This article takes an actual engineering project as an example, and the following discussion will be based on a substation in a certain community. [b]I. Design and application of power monitoring system[/b] 1. Introduction to power monitoring system: Smart grid: The operating status of equipment in the existing power network is realized by the working instructions of the equipment itself, and is unrelated to the operating status of the power grid. This is a passive distribution network. When the operation of the equipment is not only realized by its own working instructions, but also by the distribution network after self-diagnosis, and then according to the power grid capacity and load importance, the equipment operation instructions are issued and the operation is controlled according to the order of load importance level, it is an active distribution network. To transform a passive distribution network into an active distribution network: ——The power load should be reasonably distributed; ——The load should be divided into several levels according to its importance (relative dynamic concept); ——The power grid should have "self-diagnosis" capability; ——The load should have load control and regulation function. (1) Normal working state: First of all, the system should work reasonably and the load distribution should be reasonable: ——Sufficiently eliminate peak and fill valley; ——Fully utilize the overload capacity of the transformer; ——Sufficiently adopt various technical measures to save energy. Energy storage. (2) Power failure state (such as one of the two power supplies going out, a transformer malfunctioning, etc.): The intelligent system monitors, analyzes, judges, and ensures the primary load, effectively controlling the secondary and tertiary loads. 2. Features of the power monitoring system: The system software and hardware are all modular, and the hardware is all intelligent. The software and hardware design selects industrial-grade standards, and the reliability is very high. 1) The entire system's ICU (Intelligent Control Terminal) and RTU (Remote Intelligent Communication Controller) are all composed of 16-bit microcomputers. This distributed monitoring system is fast, has good real-time performance, and reliable communication with the same type of machine. 2) The ICU has its own CPU, short acquisition cycle, strong real-time performance, high system redundancy, and few communication frames, which can greatly reduce the communication error rate. 3) Each system works independently and does not interfere with each other, realizing the modularization of the control hardware system. The use of bus mode can save cable and engineering costs. 4) Each subsystem has been modularized, further improving the safety and reliability of the entire system. 5) The system can be hot-swapped, making maintenance and repair more convenient. 3. System Composition: 1) Equipment installed in the control center: The control panel includes a main control unit, monitor, printer, keyboard, backup power supply, anti-interference power supply, UPS, terminal blocks, alarm devices, etc. The control panel also includes power switches, remote control switches, remote control buttons, analog power supply, on/off indicator panels, etc. 2) The building's main control unit can be located in the building's duty room, while the main control room is located in the substation. Sensor signals are transmitted to the building's main control unit and the main control unit via a bus. Remote measurement, remote signaling, and remote control of power consumption are performed. 3) Field data acquisition and control equipment includes ICUs, current transmitters, voltage transmitters, and other sensors that send signals to the ICUs. The ICUs are connected to ZTK (smart communication card) via RTUs to achieve bidirectional data transmission. The ICUs control the power supply according to a predetermined program through contactors located in the power distribution system. Each system can accommodate 1024 ICUs, giving the system extremely high scalability. 4. System Scope: To ensure the consistency of power supply data acquisition throughout the entire community. For optimal control flexibility and load adjustability, a power monitoring system should be installed in each individual building. [b]II. Community Power Supply Load Description:[/b] 1. Building Overview: The community comprises high-end apartments, underground parking garages, and supporting facilities such as boiler rooms and transformers. The total above-ground and underground building area is approximately 140,000 square meters. Of this, the apartment area is approximately 110,000 square meters, and the underground parking garage area is approximately 30,000 square meters. 2. Load Calculation: A 10KV self-managed substation is provided, with power sourced from the power supply bureau's 110KV substation. The client requires a total power capacity of 8.5KW per household (approximately 35W/m2 to 45W/m2), with a centralized air conditioning system for each household, consuming approximately 3.0-5.0KW per household, and a lighting load of 3.5-5.5KW per household. Based on a transformer operating at 70% load (economical operation), the total substation load is 6636KVA. Preliminary calculations indicate that the transformer capacity for the residential area should be ≥6,400KVA. 3. The client requires: upgrading the apartment building's lighting load level and adopting a dual-power supply system with mutual switching. Under normal circumstances, except in the event of a fire, the apartment building's lighting power supply must be guaranteed. 4. Calculations show that, with a reliable power monitoring system as a guarantee, and fully utilizing the transformer's overload capacity, a capacity of 4 × 1,2500KVA can be installed. [b]III. Comparison of two reliable power supply methods in the community:[/b] This community is mainly composed of high-end apartments, so ensuring the reliability of power supply has become one of the hallmarks of a high-end community. However, due to the limitations of the conditions, this type of power supply and distribution system cannot guarantee all the loads, such as the requirements of the client, the external line method, etc., which determines that the principle of this power supply system is to ensure the lighting load of users. The lighting load is the electricity for the user's daily life, while the air conditioning load is the electricity for comfort. When the lighting load is cut off, it will cause psychological panic among users and cause certain losses to users. However, the short-term cut-off of the air conditioning load will not have a great impact on the user's comfort. If necessary, the user's air conditioning load can be adjusted to ensure the user's lighting load. 1. Technical implementation: 1) Feasibility of adopting a power monitoring system: (1) Functions of this system in a single building: a. Monitor the current analog quantity and switch quantity status of the lighting, air conditioning and power of the entire building, and record them to facilitate the statistical analysis of the load of the entire community. b. Switching between lighting and air conditioning distribution boxes on control floors: The lighting and air conditioning in the apartments are powered by 1,600A enclosed busbars, with each enclosed busbar responsible for half of the lighting and air conditioning in the building. When one enclosed busbar or incoming power supply fails or is under maintenance, to ensure the reliability of the residents' power supply, the lighting load of one enclosed busbar needs to be switched to another enclosed busbar. As can be seen from the load calculation table, the other enclosed busbar cannot handle the power supply for the entire building's lighting and air conditioning. In this case, the system can first disconnect the air conditioning load, then switch the lighting load to the normal enclosed busbar, and then, based on the values ​​calculated by the power monitoring system, systematically restore the air conditioning load. c. When there is insufficient power in a non-faulty state, a portion of the air conditioning load is disconnected to ensure the power safety of the entire building, while avoiding the impact of overload on the outgoing switches and even transformers of the upstream substation. When switching the air conditioning load, a cyclic switching method can be used to avoid users being unable to use the air conditioning for extended periods, thus ensuring the comfort of the residents. When the power supply system returns to normal in the above situations, the power monitoring system will then control the load to return to normal power supply mode, ensuring power supply reliability and improving power supply level, while also reducing the workload of the property management department. The switching on and off of air conditioning loads is achieved by contactors located in the floor lighting and floor air conditioning distribution boxes, which ensures a reduction in the risk of accidents, improved system adjustability, and operational flexibility. 2) Functions of this system in the substation: a. According to the technical parameters provided by the manufacturer, the transformer's output capacity can be increased by 40%-50% under forced air cooling. Therefore, with the power monitoring system's regulation as a reliable guarantee, the transformer's overload capacity can be fully utilized. When a transformer power supply fails or is under maintenance, the load of one transformer needs to be switched to another transformer to ensure the reliability of residents' electricity use. While fully utilizing the overload capacity of the transformers, the power monitoring system analyzes and judges the measured data. If inter-transformer switching may cause overload of the normal transformer and a larger accident area, some non-critical loads, such as non-fire-fighting fans and water pumps, will be disconnected. If this is still insufficient, the building's power monitoring system will disconnect some air conditioning loads as needed. Then, lighting loads will be switched to the normal transformer, and air conditioning loads will be re-energized according to the values ​​calculated by the power monitoring system. The transformer protection is only two-level, namely overcurrent and instantaneous overcurrent protection. Its function is to cut off the power supply when the load reaches these two setting values ​​of the circuit breaker, which can cause unpredictable power outages and a large accident area, causing great inconvenience to users. With this system, load trends can be calculated through monitoring elements, and effective control measures (such as the above steps) can be taken to avoid accidents before they occur. When the power supply system returns to normal, the power monitoring system will control the load to return to the normal power supply mode. b. In the early stage of community construction, due to the reliable control means as a guarantee, the transformer installed capacity can be reduced on a basis, saving a lot of initial investment. Correspondingly, the substation area is reduced and the equipment investment is reduced. 2) Report on the feasibility of transformer capacity expansion: (1) When a transformer fails, another transformer has to take over its load. If there is no reliable control means as a guarantee (for example, adding an undervoltage trip device to the non-important load outgoing switch), the load to be put into operation in the most unfavorable case is >2,000A, and the total load current of a single transformer is >3,500A. There is a possibility that the normal transformer may trip due to overload. If an undervoltage trip device is added to the air conditioning distribution box in the inner layer of each individual building, it can only cut off the air conditioning load in the faulty transformer. In the most unfavorable case, the total load current of a single transformer is >2,000A. If the air conditioning load in the normal transformer is cut off again, it will bring a lot of trouble to the building's power distribution system and increase the complexity of the system. If the overload capacity of the transformer is still used, without an automatic control system, someone needs to observe the load parameters in real time and then judge the measures to be taken. Firstly, it will cause a large workload for the on-duty personnel, and secondly, it may cause power supply accidents due to human factors. (2) For a single building: When a closed bus or incoming power supply fails or is under maintenance, in order to ensure the reliability of the residents' power supply, the lighting load of one closed bus needs to be switched to another closed bus. If it is designed to be based on one closed bus to bear the power supply of the whole building's lighting and half of the air conditioning, that is, the air conditioning load of the fault bus is cut off, while the air conditioning load of the normal bus is still retained. From the above data, it can be seen that the closed bus and outgoing switch in the building need to be enlarged. If it is not enlarged, it is necessary to add undervoltage trip or use relays and contactors to achieve it; if it is based on one closed bus to bear the whole building's lighting and the air conditioning is completely cut off, it can only be achieved by relays and contactors. An undervoltage release device is added to the air conditioning distribution box on the first floor. After the air conditioning load is cut off, the property management department must manually reset it. The interconnection between the lighting distribution box and the air conditioning distribution box on the first floor is achieved using relays and contactors, which is overly complex compared to a power monitoring system and will result in a high failure rate and heavy maintenance after operation, failing to protect reliable power supply for users under certain conditions. 2. Economic Comparison: (Excluding the cost of the already designed power distribution system, only the cost of transformer installation and related equipment modifications). The power supply bureau's cable power supply engineering fee standards stipulate: —This project uses cable power supply and is charged according to cable standards. —For users within the Fourth Ring Road of Beijing, the power supply and distribution engineering fee standard is 600 yuan/kVA. —For users with dual power supply and multiple transformers, if technical measures are in place to ensure they are not used simultaneously, the fee is double the maximum capacity of one side; otherwise, the fee is double the total capacity of the transformers connected. 1) Substation Project Fee Standard for this Community: For a 10kA incoming line with dual power supply and high-voltage interconnection, a fee of 1,200 RMB/kVA should be paid. 2) Power Monitoring System Fee: If a power monitoring system is adopted, it should be applied for at 5,000KVA (i.e., existing application conditions, already approved by the power supply bureau). The total fee should be 6,000,000 RMB. This project design recommends installing 4 sets of power monitoring systems, namely, in Building A, Building B, Building C, and the substation. The total investment in the power monitoring system should be <8,000,000 RMB. (The cost of this power monitoring system is estimated based on the price of domestic systems). 3) Transformer Capacity Expansion: If transformer capacity expansion is adopted, the minimum transformer capacity should be applied for at 6,400KVA (the maximum should be applied for at 8,000KVA). The total fee should be 76,800,000 RMB. For individual buildings, an additional 5%-10% should be added to the existing power distribution system investment. The substation will also require an additional investment of approximately 10%-15% on top of the existing capacity. The above data shows that, in terms of cost alone, the power monitoring system solution saves 880,000 yuan compared to the smallest transformer capacity expansion solution. The total savings for the substation and buildings in the entire project are approximately 1,500,000 yuan, making its cost-effectiveness self-evident. From the above, we can conclude that the investment in the power monitoring system in this community accounts for 3%-4% of the total electrical equipment investment and 30%-40% of the transformer capacity expansion investment. This is more economical and reliable than transformer capacity expansion, and reduces the possibility of transformers operating under low load. After implementation, it can also save operating costs, reduce the workload of substation management personnel, and improve the degree of automation in management. Since this project is an apartment building, the client's main objective is to increase the residential electricity load level and ensure power supply reliability. The energy-saving and energy storage features of the power monitoring system were not requested by the client, and considering that adding these functions would increase investment, the power monitoring system was not included in this project. If energy-saving and energy storage designs are adopted in the power monitoring system, the energy-saving benefits during the later operation will be quite considerable.