy saving. Main reason The inefficiency of the existing wholesale electricity market model lies in the absence in the mechanism of auction purchase and sale of electricity of an optimization procedure for distributing the load between power plants, based on their energy characteristics (characteristics of relative increases in fuel costs - RFI).
The basis of the wholesale electricity market is an auction of price bids. This circumstance makes the price bid a key position that determines the effective operation of the wholesale electricity market. Therefore, a comprehensive definition and explanation of the essence (and not just the form) of the price application is extremely important. First of all, this is important to ensure efficient work unified energy system.
The practice of market subjects, meanwhile, shows that the absence of any uniform rules for the formation of price requests not only in form, but also in content leads in fact to the search for a certain effective way their assignments, based on an analysis of previous results of work on the wholesale market. Thus, only experience and intuition determine each time the type of price request. Essentially, there is a game of price bids. But no game under any circumstances can, in principle, provide cost-effective electricity production. There is an obvious discrepancy between the accepted market model and such a specific industry as energy. And the specifics of energy production (electricity cannot be produced in excess) cannot but leave a certain imprint on the model of the wholesale electricity market.
To understand what impact the mentioned specifics of the energy industry have on the model of the wholesale electricity market, let us analyze the mechanism for using its key link - the price application.
The existing approach involves the submission of price bids by all subjects of the wholesale electricity market to participate in the auction for the sale of electricity for the coming day. Applications are sent to the administrator trading system both from electricity buyers, indicating the required volumes of electricity and their own ability to pay for them, and from suppliers, indicating the volumes of guaranteed supply of electricity at prices formed taking into account all types of costs. For the electricity supplier, however, it is very difficult to predict the full cost of electricity production to calculate the expected price, since it is not known what the volume of electricity produced will be in the coming 24 hours. Therefore, the electricity supplier, trying to get maximum profit, tries to predict, based on the experience and results of the previous day, the most effective level prices for different volumes of sold electricity. Based on requests from buyers, a demand curve is constructed, and based on requests from suppliers, a supply curve is constructed (Fig. 1 of the presentation).
V.M. Letun. Drawings for the article "Optimization of operating modes of power systems - the basis of the wholesale electricity market model"
V.M. Letun. Drawings for the article... of the electricity market"
The desire of electricity buyers to purchase more electricity at a lower price remains unsatisfied. The unsatisfied demand of some market participants can be realized on the free market.
The volume Wп is the limit for the sale and purchase of electricity on mutually beneficial terms, and the price of the CPU corresponds to it. Thus, the point of intersection of the demand curve and the supply curve corresponds to the maximum volume of sale (purchase) of electricity and price on mutually beneficial terms.
This simple auction scheme, which implements the priority purchase of cheap electricity and thereby minimizes the cost of purchasing electricity, determines the corresponding load of power plants in terms of active power. However, it does not follow from this that the cost of generating electricity at such a load will be minimal. Most likely, with this approach they will never be minimal, and the degree of deviation (in terms of costs) of the resulting regime from the optimal one will be largely determined by the specified prices in the price bids of wholesale market entities.
In such an approach, hopes for the “invisible hand” of the market are completely groundless. We must clearly understand that the “invisible hand” that the fathers of the market economy spoke about is not some mystical passage in the market model, but a subtle economic tool designed to make the model as efficient as possible.
The described model scheme does not have such a tool, so it is initially programmed for a deliberately ineffective solution from a cost point of view in the production of electricity, despite a certain market environment. Essentially, the focus is on competition in electricity prices, which, in turn, gives rise to a lot of negative phenomena (games with price bids, corruption, etc.) that aggravate the inefficient functioning of the energy sector.
Essentially, the problem of minimizing the cost of electricity production has been replaced by the task of minimizing the cost of purchasing electricity.
You can use the recommendation of RAO UES of Russia. In paragraph 12.3 of the order of RAO UES of Russia No. 52 dated January 24, 2006. “On preparation for the launch of the new wholesale electricity (capacity) market of the transition period (hereinafter referred to as NOREM) from April 1, 2006,” it is recommended to “consider it advisable to submit competitive price bids for the sale of electricity based on marginal variable costs.” According to the generally accepted definition, the limit variable costs or marginal costs are the first power derivative of the cost function for electricity production or, what is the same, a characteristic of relative cost increases.
Let’s use this recommendation and set marginal costs (MCC) as price bids; then the solution obtained in this case will be noticeably closer to the optimal one in terms of electricity production costs. But in this case, the question arises with the semantic interpretation of the intersection point (if there is one) of the demand curve and the supply curve, since marginal costs, strictly speaking, are not the price of electricity produced. Selling electricity in this situation at the price of CPU is extremely unprofitable for the supplier, because marginal costs are always lower real price for electricity.
In this situation, a natural solution arises - to calculate electricity prices after the fact, knowing the volume and load schedule of each electricity supplier and their current energy characteristics.
If we look at the problem more strictly, then it is necessary to change the architecture of the wholesale electricity market model to include a full-fledged system for optimizing the loading mode of power plants according to the criterion of minimizing the cost of burned fuel in the production of electricity. This is the “invisible hand” that will make the model effective, and this is the only possible way reducing costs for electricity production, maximizing profits as a whole for the unified energy system, creating objective prerequisites for reducing electricity tariffs.
As a basis for the wholesale market model, it is advisable to take a well-developed hierarchical system for optimizing the operating modes of energy systems in the past, with a system of mutual settlements for sold (purchased) electricity linked to it. With this approach, the problem of optimal electricity production in the above sense is automatically solved. The subject of competition is the economic characteristics of market entities, which are largely (if not mainly) determined by the use of high-tech equipment, a high level of technical operation of this equipment and, finally, optimal control of its loading mode. Market entities with such qualities will have a competitive advantage, which will ultimately ensure they produce electricity in large volumes and at the lowest cost. And this is the crux of the matter.
Now let's say a few words about general principles organization of a system of mutual settlements. Optimization of modes on upper levels hierarchy comes down to determining the volumes of intersystem active power flows. Each of the flows can be caused either by a power shortage in the neighboring power system, or by the replacement of “expensive” electricity, or by both.
Mutual settlements when eliminating power shortages in a neighboring power system. This is a classic case of trade relations between two parties, supplier - consumer, therefore in such a situation all payments for supplied electricity are carried out at a tariff that takes into account all types of costs for the electricity produced.
Mutual settlements when replacing “expensive” electricity. This is a very realistic option for establishing trade relations between two self-sufficient energy systems, beneficial under certain conditions for each of the parties.
The word “expensive” is put in quotation marks for the simple reason that it does not express the generally accepted meaning – quite large average costs over a certain period for the production of 1 MWh of electricity in terms of the fuel component – but something else. This can be stated differently as follows: the concept of expensive electricity means a large increase in fuel costs at a given time when electricity generation increases by 1 MWh. In this sense, the status of a power plant (energy system) – “expensive” or “cheap” – can change depending on the situation. The quantitative side of these cost increases is reflected by the characteristic of relative cost increases (RCI).
Thus, if two neighboring power systems A and B, which have equivalent COPP (see Fig. 2 of the presentation), have achieved relative increases in eA and eB when covering the consumption load, then they have a real opportunity to carry out a mutually beneficial trade deal: power system A can replace its expensive power in the amount of DP (MW), corresponding to the power purchased from power system B.
Volume D R is calculated in such a way that the following relation is satisfied:
e A ( R A consumption - D R) = e В ( R V consumption + D R) = e c . (1)
Selling electricity to power system A in the amount of DP (MWh) will, firstly, minimize the total costs of electricity production and, secondly, at a certain level of the selling price, make the trade transaction profitable for each of the parties. As such a price, it is advisable to choose the relative increase in costs ec or some value close to it.
Obviously, if in such a situation we sell electricity at a price that includes all types of costs and therefore is significantly higher than ес, then it will be more profitable for the buying party to produce this volume of electricity DP using its generating capacities.
And, finally, if one of the neighboring energy systems is not only deficient, but also “expensive”, then payment to it for the supplied electricity from neighboring energy systems will be carried out at two tariffs: for covered electricity deficit - at one tariff, for replaced expensive electricity - at a different rate.
Thus, at the energy system level (RDU level) in the hierarchical system of the mode optimization process, intersystem active power flows structured by tariffs will be determined. Having a forecast of consumption load and energy characteristics of power plants, it is possible to optimize the distribution of active power between power plants, taking into account the network factor and intersystem power flows in the following sequence:
if the balance of generation and consumption is disturbed in some time intervals, the composition of the operating equipment is selected;
the loading mode of power plants of the energy system is optimized;
preliminary load schedules are transmitted to the power plants of the energy system to clarify the composition of the operating equipment and, in case of its change, the corresponding recalculation of the energy characteristics of the power plant's HOPZ;
In accordance with the new HOPZ in the RDU, the loading mode of power plants of the energy system is re-optimized to clarify their load schedules.
At the end of the optimization process, for each energy system it will be determined required volume information for commercial calculations: tariffs for intersystem power flows, hourly cost of electricity production for each power plant of the energy system by fuel component, hourly volumes of electricity production, etc. Using this data, coupled with the approved conditionally fixed costs for each power plant, it is possible to calculate electricity tariffs as a whole for the region that is in the service area of the energy system. To do this, there must be appropriate trading services at the energy system level.
Conclusions:
1. Transition from competition in electricity prices to competition in technology, competition in cultural ownership maintenance equipment, competition in the optimal management of the load of power plants and energy systems, which will find expression in the HOPZ, will ensure maximum reduction in the costs of electricity production.
2. The implementation of this approach will increase the reliability of the unified energy system due to the following factors:
exclusion from the technological functions of the system operator during optimal control of the operating mode of power systems of various commercial layers that distract from solving production problems;
distributed among the levels of dispatch control of technological tasks (for example, choosing the composition of equipment) based on the principle of the occurrence of an event and taking into account the place of their occurrence.
3. The system becomes highly controllable. KOPZ indicators (equivalent to price bids) submitted by power plants to the RDU level can be easily verified by the analytical services of the RDU.
4. The system has a stimulating effect on the introduction of new technologies, on improving the culture of equipment maintenance, on the development of the principles of optimal control of loading modes of the main equipment of power plants and energy systems in general.
5. The responsibility of the system operator (SDO) for the uninterrupted supply of electricity to consumers in the region increases.
6. High level and the objectivity of production and economic information as a result of the functioning of such a system provide rich food for effective choice vector of development of energy systems.
References :
1. Stephen Stoft. Economics of power systems. Introduction to the design of electricity markets.: Per. from English – M.: Mir, 2006.
2. Markov M.V. Microeconomics. - St. Petersburg: Publishing House "Neva", 2003.
