The design of 10, 6 kV power distribution station and 10, 6/0.4kV substation is a very common and very important work in engineering construction. It is very normative and technical, and many aspects involve national compulsory provisions. Implementation. To do a good job in the design of the power distribution station, it is necessary to implement the relevant national norms and regulations, but also to meet the specific requirements of the local power supply department. Otherwise, various problems will occur, affecting the design quality and project progress. In order to do a good job in the design of the power distribution station, some of the problems found in the design drawings of the power distribution station are now sorted out, briefly analyzed, and communicated with each other to improve together.
1. The name of the substation and power distribution station engineering design should strive to be accurate when using terminology, not arbitrary. It is not advisable to use the name “distribution†in the design documents of specific projects. “Substation†is a general term for substations and power distribution stations and is used only for general purposes. When it comes to a certain category or an individual, it should be called “substation†or “distribution stationâ€. In GB50053-94 "Design specification for substation of 10kV and below", the explanation of "substation" is "the power supply of 10kV and below AC power supply to power equipment after being transformed by power transformer": Explanation of "distribution station" It is "there is only a high-voltage power distribution device that functions to open and close and distribute electrical energy, and there is no main transformer on the busbar." When both the substation and the power distribution device are used, the main function of the buck-boost is to include the high- and medium-voltage power distribution devices, which are called “substation†and “medium voltage distribution†as the main function, including 3~10/0.4kV transformers are called “distribution stations.†When a project has multiple substations, it should be named separately for each substation by its name or by serial number.
2. Types of live conductor systems and types of system grounding According to Article 312 of the International Electrotechnical Commission IEC-TC64, the type of power distribution system has two characteristics, namely the type of live conductor system, such as three-phase four-wire system, and system grounding. The type is TN-C-S system. The three-phase four-wire TN-S system shall not be referred to as the “three-phase five-wire system†in the official documents. In GB50054-95 "Low-voltage power distribution design specification" on page 37 "noun explanation" has clearly pointed out that "three-phase four-wire system is one of the types of live conductor distribution system, three-phase refers to L1, L2, L3 three-phase The four-wire refers to three phase lines and one N-line that pass the normal operating current, excluding the PE line that does not pass the normal operating current." It further clarifies that "TN-C, TN-C-S, TN-S, TT and other ground-type distribution systems are all three-phase four-wire system." In China, the low-voltage distribution voltage should be 220V/380V. The type of live conductor system should adopt single-phase two-wire system, two-phase three-wire system, three-phase three-wire system and three-phase four-wire system. In the design documents, the delineation of the TN-S and TN-C-S ground patterns is sometimes confused. The grounding type of the system is generally in terms of the power supply range of a substation or a transformer. The neutral line N line and the protection line PE line are only in a local range. When a building or a floor is separated, it should be called TN-C-S system. When the exposed conductor of the load side electrical device of a residual current protector in the TN system is grounded separately, it may be referred to as a local TT system.
3. Classification terminology and standard measurement units The various terms such as classification and classification in the design documents shall be unified with national standards and industry standards, and shall not be confused. For example, the term “electric load†should be called “first, second and third stage loadâ€. “Class†is not used here. “Lightning protection building is called first, second and third type lightning protection buildings. Here, “class†is used. There is no need for “level†new lightning protection specifications are no longer divided into industrial and civil use. The grid size of roof lightning protection nets should also be subject to the new regulations. Explosive gas environmental danger zones are divided into zones 0, 1, and 2, explosive dust environment. The hazardous areas are divided into 10 and 11 areas, and the fire danger areas are divided into 21, 22, and 23 areas. The “zones†are used here instead of “levels†or “classesâ€; and the gunpowder, explosives, ammunition, and pyrotechnics are dangerous places. For Class I, II, and III hazardous locations, the “Class†is not used here. Other terminology should also be used correctly. For example, “circuit breaker†and “substation†should be used in official documents, and “automatic switchâ€, “substationâ€, etc. should not be used. The standard symbols of the unit of measure should be correct, and the case of the letters should not be arbitrary. For example, A, V, W, kV, kW, kVA, kvar, lx, km, etc. should always use the legal unit of measurement, especially pay attention to the correctness of the case letter of the unit symbol, such as the unit symbol converted from the name of the person, such as A, The prefixes of V, W, N, Pa î—¥ and above, such as M and G, should be capitalized; otherwise, they are all lowercase, such as kV, MW, kvar, km, etc. For information on the measurement unit, please refer to Chapter 16 of the Industrial and Civil Power Distribution Design Manual, pages 773-783.
4. Requirements for civil works In GB50053-94 "Design specifications for substations of 10kV and below", the requirements for the location of substations and the requirements for construction and other related professions are clearly defined. There are still many specific problems in the implementation. Only a few examples are listed below, and the design should be taken seriously in the future.
1)   fire provocation: when the workshop is equipped with a submersible power transformer selected for substation, some do not have fire provocation above the main door of the transformer room. In Article 6.1.8 of the compulsory provisions of the engineering construction standard GB50053-94, it is stipulated that “When electrical equipment with flammable oil is placed on the bottom layer of the multi-storey and high-rise main building, the width of the upper part of the bottom wall shall be set above the opening. Fireproof provocation not less than 1.0m".
2) Safety exit: Some designs have only one outlet or two outlets in the power distribution room with a length greater than 7m but close to the same end. This does not comply with the provisions of Article 6.2.6 of GB50053-94. The specification requires that “the power distribution room with a length greater than 7m shall be provided with two outlets and shall be arranged at both ends of the power distribution roomâ€.
3) î—¥ Liang Gao: Some designs do not take into account the height of the beam when considering the indoor height. Due to the large span of the substation, sometimes the height of the beam can reach about 800mm, so the height of the beam should be considered when the condition of the soil is high.
4)   duty room: Some designs set the duty room in the corner of the traffic inconvenient. This does not comply with the provisions of Article 4.1.6 of GB50053-94, which stipulates that “the power station on duty should have a separate duty room. The high-voltage power distribution room and the duty room should be directly connected or communicated through the channel. The duty room should have Direct access to the outdoors or to the aisle door."
5) Cable trench: In some substations, the low-voltage power distribution panels arranged in double rows are only provided with trenches on the bottom and rear sides of the screen, and the trenches of the two rows of screens are not connected to each other. In order to facilitate cable entry and exit and future line adjustment, it is advisable to connect all the main cable trenches and control cable trenches.
6) Cable dividing room: Some dividing rooms do not meet the requirements of the power supply department. The Beijing Power Supply Bureau stipulates that 10kV users in Beijing must set up a cable junction room as the power supply main entrance room for the project. The cable compartment should be located close to the power line and close to the exterior wall of the building. The area is generally 6m×3.5m or 20mm2, the net height should be no less than 2.7m, and the cable interlayer with a net height of not less than 1.8m is provided, and a manhole and a ladder of 600mm×600mm are provided. The cable compartment is usually located in a building without a basement; in a building with a basement, no matter how many floors are underground, the cable compartment is required to be located on the basement. According to the regulations of the Beijing Power Supply Bureau, the cable dividing room is managed by the Beijing Power Supply Bureau, so the door of the cable dividing room should be opened to the public walkway.
5. Equipment Arrangement In the equipment layout of the power distribution station, there are also various problems, even violation of the provisions of the mandatory provisions, which are listed below only:
1) The high and low voltage power distribution system diagrams are inconsistent with the plan. There are two manifestations: one is that the system diagram is opposite to the arrangement order of the cabinet screen in the plan view. When looking at the system diagram, it is facing the front of the cabinet screen, and it is arranged from left to right as 1, 2, 3...n; on the plan view, it is facing the back of the screen, and it is arranged from left to right as 1 , 2, 3...n, must be reversed. The key to avoiding this error is to arrange the front side of the cabinet screen and the plan view from left to right in order. The second is that there is a busbar bridge between the two rows of face-to-face distribution panels on the plan, but not shown in the system diagram.
2) The width of the low-voltage power distribution screen before and after the screen does not meet the requirements of the new specification. For example, the screen is sometimes only 700mm away from the wall, and the drawer type low-voltage screen is only 1800mm apart when placed in a face-to-face arrangement. According to the provisions of Article 4.2.9 of the specification GB50053-94, the low-voltage distribution room is arranged in front of the screen and behind the screen. The minimum width of the channel is: its rear screen channel, fixed and drawer type are 1000mm; its front screen channel, fixed single row arrangement is 1500mm, drawer type single row arrangement is 1800mm, fixed double row face-to-face arrangement is 2000mm, The drawer type double row face-to-face arrangement is 2300mm. Only when the building wall surface is partially protruded by the column type, the channel width of the protruding part can be reduced by 200mm.
3) The number of outlets of the rear panel of the power distribution cabinet does not meet the specification requirements. As a mandatory provision of the Code, Article 4.2.6 of GB50053-94 stipulates that “when the length of the power distribution device is greater than 6m, the rear channel of the cabinet shall have two outlets, and the distance between the two outlets of the low-voltage power distribution device shall exceed 15m. The export should be increased. The reason for this enforcement is that when there is a sudden failure of the electrical equipment in the high-voltage cabinet or low-voltage screen, the inspection or maintenance personnel behind the screen can leave the accident point in time.
4) The wiring fixtures in the distribution room are line cranes and chain cranes, and are installed directly above the power distribution device and do not meet the safety requirements. Article 6.4.3 of GB50053-94 stipulates that “the luminaire and the exposed line shall not be arranged directly above the bare conductor in the power distribution room. When the luminaire is arranged above the bare conductor in the power distribution room, the horizontal clearance of the luminaire and the bare conductor It should not be less than 1.0m, and the lamps should not be hoisted by hanging chains and cords." Since the busbar busbars arranged on the top of the low-voltage screen are usually not closed, this regulation is to be implemented. A cable trough fluorescent lamp can be installed in the power distribution room with a boom.
5) Grounding flat steel is installed along the wall in the substation, but no temporary grounding post is provided. In order to facilitate temporary grounding during testing and maintenance, temporary grounding posts should be properly set up. The grounding terminal can be found in the National Standard Atlas 86D563 "Grounding Device Installation" on page 25.
6. It is recommended to use D, yn11 junction transformer. In the last ten years, D, yn11 junction group transformers have been widely used in TN systems, but there are still many projects that still use Y, ynO junction group transformers. The main reason is that the advantages of the former are not clear. Article 6.0.7 of GB50052-95 "Design Specification for Power Supply and Distribution System" stipulates: "In the low-voltage power grid of TN and TT system grounding type, the three-phase transformer of D, yn11 junction group should be selected as the distribution transformer. ". The reason for "optional" here is mainly based on D, yn11 junction line than Y, ynO junction transformer has the following advantages:
1) It is beneficial to suppress high harmonic current. Three or more higher harmonic excitation currents can form a circulating current on the primary side under the condition that the primary side is connected to the delta shape, which is beneficial to suppress the high harmonic current and ensure the quality of the power supply waveform.
2) It is beneficial to cut off the unit phase short circuit fault. Because the D, yn11 junction is much smaller than the zero-sequence impedance of the Y, ynO junction, the single-phase short-circuit current of the transformer distribution system is expanded by more than three times, which is beneficial to the removal of the single-phase ground short-circuit fault.
3) Can make full use of the equipment capabilities of the transformer. The Y, ynO junction transformer requires that the neutral current does not exceed 25% of the rated current of the low-voltage winding. See Section 6.0.8 of GB50052-95, which severely limits the capacity of the single-phase load and affects the capability of the transformer equipment. Fully utilized; while the neutral current of the D, yn11 junction transformer is allowed to reach more than 75% of the phase current, and even 100% of the phase current, so that the capacity of the transformer can be fully utilized, which has a large single-phase load capacity. The system is very necessary. Therefore, in the low-voltage power grid of the TN and TT system grounding type, it is recommended to use the D, yn11 junction group distribution transformer.
7. Cable type and cross section selection 1) Cable selection: YJV type XLPE cable and VV type PVC cable are two cables commonly used in engineering construction. YJV type cross-linked cable is slightly more expensive than VV type cable, but has small outer diameter, light weight, large current capacity and long service life. YJV type cable can last up to 40 years, while VV type cable is only 20 years. Years and other significant advantages, so in the engineering design should try to use YJV type cross-linked polyethylene cable, and gradually phase out VV-type PVC cable.
2) Selection of cable section: As a kind of conductor, the section of the cable should meet the requirements of Article 2.2.2 of the mandatory provisions of the specification GB50054-95, and the four-point requirements for selecting the conductor section should be met. However, it does not meet the requirements of the first and second points in the specification.
The first point: "Line voltage loss should meet the requirements of the normal operation of the electrical equipment and the voltage at the starting end." In addition to the current requirements to meet the calculated current requirements, the cable cross-section should be verified against voltage loss. Since the voltage loss check has not been carried out, we have repeatedly found that the cable of 6mm2 and 10mm2 cross section is used as the long-distance power distribution trunk and cannot meet the error of the voltage requirement of the power equipment. Therefore, the voltage loss calculation should be performed to verify the Whether the selected cable cross section meets the requirements of the terminal voltage of the powered device. The specification of Article 4.0.4 of GB50052-95 has the following requirements for the allowable value of voltage deviation of the terminal of the electric equipment: ±5% for the motor machine; ±5% for the illumination in the general workplace, and the general work away from the small area of ​​the substation Location lighting, emergency lighting, road lighting and guard lighting are +5%, -10%; other electrical equipment is ±5% when there is no special regulation.
The second point: “The current carrying capacity of the conductor determined according to the laying method and environmental conditions shall not be less than the calculated current.†The implementation of this article shall take into account the influence of ambient temperature, conductor operating temperature, parallel coefficient, etc. on the cable current carrying capacity, especially the cable. The effect of the number of parallels on the current carrying capacity during laying. For example, if the cable is placed on the bridge without spacing, the correction factor of the continuous current carrying capacity when the two layers are juxtaposed, the horizontal arrangement of the ladder frame is 0.65, and the horizontal arrangement of the tray is 0.55  see 92DQ1-77. Various correction factors for the current carrying capacity of wires and cables can be found in the North China Standard Building General Atlas of Buildings, 92DQ1-75-77.
In addition, the choice of cable cross-section must also take into account the use of spare equipment and the use of new equipment.
8. Circuit Breaker Selection and Short-Circuit Current Calculation There are two types of circuit breakers and fuses used as protective devices in low-voltage power distribution systems. At present, we use the most circuit breakers, which are used for short-circuit protection and overload protection of distribution lines. However, there are many problems in selecting a low-voltage circuit breaker, and the outstanding problem is that no short-circuit current calculation is performed. The breaking capacity of the short-circuit protection device of the distribution line should be greater than the expected short-circuit current at the installation. The circuit breaker should first calculate the short-circuit current at the outlet end, but some designers do not calculate the short-circuit current. The ultimate short-circuit breaking capacity of the selected short-circuiter is not enough to cut off the short-circuit fault current. To determine the short-circuit current at the circuit breaker installation, it can be calculated according to the design manual, but it is more complicated; it can also be used to determine the calculation current by using the "short-circuit current curve method", which is relatively simple. A "short-circuit current check curve method" provided by the Shanghai Electric Apparatus Research Institute and the circuit breaker product data of Zhejiang Rui'an Wansong Electronic Appliance Co., Ltd. is attached. By looking at this curve, it is convenient to obtain an approximate value of the short-circuit current at any installation position. The short-circuit point of the example is only an assumption, and the most commonly used short-circuit point in actual engineering design is selected at the exit end of the protection device.
9. When the circuit breaker and the circuit breaker are cascaded to cooperate with the low-voltage distribution line for short-circuit protection, the breaking capacity of the circuit breaker must be greater than the short-circuit current that may occur at the installation. But sometimes this requirement cannot be met. For example, the breaking capacity of C45N and C65N/H miniature circuit breakers is only 6kA and 10kA respectively, but the short-circuit current at the outlet end of the installation can sometimes reach 15kA or even higher. At this time, two ways can be used to solve this problem. The first is to use a molded case circuit breaker with high short-circuit breaking capacity. The second is to use a miniature circuit breaker to realize short-circuit protection by using the cascade connection with the upper-level open circuit. However, the selection of the upper and lower circuit breakers for cascading cooperation must meet the following conditions:
1) The prerequisite is that the inherent breaking time of the upper circuit breaker is shorter than the full breaking time of the lower circuit breaker. That is to say, when the outlet of the lower breaker is short-circuited, the lower stage can cut off the short-circuit current in the future, and the short-circuit current is cut off first.
2) Although the lower-level circuit breaker cannot cut off the short-circuit current, the lower-level circuit breaker and its protected line should be able to withstand the short-circuit current.
3) The step-by-step cut-off circuit shall not cause the interruption of the power supply of the first and second stage loads other than the faulty line.
4) The upper and lower circuit breakers should adopt the same series of products, and the rated current level is preferably 1 to 2, or according to the cascade matching table provided by the manufacturer. The cascading cooperation table provided by Schneider Electric is attached. It can be seen from this table that the C65N/H type circuit breaker can be cascaded with NS100, NS160, NS250 type circuit breakers, and can not be matched with larger NS400, N630 and above circuit breakers, and can not be directly connected to the low voltage side of the transformer. On the low voltage screen of the busbar after the frame type main switch.
10. Disconnecting the neutral line and applying the four-pole switch GB50054-95 "Low-Voltage Power Distribution Design Specification" Since the implementation of the specifications and understanding of the specifications, the designer disconnected the neutral line when designing the low-voltage distribution system. And the application of four-pole switches is difficult to unify. In response to this situation, "Electrical Engineering Applications" magazine has published a number of domestic and international experts' monographs since the first issue in 1999. Experts have clarified their respective views on the regulations and practices for disconnecting the neutral line and applying the four-pole switch at home and abroad, and benefiting us a lot. Some opinions that are generally accepted by experts and closely related to our design work are summarized below. Although these views have not yet been incorporated into national norms, they have practical guidance for our design work.
1) When power conversion is required between two power supplies, if the grounding type of the two power supply systems is different, or the wiring group of the power supply transformer winding is different, the neutral line should be disconnected and a four-pole switch should be used.
2) The IT system and the TT system should isolate the neutral line. It is forbidden to disconnect the PEN line in the TN-C system.
3) In the TN-S system, the neutral line does not need to be disconnected; the main switch of the low-voltage side of the transformer does not need to disconnect the neutral line; the incoming line of the external low-voltage power supply to the civil building should be isolated.性                                                 Resident users are single-phase loads, and bipolar switches can solve the problem.
4) The transfer switch between the normal power supply and the emergency backup generator power supply needs to use a four-pole switch that can disconnect the neutral line, and the two cannot be connected in parallel.
5) In Zone 1 where there is a risk of gas explosion and Zone 10 where there is a risk of dust explosion, in the special wet places such as swimming pools and baths, isolation appliances with neutral and phase lines should be installed.
6) In order to protect personal safety during maintenance and repair, an isolation appliance must be installed to isolate the neutral line potential that endangers personal safety.
In summary, there are various problems in the design of power distribution and distribution.
for reference only. Improper, please correct me
BIOTEPT 1/4 HP 3/4 hp. 1hp. 2hp General Purpose Motor, 3 phase, 1200 RPM, 208-230/460 V, 56C Frame, TEFC TENV ODP All acceptable
56 Frame Motor,56C Frame Single Phase Motor,56C Frame Motor ,56C Motor
Ningbo Biote Mechanical Electrical Co.,Ltd , https://www.biotept.com