In the rapid development of the power industry, the investment share of distribution network protection automation will gradually increase. It has become a hot project in the domestic implementation plan and is receiving wide attention from the power industry. With the development of microelectronics technology, computer technology and communication and transmission information technology, as well as the successful development of mechatronics high-voltage switchgear, distribution automation technology has been widely used in the field of power distribution networks, and has achieved gratifying results. The specific performance of the optimized combination is diverse, full-featured and well-protected.
The development of distribution network automation requires a large number of intelligent high-voltage switches. Nowadays, due to the combination of technologies with good technical performance and microelectronics, a new high-voltage switchgear with high degree of system automation and strong self-function is formed. The main products are automatic reclosers, sectionalizers and automatic distribution switches. The most notable feature of these devices is the unit that integrates protection, monitoring, telecontrol, self-judgment memory and execution, reducing interaction and interference, improving power supply continuity and reliability. This will be the trend of domestic distribution network automation development.
1 Distribution system protection function and mode Distribution system protection automation is an important part of the distribution automation system control and management, there are four main functions: 1 to isolate the fault section, reduce power outages and failure time; 2 power system network Overload monitoring; 3 real-time adjustment to change the grid operation mode and load transfer; 4 improve user service quality, reduce power loss, save overall investment, reduce power distribution maintenance costs, improve power supply quality and power supply reliability.
At present, the distribution type f which realizes the above functions is of the Anglo-American method; the other is the Japanese method. The former mainly operates the reciprocator and segmenter of the mechatronics function; the latter mainly relies on the Japanese Toshiba vacuum switch and an automatic power distribution intelligent switch.
In the late 1980s, many electromechanical integrated switchgear automatic reclosers, sectionalizers and distribution switches were introduced in rural areas of China. Most of them have been operated in rural miniaturized outdoor substations, and they are used as substation 10kV outlet protection. The power distribution system currently has only on-column oil switches and drop-type load switches, and there are no other protection devices. Therefore, when a permanent fault occurs on the distribution network, most of them rely on the substation outlet recloser to trip, causing the entire line to be powered off. The recloser is only equivalent to a circuit breaker with a coincidence function, which acts as a 10kV switch for the outdoor substation, and the advantages of the technical performance of the smart device are far from being exerted. The true function of the recloser is not only used as a substation protection, but also should be matched with the online segmenter and distribution switch to form a hierarchical and logical progressive protection to realize the automation of the distribution system.
1.1 US-British system US-UK system adopts grid current control mode, US power grid 10kV system is directly grounded at neutral point, online product insulation withstand voltage level is less than 42kV/min, usually single-phase grounding trip current 1.3.2 recloser (R) and segmentation The device (S) is matched with the second 12 Japanese method R and S are connected with the wiring, and the wiring is a dendritic structure. When point a is a transient fault, R trips, S1, S2S3 lose pressure and disconnect, R re-closes, S1, S2, S3 are each put into the converter, the time limit is 7s delay into the whole line to restore normal power supply. When point a is a permanent fault, R trips, S1, S2, S3 lose voltage and disconnect, R coincides, and sequentially inputs S1 and S2. Since no voltage is found in the time limit detected by S2, S1 and S2 are after R is tripped again. Disconnected, S2 closed and locked. R coincides, S1 is put in, A and B segments resume normal power supply, and C and D segments are powered off. In the middle, the electronic control unit is set to a limit of 7s. /T3 can make S3 disconnect, and the rest of the segments are analogous. If the C segment fails, the short circuit current caused by the ITC causes the R to trip, the segmenter S2 counts once, and the R delays the reclosing. If it is a transient fault, the reclosing is successful, and the power is restored to the whole line; if it is a permanent fault, S2 is counted once again for a total of two times. After the appropriate delay of the R trip, 82 is disconnected when there is no current in the line. Closing lock, R resumes normal power supply after closing again. After the automatic disconnection of the grid fault section, Rissa and the protection wiring 3 indicate that the Japanese system adopts the grid voltage control mode. The substation relay can detect the fault current and determine the switch in the station. Whether the CB operates, whether the FDR is necessary to respond to the fault current, etc., requires a function of detecting a voltage change in a real-time state. At this time, it is very convenient to detect the single-phase ground fault. As long as it is matched with the upper-stage short-circuit protection switch, the number of segments can be arbitrarily added in the distribution network within a certain range. see. Medium: FSI is the fault zone indicator; FDR is the fault detector; R is the coincidence relay; S is the automatic power distribution switch.
1.3 Working principle of the protection mode of the distribution system 1.3.1 Coordination of the recloser (R) and the segmenter (S). See the matching connection of R and S. A power supply line has a total of ABCD 4 sections. The farther the line impedance is from the recloser, the smaller the short-circuit current is. Therefore, ItB>ITC>ITD; ItR, 1t1, 1t2, 1t3 are the minimum tripping currents of each segmenter, respectively, and R is matched with the protection wiring. 1.3.3 Recloser (R) and segmenter (S) The third R and S match wiring see the wiring method is a single power supply loop. When point a is a transient fault, the recloser is opened, and S1~S5 are disconnected due to the loss of pressure. After R is overlapped, it is powered by the setting time of 0s. When point a is a permanent fault, after S trips, S1~S, 5 are disconnected due to loss of pressure, and R is coincident. After 7s delay, S1 is put into operation. Because there is no voltage, S1 will be closed and closed, and S1 will be broken after R trip. Open; once again, after 14s delay, S2 is put in, S4 is closed after 14s delay, and finally S5 is closed by 14s delay. The A, B, C, D, and E segments resume normal power supply. In the electronic control unit, the whole 1.3.4 recloser (R) and the sectionalizer (S) cooperate with the four R and S mating wiring, and the wiring mode is a dual power supply loop. When the power grid is normally powered, there are two ends of the S5. Electric, but S5 is in the off state. When the point a transient fault, the R-second coincidence can restore the normal power supply. After a long delay, the S3 will be closed when there is no voltage at one end. Therefore, except for the power failure of the A2 section, the rest will resume normal power supply. In the middle, the electronic control unit is set to the limit of the input time: Si~S47s; S, s90~ R and S are matched with the protection wiring 4. The wiring of the 1.3.5 recloser (R) and the sectionalizer (S) see. The recloser is used as the feeder segmentation switch to replace the segmenter, and it has the ability to break short-circuit fault and its own FTU protection and control function to realize automatic fault isolation, and the non-fault section is normally powered. Under normal conditions of the power grid, the switches at F and G and ABCD4 are all closed, and the contact point E at the ring network is disconnected. When the point a fails, the switch at A is tripped. If the fault is transient, the switch at A is successfully overlapped; if the fault is permanent, the switch at A is unsuccessful and is automatically blocked again, and is in the open state. A, B section loses power, and the E-contact switch is automatically closed due to one-side voltage loss, and the line is closed and the B section resumes power supply. After the delay, the switch at B is also closed. At the A and B switches, the switch trips again and self-locks in the open state, and the load of the B segment is transferred to the SP2.
One of its advantages is that the fault is isolated on the ground, avoiding a certain fault causing the whole line to be cut off, thereby greatly reducing the number of operations such as switches at the substation F and G, and reducing the impact on the primary line and the distribution system of the entire line. The second advantage is that there is no need to increase investment and other investment, and the automatic re-segmentation of the feeder can be completed by using multiple coincidences such as recloser and protection action time limit program.
1.3.6 The recloser (R) and the segmenter (S) are matched in the same way as the wiring. The substation switch adopts time-limited quick-break protection, and the line segment switch has short-circuit current breaking capability. 4. The detecting circuit controlled by the segmenter detects the voltage at both ends and detects the line current. When the switch is closed to the fault, the segmenter is immediately opened and self-locking. If a permanent fault occurs at point a, the outgoing switch and the segmenter operate in the same order as the voltage type. However, when the switches at F and G are closed to the fault point, they are immediately opened, the fault is removed, and the normal power supply of the non-fault line segment is restored.
The R and S cooperate with the protection wiring. The schematic diagram of the 1.3.7 recloser (R) and the sectionalizer (S) is the connection method. The recloser R is installed at the outlet, the segmenter S1 is installed on the line, and the fuse FU is used at the branch line branch point between R and S1. The R has dual-time protection function, and the motion curve i+t has a fast and slow selection. The fuse characteristic curve is between the fast and slow curves. If line a fails, R uses the fast action feature to trip before the FU blows and switches to the slow action curve. If point a is a permanent fault, the FU is blown before the R action, and the branch fault point is cut.
This system is suitable for radial open loop operating lines.
R and S cooperate with the protection wiring. In summary, the electronic controller's safety characteristics are accurate and reliable, the adjustment range is wide, and the setting is convenient, so that the power distribution line distribution automation hierarchical protection can be realized. Especially suitable. If the Japanese-style input is used to find the faulty section, the advantages are clear, fast and reliable, set delay, easy to operate, and the power supply is graded. Therefore, it is not controlled by the whole timing limit and the set value. Therefore, the selectivity is strong, and the fault section can be quickly removed, and the entire operation input time is short and fast.
2 Distribution network protection 2.1 The principle of cooperation must follow the following cooperation principles: 1 When a short-circuit fault occurs in the distribution system, the load side segmenter must isolate the fault before the power supply side backup protection recloser is closed; 2 caused by permanent failure The power supply interruption must be limited to the minimum fault section in the distribution network; 3 any point in the distribution network should be within the protection range; 4 before the switching equipment close to the power supply side breaks the line or operates the lock, the load side protection equipment must Cut off instantaneous or permanent faults; 5 When the length of the main line of the power distribution exceeds 10km, at least one section should be segmented; when the branch line exceeds 4km, a segmenter or distribution switch should be installed.
2.2 Coordination requirements 1 segmenter should be installed on the loader side of the recloser.
2 The backup protection recloser must be able to detect and break the minimum fault current within the ranger protection range.
The starting current of the 3 segmenter should be less than the minimum fault current within its protection range and 80% of the minimum tripping current of the backup protection recloser and greater than the expected maximum load current.
The dynamic thermal stability current of the 4 segmenter must be greater than the maximum short-circuit current at the installation site, and the thermal stabilization time must be greater than the breaking time of the backup protection recloser.
The memory time of the 5 segmenter must be greater than the total accumulation time (TAT) of the backup protection recloser. Is the total accumulation time of the backup protection recloser. Medium: TAT is the total accumulation time; F1, F2, F3 are the fault protection current breaking time of the backup protection recloser; R1 and R2 are the backup protection recloser coincidence time; SMT is the sectionalizer memory time and the sectionalizer is combined and closed. The brake is locked.
2.3 Recloser and sectionalizer with protection constraints 2.3.1 Recloser with protection constraints 1 Electronic recloser protection can be achieved by the change of current and time one-second characteristic curve. The key is the time difference between the two sets of recloser time-current curves corresponding to any current value.
2 When the secondary side recloser of the substation is protected with the recloser on the line, in order to eliminate the transient fault, the substation recloser should have at least one quick action, and the number of the load side recloser with the load side should be more than or equal to the substation. Recloser fast motion times. The recloser on the load side should break the fault current and lock it after the backup protection recloser is fast moving and slow down to cut off the permanent fault point section.
2.3.2 Segmenter with protection constraint The minimum operating current of the segmenter shall be 80% of the minimum breaking current value of the power supply side protection device. 2 The segmenter without the ground fault detection accessory shall be connected with the backup protection device. The minimum breaking current value of the phase-to-phase short circuit is matched.
3 When several component segments are used in series in the same distribution network, the number of times of memory time should be less than that of the backup protection recloser.
The count retention time of the 4 segmenter should match the break and coincidence time of the backup protection device.
5 When using the three-phase segmenter, it can only be matched with the three-phase synchronous operation of the backup protection device. Otherwise, the recloser may fail to break, causing the power grid to lose power.
6 When the electronic segmenter is combined with the recloser, adjust its operating current and memory time. Select the rated continuous working current of the segmenter to be equal to or greater than the actual load current at the position, and the minimum operating current is the minimum breaking of the recloser. Current selection. The electronic segmenter usually selects 3s of memory time of 30s45s90s. The memory adjustment range of the FDL4-12/200 SF6 automatic segmenter developed by Shanghai Huatong Switch Factory is 15~120s. The selection of memory time should be determined according to the action sequence set by the backup protection recloser. Slightly larger than the first break time of the recloser and before the action of the segmenter, that is, the cumulative time of the last break of the recloser.
3 Discussion on the issue of distribution protection automation and thinking Most of the medium voltage distribution network is ungrounded. 3.1 Unbalanced current detection is different. Therefore, if a single-phase ground fault occurs in the US-British mode, the fault current is small and difficult to detect. In order to detect the result, an open delta voltage transformer and a zero-sequence current transformer must be added to the recloser and the segmenter so that the faulty section can be cut. Because the single-phase ground fault occurs in the power grid, there is no short-circuit or over-current, but only three-phase unbalanced current is generated. Therefore, the power supply radius of the agricultural network is large, and the total length of the line is also long. The capacitance current is generally above 3A, which has high sensitivity. Electronically controlled reclosers and segmenters detect faults. This means that unbalanced currents can also be detected when the length of the outgoing line is short with the 10kV bus. This provides conditions for the use of mechatronic products in a city network with a short power supply radius.
The current operating rules of the domestic grid allow the line to continue running for 2 hours under single-phase earth faults, so that there is sufficient time to find and eliminate the fault points. If the problem cannot be solved within 2 hours, the route is taken out of the post-run processing. Such a treatment is obviously unfavorable for the quality and reliability of the distribution network protection power supply.
3.2 Electronic Control Device Problem The auto-recloser can be used with the segmenter or with the high-voltage side and the load-side fuse. The segmenter also cooperates with the circuit breaker, the recloser and the fuser. In terms of the electronic control and matching characteristics of its mechatronic devices, it can be roughly classified into three categories. The first type is the pulse counting type, and the segmenter counts the recloser action and the number of breaking faults. When the system returns to normal and the number of actions is less than the number of times the segmenter is set, the segmenter counting device is reset; when the number of actions reaches the set number of times, the segmenter opens during the breaking of the recloser. Since the starter currents of the different segmenters are different, only the segmenter closest to the fault point can be opened and the fault is isolated. When the recloser is closed again, the power supply is restored with the non-faulty section. The second type is voltage memory type, the distribution network line is faulty, the recloser trips, and the whole line loses pressure. Since each segmenter has a delay in opening, when the recloser is rapidly re-engaged, each segmenter does not operate, thereby eliminating transient lightning strikes and the like. In the case of a permanent fault, each segmenter opens when the recloser enters the delay coincidence procedure. The recloser is closed again, and the segmenters are sequentially closed from the power supply end. When a segmenter closes when short-circuited, the recloser is disconnected again. The segmenter compares the fault time with the lock-up memory time. If the former is smaller than the latter, the brake is closed and the lock-lock is closed. After the faulty section is cut off The recloser is closed again to restore normal line power. The third type is centralized control type, and the centralized control device is installed in the two-channel radio command system of the dispatch center. Therefore, it needs to be solved between the original SCADA (monitoring and data collecting device) and the fault detector, segmenter, etc. in the system. Interface problem. Among the three categories, the third category is the most complex and the command center and SCADA devices are added in the dispatch center, and the interface problem is solved. The first type only requires the installation of the counting device and the operating current regulating device on the spot. The second type guarantees the loss of voltage and locks the memory. Each of the three categories has its own characteristics. If the segmenter is set according to the second type, it should have a strong ability to close the short circuit fault according to its action process. From the time of the fault removal, the third category is the fastest, and its contact mode and the motion of the segmenter are not delayed. The second type of resection fault has the longest time, because it can be closed at time intervals to find the faulty segment, but its action logic is the closest to manually finding and isolating faults.
The SCADA system control is integrated by microelectronics technology, communication information transmission and computer system. See the wiring method. It has a central coordination station and communication channel, communication point master-slave communication mode, and each segment switch intelligent control unit FIU (Feeder TrminalUnit, feeder terminal unit) can communicate with the central master station RTU (RemoteTerminalUnit, remote terminal unit) The fault isolation operation is centralized by the central coordination station in a telecontrol manner. Suppose a permanent fault occurs at point a, and the outgoing switch protection action at F is unsuccessful. The central coordination station CPU queries the FTU status and information on the faulty line through POLLING mode. The RTU fault detection software identifies the fault point according to the fault current. At point a, the central station issues a remote command, disconnects the two switches A and B, switches the switch at F, and closes the contact switch at E. The fault identification and isolation are completed, the load is transferred, and the non-fault section is automatically restored. Normal power supply.
This mode features: computer and communication technology communication transmission can be fiber, cable, wireless spread spectrum, carrier; can also be public telephone line or dedicated line. Real-time monitoring of feeder operation under full working conditions greatly improves the reliability of power supply. This control method is applicable to high load density areas such as urban centers, development zones, and commercial and residential centers.
3.3 Distribution network master station setting mode 3.3.1 Integrated implementation mode Miscellaneous not only need to install the fault detector response device on the spot, etc. It is not appropriate to use the integrated feeder automation party: when the integrated feeder automation function is realized in the substation automation system, the substation The local master station of the automation system or the RTU accepts and manages the information of the FTU and substation RTU and intelligent monitoring devices on the line to realize the monitoring and feeder automation functions of the equipment in the substation. Directly use the SCADA/DA/DMS master station platform to implement the feeder integrated function of the line equipment in the jurisdiction of the entire power supply department. The advantage is that it shares software resources with the substation integrated automation SCADA/DA/DMS main station. The disadvantage is that the main station requires the system to be large and complex, with many difficulties and long engineering cycles. A considerable part of the power supply department has a substation integrated automation or SCADA main station system 3.3.2 separate setting mode as the distribution automation secondary primary station, firstly should automatically process the data from the line FTU, locate the fault point and remotely control the line switch to Realize the automatic isolation and recovery of power supply at the fault point; secondly, it should have the necessary computer interface function, complete the monitoring of the line equipment and the debugging and maintenance of the system, and can be used as a node of the distribution automation system; in addition, it should also have the function of data forwarding. Communicate with the superior SCADA/DA/EMS master station, upload and download the monitoring, management and information commands of the entire power distribution system. This level of FA control of the primary station helps maintain system independence and integrity. The system can operate independently of other automation systems, thereby increasing system reliability. When the FA control main station is in line fault, it accepts the FA-RTU fault data, makes fault location judgment in real time and issues a switch operation control command. It has advantages in reducing the level of data processing transmission processing, improving system response speed and reliability.
3.4 Current grid operation problems Distribution grid automation is a high-input, high-output engineering column. The reliability of the upper type intelligent high-voltage switch is crucial. It is the basic unit of the feeder automation system. China has a vast territory, and the operating environment, conditions and climate of the north and south, the coastal inland, and the Pingchuan plateau are very different. The environmental conditions of the outdoor weather are much worse than the indoors. Therefore, it is difficult to ensure the safe and reliable operation of the power grid. Fortunately, the construction of the national urban and rural power grid is getting faster and faster, and the intensity is getting bigger and bigger. The automation of electric power is getting higher and higher, so that the above-mentioned distribution network operation mode has been in Guangdong, Hunan, Zhejiang, Jiangsu, Shaanxi, Hebei, Dalian, Beijing and other places across the country to promote applications. Domestic and foreign manufacturers have been focusing on this goal, opening up the market and gradually introducing various electromechanical integrated devices. It is worth mentioning that the original old network and the existing segmenter match the recloser, you can use the common simple action program (only requires one fast automatic reclosing and two strong power transmission) and the distribution network switch After the equipment has been modified slightly, it can be equipped with one automatic closing, and some can be adjusted by slightly adjusting the relevant management regulations (such as allowing two strong power transmissions). The old network will be transformed into a new network to reduce cost and increase functionality and improve reliability. This will be a viable way to develop and improve the automation technology of domestic power supply line distribution.
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