Pre-set optimization of the transportation food site lighting system

1 lighting system power supply scheme

The terminal lighting network voltage is 380V/220V. The terminal low-voltage power supply system generally adopts the radial connection mode. The lighting load (this article refers to the lighting distribution box) is led out by the low-voltage bus. This paper summarizes the power supply methods of lighting loads into three types:

1) Special transformer for lighting - load type: When the lighting installation power is very large, or most of the lighting load is distributed far away, the protection sensitivity of the branch circuit switch is not easy to meet the requirements, or the load level of the grain terminal is very high, and the lighting load therein When it is very important, you can consider configuring a dedicated lighting transformer (see 1a); 2) Lighting cabinet-load type: When the lighting load is relatively large and there are many outlet circuits, in order to facilitate management and metering, the feeding circuit is taken from the low-voltage busbar to the dedicated Lighting distribution cabinet (see 1b), lighting power supply main line switch protection device and metering device; 3) direct load type: when the lighting load is relatively small, can not be measured, the small grain terminal can also be directly led out by the low voltage bus The feeder circuit goes to each lighting distribution box (see 1c).

The special transformer for lighting - the load-type power supply scheme avoids the impact of high-power impact loads that may exist in the power equipment on the lighting system. The independent feature of the lighting part relative to the power supply system is that the lighting system will not be affected when the power supply system is partially powered down due to a certain equipment failure. In fact, the lighting installation power of most small and medium-sized grain terminals will not be too large, and large grain terminals are often divided into several areas according to the process conditions, and several substations are installed in the power load centers of each area. Therefore, the lighting load is generally not transmitted over a long distance, thereby ensuring the protection sensitivity of the lighting branch circuit switch. At the same time, since the special transformer for lighting has increased the initial investment, this power supply scheme is not common in general grain terminals.

The direct load type power supply scheme is only applicable to small terminals with relatively small lighting loads and low requirements on lighting systems.

The lighting cabinet-load-type power supply scheme makes the lighting part self-contained system, the wiring structure is clear, the outlet is convenient and flexible, easy to manage and measure, and it is the most commonly used power supply mode for modern grain terminals.

In some grain terminals, there may be some lighting loads that are relatively large and relatively concentrated, and at the same time away from the distribution room. For example, a far-off grain outbound loading train system or a dock front grain unloading system can be considered at the work site. The lighting cabinet is responsible for the supply of lighting distribution boxes in the site area. At this time, the selection of the lighting cabinet is more strict, in addition to meeting the requirements of the lighting system capacity, short circuit protection, etc., it should also meet the restrictions of its environment and working conditions.

2 Special protection requirements for lighting equipment for grain terminals

Lighting equipment includes on-site lighting cabinets, lighting distribution boxes, lighting sources, lamps, lighting switches, sockets, and distribution boxes, lines, and the like. The equipment should be selected according to environmental conditions. Due to the foggy, windy and humid humidity of the terminal, the protection level of the lighting equipment is relatively high. It is usually required to reach IP55, and the equipment directly bearing the wind should be installed firmly.

The lighting area of ​​the grain terminal usually includes a grain transport corridor, a grain transfer machine room, a wharf front, a grain outbound operation area, a related power distribution station, and an auxiliary work area. According to the relevant regulations, agricultural products such as wheat, corn, sugar, flour and so on are flammable non-conductive dusts. During the process of loading, unloading, transportation, storage and processing, the diffused dust may explode when the concentration reaches the explosion limit.

Therefore, the working area of ​​the grain terminal is basically a dangerous environment for dust explosion. When designing the power supply lighting in the working area, it should be designed according to the requirements of this special environment. In particular, lighting equipment such as lighting cabinets and lighting distribution boxes should be dusted. For explosion-proof type, the cable should be clamped and sealed at the entrance and exit of the cable.

When the substation and the auxiliary area are far away from the grain operation area, the grain dust will not accumulate in a large amount, and its concentration will not reach the explosion limit; in the outdoor environment, due to the good natural ventilation conditions, the dust in the air is easily diffused and the concentration is also Do not reach the explosion limit. Therefore, these places in the grain terminal can be treated as non-explosive hazardous areas, and the protection of lighting equipment can not be selected as dust explosion-proof type.

3 lighting system wiring

3.1 Relationship between lighting power input mode and grounding mode of power supply system

There are three types of grounding methods for low-voltage power supply systems.

1) TT system -- indicates that the power supply end of the system is directly grounded. The outer casing of the electrical equipment is also directly grounded, and it is not directly related to any other grounding point in the system.

2) TN system -- indicates that the power supply terminal in the system is directly grounded, and the outer casing of the electrical equipment is directly electrically connected to the grounding point of the low voltage system.

The TN system is divided into a TN-C system (the neutral line and the protection line are combined), a TN-S system (the neutral line is separated from the protection line), and a TN-C-S system according to the combination of the neutral line and the protection line ( There are three types, such as the neutral line and the protective line part.

3) IT system --- means that all live parts of the power supply in the system are not grounded and the electrical equipment housing is directly grounded.

China's port terminal power supply system generally adopts TN-S system or TN-C-S system. As part of the power supply system, the grounding of the lighting system should be consistent with the overall power supply system of the terminal. Therefore, when the power supply system adopts the TN-S system, the power supply line of the lighting system is a three-phase four-wire system with a protective grounding wire, that is, 3P+N+PE, and a 5-core wire is selected; when the power supply system adopts the TN-C-S system, the lighting system The power supply line is a three-phase four-wire system, that is, 3P+PEN, and a 4-core wire is selected.

3.2 wire selection

According to the literature [3], in the dust explosion hazardous environment, the copper conductor wire should be selected for the electrical equipment wire; at the same time, considering that the salt spray erosion of the terminal is serious, and the corrosion resistance of copper is better than that of aluminum, the power supply system of the terminal is carried out. Copper conductors are often used when designing with lighting systems.

Another notable feature of the grain terminal is that the rat condition is more serious. In order to prevent damage caused by rat bites to the cable, the lighting power supply cable of the grain terminal usually uses armored cable, and the non-armored cable must be laid with steel pipe.

The choice of the cross section of the lighting system is similar to that of the power supply system. The following aspects need to be considered:

1) Meet the requirements of current carrying capacity -- the actual working temperature of the line does not exceed the allowable value, the calculated current of the line should be less than the long-term allowable working current of the wire (current carrying capacity); 2) meet the mechanical strength requirements --- should meet different conditions The minimum wire cross-section requirement allowed by the mechanical strength; 3) The requirement for voltage loss--the voltage loss of the line generally cannot exceed 5%. When the equipment is away from the outlet point of the lighting power supply, or the equipment that is not used frequently, the voltage loss The requirements can be appropriately relaxed; 4) meet the requirements of the sensitivity of the protection device--the selected wire cross-section must meet the requirements of the protection device operation when short-circuiting, that is, the lighting circuit of a certain length and a certain section, when the terminal lamp is short-circuited, The setting current of the protection equipment should be compatible with the short-circuit current; 5) The cross section of the neutral line -- when the lighting load is mostly the discharge of the gas discharge lamp, the neutral line section of the lighting line should satisfy the unbalanced current and harmonic The wave current requirement should not be less than the phase line cross section.

4 parts of lighting equipment selection

4.1 Choice of light source

The most common sources of light for terminal operations are fluorescent lamps and high-pressure sodium lamps. In some places where the vibration is small, the illumination is not high, and it may be frequently turned on, incandescent lamps with lower price and convenient installation can also be used; some ports also use metal halide lamps, such as process or other factors, which are special for light color. Requirements, or ample funds.

4.2 Selection and arrangement of luminaire protection

The choice of luminaires is one of the main tasks in the design of lighting systems. According to the protection requirements proposed in Section 2 of this paper, dust-proof explosion-proof lamps should be selected in dust transfer places such as grain transfer machine rooms and grain conveying corridors. The distribution box or chandelier box used should also be dust explosion-proof; In the substation of the substation or office building in the operation area, ordinary protective lamps can be used, but the protection level is generally required to be IP55 and above.

The arrangement of the luminaire determines the spatial position of the luminaire in the room, and it has a direct influence on the direction of light projection, the illumination of the working surface, and the uniformity of illumination. The following aspects are often considered when arranging lighting fixtures.

1) Rationality of luminaire layout--To determine the layout of the luminaire, first of all, the lighting method required by the production process should be examined.

Grain wharf operations usually only need general lighting, and uniform lighting can be selected, that is, the illumination distribution of the whole working surface is relatively uniform, and the interval and row spacing of the lamps are the same. When localized illumination is required, the luminaire can be added locally at the desired location to maintain sufficient brightness, i.e., selective lighting.

2) Installation method of the lamps--The installation methods of the lamps in the terminal work place are generally hoisting, wall mounting, ceiling mounting, platform pole mounting and high pole lamp installation. The choice of installation method is limited by the structure of the building. The hoisting or ceiling installation should be selected according to the height of the space and the layout of the process equipment. When the taller factory buildings are not suitable for hoisting and ceiling installation, wall installation is usually adopted. Determine the direction in which the light source is projected. The installation method should be based on the principle of not obstructing the production operation, avoiding the position conflict with the process equipment, and the shadow caused by the equipment in the illumination area should be avoided as much as possible.

3) The distance of the lamp from the wall--When multiple lamps are used together to illuminate a certain area, in order to ensure the uniformity of illumination, the distance between the lamps should not be too large, and the distance between the lamps and the wall should not be too far. Generally, the number of lamps of a certain power required in the area is calculated by illumination, and then evenly distributed. Usually the distance between the ceiling-mounted or ceiling-mounted luminaires to the wall is 1/2 to 1/3 of the distance between the lamps.

4) Suspension height of the luminaire -- Table 1 shows the minimum suspension height of the common luminaire under normal circumstances.

In fact, because the working area of ​​the terminal except the office space, the required illumination is relatively small, generally below 50lx, and subject to the existing building conditions, the minimum installation height of the lamps is sometimes less than the values ​​listed in Table 1. For example, the height of the cable interlayer is generally 2.2 meters, and the installation height is not higher than this value regardless of the type of lamp. However, the installed luminaires must not interfere with production work and pedestrian access.

5 Conclusion

In the design process of the lighting system of the grain terminal, in addition to considering the conventional design specifications, it is more important to strictly comply with GB-50058-92 "Code for Design of Electrical Equipment for Explosive and Fire Hazardous Environments" and GB4942.2-85 "Class of Protection for Low Voltage Electrical Enclosures" 》 and other standards and specifications, focusing on the field box, wiring device, cable seals, on-site testing devices and other outdoor devices in the explosion-proof area are selected according to the explosion-proof places to ensure the safety, stability and reliability of the grain terminal lighting system.

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