3205results about How to "Improve power supply reliability" patented technology

A smart electricity meter with a function of monitoring and protecting power failure comprises a metering chip, a leakage current sampling circuit, a phase current sampling circuit, a phase voltage sampling circuit, a CPU (central processing unit), a power module and a low voltage breaker. The leakage current sampling circuit is electrically connected with the metering chip which is mutually electrically connected with the CPU. The CPU is electrically connected with the low voltage breaker through a trip output port. The low voltage breaker is electrically connected with the CPU through a status acquisition interface. The invention further provides a power failure monitoring and controlling method of the smart electricity meter. The smart electricity meter has the advantages that the reliable power module for power failure protection and control is provided, various types of power failure warning and protection are provided, failure warning and failure protection for voltage, current, power and the like are achieved for power users, failure spots are prevented and isolated, economic loss and personal safety accidents due to failure of electric circuit equipment of the users are prevented and reduced, and reliability of low voltage grids is effectively improved.

The invention specifically discloses a power distribution network simulation research and analysis system and method based on network-wide data. The system comprises a three-layer structure: a data layer, a platform layer and an application layer. The data layer mainly collects basic and operation data of a distribution network; the platform layer mainly gathers and summarizes various data of the distribution network and provides corresponding services to the application layer; and the application layer mainly, under the support of the platform layer and based on network-wide equipment and operation data, carries out a series of correlated application researches related to the power distribution network on scientific modeling, load flow calculation, fault analysis, closed-loop calculation, network reconstruction and self-healing simulation modules of the power distribution network comprising a lot of distributed generation, so as to realize comprehensive digital simulation of the power distribution network, and to provide decision reference for the construction and operation of the power distribution network.

The invention relates to an assessment method of efficient operation of an intelligent power distribution network. The assessment method comprises the steps of: (1) determining boundary conditions; (2) determining service objects; (3) building an assessment index system which includes a power distribution network safety index, a power distribution network reliability index, a power distribution network economical efficiency index, a power distribution network high operation quality index and a power distribution network intelligence index; (4) determining assessment index numerical values of single items; (5) scoring for single items of assessment indexes; (6) performing comprehensive scoring of the assessment index system; and (7) judging whether efficient operation of the power distribution network is achieved according to a comprehensive score of the assessment index system in Step (6). The assessment method for efficient operation of the intelligent power distribution network in the invention has a relatively wide range of application, can comprehensively assess the operating state of the intelligent power distribution network, and an assessment result provides an importance basis for decision-making work of power grid dispatching, planning and operation management personnel.

The invention, which belongs to the grid-connected optimization operation field of the new energy, relates to a combined system energy optimization method with consideration of wind power consumption; and thus in order to solve a wind curtailment problem, the combined system energy optimization method uses a cogeneration system based on combined operation of a wind power-electric energy storage-heat accumulating type electric boiler and takes economic optimum as an objective to reduce the wind-curtailment power effectively by increasing the load space. To be specific, the method comprises the following steps: (1), establishing an overall system framework including a conventional thermal power generating unit, a cogeneration unit, a wind turbine generator, an electric energy storage and heat accumulating type electric boiler; (2), carrying out comprehensive modeling of a cogeneration system; (3), establishing an optimal economic objective function; (4), establishing a power and heating power balancing relationship and operational constraints of all units during the operation period of the cogeneration cooperation system; and (5), carrying out optimization for active power outputs of all units. Therefore, development and utilization of the wind power are promoted; and power supply reliability of the power system is improved. The method can be applied to large-scale-wind-power-included provincial companies of all stages and has the broad application prospects.

The invention discloses a microgrid energy management system which comprises an information collection and data preprocessing unit, a network analysis unit and an energy optimization unit, wherein the information collection and data preprocessing unit performs data mining preprocessing on information, collected by SCADA / PMU mixed measurement, by adopting a CIM model and combining historical section management, the network analysis unit is used for realizing mixed measurement-based microgrid state estimation on the basis of network topology analysis, performing risk analysis and assessment and sensitivity analysis to realize early warning and warning for failure threat, and adopting corresponding precautionary measures or performing emergency control, and the energy optimization unit is used for performing microgrid energy optimization scheduling by combining forecast information and system operation analysis according to the information of the microgrid state estimation. The invention also provides a method which adopts the microgrid energy management system to perform microgrid energy management. The functions of the microgrid energy management system are further perfected, and the system safety, the power supply reliability and the system control accuracy and effectiveness of a microgrid are improved.

A plurality of separators are arranged to line up in an X-direction on a cooling plate to respectively correspond to a plurality of battery cells. The separators corresponding to the odd-numbered battery cells and the separators corresponding to the even-numbered battery cells are arranged in opposite directions in the X-direction. On a bottom surface portion of each of the separators, the corresponding battery cell is arranged. In this case, one side surface or the other side surface of each of the battery cells contacts a side surface portion of the corresponding separator, and a bottom surface of each of the battery cells contacts the bottom surface portion of the corresponding separator.

The invention discloses a power distribution network single-phase grounding fault judging and locating method which mainly achieves accurate and quick judging of a fault section when a single-phase grounding fault occurs in a power distribution network. The power distribution network single-phase grounding fault judging and locating method comprises the following steps that a section switch is arranged on a circuit of the power distribution network, power distribution automation feeder line terminals are arranged on the section switch and network communication is established among the power distribution automation feeder line terminals; the power distribution automation feeder line terminals judge the circuit single-phase grounding fault and the s that a single-phase grounding fault point is located at a section adjacent to the section switch where the power distribution automation feeder line terminals are located. Compared with the prior art, the single-phase grounding fault is judged and detected through the power distribution automation feeder line terminals, network communication is established among all the power distribution automation feeder line terminals, fault judgment information is interacted among the power distribution automation feeder line terminals, the specific position of the fault point is determined, therefore, the fault region can be determined quickly, the fault processing time can be shortened and the power supply reliability can be improved.

The invention discloses an alternating current and direct current hybrid micro-grid system and a control strategy of the micro-grid system. The micro-grid system comprises multiple generation units, load, a distribution line for connecting the generation units and the loads, and a monitoring protection unit; each generation unit comprises a large power grid, grid-connected AC / DC (alternating current / direct current) of the large power grid, an energy storage system, a DC / DC (direct current / direct current) converter of the energy storage system, a wind power generation system, an AC / DC converter of the wind power generation system, a photovoltaic power generation system, a DC / DC converter of the photovoltaic power generation system, and a diesel generator; said load includes AC non-significant load, AC significant load, AC / DC load, DC significant load and DC non-significant load; the distribution line comprises a DC distribution line and an AC distribution line; the operating status of each energy conversion device can be monitored in real time by the monitoring protection unit, two operating ways such as grid connection and isolation of the system can be realized by different control strategies, the distributive generation unit and the energy storage unit realize coordination and cooperation by controlling energy storage DC / DC, photovoltaic DC / DC, and wind power AC / DC, so that the power supply reliability is improved and the significant load can continuously operate.

The invention discloses an abnormal electricity utilization judgment method based on abnormal analysis of electric quantity, voltage and current. The abnormal analysis of the electric quantity comprises a fluctuation electric quantity analysis process and a zero electric quantity analysis process, wherein the abnormal analysis of voltage comprises voltage phase-failure abnormal analysis, voltage off-normal abnormal analysis and voltage unbalanced abnormal analysis; the abnormal analysis of current comprises a current loss abnormal analysis and current unbalanced abnormal analysis. By analyzing and comparing abnormal data of electric quantity, voltage and current of the users, real abnormal users or electricity stealing users can be determined. The abnormal electricity utilization judgment method based on the abnormal analysis of the electric quantity, the voltage and the current, disclosed by the invention, has the advantages that electricity information of power users can be timely grasped, the electricity stealing behavior is prevented and monitored, and the reliability of power supply is improved.

The invention provides a control method of a grid friendly type distributed power source based on hybrid energy storage. The method comprises the steps of optimally designing a topology structure of the distributed power source, controlling a direct current power supply system in a coordinating mode through a direct current (DC) / DC converter controlling a model normalization model, and self-adaptively controlling a grid of an alternating current (AC) side DC / AC converter. The distributed power source not only can be connected in a large grid to operate so as to reduce the influence of intermittent renewable energy power generation grid connection on the grid and provide support of voltage and frequency for the grid, but also can be connected into a micro-grid to operate as a network unit of the off-network type micro-grid to maintain stability of voltage and frequency of the off-network type micro-grid. When an outer grid breaks down, the distributed power source can realize switch between a grid mode and an island mode so as to improve power supply reliability of important loads in the system. The distributed power source improves technical performance and economic performance of the whole system through matching utilization of an energy type system and a power type energy storage system.

The invention provides a real-time data collecting and fault positioning system of a power distribution network and a working method thereof. The real-time data collecting and fault positioning system comprises transformer substation voltage collecting units, a plurality of line units, a real-time data server, a background monitoring computer and a handheld terminal, wherein each transformer substation is provided with one transformer substation voltage collecting unit; each transformer substation voltage collecting unit comprises one intelligent voltage detection terminal; each line unit comprises three fault positioning and data collecting sensors and one communication and calculation terminal; the intelligent voltage detection terminal, the communication and calculation terminal and the handheld terminal are in wireless communication with the real-time data server; the three fault positioning and data collecting sensors of the same line unit are in short-distance wireless communication with the communication and calculation terminal. The working method mainly comprises the step of carrying out real-time data collection and fault judgment. The information precision of power transmission line data which is collected in real time is high, short circuit and grounding faults are rapidly and accurately judged, the time of powering off and overhauling is shortened, the quantity of fault line patrolling workers is reduced and manpower and material resources are saved.

The invention relates to an optical storage alternating current and direct current hybrid micro-grid system and a control method of the system. The system and the method are characterized in that a hybrid micro-grid comprises an alternating current micro-grid subsystem, a direct current micro-grid subsystem and a power exchange control system; the alternating current micro-grid subsystem comprises an alternating current side photovoltaic power generation unit, an alternating current load and a grid-connected interface; the direct current micro-grid subsystem comprises a direct current side photovoltaic power generation unit, a storage battery energy storage unit and a high / low voltage direct current load; the power exchange control system comprises a two-way AC / DC power converter, a transformer, a micro-grid controller and a communication system, the storage battery energy storage unit is used for controlling direct current bus voltages, and P / Q control is adopted in the two-way AC / DC power converter. Under the stabilizing effect of direct current side energy storage, the direct current micro-grid subsystem conducts photovoltaic power generation and is connected to a large power grid through the alternating current micro-grid subsystem at constant power, and the photovoltaic utilization rate is increased. By means of the control method, the power supply reliability and economical efficiency of the hybrid micro-grid are effectively improved.

The invention discloses a grid-connected non-networking micro-grid system and a control protection method thereof. On the premise of basically not changing the structure of the original power distribution system, multiple types of distributed power sources, such as wind power generation system, photovoltaic power generation system, cell accumulation system and the like, are connected into a common power grid along with user loads through AC buses, and reasonable load layout and active energy management are utilized to implement grid-connected non-networking of the micro-grid system. By using the structural design and the active energy management of the micro-grid central control unit, the new energy power generation system can be completely self-sufficient, and does not reversely transmit power to the common power grid, thereby avoiding impacting the normal power supply of the common power grid; and meanwhile, by the aid of the common power grid, the user loads have higher power supply reliability and electric power quality.

The invention relates to a method and device for performing on-load scheduling on a single-phase load in the intelligent power grid field. A master controller is mounted at an input end of a three-phase wire, a secondary controller is mounted at each single-phase branch of the wire, and the master controller exchanges information with the secondary controllers through communication interfaces. When the wire power unbalanced degree is over limit, the master controller optimizes and formulates a control scheme to operate the secondary controllers to convert the single-phase load between the phases; in the conversion process, the load is free from instant power off, and the power grid is free from impact and interference; and therefore, the distribution circuit dynamically runs in a load balance state, the unbalanced consumption problem of the circuit is completely solved.

The invention discloses a control method for a quality control system of micro source internetworking electric energy. A primary side of the coupling voltage transformer on a serial active power filter side of a UPQC (unified power quality controller) is connected with a larger current-limiting inductor in parallel, and a direct-current large-capacitance side of the UPQC is connected with a photovoltaic generating power supply in parallel. Due to effects of cooperative control, the photovoltaic power supply is internetworked for power generation during normal operation, active power is provided for a power grid by the parallel active power filter of the UPQC, and the harmonic current from a load side and the voltage fluctuation and harmonic voltage from the power grid side are governed and compensated by the UPQC. In the case of short-circuiting failure on the load side, the main circuit of the UPQC stops operating, a secondary side of the coupling voltage transformer is subjected to high impedance, and the current can be limited by the parallel current-limiting large inductor. By adopting the method, the functions of failure current limitation, harmonic treatment, voltage support, photovoltaic power generation and the like can be realized during micro grid internetworking operation, and the optimized protection and operation of the quality of electric energy in micro grid internetworking can also be realized.

The invention provides a high efficiency power distribution network fault first-aid repair system and method based on data analysis; the system comprises the following units: a real time analysis unit used for real time displaying fault density, power off scope, line and equipment heavy overload conditions, and visualization monitoring first-aid repair vehicle and process; a first-aid repair analysis unit used for parsing fault equipment, fault reason and work intensity; a first-aid repair prediction unit used for parsing and handling power distribution network fault rules; a quality service manage unit used for parsing user complaint data and providing Internet electric power services; and a decision unit used for integrating fault data so as to provide operational auxiliary decision information. The method can collect and sort power distribution network first-aid repair related data, and can build a data-based analysis platform, thus realizing power distribution network first-aid repair streamlining, gridding and integrated management, and providing basis data and effective support for distribution network equipment management, quality service management and distribution network planning construction works.

The invention discloses a V2G technology-based power distribution scheduling control method for electric vehicles. According to the power distribution scheduling control method, besides that the influences of charge and discharge power of the electric vehicles are considered, the limiting factors of the capacity of a power distribution network, technical conditions of the electric vehicles and the like are also considered; the traffic factors of drive routes, charging / discharging access and the like of the electric vehicles are further considered; optimized charging and discharging scheduling strategies, for the electric vehicles, conforming to the reality are comprehensively determined; charging and discharging of the electric vehicles are controlled by a V2G system; and the power distribution scheduling control on the electric vehicles is achieved. The embodiment and related data show that according to the V2G technology-based power distribution scheduling control method for the electric vehicles, the negative effects on the system reliability due to the fact that the electric vehicles are accessed on a large scale can be effectively improved; the load utilization rate of the power distribution network is improved; the load peak and off-peak difference of the power distribution network is reduced; and improvement of power distribution scheduling economical efficiency of the electric vehicle and power distribution network operation economical efficiency is helped.

The invention discloses a combined cold heat and power supply microgrid multi-objective dynamic optimal operation method; characteristics of translatable electrical load are firstly considered in an optimization process, then schedulability of source side and energy storage system are considered, contribution in each period in three kinds of controllable units serves as optimization variables, minimum system operation cost and minimum pollutant emission control expense serve as optimal operation targets, and a mathematical model of current multi-objective optimal operation problem is established; an excellent particles leading multi-objective particle swarm optimization algorithm is adopted to solve the optimization problem, that is, a single objective genetic algorithm is utilized to respectively find two points including minimum system operation cost and minimum pollutant emission control expense, and the two points serving as excellent particles is utilized to lead an optimal direction of the multi-objective particle swarm algorithm; the invention provides an effective multi-objective dynamic optimal operation method, and the method is significant for improving energy source comprehensive utilization efficiency of a multiple energy coupled system and promoting renewable energy source development.

The present invention relates to a centralized and networked protection system and method of regional distribution network, and belongs to the field of electrical system automation and relay protection. The protection system includes at least two centralized protection devices, an intelligent terminal and a communication network module, the centralized protection devices being communication with the intelligent terminal via the communication network module, the intelligent terminal being configured along with switching devices to distribute in each line section, for sampling data, backup protection and executing of tripping and closing commands, the centralized protection devices configured in the monitoring center of the regional distribution network, for generating differential protection elements based on the information sampled by the intelligent terminal and the topologic structure of the regional distribution network; and for determining the region where fault occurs and sending tripping and closing control commands.

The invention discloses an intelligent electric meter system for residents for an intelligent smart grid. According to the intelligent electric meter system for the residents for the intelligent smart grid, one intelligent electric meter is arranged in home of each resident, two control terminals are respectively arranged on each controlled electric appliance and each user switch, and each distributed power supply is provided with a distributed power supply access device; each control terminal and the distributed power supply access device are interconnected through a PLC (Programmable Logic Computer) communication network, and the intelligent electric meter and a high-class measuring system AMI (Advanced Metering Infrastructure) carry out information interaction. The intelligent electric meter system is suitable for the residents having tiered pricing for electricity and time-sharing pricing for electricity, and aims at minimum electric charge expenditure of users, and is used for intelligently controlling the electric appliances and the distributed power supplies of the residents so as to realize peak clipping and valley filling of the electric charge, and provide power supply quality and power supply reliability.

The invention discloses a breakdown intelligent classification and positioning method of an electric transmission line. The technical scheme of the breakdown intelligent classification and positioning method of the electric transmission line breakdown is that the advantages of three kinds of technologies of a support vector machine (SVM), self-adaptation nerve fuzzy inferences (SVM) and radial based function (RBF) neural networks are concentrated. The breakdown classifiers and positioners of the SVM, the SVM and the RBF neural networks are designed. Positioning errors, classification accuracy and model operation time are used as evaluation indicators. According to the standard that accuracy is preferred and efficiency is taken into account, intelligent selection of an optimal classifier and an optimal positioner is achieved under different breakdown conditions, and optimal breakdown classification and positioning effect is achieved. Meanwhile breakdown serious extent and repair indicators are designed to evaluate breakdown injury extent and breakdown repair difficulty. The breakdown intelligent classification and positioning method of the electric transmission line effectively improves power supply reliability, reduces outage cost, and meanwhile greatly reduces workload of maintenance personnel and improves working efficiency.

The invention relates to a direct-current micro-grid system and a control method thereof. The direct-current micro-grid system comprises a direct-current power distribution circuit, a bi-directional AC / DC (alternating current / direct current) rectifying / inverting device, a distributed energy generating device, an energy storing device, direct-current loads, alternating-current loads, a urban microclimate interactive system, a clock interactive system, a micro-grid control system and micro-grid protecting devices, an upper scheduling management system is arranged in the micro-grid control system so as to form layered management for micro-grid energy. The direct-current micro-grid control method includes: entering a grid connection mode or an island model according to working state of a large power grid, and determining the working states of the energy storing device and the distributed energy generating device according to information of the urban microclimate interactive system and the clock interactive system. The direct-current micro-grid system can independently supply power to the alternating-current and the direct-current loads and can be connected with a power grid to generate power according to processed result of urban microclimate interactive information, so that requirements on power supply for users are met, cost is reduced, designing, controlling, operation and maintenance of a micro-grid are benefited, and reliability, economy and efficiency of the micro-grid are effectively improved.

The invention relates to a method for restoring power supply of a power distribution network containing a distributed power source. The method is based on heuristic rules, performs dynamic island partition on the distributed power source, utilizes a connection switch to guarantee a power supply restoration scheme of the power distribution network to be adaptive to output changes of the distributed power source and continuous power supply of important users, and enables the intelligent power distribution network to operate safely, reliably and economically. Power supply restoration of the power distribution network comprises the steps that the power failure range of the power distribution network is determined by fault location information and an operating state of the power distribution network before the fault happens; and the distributed power source in the fault area is matched with the connection switch connected with the fault area, corresponding section switches are actuated, and radial operation of the power distribution network except for the distributed power source is ensured. The distributed power source is fully utilized to improve reliability of the power supply of the power distribution network, searching space is greatly reduced, and optimum strategy searching time is shortened. Therefore, the method is suitable for power supply restoration real-time operation of the power distribution network containing the distributed power source.

The invention discloses a grid-connected control method and system based on a virtual synchronous generator. The method comprises the steps as follows: simulating synchronous impedance with a synchronous impedance method based on cascade connection of an order-reduced resonator and a three-order generalized integrator to improve stability of the system, inhibit current deviation formed by load disturbance and realize power equalization, and inhibiting imbalance of output voltage and harmonic component by using quasi-proportional resonance controller. An order-reduced resonator phase-locked loop is combined with a quasi-synchronous parallel algorithm, asymmetry of grid voltage and output voltage of an inverter as well as the effect of harmonic waves on detection accuracy is avoided, the frequency, amplitude and phase of the output voltage of the virtual synchronous inverter track grid voltage quickly without static errors by the aid of the quasi-synchronous parallel algorithm, so that flexible off-grid / grid-connected switching is realized, the power supply reliability of the system is improved, and the electric energy quality is improved.

The present invention relates to a hybrid energy storage system and an energy management method thereof in a micro-grid. The system comprises a lithium iron phosphate energy storage system equipped with a lithium iron phosphate storage battery, a bidirectional energy storage AC / DC, and a super capacitor energy storage system equipped with a super capacitor, and is characterized by comprising a bidirectional energy storage DC / DC of which one side is connected with the super capacitor, and the other side is connected with a DC bus distribution line, wherein the DC bus distribution line is connected with one side of the bidirectional energy storage AC / DC, and the other side of the bidirectional energy storage AC / DC is connected with an AC bus distribution line. An energy management system detects and judges the charge states of the energy storage units of the hybrid energy storage system separately and real-timely, adjusts and controls the energy flow directions and amplitudes of the energy storage units of the hybrid energy storage system separately and real-timely, gives full play to the function that the super capacitor compensates the fluctuation of a power grid rapidly, satisfies the seamless switching and island transient operation requirements, keeps the uninterrupted power supply, enables the power supply reliability to be improved substantially, and realizes the operation benefit and cost optimization of the micro-grid.

The invention provides a power distribution network self-healing control method. The method mainly comprises fault positioning, fault recovery and self-healing evaluation; continuous online diagnosis and evaluation are performed on the operating conditions of the power grid by use of an advanced monitoring method so as to discover and eliminate hidden fault danger immediately; in case of a fault, the fault can be isolated quickly and self-recovery can be realized; the influence of the fault is minimized, and safe and stable operation of the power grid and good power supply quality are ensured.

The invention relates to a method for locating a single-phase disconnection non-ground fault of a power distribution network. After the single-phase disconnection non-ground fault occurs, the positive sequence voltage of the high-voltage side of each distribution transformer after a fault point is far lower than the positive sequence voltage of the high-voltage side of each distribution transformer before the fault point and the positive sequence voltage of the high-voltage side of each distribution transformer of a non-faulty line, and the positive sequence voltage of the low-voltage side of each distribution transformer after the fault point also correspondingly becomes about 50 percent of the positive sequence voltage before the fault point. For three-phase voltage information acquired by different types of measuring devices installed at load points, the positive-sequence component of the voltage of each load point is calculated in real time; and if the positive sequence voltage of a certain load point and the positive sequence voltages of all downstream load points of the load point are obviously reduced at one point, and the positive sequence voltages of upstream load points of the load point are constant, the single-phase disconnection non-ground fault can be determined in an upstream adjacent line connected with the load point. According to the method for locating the single-phase disconnection non-ground fault of the power distribution network disclosed by the invention, new equipment does not need to be equipped; the calculation is simple; and the fault can be located between two load points to realize the diagnosis and the location of the single-phase disconnection non-ground fault.

The invention discloses a power distribution network fault diagnosis system and method based on multi-source information. The system comprises a data collection layer, a knowledge representation layer and a fault diagnosis layer, wherein the data collection layer collects fault warning information in each power distribution substation and provides the collected information for the knowledge representation layer in time sequence; the knowledge representation layer describes and buffers data of all kinds of data sources of the information and provides all kinds of heterogeneous data for the fault diagnosis layer in a unified data view mode; the fault diagnosis layer makes different diagnosis methods according to the different data sources, a fault result is comprehensively judged finally, and the diagnosis result is used for analysis after an accident. The utilization rate of the fault information is improved, the reliability of the fault diagnosis is ensured, the fault reason, the fault influence degree and the like are analyzed preliminarily after a fault happens, the analysis result can assist operating personnel in building a timely and effective power distribution network fault repairing strategy, and the power supply reliability of a power distribution network is improved.

A distribution network automation system comprises a power distribution main station, power distribution substations and power distribution terminals. The power distribution main station is responsible for monitoring and managing global information and used for monitoring and acquiring data of a whole distribution network to complete fault handling within the whole network; the power distribution substations are used for managing distribution station terminal monitoring equipment such as switchgear cubicles for loop networks, switching stations for distribution networks and the like, acquiring, gathering and uploading signals of the power distribution terminals to the power distribution main station, and transmitting orders of the power distribution main station to the power distribution terminals; the power distribution terminals mainly used for acquiring data of primary equipment, controlling switchgears, detecting and recognizing faults and sending fault information to the power distribution substations and the power distribution main station. The distribution network automation system has the advantages that power supply reliability can be greatly improved, fault time can be greatly shortened, voltage quality can be greatly improved to provide optimal voltage for users, and labor intensity can be relieved for operators; management level of the whole power distribution system can be improved, working efficiency is improved, and user service level is improved.

In a filter circuit (1), a common mode choke (2) and a normal mode choke (3) have extremely high and low impedances, respectively, for common mode signals received through two input terminals (1a and 1b). The chokes have the opposite impedance characteristics for differential signals. In particular, the difference in impedance is large. Furthermore, the normal mode choke (3) is installed as a previous stage of the common mode choke (2). Accordingly, common mode noises which enter the two input terminals (1a and 1b) penetrate the normal mode choke (3), but neither penetrate the common mode choke (2) nor are reflected from the common mode choke (2). In particular, common mode currents flow through the normal mode choke (3) but do not flow through the common mode choke (2).