The rated current of the low-voltage power distribution cabinet is AC 50Hz, rated power 380v power distribution system for power, lighting and power distribution of electrical energy conversion and control. The product has strong breaking ability, good dynamic thermal stability, flexible electrical scheme, convenient combination, series, practicality and novel structure.
Main technical parameters of low voltage distribution cabinetWhen purchasing the low-voltage power distribution cabinet, the user should not only know the technical parameters such as the rated voltage, rated current, rated frequency, and cabinet size of the power distribution cabinet, but also pay attention to the following parameters:
(1) Maximum rated current of main bus: The rated value of the maximum current that can be carried by the main bus.
(2) Rated short-time withstand current: The rms value of the short-time withstand current that can be safely carried by a certain circuit in the complete equipment under the test conditions specified in the national standard GB7251.1-2005.
(3) Peak short-time withstand current: Under the test conditions specified in the national standard GB7251.1-2005, the circuit specified in the national standard GB7251.1-2005 specifies the peak current that the circuit can withstand satisfactorily.
(4) Enclosure protection rating: The degree of protection against access to live parts provided by the plant in accordance with IEC 60529-1989, as well as the intrusion of foreign solids and the entry of liquids. The specific classification is detailed in the IEC60529 standard.
(5) Internal separation method: According to the IEC60529-1989 standard, in order to protect personal safety, the switch cabinet is divided into several compartments in different ways.
(6) Functional unit form: According to the national standard GB7251.1-2005, the installation method of components in complete sets of equipment.
Low-voltage power distribution cabinets contain different components depending on the application and function. This article only briefly introduces the technical requirements of several commonly used components in the power distribution cabinet [2].
(1) Basic requirements:
The upper limit of the ambient temperature is provided; the size of the exterior is miniaturized; the size of the installation is modularized, the installation method is diversified; the function is modularized, and the assembly is integrated to facilitate function increase and decrease and shorten the maintenance time.
(2) Requirements for circuit breakers:
First of all, to have high breaking capacity, the breaking capacity of the low-voltage power distribution cabinet is based on the breaking capacity of the main bus. Secondly, it is required to be installed left and right, and the direction of the incoming and outgoing lines can be interchanged; it has three-stage protection and grounding protection functions, with unbalanced load display, fine resolution of accidents, early warning and alarm functions; memory function is required, and the number of operations can be automatically recorded. And the number of short circuit work, the accessories are complete. Third, there are mechanical interlocks, interlocks between switches, interlocks between switches and cabinet doors; accessories are modular in function; in multi-level protection, regional selective interlocking is required, and pre-stage protection and backup protection are step-by-step. Interlocking to achieve timing interlock trip; Fourth, the installation method is diversified, and there are power, test and extraction position display.
(3) Requirements for AC contactors
With a variety of functional modules, it can adapt to the needs of various current specifications, can be built with modular installation; improve the ability to withstand overload current and breaking capacity; improve the ability to withstand high temperatures, the contactor should be reliable at high ambient temperatures Action characteristics.
(4) Requirements for thermal relays
With three-phase balance, unbalanced overload and continuous phase protection. There are manual, automatic reset function and trip display function; limit its own heat consumption; expand the temperature compensation range.
In order to prevent the misuse of low-cost components and affect the performance of the power distribution cabinet in the future, it is best to indicate the model specifications and brand of the main components such as the frame, circuit breaker and transformer used when ordering. At the same time, in the process of technical disclosure, it is sometimes necessary to accept the rationalization proposal of the manufacturer to avoid the use of technical indicators that far exceed the distribution load requirements, resulting in unnecessary investment, material waste and maintenance costs.
Selection of low voltage distribution cabinet1) The main technical parameters of the low-voltage power distribution cabinet, and choose according to actual needs.
The best choice of low-voltage power distribution cabinet, in addition to clearing the rated voltage, rated frequency and rated current parameters, such as the size of the cabinet should also pay attention to the following: maximum rated current value, rated short-time resistance current, peak current, short-tolerance functional unit Form, interior space, enclosure protection rating, and more. These references to all relevant standards must be strictly in accordance with the standard selection, and the value cannot be selected to meet the engineering requirements.
2) Clearly require important components of low voltage distribution cabinets. First of all, the most basic requirements. The function module block is simple to assemble, and the cabinet's position is modularized and miniaturized. The installation method is diversified and the installation size provides the operating temperature limit.
Second, the circuit breaker. High breaking capacity, can control installation, allow switching to the exit, ground fault protection function, three protection and protection functions, memory function, can display unbalanced load, early warning function, accident alarm, attachment is a high;
In addition, you must have an interlock switch between, switch cabinet door interlock, mechanical interlock, interlock protection front level, backup protection interlock, zone selective interlock, step by step sequence chain trip, etc. But the functionality of the accessory function is modular.
AC contactors have many functional modules that meet current requirements and can be modularly installed to improve the ability to withstand overload currents and damage. Improve high temperature resistance. Contactors should be reliable in high temperature environments. Action characteristics.
1, the role of the power distribution screen
The role of the power distribution panel is mainly to distribute power and distribute the voltage across the transformer to each power unit. The low-voltage power distribution panel is used to assemble low-voltage primary and secondary equipment according to a certain wiring scheme, and is used for power and lighting power distribution in low-voltage power distribution systems.
2, the main components of the power distribution screen
The power distribution panel is mainly composed of an incoming line cabinet, an outlet cabinet, a capacitor cabinet, a metering cabinet, and the like.
Incoming cabinet: Also known as the receiving cabinet, it is used to receive power from the grid (from the incoming line to the bus), and is generally equipped with circuit breakers, CT, PT, isolation knives and other components.
Outlet cabinet: also called feeder cabinet or power distribution cabinet, is the equipment used to distribute electric energy (from bus to each outlet), and is generally equipped with circuit breaker, CT, PT, isolation knife and other components.
Busbar connection cabinet: also called busbar branching cabinet, which is used to connect two busbars (from busbar to busbar). In single busbar section and double busbar system, busbar contact is often used to meet different operating modes. The requirements or guarantees a selective removal load in the event of a fault.
PT cabinet: The voltage transformer cabinet is usually installed directly on the busbar to detect the bus voltage and realize the protection function. Mainly installed voltage transformer PT, isolation knife, fuse and lightning arrester. Isolation cabinet: It is used to isolate the busbars at both ends or to isolate the power receiving equipment from the power supply equipment. It can provide the operator with a visible end point for maintenance and maintenance work. Since the isolation cabinet does not have the ability to break and switch the load current, the handrail of the isolation cabinet cannot be pushed and pulled in the case that the circuit breaker with which it is fitted is closed. In general applications, it is necessary to set the interlock between the auxiliary contact of the circuit breaker and the isolated handcart to prevent the operator from misoperation.
Capacitor cabinet: also called compensation cabinet, is used to improve the power factor of the power grid, or reactive power compensation, the main components are the group of capacitor banks, switching control loops and fuses in parallel. Use electrical appliances. Generally installed side by side with the incoming line cabinet, one or more capacitor cabinets can be operated side by side. After the capacitor cabinet is disconnected from the grid, since the capacitor bank needs a period of time to complete the discharge process, it is not possible to directly touch the components in the cabinet, especially the capacitor bank; within a certain period of time after the power is cut off (according to the capacitor bank) Depending on the size of the capacity, such as: 1 minute), re-closing is not allowed to avoid overvoltage damage.
Capacitor. When making automatic control functions, it is also necessary to pay attention to the reasonable number of switching times of each group of capacitor banks, so as to avoid a group of capacitors being damaged, while other groups are rarely switched.
Metering cabinet: mainly used for metering electric energy (kilowatt hours), high voltage and low voltage. Generally installed with isolating switch, fuse, CT, PT, active energy meter (traditional meter or digital meter), no Power meters, relays, and some other auxiliary secondary equipment (such as load monitors, etc.).
3, the internal wiring of the power distribution screen
Considering the scope of protection, the connection order of the primary equipment and the outlet cabinet is different. The connection sequence of the primary equipment in the incoming cabinet is the busbar cutter, CT, switch, and line knife gate. The connection order of the primary equipment in the outlet cabinet is the busbar switch, switch, CT, and line knife gate. The connection sequence of the secondary equipment of the outlet cabinet is circuit breaker, fuse, relay, contactor, and electrical equipment.
4, common control loop
Under normal circumstances, the circuit breaker QF is closed by the duty officer, and the start and stop of the motor can be operated on the field operation column. The switch in the field operation column has a set of normally open and normally closed electric shocks. The stop signal (red light) is connected by the normally closed electric shock of the transfer switch and the normally closed electric contact of the contactor KM. Therefore, when the motor stops, the red light is on. Press the start switch, the start signal light (green light) is on, the attracting coil of the contactor KM (composed of two normally open electric shocks, one normally closed electric shock) is turned on, the main contact is closed, and the motor M is connected to the three-phase power supply. At the same time, KM's normally closed auxiliary contact is disconnected, the red light is extinguished, KM's normally open electric shock is closed, and the KM's attracting coil is kept energized (when the hand leaves the button), the motor continues to run, achieving "self" Lock" function.
1: Low-voltage switchgear and control equipment are commonly known as low-voltage switchgear, also known as low-voltage switchgear. It refers to complete electrical installations with AC and DC voltages below 1000V.
2: China's low-voltage power distribution cabinet market has maintained rapid growth with the development of smart grids, infrastructure construction, manufacturing investment and the development of new energy industries.
3: Monitoring data shows that in 2010, the total sales of China's low-voltage power distribution cabinet market was 10.633 billion yuan, an increase of 11.2%; in 2011, the overall sales of China's low-voltage power distribution cabinet market reached 11.96 billion yuan, an increase of 12.5%.
4: Under the environment of high demand for low-voltage power distribution cabinets in China, the internal competition of the industry will intensify. Suppliers providing a new generation of low-voltage complete sets of equipment and system solutions will gain opportunities in the future market competition. With the above characteristics, we can win certain advantages in the future competition, so as to seize the commanding heights of the fourth generation of low-voltage electrical products.
Low voltage distribution cabinet wiring1. Site selection: In order to ensure the normal and safe operation of the low-voltage power distribution cabinet, the position of the low-voltage power distribution room should be close to the load center. Do not place dust or corroded media in the place where it is placed. Otherwise, it should be cleaned in time to ensure safety and environment. It is best to be dry and place as far as possible without vibration.
2. Arrangement of power distribution equipment: The power distribution equipment of the low-voltage power distribution room must be arranged under the premise of safety, reliability, application and economy, and it is also convenient to install, operate, transport, overhaul, test and monitor. Appropriate distances and access to the passages must be left between the high and low voltage electrical equipment in the same room and the power distribution cabinets arranged in rows. The necessary safety measures should be taken when arranging the power distribution equipment. If the dangerous potential is bare, it should be shielded or placed outside the reach of the person. When it is difficult to use the visor and the cover, the barrier can be used for protection.
3. The layout of the distribution line should meet the following conditions: meet the environmental characteristics of the location, conform to the characteristics of the building, consider the distance between the person and the line should be moderate, consider the electromechanical stress that may occur due to the short circuit, and consider the installation and use. The wiring may be subject to other stresses and the weight of the wires during the process.
4. What are the factors that affect the layout of the distribution line: prevent external heat from affecting the use, prevent the influent from affecting the use, prevent external mechanical damage from affecting the use, prevent the use of falling ash on the wiring, and prevent the use of strong radiation.
(1) Equipment requirements
1) The appearance of the cabinet (disc) should be inspected without damage and deformation, and the paint should be intact. Internal inspection of the cabinet (disc): electrical equipment and components, insulating porcelain parts are complete, no damage, cracks and other defects.
2) Before installation, check whether the distribution box number is consistent with the installation position, and check the box number and the circuit number inside the box according to the design drawings. The grounding of the door should be made of soft copper braided wire and special terminal block. The wiring inside the box should be neat and meet the requirements of design requirements and acceptance specifications (GB50303-2002).
(2) Working conditions
The civil works of the installation box of the distribution box shall have the basic conditions for the completion of the internal painting and the installation of the doors and windows. The buried pipeline and the embedded parts should be cleaned up; the site has transportation conditions to keep the road smooth and smooth.
(3) Distribution box positioning
According to the design requirements, determine the location of the distribution box and the actual equipment installation on site, and locate the elastic line according to the outer dimensions of the box.
(4) Basic steel installation
1) Prefabricated and processed basic steel frame according to the requirements of the drawings, and do anti-corrosion treatment. Place the prefabricated basic steel frame on the reserved iron piece according to the position marked on the construction drawing, leveling and aligning the basic steel. The frame, the embedded iron parts and the gasket are welded and welded firmly. Finally, the top of the basic steel should be 10mm higher than the flat surface.
2) Basic steel grounding: After the basic steel is installed, the grounding wire should be welded to both ends of the basic steel. The welding surface is twice the width of the flat steel, and then connected to the grounding bar of the cabinet. And do anti-corrosion treatment.
(5) Distribution cabinet (disk) installation
1) Cabinet (disc) installation: According to the layout of the construction drawing, the power distribution cabinets should be placed one by one on the basic section steel. The vertical adjustment of the cabinet surface and the side of the cabinet (disk) can be solved by adding the iron, but not more than three pieces, and the welding is firm. After each row of cabinets (discs) is in place, the level and panel deviation of the cabinets should be adjusted and adjusted to meet the construction specifications.
2) The wall-mounted distribution box can be fixed to the wall by expansion bolts, but the hollow brick or block wall should be pre-embedded with dovetail bolts or fixed by pulling bolts.
3) The installation of the distribution box should be pre-embedded, and the rear panel should be level with the wall.
4) After the adjustment of the cabinet (disc), apply the bolts to fasten the cabinet to the basic section steel.
5) Cabinet (disk) grounding: Each cabinet (disk) is connected to the basic steel separately. The copper wire can be reliably connected with the grounding bolt and the spring washer can be used for anti-loose treatment. Each cabinet door should be reliably connected to the PE row by a copper braided wire.
6) The top of the cabinet (disc) is connected with the busbar. Note that the busbar supporting wrench should be used for fastening according to the requirements. The contact surface should be coated with neutral Vaseline. When connecting the busbars between cabinets, please pay attention to whether the busbars are too close to other devices or housings, and pay attention to the correct phase.
7) Control circuit check: It should be checked whether the line is loosened due to transportation and other factors, and tightened one by one, and the electrical components are damaged. In principle, the cabinet (disc) control line is verified at the factory, and the line inside the cabinet should not be adjusted privately. If problems are found, contact the supplier.
8) After the control line is calibrated, each core wire is circled and connected to each terminal plate with galvanized screws, eye circles and spring pads. One terminal on each side of the terminal block is usually pressed by one wire, and the maximum number of wires cannot be more than two, and the eyelets are added between the two wires. Multi-strand lines should be tinned, and no breaks are allowed.
(6) Cabinet (disk) test adjustment
1) The high voltage test shall be carried out by a test unit licensed by the local power supply department. The test standards are in line with national regulations, local power supply department regulations and product technical data requirements.
2) Test content: high voltage cabinet frame, bus bar, lightning arrester, high voltage porcelain bottle, voltage transformer, current transformer, various switches, etc.
3) Adjustment content: overcurrent relay adjustment, time relay, signal relay adjustment and mechanical interlock adjustment.
4) Secondary control small line adjustment and simulation test, tighten all the terminal screws again.
5) Insulation test: Test the resistance of each circuit at the terminal board with a 500V insulation resistance tester. The resistance must be greater than 0.5MΩ.
6) If there are transistors, integrated circuits or electronic components in the secondary small-line circuit, use a multimeter to test whether the circuit is connected.
7) Turn on the temporary control power and operating power; remove the upper phase of the control and operation power circuit fuses in the cabinet (disk) and connect the temporary power supply.
8) Simulation test: Simulate test control, interlocking, operation, relay protection and signal action according to the requirements of the drawings, which are correct, sensitive and reliable.
9) Remove the temporary power supply and reset the removed power cord.
(7) Conditions for power transmission operation
1) The installation work should be completed, and the quality inspection department checks all the qualifications. The test items are all qualified and have a test report.
2) The electroscope, insulating boots, insulated gloves, temporary grounding braided copper wire, insulating rubber pad, powder fire extinguisher, etc. for testing shall be prepared.
3) Check for any debris left on the busbar or equipment.
4) Do a good job in the organization of the test run, and clarify the test run commander, operator and guardian.
5) Clean the equipment and dust in the power distribution room and control room. Clean the appliance and instrument components with a vacuum cleaner.
6) The relay protection action is sensitive and reliable, and the actions of control, chain, and signal are accurate.
(8) Power transmission
1) After passing the inspection by the power supply department, the power is sent into the building, and the electricity is checked and the phase is correct.
2) The installation unit is connected to the line cabinet switch to check whether the three-phase voltage of the voltmeter on the PT cabinet is normal.
3) Combine the transformer cabinet switch to check if the transformer has electricity.
4) Connect the low-voltage cabinet inlet switch to see if the voltage of the three-phase voltage meter is normal.
5) Power is sequentially supplied in the above order.
6) In the low-voltage communication cabinet, perform the in-phase check on the upper and lower sides of the switch (the switch is not in the closed state). Use a voltmeter or multimeter voltage file 500V, use the net stylus of the watch to contact the two phases of the same phase. At this time, the voltmeter has no reading, indicating that the two circuits are in the same phase. In the same way, check the other two phases.
7) Acceptance: The power supply runs for 24 hours without any abnormality, and the procedures for acceptance are accepted and submitted to the construction unit for use. At the same time, submit technical information such as change negotiation records, product certification, instructions, test report forms.
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