What are the Classifications of Electrical Panel Boxes? Classification of Electrical Panel Boxes

The electrical panel box is an electrical equipment with small size, easy installation, special technical performance, fixed position, unique configuration function, not limited by the site, widely used, stable and reliable operation, high space utilization, less land occupation and environmental protection effect specialty.

The massive parameters on the data of the electrical panel box generally constitute a low-voltage electrical panel box. During normal operation, the circuit can be connected or disconnected by means of a manual or automatic switch.

1. The purpose of the electrical panel box

The electrical panel box has the characteristics of small size, easy installation, special technical performance, fixed position, unique configuration function, not limited by the site, widely used, stable and reliable operation, high space utilization rate, less land occupation and environmental protection effect. It is the control center that directs the various components in the power supply line to distribute power reasonably. It is the control link that reliably receives the upper-end power supply and correctly feeds out the load power. It is also the key to obtain whether the user is satisfied with the power supply quality. Improving the operational reliability of the power electrical panel box is the goal of creating high-quality projects.

The purpose of the electrical panel box: to distribute electric energy reasonably, and to facilitate the opening and closing operation of the circuit. It has a high level of safety protection and can intuitively display the conduction state of the circuit.

2. Classification of electrical panel boxes

Commonly used electrical panel boxes are made of wood and metal. Because the protection level of metal electrical panel boxes is higher, metal is still used more.

2.1 Classified by structural features and uses:

2.1.1 Fixed panel switchgear, often called switchboard or power distribution panel. It is a kind of open switchgear covered by a panel. The front has a protective effect, and the back and sides can still touch the live parts. The protection level is low, and it can only be used in industrial and mining enterprises with low requirements for power supply continuity and reliability. Centralized power supply for transformer room.

2.1.2 Protective (closed) switchgear refers to a low-voltage switchgear whose sides are closed except for the installation surface. The electrical components such as switch, protection and monitoring control of this cabinet are all installed in a closed shell made of steel or insulating material, which can be installed on the wall or away from the wall. There may be no isolation measures between each circuit in the cabinet, or a grounded metal plate or insulating plate may be used for isolation. Usually the door is mechanically interlocked with the main switch operation. In addition, there is also a protective table-type switchgear (that is, the console), and the control, measurement, signal and other electrical appliances are installed on the panel. The protective switchgear is mainly used as a power distribution device on the process site.

2.1.3 Drawer type switchgear. This kind of switch cabinet is made of steel plate to make a closed shell, and the electrical components of the incoming and outgoing circuit circuits are all installed in drawers that can be drawn out to form a functional unit that can complete a certain type of power supply task. The functional unit is separated from the bus bar or cable by a grounded metal plate or a plastic functional plate to form three areas: bus bar, functional unit and cable. There are also isolation measures between each functional unit. Drawer-type switchgear has high reliability, safety and interchangeability, and is a relatively advanced switchgear. Most of the switchgears refer to drawer-type switchgears. They are suitable for industrial and mining enterprises and high-rise buildings that require high reliability of power supply, as a centralized control power distribution center.

2.1.4 Power and lighting distribution control box. Most of them are closed vertical installations. Due to different use occasions, the enclosure protection level is also different. They are mainly used as power distribution devices in the production sites of industrial and mining enterprises.

2.2 Structure: There are two types of electrical panel box structures

2.2.1 Welding structure: Simply cut, bend, open holes and weld the sheet metal parts.

2.2.2 Assembled structure: The sheet metal parts are processed separately, and each part is assembled after processing, reinforced and locked with screws and tees. The appearance is beautiful, the operation is simple, and a lot of transportation costs can be saved.

electrical panel boxes and cabinets, distribution boards, distribution panels, electrical cabinets, etc., are complete sets of equipment for centralized installation of switches, meters and other equipment.

3. The principle of the electrical panel box

Power electrical panel box is assembled in closed or semiclosed metal safe by electrical wiring requirement by switchgear, measuring instrument, protective device and auxiliary equipment or on screen width, forms low-voltage electrical panel box. During normal operation, the circuit can be connected or disconnected by means of a manual or automatic switch. Cut off the circuit or alarm with the help of protective electrical appliances in case of failure or abnormal operation. Various parameters in operation can be displayed by means of measuring instruments, and some electrical parameters can also be adjusted to prompt or send out signals for deviations from normal working conditions.

4. Common faults of the electrical panel box

4.1 Reason

4.1.1 Faults caused by the influence of ambient temperature on low-voltage electrical appliances
The low-voltage electrical appliances in the electrical panel box are composed of fuses, AC contactors, residual current action protectors, capacitors and meters. The upper limit of the ambient air temperature shall not exceed 40°C; the average value of the ambient air temperature for 24 hours shall not exceed 35°C; the lower limit of the ambient air temperature shall not be lower than -5°C or -25°C.

The electrical panel box transformed from the rural power grid operates outdoors. It is not only exposed to direct sunlight to generate high temperature, but also generates heat itself during operation. Therefore, in the midsummer high temperature season, the temperature inside the box will reach above 60°C. The temperature greatly exceeds the ambient temperature specified for these appliances.

4.1.2 Failure caused by product quality
During the transformation of the rural power grid, due to the large number of electrical panel boxes required and the short construction period, the electrical panel box factory needed to supply low-voltage electrical appliances in a short time and in large quantities. Some products failed shortly after being put into operation. For example, some types of AC contactors cannot operate due to the burnout of the contactor closing coil shortly after the electrical panel box is put into operation.

4.1.3 Faults caused by improper selection of electrical appliances in the electrical panel box
Due to the inappropriate selection of AC contactor capacity during manufacture, AC contactors of the same capacity are installed for different outlet circuits, and the unbalanced three-phase load is not considered, and the current level of some outlet contactors cannot be adjusted to normal On the basis of the selected model, increase the selection of a current level.

4.2 Improve

4.2.1 For the electrical panel box with a distribution transformer capacity of 100kV·A and above, it should be considered to install a temperature control relay (JU-3 or JU-4 ultra-small temperature relay at the side wall of the heat dissipation window in the box) ) and an axial flow fan, which are installed on the box on the left side above the control electrical panel, so that when the temperature in the box reaches a certain value (such as 40°C), the exhaust fan can be automatically activated to forcibly discharge heat to dissipate heat from the box.

4.2.2 Use a protection circuit to prevent the occurrence of external circuit failures powered by the electrical panel box. Choose a smaller intelligent phase loss protector, such as the DA88CM-II motor phase loss protection module (Shanghai product) installed in the electrical panel box to prevent the motor from being burned due to low-voltage phase loss operation.

4.2.3 Improve the wiring mode of the low-voltage capacitor bank of the original electrical panel box, and change its installation position from the pile head of the AC contactor to be connected between the low-voltage incoming line of the electrical panel box and the meter. To prevent the inaccurate measurement of the metering device due to a phase failure of the capacitor circuit during operation or damage to the capacitor. In addition, the capacitor selection model should be BSMJ series products to ensure reliable quality and safe operation of components.

4.2.4 If the distribution rack on the pole is added, when making the electrical panel box shell, the stainless steel plate with a thickness of 2mm can be selected, and the size of the electrical panel box will be enlarged in proportion (JP4—100/3W used in the agricultural reform project) On the basis of the type, the size of the width direction of the original box is increased by about 100mm, that is, the original 680mm is changed to 780mm. The overall size of the improved electrical panel box is: 1300mm×780mm×500mm), in order to increase the distance between the outgoing lines of each branch, The electrical safety distance between the outgoing line and the box shell is conducive to the operation and maintenance of agricultural electricians and the replacement of fuses, and it can also dissipate heat.

4.2.5 Select an energy-saving AC contactor (similar to CJ20SI type) products, and pay attention to the AC contactor coil voltage is connected to the corresponding terminal of the selected remaining current-operated protector, and pay attention to correct load matching. When selecting an AC contactor, you should choose a product with an insulation class of A and above, and you must ensure that the rated current of the main circuit contact should be greater than or equal to the load current of the controlled line. The rated voltage of the electromagnetic coil of the contactor is 380V or 220V.

4.2.6 Selection of residual current action protector. Products that meet the standard of GB 6829 "General Requirements for Residual Current Operated Protectors" and have been certified by China Electrical Product Certification Committee must be selected. A power-saving and low-sensitivity time-delay protector similar to LJM (J) series can be selected. The way of the protector device must comply with the national GB13955-2005 "Installation and Operation of Residual Current Action Protection Device" standard. The breaking time of the leakage protector, when the leakage current is the rated leakage current, its action time should not be greater than 0.s.

4.2.7 Low-voltage cables are used for the incoming and outgoing lines of the electrical panel box, and the selection of cables should meet the technical requirements. For example, the incoming lines of the electrical panel boxes of 30kVA and 50kVA transformers use VV22-35×4 cables, and the branch outgoing lines use VLV22-35×4 cables of the same specification; the incoming lines of the electrical panel boxes of 80kVA and 100kVA transformers respectively use VV22-50 ×4, VV22-70×4 cables, VLV22-50×4 and VLV22-70×4 cables are used for the branching lines respectively, and the cables are crimped with the copper-aluminum wiring nose and then connected with the wiring pile head in the electrical panel box with bolts.

4.2.8 Selection of fuses (RT, NT type). The rated current of the total overcurrent protection fuse on the low-voltage side of the distribution transformer should be greater than the rated current on the low-voltage side of the distribution transformer, generally 1.5 times the rated current, and the rated current of the melt should be in accordance with the allowable overload multiple of the transformer and fusing The device characteristics are determined. The rated current of the melt of the overcurrent protection fuse of the outlet circuit should not be greater than the rated current of the total overcurrent protection fuse. The rated current of the melt is selected according to the normal maximum load current of the circuit, and should avoid the normal peak current.

4.2.9 In order to analyze the reactive power of the rural low-voltage power grid, a DTS (X) series active and reactive two-in-one multifunctional electric energy meter (installed on the side of the meter board) is installed in the box for replacement Three single-phase watt-hour meters (DD862 series meters) were originally installed to facilitate online monitoring of loads.

5. Product selection of electrical panel box

There are many types of power distribution cabinets in the domestic power supply and distribution system, and their cabinet structures and technical parameters are different. Under the influence of the following factors, the designed drawings often need to be modified or even redesigned, which not only affects the construction plan of the power supply and distribution system, but also brings certain pressure to the power distribution cabinet manufacturers to complete the production of the power distribution cabinet on time and with high quality. troubled.

5.1 The factors affecting the change of the designed drawings are as follows:
5.1.1 Manufacturers of power distribution cabinets recommend products produced by themselves to users that may not be suitable for users.
5.1.2 The Design Institute does not know much about some newly launched cabinet types, but designs according to user requirements.
5.1.3 Users don't know their needs very well, so they can't choose according to their needs when choosing a cabinet type.

In order to solve the above problems and meet the needs of users, select the specific model of the power distribution cabinet more accurately. The following is an analysis of the characteristics of the low-voltage power distribution cabinets commonly used in the domestic power supply and distribution system.

The cabinet structure and technical parameters of the above-mentioned imported distribution cabinets are analyzed below.

The main feature of domestic distribution cabinets is that the specific models of the same type of distribution cabinets produced by domestic manufacturers are inconsistent, and the specific structure of the distribution cabinets is also different. The main electrical components installed in the distribution cabinets can be imported well-known brands or can be imported. For domestic brands.

5.2 The relevant technical parameters are described below.

5.2.1 The maximum rated current of the main busbar: the rated value of the maximum current that the main busbar can carry.
5.2.2 Rated short-time withstand current: given by the manufacturer, a certain circuit in the complete set of equipment can safely carry the root-mean-square short-time withstand current under the test conditions specified in 8.2.3 of the national standard GB7251.1-2005 value.
5.2.3 Peak short-time withstand current: Under specified test conditions, the manufacturer specifies the peak current that the circuit can withstand satisfactorily.
5.2.4 Enclosure protection level: according to the IEC60529-1989 standard, the complete set of equipment provides the level of protection against touching live parts, as well as the intrusion of foreign solids and the ingress of liquids. Please refer to the IEC60529 standard for specific classification.
5.2.5 Internal separation method: According to the IEC60529-1989 standard, in order to protect personal safety, the switchgear is divided into several compartments in different ways.

The technical parameters of different types of distribution cabinets are very different, and the technical parameters of imported distribution cabinets are basically better than domestic distribution cabinets, but it cannot be considered that imported distribution cabinets are necessarily better than domestic distribution cabinets. .

5.3 Based on the actual work experience, the following points are discussed:

5.3.1 Imported power distribution cabinets are developed abroad and are generally sold for the global power supply and distribution market. Since each country has different requirements and habits for power supply and distribution systems, imported power distribution cabinets may not be fully applicable to the domestic market.

5.3.2 The main electrical components used in imported power distribution cabinets are all imported brand products, and some cabinets or some cabinet accessories must be imported from abroad, so that the price of imported power distribution cabinets is generally higher than that of domestic power distribution cabinets a lot of.

5.3.3 Although the technical parameters of imported distribution cabinets are very high, in most cases only a part is used, or even cannot be used at all. For example, the number of circuits that can be installed in one cabinet of imported distribution cabinets is more than that of domestic distribution cabinets, but that can only be achieved on the premise of reducing the circuit capacity, which cannot meet the needs of users in most cases.

5.3.4 Although the technical parameters of domestic power distribution cabinets are lower than those of imported ones, they can already meet the needs of users in most domestic power supply and distribution systems.

5.3.5 Regarding the quality of the distribution cabinets, as long as the manufacturers strictly follow the requirements of 3C for production and inspection, the quality of domestic distribution cabinets is not necessarily inferior to that of imported distribution cabinets.

5.4 In summary, when selecting the model of the power distribution cabinet, the following points should be done:

5.4.1 Understand the user's needs, and choose the most suitable cabinet type for the user according to the actual situation.
5.4.2 Try to use the domestic cabinet type of well-known domestic manufacturers, and you cannot blindly choose imported distribution cabinets with relatively high technical parameters, which will easily cause waste of resources.
5.4.3 Because the brands of the main components used in the imported distribution cabinet are consistent with the cabinet body. Therefore, when choosing an imported distribution cabinet, attention should be paid to the parameters of the main components, which must be able to meet the needs of users.

6. Precautions for electrical panel box

6.1 The construction power distribution system shall be equipped with a main electrical panel box, a electrical panel box, and a switch box, and shall be set in stages according to the order of "general-divided-open" and form a "three-level power distribution" mode.

6.2 The installation position of each electrical panel box and switch box of the power distribution system for construction shall be reasonable. The main electrical panel box should be as close as possible to the transformer or external power supply to facilitate the introduction of power supply. The electrical panel box should be installed as far as possible in the center of the relatively concentrated electrical equipment or loads to ensure that the three-phase loads remain balanced. The installation position of the switch box should be as close as possible to the electrical equipment it controls according to the site conditions and working conditions.

6.3 To ensure the three-phase load balance of the temporary power distribution system, two power circuits should be formed for power consumption and lighting power consumption on the construction site, and power electrical panel boxes and lighting electrical panel boxes should be installed separately.

6.4 All electrical equipment on the construction site must have their own dedicated switch boxes.

6.5 The cabinets and internal settings of electrical panel boxes at all levels must comply with safety regulations. Switching appliances should be marked with purpose, and the cabinets should be numbered uniformly. The power electrical panel box that is out of use should be cut off and the door locked. The fixed electrical panel box shall be provided with a fence, and measures shall be taken to prevent rain and smashing.

6.6 The difference between electrical panel box and distribution cabinet. According to GB/T20641-2006 "General Requirements for Empty Shells of Low-Voltage Switchgear and Control Equipment", electrical panel boxes are generally used in households, while distribution cabinets are mostly used in centralized power supply, such as industrial electricity and building electricity etc. Both the electrical panel box and the distribution cabinet are complete sets of equipment, the electrical panel box is a low-voltage complete set of equipment, and the distribution cabinet has high voltage and low voltage.