Turbine Unit Research Articles

ПОВЫШЕНИЕ ЭФФЕКТИВНОСТИ РАБОТЫ ТЭЦ ПАО «ГАЙСКИЙ ГОК» ЗА СЧЕТ ДОЗАГРУЗКИ ТУРБОАГРЕГАТОВ

Competitiveness of Gaysky GOK depends on energy costs, including the purchase of electricity for technological needs. Turbine units additional load is often considered in the context of optimization of power plant operation under changing conditions of electricity demand. By increasing the turbine load at certain times or when necessary to respond to changes in grid load, it is possible to improve resource utilization efficiency and reduce power generation costs. This article describes the methods of increasing the efficiency of steam-turbine units of thermal power plant of PJSC "GAYSKiy GOK", due to additional loading of operating turbine units up to nominal capacity. At low cost of electricity produced by the CHPP, compared to electricity purchased on the wholesale electricity market, which will reduce the company's costs for electricity purchase. 
 Steam, which is produced during the operation of turbine units in nominal mode and in the winter period is used for heating the city, in the fall-summer-spring periods it is proposed to use for the operation of evaporator plant, which will be used for desalination of clarified water, which after processing will be used in the technological process of the CHPP itself, as feed water for boilers, which will eliminate the need for water treatment of the CHPP.

Failure Analysis of Second Row-Nozzles Based on FSX-414 Cobalt Alloy in a Gas Turbine Unit

Failure Analysis of Second Row-Nozzles Based on FSX-414 Cobalt Alloy in a Gas Turbine Unit

A multi-criteria decision study with sensitivity analysis on a tri-generation system based on gas turbine fueled by wheat straw biomass

Wheat straw biomass plays a key role in the field of energy and developing different energy systems. A tri-generation system of power, hot air, and hot water has been developed and modeled in this research work based on a gas turbine unit fueled by wheat straw biomass. Although air usually is utilized as a combustion agent, this study has focused on the air, carbon dioxide, oxygen, and steam agents as the combustion agent in the gas turbine unit and compared their performances with respect to energy and environmental viewpoints. A multi-criteria decision-making analysis based on a sensitivity analysis has been carried out to compare the system performances in two cases of base case and normalized case (performance per mole of input agent). In base case, the system based on the steam agent has produced the maximum power (204.5 kW) and hot air (439 m3/min) and is the most efficient system (46.8 %) and has emitted the lowest emission (12.91 g/kW.min). This system was the best system according to the sensitivity analysis in the base case. In normalized case, the system based on the carbon dioxide agent has presented the best performance according to the sensitivity analysis because it requires the minimum required input agent. Normalized power of 24.6 kW/mol, normalized hot air of 0.65 m3/mol, and normalized hot water of 0.25 L/mol are presented by the system based on carbon dioxide.

Study on the Cavitation Characteristics of Shroud Clearance in Prototype and Model of a Kaplan Turbine

Model tests and model calculations are the most basic means currently available to study the characteristics of the axial-flow pumps and Kaplan turbines in a systematic manner. Large and medium-sized turbine units and axial-flow pumps must rely on model tests and model calculations to ensure the performances of prototype units before designing. The conversions between models and prototypes are mainly carried out through similarity criteria. However, it is difficult to meet all the similarity criteria in the model tests and the similarity conversions, and the hydraulic and cavitation performances of the model and the prototype are often different. In this paper, numerical calculations of shroud clearance cavitation are performed on both the prototype and model using different cavitation coefficients. The results indicate that the prototype and model have a similar clearance cavitation flow regularity when the cavitation coefficient changes, but they have different energy characteristics and cavitation characteristics. In cavitation conditions, the prototype has higher energy characteristics than the model and the critical cavitation coefficient is similar to the model. When the cavitation coefficient is higher than the critical cavitation coefficient, compared to the model, the blade cavitation performance of the prototype is worse, and the clearance cavitation and runner chamber cavitation are more serious. If the cavitation coefficient decreases to the device cavitation coefficient, the runner chamber of the prototype will cavitate, even though the model has not cavitated yet. The comparison of shroud clearance cavitation between the prototype and the model can be used as a reference for the accuracy of similarity conversion results between the model and the prototype. It also has a positive impact on the design and operation of the prototype.

Effect of hydrogen on nickel oxide reduction on the surface of nozzle blade of a gas turbine unit

Currently, there is a growing interest in the use of hydrogen in the composition of fuel mixtures for turbojet engines and gas turbine units (GTU). The effect of hydrogen on heat-resistant nickel alloys of gas turbine blades has been little studied. In this regard, this work is devoted to studying the effect of hydrogen on nickel oxide reduction on the surface of the nozzle blade of a gas turbine engine. Hydrogen is a good reducing agent. Therefore, this article discusses the effects of hydrogen under various conditions with metal oxides, and methods of metal oxides reduction on the surface of the blades of a gas turbine engine. The thermodynamics of the interaction of aluminum, titanium, nickel and tungsten oxides with hydrogen fluoride and reactions of fluoride with hydrogen was investigated in the temperature range 273 – 1373 K. It was established that the interaction of aluminum oxide with hydrogen fluoride occurs in the temperature range from 273 to 1073 K, titanium oxide with hydrogen fluoride – from 273 to 373 K, nickel oxide with hydrogen fluoride – from 273 to 873 K. In this case, of the resulting fluorides, only nickel fluoride interacts with hydrogen at temperatures above 673 K. Hydrogen interacts with nickel oxide throughout the entire temperature range, and with tungsten oxide at temperatures above 1173 K. We studied the effect of hydrogen on heat-resistant nickel alloys of gas turbine blades subjected to preliminary fluorination and not treated with fluorine compounds. Nickel oxide reduction with hydrogen proceeds better after the preliminary fluorination process. In this case, particles 2 – 5 μm in size containing 90.16 % Ni are formed on the surface of the blade sample. Without fluorination, this process at 1223 K and duration of 1 h does not occur.

A state detection method of offshore wind turbines’ gearbox bearing based on the transformer and GRU

Through the analysis of data from the SCADA system of a wind turbine unit in a specific offshore wind farm located in Zhanjiang, it was observed that the most prevalent type of fault is bearing alarms on the gearbox’s generator side. Considering the growing need for intelligent offshore wind turbine maintenance, this study employed GRA on SCADA data collected over a significant duration from a representative wind turbine unit. Relevant features were extracted, with temperature serving as the target parameter. To address the challenge of long-term dependencies in long-term time series forecasting tasks, this study uniquely combined the GRU with the advanced Transformer neural network which incorporates attention mechanisms, to predict the temperature trend of the gearbox’s generator-side bearing. Based on the prediction residuals obtained during normal operation and their subsequent analysis, the study devised an effective anomaly detection process to identify early abnormal states of the gearbox’s generator-side bearing. Comparative performance evaluations were conducted, comparing the combined model with its individual component models, as well as the traditional LightGBM, in terms of temperature time series prediction and their application in anomaly detection. The results unequivocally demonstrate that the combined model outperforms both the individual models and LightGBM in terms of time series prediction accuracy and anomaly detection effectiveness, indicating an enhanced ability to handle long-term memory challenges. Furthermore, the combined model exhibits great potential of practical application for the early warning of gearbox bearing anomalies during actual wind turbine daily operation and maintenance, providing a valuable solution for the offshore wind turbine industry.

VERIFICATION OF GEOMETRIC MODELS OF THE LPC ROTOR OF THE K-1000-60/3000 TURBINE UNIT BASED ON NATURAL AND CRITICAL FREQUENCIES IN THE ANSYS SOFTWARE COMPLEX

One of the priority tasks of the energy industry is to ensure the reliable and safe operation of steam turbine units of thermal power plants and nuclear power plants. Given the difficult situation in the country, it is impossible to replace outdated equipment that has exhausted its design resource with new ones. As is known, the safety factor of the material taken into account during the design of steam turbine equipment was very approximate. At that time, there were no data on the operation of power equipment, which would have already worked for 200-220 thousand hours. in difficult operating conditions. The situation has changed now. There are power installations that have exhausted or are close to exhausting their design resource. By conducting experimental studies with metal samples of this equipment, it is possible to significantly clarify the physical and mechanical properties of steels and their damage due to operation. Therefore, the problem of extending the resource is becoming increasingly important. Computer modeling has greatly simplified the task of calculating the resource of the equipment. However, such a complex object as a steam turbine requires significant computing resources, and the calculation of equations in all finite element nodes is quite time-consuming. It is necessary to look for ways to rationalize calculation mathematical models. At the same time, the accuracy of the calculation should remain at a satisfactory level. In this work, were created simplified geometric models of the rotor of the LPC turbine unit К-1000-60/3000. The option is considered of replacing the working blades with equivalent distributed masses and toroidal rings. Verification of the obtained models based on critical rotation frequencies confirmed the possibility of replacing the working blades with distributed masses. On the other hand, the presence of toroidal rings of large radii leads to a significant reduction of critical frequencies in comparison with normalized values.

CRITERIA AND CONDITIONS OF THE INTER-CIRCUIT THERMODYNAMIC INSTABILITY OF THE NPP’S MODERNIZED TURBINE SYSTEM

The original method of determining the criteria and conditions of inter-circuit thermodynamic instability in the modernized system "steam turbine - regeneration system with absorption heat pumps" is presented. This was developed through a thermodynamic analysis of the effect of independent fluctuating deviations from equilibrium in both the wet vapor flow at the absorption heat pump inlet and the measured pressure in the absorption heat pump/low pressure mixing heaters. Unlike known approaches to modeling thermodynamic processes, the thermodynamic model of the developed method takes into account the influence of fluctuating deviations from the equilibrium state of thermodynamic parameters, which determine the criteria and conditions of interloop thermodynamic instability. Based on the analysis of the received criteria and conditions, it was established that the main cause of inter-circuit thermodynamic instability in the modernized system "steam turbine unit — a regeneration system with absorption heat pumps" is determined by the incompleteness (inertia) of heat-mass exchange and hydrodynamic processes during fluctuating deviations from the equilibrium state of thermodynamic parameters. Prevention of the conditions for inter-loop thermodynamic instability in the modernized system "steam turbine unit — a regeneration system with absorption heat pumps" can be ensured by installing flow controllers in the wet steam supply circuits from the high-pressure cylinder of the turbine to the absorption heat pumps, and absorption heat pumps in mixing heaters low pressure to maintain a constant pressure in absorption heat pumps and low pressure mixing heaters. It is also necessary to consider that the modernization of the "steam turbine unit — a regeneration system with absorption heat pumps" system can affect the performance and conditions of inter-loop thermodynamic instability of "neighboring" systems. These issues determine the need for further analysis of the validity of the modernization of the "steam turbine unit — a regeneration system with absorption heat pumps" systems.

Optimization of Operating Modes of CHPPs as a Way to Reduce Greenhouse Gas Emissions

The aim of the work is to analyze and evaluate the operating efficiency of CHPPs to develop an optimal operating strategy based on minimizing fuel consumption and greenhouse gas emissions. To achieve this goal, the following tasks were solved: a quantitative assessment of the most effective methods of operating units in typical operating modes was given; dependences of changes in the main energy and environmental parameters based on mathematical models of turbine units using real energy characteristics of turbine stages and compartments were constructed; long-term optimization method to exploitation operation of CHPРs to the point of view of reducing greenhouse gas emissions was shown on specific examples. The most significant results are the following: a comprehensive method-ology for applying mathematical models for solving the most typical problems for CHPP was used, both from the point of view of saving primary fuel and reducing carbon emissions; the dependences of the influence of operating parameters on the carbon footprint were calculated; it has been established that the specific consumption of equivalent fuel and the carbon footprint are reduced when the loads are redistributed between turbine units during the heating period; the advantages of two-stage heating of delivery water over single-stage heating and sequential loading of turbines of the same type over parallel loading have been determined. The significance of the results obtained lies in their applicability in solving problems of optimizing the operating modes of CHPPs, taking into account the determination of the values of reducing greenhouse gas emissions.

Fixed-Time Control of Asymmetric Output-Constrained Nonlinear Systems and Its Application to Boiler–Turbine Unit

Fixed-Time Control of Asymmetric Output-Constrained Nonlinear Systems and Its Application to Boiler–Turbine Unit

Analysis of the Exothermic Reaction of Flame Ignition in the Combustion Chamber of a Gas Turbine Unit

This article analyses the exothermic reaction of flame ignition in the combustion chamber of a gas turbine unit, which is characteristic of combustion chambers operating on traditional hydrocarbon fuels. The combustion of gases as an explosive process in confined and semi-enclosed areas remains a poorly understood section of thermal physics. Without a detailed review of the physical and chemical processes taking place in the combustion chamber, it cannot be said whether the gas turbine unit will run sustainably. It is also important to know what combustion modes are in principle possible after a loss of stability in the combustion chamber in order to take action against this in advance. To describe flame ignition and quenching in the flow of the fuel–air mixture through a combustion chamber, a system of differential conservation equations of energy and reactive species supplemented with the equation of state is used. Nonstationary combustion processes in gas-turbine engines were studied, and flame ignition and blow-off were determined by the heat balance and by the continuity of chemical processes. Calculation methodologies for various operating modes of the combustion chamber of a gas turbine unit are developed and realized. The results of the calculations that were carried out are presented with graphical interpretation and with their analysis provided in sufficient detail. Based on this analysis, recommendations are then provided. From the graphs, it can be observed that the combustion chamber of a gas turbine unit reaches its maximum limit of stable operation at the optimum value of the reduced flow velocity in the openings of the air supply to the combustion and the mixing zones of the flame tube (λOC)opt = 0.22 when the fuel–air mixture is at maximum depletion, ensuring that combustion does not stop and flame failure does not occur. The topic of this article relates to the intensification of hydrocarbon fuel combustion and the technological improvement of combustion chambers in gas turbine units. This topic is of exceptional importance and relevance, emphasizing its significance. The purpose of this work is to develop and implement a methodology for calculating various modes of operation of the combustion chamber of a gas turbine unit.

Institute Teploelektroproyekt - 105 years in the service of the country's energy industry

The article is devoted to the 105th anniversary of Institute Teploelektroproyekt. Thermal power plants built according to the Institute's designs over the past twenty years, with installed combined-cycle and steam-power units running on gas and coal, are presented. The article describes the current environment of the institute's activities, the limitations of centralized financing of projects, the withdrawal from the market of power equipment of a number of foreign manufacturers of gas turbines due to sanctions, the adjustment of business plans of traditional customers of energy projects. The Institute actively accepts challenges, works with Russian manufacturers of gas turbine units, capitalizes on the accumulated experience of designing combined-cycle power plants (CCPP). An experience of construction and operation of the first stage of Sakhalinskaya SDPP-2 operating on coal, with a seismicity of the site at 9 points on the MSK scale on the coast of the Tatar Strait, is presented. During the time of operation of the station, the Sakhalin coal was found to be extremely viscous, which is associated with the presence of bentonite in its mineral part. The measures taken to partially reconstruct the fuel supply path led to a significant improvement in the operation of the path. The Institute-designed Svobodnenskaya thermal power plant (TPP) was put into operation, generating electricity and steam to provide consumers of the Amur Gas Processing Plant. Gas fuel is supplied from the main gas pipeline Power of Siberia-1. This implemented project is one of the examples of choosing a gas-fired steam turbine unit in favor of CCGT. The project Boiler House as Part of Ethane-Containing Gas-Processing Combine in the settlement of Ust-Luga on the Baltic Sea coast is unique as an example of the full integration of thermal power plant into a large industrial enterprise in order to solve the problem of minimizing the possible consequences of a major accident at the combine. The design of combined-cycle power plants of Novocherkasskaya SDPP and Artemovskaya CCPP-2 on the basis of domestically produced GTUs with a unit power of 110 and 160 MW, construction projects of new power units of Norilskaya CCPP-3 and Yakutskaya SDPP-2 for permafrost conditions are close to completion. The projects for the successive modernization of the Kirishskaya SDPP and Surgutskaya SDPP-1 power units with the replacement of steam turbine units are at the stages of designing and implementation. Institute Teploelektroproyekt is, as before, holding one of the leading positions among the design organizations of the industry, making a significant contribution to the development of the country’s energy industry.

Векторная постановка задачи совместного сведения материального и энергетического балансов при расчете фактических показателей тепловой экономичности газотурбинных установок

A scalar formulation of the problem of regularization of material flows in respect to gas turbine units is known. It allows you to consider the maximum permissible overall imbalance of mass and energy, as well as the maximum deviation of parameter values adjusted according to the results of balancing of their initial values. At the same time, there is no possibility to consider the individual standardized metrological characteristics of the measuring instruments used to obtain the initial values of the controlled parameters. The problem of simultaneous equations of the material and energy balances of a gas turbine unit is formulated in a vector value within the framework of Tikhonov’s regularization concept when solving ill-posed problems. To solve the problem, the authors have used the analytical method, the method of iteration of analytical solutions, as well as the method of statistical programming. Analytical and numerical solutions of the stated problem are obtained. They, among other things, consider restrictions on the range of permissible parameter values which are determined by the standardized metrological characteristics of measuring instruments. The impact of the applied method of balancing procedure on the results of calculation of the thermal efficiency indicators of gas turbine plants is shown. To apply thermal efficiency indicators of gas turbine units in the systems of automated monitoring, it is recommended to use a vector formulation of the problem of simultaneous equations when solving it by the method of iterations of analytical solutions or by the method of statistical programming. The developed methodology makes it possible to determine reasonable actual values of the indicators of equipment thermal efficiency under condition of the coincidence of the permissible error of the gross efficiency values of a gas turbine plant, calculated according to direct heat and indirect heat balances.

АЭС малой мощности с аккумулятором теплоты фазового перехода

Nuclear power plants (NPP) are characterized by low maneuverability. This fact exacerbates the problem of the balance of generated and consumed power when nuclear power plants are used as an energy source. This problem is especially relevant for isolated power systems. One of the ways to increase the maneuverability of nuclear power plants is to use heat accumulators directly in the NPP circuit. The study is carried out for two most attractive options of including a heat accumulator in the NPP circuit: 1) parallel to a high-pressure heater to heat feed water; 2) to generate additional steam for a low-pressure cylinder. The efficiency of each of the options is determined based on the calculation of thermal schemes of nuclear power plants with a heat accumulator. The authors have calculated the power of the turbine unit and electricity generation when a heat accumulator is included in the nuclear power plant circuit. The analysis of the data obtained shows that when using a heat accumulator in the NPP circuit in parallel with high pressure heater to heat feed water, the power of the turbine unit is increased by 7,2 % in the accumulator discharge mode, and additional electricity generation due to accumulated heat is 0,63 MJ for each kilogram of waste steam. When using a heat accumulator to generate additional steam for a low-pressure cylinder, the power of the turbine unit is increased by 6,6 % in the accumulator discharge mode, and the additional power generation due to the accumulated heat is 0,40 MJ per kilogram of waste steam. Application of heat accumulators in the NPP circuits will allow using the accumulated heat to generate additional electricity during high demand hours. Thus, the use of heat accumulators in NPP circuits is a way to increase the maneuverability of nuclear power plants, to reduce the negative impact of maneuverable modes on NPP equipment, and to reduce the number of liquid radioactive waste. The most effective and simple way to use the heat accumulator in the NPP circuit is to install it in parallel to the high-pressure heaters. In future, it is planned to determine the design of the heat accumulator, to model heat exchange processes in the heat accumulator

Comparative Study on Numerical Calculation of Modal Characteristics of Pump-Turbine Shaft System

Because a pump-turbine mainly undertakes the role of energy conversion and pumped storage in the field of hydropower engineering, the complex transition process and frequent conversion between different working conditions lead to the increase in the stress and strain of core components such as the unit shaft system, and even cause resonance phenomena. Based on ANSYS finite element numerical calculation software, this paper adopts the acoustic fluid–structure coupling method to study the influence of the shaft of the pump-turbine on the dynamic characteristics of the runner. At the same time, the paper analyses the influence of different contact modes between the runner and the shaft on the modal characteristics of the shaft system. The numerical simulation results have shown that the runner is affected by the added mass of the water. The natural frequency reduction rate of each order of wet modal is ranged from 19% to 64%. The main shaft has a greater influence on the simplification of the shaft system calculation method. The type of contact surface between the main shaft and the runner has a smaller influence on the modal characteristics and the natural frequency of the shaft system. The research in this paper contributes an evaluation of the dynamic characteristics of the runner of a hydraulic turbine unit, which is of great significance for the optimization of the analysis algorithm of the runner structure for large pumped storage units.

Analysis of PV/Wind systems by integer linear programming

This paper presents a mathematical formulation for integrating renewable energy sources in order to build up economical hybrid energetic systems in the case where each type of energy are only available as specific units. For instance, we may need to combine photovoltaic panels and wind turbines with specific capacities to meet an energetic demand in a specific site with a lowest cost. Therefore, determining the optimal energy to be installed leads of determining the number of units from each source. This problem is formulated as an integer linear program where the objective function to be minimized is the initial capital investment and where the decision variables are the numbers of units which should be pure integer numbers. The proposed method is generic since it is directly adaptive to various sites, demands, and different type of renewable energy sources. To illustrate our approach, we provide some examples and scenarios combining PV and wind turbines units.

Open Source High Fidelity Modeling of a Type-5 Wind Turbine Drivetrain

The increasing integration of renewable energy resources in evolving bulk power system (BPS) is impacting the system inertia. Type-5 wind turbine generation has the potential to behave like a traditional synchronous generator and can help mitigate the impact on system inertia. A hydraulic torque converter (TC) and gearbox with torque limiting feature are integral parts of a Type-5 wind turbine unit. A high fidelity model of Type-5 wind turbine drivetrain is not openly and widely available for grid integration and transient stability studies. This hinders appropriate assessment of Type-5 wind power plant’s contribution to bulk grid resilience. This work develops and validates a TC model based on those generally used in automobile’s transmission system. Moreover, the concept of torsional coupling is leveraged to integrate the TC and gearbox system dynamics. The entire integrated model will be open sourced and publicly available for grid integration studies.

A Cogeneration-Coupled energy storage system utilizing hydrogen and methane-fueled CAES and ORC with ambient temperature consideration enhanced by artificial neural Network, and Multi-Objective optimization

The increasing demand for energy in both commercial and residential sectors poses a pressing challenge, driving the ongoing quest for sustainable and virtually limitless energy resources. As nations become increasingly reliant on energy, the need to enhance energy system efficiency while curbing costs and reducing greenhouse gas emissions, particularly CO2 from fossil fuel combustion, becomes imperative. This paper presents a thermodynamics modeling, economic assessment, and optimization of a multigenerational module that utilizes compressed-air energy storing and polymer electrolyte membrane electrolysis with methane and hydrogen fuels, with a case study focused on Munich, Germany. Using EES, a system comprising of a modified organic Rankine cycle, gas turbine, PEM electrolyzer, and CAES unit was modeled. The combustion chamber was used to exploit methane and a combination of methane and hydrogen. The performance of the suggested module under these two scenarios was evaluated using multi-objective optimization to select the optimal scenario based on TOPSIS. In this study, we conducted 700 runs and obtained data on seven inputs. To derive a mathematical function from this data, we employed an Artificial Neural Network (ANN). This function was subsequently integrated into a multi-objective optimization system, allowing us to optimize the desired objectives. It was determined that Scenario 1 was the best choice for lowering the cost rate, reducing CO2 emissions, and optimizing energy round-trip effectiveness (ERTE). The highest exergy destruction rates were observed in the gas turbine, combustion chamber, and recuperator of the suggested system. The cost rates for ORC, CAES, and PEM electrolyzer were the highest according to the economic evaluation of the proposed module. Moreover, the gas turbine had the highest price. The study assessed the power demand of a building and evaluated the efficiency of the proposed power supply system. Additionally, an investigation was conducted in Munich, Germany, to examine how the system's performance is influenced by daily changes the annual variation in the environment temperature. The results revealed that the exergy destruction rates for the charging and discharging units were identified as 1706.38 kWh and 3019.31 kWh, respectively. additionally, based on the economic analysis, the total cost rate for the proposed energy production system was projected to be 68.073 USD per hour. The subsystems were ranked in the following order of costs: CAES > ORC > PEM electrolyzer. Additionally, within the specified system equipment, the gas turbine equipment exhibited the highest cost rate.

A novel district heating system based on absorption heat exchange and water-heat combined supply

Considering the challenges posed by long transportation distances and poor heating economy in large-scale heating systems based on conventional steam extraction cogeneration in nuclear power plants, a novel district heating system is proposed. This novel system is based on absorption heat exchange and water-heat combined supply. It offers significant improvements in heating and transportation capacity, while reducing the required investment in pipelines and transportation power consumption. In this study, an example of an AP1000 nuclear power turbine unit was used to construct a novel system. Additionally, a comprehensive energy efficiency evaluation model was established for this system. A comparison with the conventional district heating system based on cogeneration revealed several notable advantages of the novel system: (1) the comprehensive equivalent electricity decreased from 45.3 kWh/GJ to 31.2 kWh/GJ, representing a 31.1% reduction; (2) the unit heating cost decreased from 51.1 CNY/GJ to 42.0 CNY/GJ, resulting in potential savings of 10,726.17 × 104 CNY during a heating season; and (3) the emissions of CO2, SO2, and NOx were reduced by approximately 117.78 × 104 tons, 3.55 × 104 tons, and 1.77 × 104 tons, respectively.

Analysis of the cause of power system inertia generation and decline

Variable renewable energy sources (RES) are becoming more and more common, and traditional power generation plants are rapidly being replaced by them. As RES are used more frequently, power electronics are also utilized more frequently, both to connect RES and as drives for electric motors. As a result, the inertia level of the power system is continuously decreasing, and the frequency stability of the power system is facing severe challenges. Traditional power-generating methods such as thermal, hydroelectric, nuclear, and natural gas use generators to produce electric energy. By utilizing the rotational inertia of the steam turbine unit, the frequency fluctuation trend that occurs in the power grid can be delayed. However, photovoltaic power generation lacks rotating machinery and has no rotational inertia, whereas wind turbines operate at a modest speed and have negligible rotational inertia. The response capability is reduced significantly when the power grid's frequency changes. Any electric power system tends to rely on rotational inertia. The relevant factors impacting the inertia level of the power system are introduced based on the concept of inertia of the power system. The power system experiences inertia from the synchronous grid-connected generation side, the load side, and the grid-connected generation side of the converter. These three sources make up the majority of the inertia in the system. From the aspects of the power generating side, grid side, and load side, approaches and strategies to increase the frequency stability of power systems are introduced.