1. The significance, objects and measures of load control (DSM) (1) The DSM brochure of China State Power Corporation points out that although China's installed power generation capacity has exceeded 300GW, with the rapid development of the economy, China's power supply gap has reached 140GW, the grid operation efficiency is low, and the power supply in 15 provinces (cities) is tight. Due to the different structures of electricity-consuming industries, regions, seasonal changes and economic development levels, the imbalance of electricity load in time has produced peak and valley loads. The larger the peak-valley difference, the less economical the power grid operation is. Taking Shanghai as an example, in the summer of 2006, the peak load peak-valley difference was 40%, a huge 6GW! In order to meet the peak electricity demand, the power supply must be guaranteed to a sufficient extent. Otherwise, due to the supply being less than the demand, power rationing will inevitably occur. However, once the peak electricity demand period is over, the supply will exceed the demand, causing the power generation equipment to run or shut down. Therefore, the large peak-valley difference in the operation of the power grid wastes power investment and increases power generation and supply costs. Large power-consuming enterprises have to pay a large amount of peak (demand) electricity fees every year. On the other hand, the frequent start-up and shutdown of generator sets or compressor operation causes resource waste and threatens the safe operation of the power grid. (2) Since the peak-valley difference is the main factor causing low power supply efficiency and power shortage, the main goal is to manage the peak-valley difference. For a city, the serious uneven load of its major power-consuming enterprises is the key to this problem. Among these major power-consuming enterprises, steel mills are also the main targets. In addition, large foundries, glass factories, alloy plants, smelters, electrolytic aluminum, petrochemicals, as well as shopping malls, buildings, and hotels with large peak-valley differences are all targets for management. According to preliminary estimates, the peak avoidance capacity of major terminal power equipment in China is more than 30GW. According to successful foreign experience, the system peak load capacity can be avoided by more than 10GW, which has huge potential. At the same time, it is a low-investment, short-cycle, and quick-effect solution that meets the needs of load growth! (3) Although load balancing has multiple measures such as management, economy, guidance and technology, its technical means is currently the least used, most effective, most reliable and most conscious method! It mainly realizes the peak-shaving and valley-filling load balancing of large electricity-consuming enterprises. Since 2000, Frank Gemp Energy Control (Wuxi) Co., Ltd. of Germany, together with the Wuxi Energy Conservation Monitoring Station, has cooperated with some large electricity-consuming enterprises in China and achieved good results. Among them, the Jiangsu Xigang Load Control (DSM) project won the Jiangsu Province DSM Project Award. 2. Design principles and means of implementing load control (DSM) for large electricity-consuming enterprises (1) The generation of high power peaks is often due to the simultaneous operation of many electrical devices. Load control avoids the power usage in each measurement cycle from exceeding the pre-given rated value. Accordingly, the load can be balanced and adjusted to reduce the maximum load power and reduce the basic electricity cost. The core part of the load control system is a dedicated, intelligent program computer. It can predict when a load peak danger will occur and automatically disconnect suitable electrical devices or switch them to a lower power level. The input and output instrument is a dedicated computer. When calculating based on the tested power, it is possible to reduce the maximum load power (and basic electricity charge) by about 15% based on experience. It can even be reduced by more than 20%. (2) The purpose of load control is to avoid the randomness of forming excessively high power peaks. Based on this purpose, the load is made more balanced and power consumption is reduced. For this purpose, it is necessary to measure the changes in power and carry out load control. Since the decisive power is the average value formed in a 0.25 h period, there is no need to limit the instantaneous power. (3) A truly meaningful load control is to reduce the maximum load power and save basic electricity charges. In foreign countries, all users pay basic electricity charges based on the power consumption reported to the power supply bureau. Therefore, every enterprise attaches importance to continuously reducing the maximum demand power so that their grid load is relatively balanced. However, in China today, the electricity billing method is far from being in line with international standards. It can only be well implemented among users who report the power consumption to the power supply bureau and are billed based on the maximum demand power. Although many users who are billed based on basic capacity can also reduce their peak power and contribute to alleviating power shortages, they obviously do not have a high level of enthusiasm because they have lost the motivation to save basic electricity charges. (4) Load control is the use of appropriate measures to prevent electricity consumption in each cycle from exceeding the pre-given rated value. It can generally be achieved through the following means: 1) Reducing the power of electrical equipment before it is predicted that it may exceed the limit. 2) Disconnecting electrical equipment before it is predicted that it may exceed the limit. 3) Not connecting electrical equipment when it is predicted that it may exceed the limit (delayed start). 4) Using its own generator when it is predicted that it may exceed the limit, thereby limiting the power of the public power supply. Usually, the electrical equipment is switched to a lower power or temporarily disconnected in order to reduce the electricity consumption. Particularly suitable electrical equipment is: electrical equipment that has been running for a long time but can be switched to a lower power or can be temporarily disconnected and restarted, without affecting the normal operation of the enterprise (e.g., electric furnaces, blowers, gas presses and mills). Based on experience, every large enterprise has electrical equipment suitable for load control. Using a generator to reduce the peak power primarily refers to an emergency power supply device. It usually must be connected in parallel with the circuit, but it can also be switched to a lower power or temporarily disconnected when a generator is available. [ALIGN=CENTER] Figure 1 The actual power demand after management can be greatly reduced [/ALIGN] (5) In order to achieve the accuracy of the load control system, the optimization control computer is usually pulse control. It requires total pulses and test cycle pulses. In Germany, the total number of pulses is usually provided by the power supply from its meter, which avoids the error caused by reinstalling the pulse signal source and affecting the control accuracy. (6) The operation of reducing power and disconnecting electrical equipment is carried out by relays with no potential. Due to the application of traditional electronic technology, this control is almost impossible to be disturbed. In order to meet the high insurance requirements of enterprises, the optimization computer is equipped with a self-monitor. When an error occurs, an interference report will be given. Even external errors (such as the total number of pulses of the power supply meter) can be identified and reported. (7) The load control system monitors the pre-given maximum power and ensures that this maximum value is not exceeded by the appropriate disconnection and opening of electrical equipment. Therefore, the core issue is the design of the software! This is the trend analysis software that uses "trend calculation". It can ensure that the operation is below the limit power with the fewest number of adjustments, so as not to affect the production operation of the enterprise. Figure 2 and Figure 3 show the principle of trend statistics change when calculating each adjustment process. The adjustment command is only issued when the time is right. [ALIGN=CENTER] Figure 2 Trend calculation principle diagram [/ALIGN] [ALIGN=CENTER] Figure 3 Note: The blue curve in the figure is the actual operating power, the red straight line is the limit power. The green line is the simulated actual operating power. If the green line is below the red line, it means that the operation has not exceeded the limit power, and vice versa. [/ALIGN] (8) The load control system can directly input the adjustment command through the monitoring PC, or it can input the adjustment command through the simulated dialing method to realize remote or remote centralized control, which is simple and economical. 3. Load Control (DSM) Project of Xigang and Zhungang Group Jiangsu Xigang Group has a maximum load of 74,422 kW and an annual average load of 54,194 kW. Paying basic electricity fees on a maximum demand basis, its annual electricity costs are nearly 200 million yuan, accounting for 12.8% of the company's total costs, making it a "power hog" in the city. However, its average daily load rate is only 43%, indicating very low power efficiency. Jiangsu Huaigang Steel Group's power load is around 100,000 kW, with the 4601 steelmaking line at around 67,000-68,000 kW and the 4939 power line at around 35,000 kW. The potential for load control is enormous. 3.1 Project Overview 3.1.1 Xigang 1) The plant has two power supply lines, including the 110 kV Yanggang line with a capacity of 71.5 MVA, mainly for steelmaking load and the primary source of peak power generation; therefore, it was selected as the controlled line for this project. 2) Yanggang line has two 30t electric arc furnaces (furnaces No. 6 and No. 7) with a total power of 50,000 kVA and three refining furnaces with a total power of 18,500 kVA. Based on the production process, two electric arc furnaces are selected as the main controlled equipment. 3) The remaining load of Yanggang line, such as the refining furnaces, is the next step to refine the control object. (1) System design 1) The core software of German Frank Gemp "Trend Analysis" is adopted. The important basis of the software design is a large amount of historical data of state power load provided by the factory. The software can predict whether a peak will occur in the next time interval. If a peak occurs, whether the peak and the average value of the current power will exceed the set limit power. If they exceed, an automatic control signal will be issued. The software measurement cycle is every 15 minutes as a time interval, that is, 96 time periods per day. 2) Controlled equipment regulation power design Based on the process of resistance control, the rated power of furnaces No. 6 and No. 7 is selected for regulation. It is designed as a 4-level graded power, with each level being about 800 kW. Based on the parameters of the customer's electric furnace control board, the electric furnace control voltage (current) is changed by using a relay-connected resistor method, which causes the electrodes to automatically rise and fall to regulate the power. See Figure 4. [ALIGN=CENTER] Figure 4 [/ALIGN] 3) Signal Source Acquisition: Since the signal source must be a pulse signal, high-precision pulse-type electricity meters are installed on the low-voltage side of each measuring cabinet in the factory as the signal source. The meter pulse quantity is 1000 IMP/H, with an accuracy of 0.2 class. 4) Main Unit Location and Connection Control System Design: The main unit is located in the factory's 110 kV main substation. The connection system adopts an advanced bus structure design, with wiring led from the control boards of electric arc furnaces No. 6 and No. 7 to the factory's central substation, connecting to the main control unit. The control system uses a low-voltage relay system to receive the main unit's output signal and start the electric arc furnace electrode automatic rising and falling control board, regulating its various control levels. 5) The setting of the power limit (saving ratio) mainly considers the historical average peak power of Plant T and is generally set at 5% to 30% under the premise that production is not affected. The average demand of the plant before implementation is about 50,000 kW. The project is set at about 10%, that is, a reduction of about 5,000 kW. (2) System diagram (as shown in Figure 5) 1) The remote monitoring system in the figure is located at the headquarters. It can provide monitoring services to users 24 hours a day through a simple dial-up Internet access method. 2) The extended equipment in the figure can be continuously refined by the plant, such as refining furnace, power load, etc., and the maximum efficiency can be explored through refinement. 3) Operating principle 1) When the system software predicts that the peak power of the limit will occur through trend calculation, the system sends an automatic control signal. The signal first starts the first level of the adjusted power of the first controlled electric arc furnace. If the first level of adjusted power can still offset the peak power of the limit, the system will start the first level of the adjusted power of the second controlled electric arc furnace, and so on. Thus, the maximum demand power can be controlled below the limit target without affecting production. The start-up sequence for each controlled electric furnace can be represented as: Furnace 1/1 level—Furnace 2/1 level—Furnace 1/2 level—Furnace 2/2 level—Furnace 1/1 level [ALIGN=CENTER] Figure 5 [/ALIGN] 2) The system control is fully automatic; furnace workers do not need to consider the control status, and the original production procedure and sequence are not affected by any changes. 3) The power limit (saving ratio) can be adjusted according to the different monthly production conditions of the factory to achieve optimal efficiency. 3.1.2 Huai Steel The difference between Huai Steel and Xi Steel is that the electric arc furnace is controlled by PLC. Based on the success of the Xi Steel project, a major improvement has been made. (1) The electric arc is controlled by PLC. It is designed to be directly selected in its PLC range and directly controlled by the switch signal of the energy control device (see schematic diagram 1, the range is the million-fold ratio of the rated power. This percentage is 90%, 85%, 75%... Furnace lifting procedure: adopts the cyclic push method, that is, all controlled equipment share the way to digest the peak rate, without affecting normal production (the best is that normal production does not feel it), as shown in Figure 6 and Figure 7. [ALIGN=CENTER] Figure 6 Power change of Huai Steel electric arc furnace under control Figure 7 Power change indicator light of Huai Steel electric arc furnace under control [/ALIGN] (2) Features 1) Improvement of signal source: from the past detection of electricity signal, to direct detection of voltage and current signal. ① Avoid calculation error and improve accuracy. ② Signals can be obtained directly from the user's metering cabinet, changing the previous situation where signals could only be obtained from the power supply department's meters, which required consent and hindered the implementation of some projects. 2) All major loads of Huaigang (capacity up to 247 units) are monitored in the same system: power line 4939, generator No. 1 on line 1313, generator No. 2 on line 1303, and controlled steelmaking line 4601. 3) The system has all real-time electricity parameters and can replace manual meter reading. ① The system has electricity cost management functions. ② It can automatically generate daily, monthly, and annual electricity charges. 4) It can further realize the electricity cost accounting of different production units within the system. 5) It can further realize the monitoring of internal power factor and harmonics, and automatically switch to reactive power compensation and filtering devices, thereby reducing peak electricity consumption while improving power efficiency and controlling grid pollution. 6) This project is the first successful example of a modern steelmaking furnace controlled by PLC. Since most steel plants currently use modern steelmaking furnaces controlled by PLC, it has great guiding significance for promotion. 3.2 Implementation Results 3.2.1 Wuxi Steel (1) Before implementation, the maximum load was 50,430 kW, and after implementation, the maximum load was 45,408 kW, reducing the maximum load by 5,022 kW, saving 1.627 million yuan per year (the maximum load charge in Jiangsu is 27 yuan/kW). (2) The load curves of the factory before and after implementation are shown in Figure 8 and Figure 9. [ALIGN=CENTER] Figure 8 Figure 9 [/ALIGN] (3) The Wuxi Energy Saving Monitoring Station conducted a comprehensive test on the project in April 2003. The test comparison data is shown in the appendix. Before the maximum demand control system was put into operation: the average demand was 37,594 kW, the average steel output was 24,524 t, and the average unit value of maximum demand/output was 1.57. After operation: when the average steel output increased to 36,083 t (an increase of 16%), the average unit value of maximum demand and output decreased to 1.2. The power consumption efficiency was significantly improved by 24%. [ALIGN=CENTER] Appendix [/ALIGN] This project received a 1.2 million yuan reward for the achievement of the Jiangsu Province Electricity Demand-Side DSM Project in 2003. Conclusion: ① Although steel production increased by 16% after use, the unit demand decreased by 24%. ② The normal maximum load before use was 50,430 KW, and the maximum demand after use was 45,408 KW. The savings exceeded 10%, and the annual electricity cost savings were 1.672 million yuan. ③ In accordance with the spirit of Jiangsu Provincial Economic and Trade Commission document (2002) 1963, the plant received a special government reward of 1.2 million yuan. 3.2.2 Huai Steel (1) This project was implemented on the 4601 steelmaking line of Huai Steel. (2) After implementation, the first step was to control the 4601 line at around 60,000 to 62,000 kW. (3) This project saved about 5,000 to 8,000 kW of power load. Specifically: 1) It contributes approximately 5,000–8,000 kW of power load to society, contributing to alleviating power shortages. 2) It reduces annual electricity demand costs for enterprises by 1.62–2.59 million RMB, lowering enterprise costs and enhancing competitiveness. 3) It balances the enterprise's power load, extends the service life of primary power supply equipment, and achieves safer electricity use. 4) It improves the level of enterprise power dispatching and management, as shown in Figure 10. Nanjing Iron and Steel's maximum load is 90,180 kW, and the minimum is 6,900 kW, with a peak-to-peak difference of 33%. The set load-level ratio is 10% to 15%. [ALIGN=CENTER] [B]Figure 10 Nanjing Iron and Steel's maximum load is 90,180 kW, and the minimum is 6,900 kW, with a peak-to-peak difference of 33%. The set load-level ratio is 10% to 15%.[/B][/ALIGN] 3.3 Other functions of the load control system 1) Peak, valley, and flat management function The factory can set the allowable power load at peak, valley, and flat times according to the electricity price and production schedule at different times. The system can automatically control and manage this, thereby further saving electricity costs. 2) Power parameter management function The system can display and store all power parameters, such as P, I, S, Q, cosφ, etc., which can completely change the history of manual meter reading by substation staff. Its software interface is shown in Figures 11 and 12. These data can be statistically analyzed, thereby improving the enterprise's power management level. 3) Due to the balanced power load, the reliability of power grid equipment is improved. Thus, electricity can be used more safely. 4) It can also be extended to the comprehensive energy management of electricity, water, gas and coal, all of which can be managed in the same system. There are still huge topics to be explored in this regard, which can greatly improve the management level and comprehensive competitiveness of enterprises. 3.4 Project significance (1) This project can use large electricity users to balance the load, save costs, and improve management level and market competitiveness. (2) The load balancing of large urban users can also reduce the peak-valley difference of the overall urban load curve, improve the efficiency of urban electricity use, and at the same time improve the electricity sales efficiency of power generation enterprises. (3) In view of the concept of volunteer service, this project adopts the approach of "providing equipment for free and sharing the savings between the two parties" by the foreign party (Germany Frank Gemp Energy Control (Wuxi) Co., Ltd.), thus realizing the possibility of enterprises to carry out energy-saving technology transformation without increasing investment. (4) It can be used by power departments and government departments to centrally or regionally monitor large electricity users. Especially in the current situation of tight power supply and severe peak summer situation, the centralized management of large urban electricity users can alleviate the pressure of electricity use and improve the efficiency of electricity use, which has obvious social benefits. (5) It provides a good example for promoting energy management through technological means. (6) Both the power supply department and the power plant can obtain multiple benefits: 1) Improve the peak-valley difference of its power supply network, increase the power supply capacity, and alleviate the power supply pressure. For medium-sized cities, every 5% reduction can increase the power supply capacity, and its economic benefits are huge. 2) By regulating the peak value of the capacity measurement unit, the power supply department can further increase the power supply capacity and electricity revenue. 3) In the future, with the independent accounting of the power supply company, without affecting the overall kW·h revenue, the investment efficiency can be improved by reducing the power purchase capacity from the power plant. 4) After the grid peak value is evenly distributed, the grid impact will be reduced, the accident risk will be reduced, and it will be safer. This is of great significance and is important abroad. 5) The power plant can develop the efficiency of investment and reduce the capacity idle during the off-peak. 6) Realize the load control and electricity management, computer networking and automation, and improve the management level. (7) It provides a guarantee for promoting power reform, especially the pricing system reform, and the possibility of carrying out demand-side management in a better way. (8) Demand-side management by enterprises can be extended to demand-side management of the entire city, and from electricity demand-side management to integrated energy demand-side management. [ALIGN=CENTER] Figure 11 Integrated Energy Demand-Side Management Interface Figure 12 Integrated Energy Demand-Side Management for Water, Electricity, and Gas [/ALIGN] 4. Recommendations for Better Implementation of Load Control (DSM) for Large Electricity Consumers 1) Given that most enterprises lack understanding of the methods and benefits of load control (DSM), the widespread promotion of DSM technical measures and successful cases will help enterprises understand and accept the feasibility of this work, and encourage suitable enterprises to carry out this work first. 2) Given that a considerable number of enterprises have already installed load controllers, these load controllers can only play the role of "power rationing" every year and do not have year-round management functions. Therefore, enterprises that have already installed these older generation load controllers can be upgraded so that they can not only play a role when "power rationing" is needed, but also reasonably regulate the load for enterprises, reduce peak power, and save electricity costs for most of the time outside of that. This could change enterprises' perception that the old load controllers only cut off their power, and would be widely welcomed by enterprises, thus encouraging them to voluntarily and actively install load controllers and carry out load control work. 3) Reform the basic electricity charge method. If it can transition to the same maximum demand (peak value) basic electricity charge method as in foreign countries, or first adopt the MD declaration basic electricity charge method like that of Shanghai enterprises, it will greatly promote enterprises' enthusiasm for carrying out load control (DSM) work. 4) For a considerable number of enterprises currently charged according to the basic capacity basic electricity charge method, could a maximum allowable peak-to-valley difference assessment requirement be proposed to encourage them to carry out load control (DSM) work on their own? At least during the two peak electricity consumption seasons of summer and winter each year, they should be required to carry out load control (DSM) work to alleviate electricity pressure and delay and reduce the period of operation of power outage measures. Given that these enterprises currently do not benefit from basic electricity charge savings, could the government provide certain rewards based on the peak power reduction they achieve? 5) Local power supply departments need to change their mindset, especially regarding the idea of ​​reducing basic electricity charges for enterprises by lowering demand. From a broader perspective, and in accordance with the requirements of the China State Power Corporation's DSM brochure, they should support and promote the widespread implementation of enterprise load control (DSM) work. They should provide enterprises with convenience in terms of billing method selection, peak power signal source provision, and historical load data provision. 6) In the long term, reforms to billing methods and power supply technology assessment requirements, such as promoting basic electricity charge billing methods based on maximum demand (peak value) or MD (Maximum Demand) declaration, and simultaneously adding assessment requirements for peak-valley differences in enterprise electricity consumption, are the foundation for the long-term implementation of load control (DSM), continuous optimization of enterprise and urban/rural electricity consumption, gradual reduction of peak-valley differences, continuous improvement of power generation, supply, and consumption efficiency, and safer and more reliable grid operation. 7) Change the power sector's assessment system for enterprise power quality. From the current single reward and penalty assessment based on power factor, add reward and penalty assessments for peak-valley differences (and possibly harmonic indicators) to give users more initiative. 8) Change the power supply system. Even if the power supply department reduces the peak-valley difference, it cannot reduce the cost of purchasing electricity. Therefore, the power supply system should be reformed.