Application Practices on the Design of Power Supply System in Outdoor Lighting System Liu Shuilong, Shashan Coal and Electricity Group Corporation, Xiqu Mine, Taiyuan 030002, China) Selection of power supply lines, selection of power supply system standards, and new control methods in lighting systems.
â€•01â€•06 Author Liu Shuilong male 38-year-old engineer 01: A common lighting design is the lighting of roads, squares, open-air goods, etc. The function is to ensure the safety of people in the dark, to meet the normal outdoor activities and work. Claim. There are many contents involved in outdoor lighting design, the most important of which is the power supply and distribution system. Due to the different uses of outdoor lighting and different places, the design content should be different.
1 power supply line due to low-voltage power supply has the advantages of small engineering volume and low investment. At present, most of the street lamps in China use low-voltage power supply. According to China's power supply situation and the use requirements of different places, the national regulations have stipulated the voltage deviation of the lighting power supply. In order to ensure the life of the light source, the terminal voltage of the street lamp must not exceed 105% of its rated voltage. In the industrial enterprise lighting design standard GB5003492, the requirements for industrial and mining enterprises' roads are that the voltage is not less than 90% of the rated value. The urban road lighting is based on the requirements of urban road lighting design standard G4591, from the reliability of power supply and energy saving. From the perspective of the point of view, it is advisable to use 10KV distribution line to connect the special transformer for road lighting, the optimal load factor is 70%, the end voltage requirement of the lighting line is the same as above; for the road lighting line powered from the common transformer, the terminal voltage It must not be lower than 95% of the rated value. Therefore, when designing road lighting supply and distribution lines, the voltage loss calculation of the line should be carried out according to different technical conditions, so that the power supply and distribution network has certain conditions under the premise of meeting the plan. The redundancy, the terminal voltage meets the above requirements, and the line section is economically reasonable.
With the development of economic construction, the use of underground direct buried cables for road lighting has been the most common laying method. The advantages of direct distribution of distribution lines are obvious, high heat dissipation, high current carrying capacity, and parallel distribution capacitance between the cores of the cable. On the line. It can improve the natural power factor without being affected by the climate, reduce the damage of external forces, and improve the reliability of power supply. In addition, buried cables help the environment to be more aesthetically pleasing. Therefore, the national regulations stipulate the use of underground cables to power road lighting in the case of technical and economic conditions. In addition, from the perspective of energy saving, road lighting fixtures use more gas discharge lamps, and the neutral line section of the three-phase four-wire power supply line should be selected according to the maximum one-phase current.
In the actual design process, the common load torque table for the verification of the street lamp line is simplified. The load torque table in the current design manual lists fewer cases of direct cable burying, especially the cross-linked cable widely used in recent years. Compared with other lines, the price of the cable is relatively high. Therefore, it is particularly important to select a reasonable cable type. In the power supply network of road lighting, the street lamp load is spaced at a certain distance and is substantially evenly distributed on the line, for its end. The voltage drop is obviously not accurate enough to be calculated by the load torque meter, and the computer's analysis and calculation of the lighting distribution network can quickly and quickly check the voltage loss at the end of the line according to different environmental conditions. If a high-intensity discharge lamp is used, the voltage loss value of the line should also be checked according to the starting and restart characteristics. So, for the distribution of road lighting. Especially for the end load far from the power supply, after determining the specific line and laying method, the necessary analysis and calculation should be carried out in combination with the environmental conditions to optimize the design of the road lighting power supply and distribution line to ensure the reliability of the power supply and the service life of the lamp.
2 line practice protection measures Because of the vulnerability to outdoor open air environment factors such as day and night temperature difference, wind blowing and sun and rain, road lighting devices and lines are prone to failure, so limit the fault range. National regulations require that each street light be equipped with a separate fuse protection, and the corresponding protection should be installed on the power supply line. The general requirements for distribution lines in the design specification of low-voltage power distribution GB50054 95 are short-circuit protection and load protection. Outdoor lighting lines do not require overload protection. However, overload protection should be installed for lines in explosion and fire hazard areas. To prevent excessive temperature rise due to insulation failure.
The current national regulations have gradually been consistent with the IEC standards, so the requirements for preventing direct and indirect contact with electrical installations are more stringent. In addition to short-circuit and overload protection to ensure the safety of lighting equipment, in order to protect the safety of personnel, ground fault protection should also be adopted. Ground fault refers to the short circuit between phase-to-ground or ground-connected conductors. For cable circuits laid underground, it is common to damage the electrical insulation, resulting in phase and PE/PEN lines, exposed conductive parts and A short circuit occurs between the earth, a short circuit occurs between the conductive part of the street lamp and the earth, and a fault voltage is formed between the conductive part of the street lamp and the ground or other grounded conductive part, causing the electric shock or sparking of the person to cause a fire or explosion. . Measures to prevent such accidents are: shortening the time to cut off the fault and reducing the expected contact voltage. The former is accomplished by the correct selection and setting of line protection appliances, while the latter is achieved by grounding and equipotential bonding of exposed conductive parts of adjacent equipment. Since the ground fault protection is more complicated, and the protection mode is related to the grounding form and the fault loop impedance, the following is a description of the ground fault protection measures and setting and setting of the power supply and distribution lines according to the commonly used TN grounding system for road lighting in different occasions.
Since the special protection line PE is set between the power supply point and the street lamp, the exposed conductive part is required to be electrically connected with it, and the ground potential of the phase zero short circuit or the neutral line potential offset is not reflected on the PE line, and the ground fault protection is set. The purpose is mainly to prevent the insulation damage of the underground cable line, usually by the overcurrent protection of the protective device, but the sensitivity is not high, it should be verified according to the following formula: R fault current is exposed between the conductive part and the power point through the street lamp The resulting voltage drop causes the resistance of a line of contact voltage.
I. When the above-mentioned requirements are not met, the national regulations are based on the existing technical level and economic conditions in China. It is stipulated that if the zero-sequence protection sensitivity is sufficient, the protection setting can be adopted. Need to avoid the unbalanced current of the line. Since the zero-sequence protection is not sensitive enough compared to the leakage protection, the IEC standard is also included, so the leakage protection is most effective.
For urban road lighting systems. Because the distribution line is long and the cross section is small, the ground fault current is often insufficient to make the overcurrent protection action. In addition to the lack of professional operation and maintenance management, it is most feasible to set the leakage protection at the power point. The priority value of the leakage protection non-action value is the rated action current. 1 The ice should be greater than the normal operation. The line and street lamp leakage current can be estimated at 22 mA/km. The two-phase cable line is equal to the supply voltage balance and the three relative distribution capacitances. The leakage current is close to zero, but in actual operation, the system voltage cannot be completely balanced, the distributed capacitance of each phase is not equal, and there is an asymmetric operation. Therefore, the three-phase cable can still be considered at 22 mA/km. The street lamp can be calculated according to 1 mA/set. Therefore, the normal leakage current of road lighting is usually greater than 30 mA level, which prevents direct contact with the leakage protection value of the personnel. The general installation height of the street lamp facility can prevent direct contact, thus, leakage Protected 1N=500mA, but should not use its upper limit. The best protection is achieved by leakage protection of 1N=300mA. Therefore, according to the general requirements of residual current operated protector, GB6829-95, the rated leakage current is given priority. Value requirement, 1AN=300mA is more reasonable.
For the road lighting of industrial and mining enterprises, it is usually a transformer with other loads. According to the ground fault current value and line type at the low-voltage side outlet of the transformer provided in the design manual, the allowable line length when using over-current protection and ground fault protection can be calculated. If the actual length of a line is greater than the calculated value, set 1 leakage protection of ice = 300 mA; the line within the allowable length does not need to be installed.
For the road lighting of residential buildings, shopping malls, hotels and other civil buildings, there are more garden lights and lawn lights, and the distribution lines are relatively short. From the perspective of user safety, it is recommended to set the leakage protection of lAN=300mA to prevent direct contact with electricity. .
â€•C system, the protection line is in common with the neutral line, and the external part of the street lamp must be directly connected to the PEN line, that is, the PE line and the N line of the lighting device are independently connected to the PEC line. Road lighting is mainly based on single-phase load, and adopts three-phase four-wire power supply. When the PEN line breaks, the exposed part of the street lamp has a phase voltage of 220V, and the fault is difficult to find in time. Therefore, the danger is added. According to foreign experience, it can only improve the mechanical strength of the PEN line and strengthen the protection measures. To overcome, IEC/TC64 has strict requirements for reducing the cross section of PEN line. It is stipulated that only when concentric cable is used and PEN wire terminal is double connected, it is allowed to reduce the cross section of PEN line, but not less than 4mm2. Install ground fault protection device Only the phase line can be disconnected, that is, only the three-stage/unipolar switch can be installed, and the phase-zero short circuit of the line also turns into the ground fault. After the protection action, the fault type is difficult to judge. When the phase-zero short-circuit or neutral potential shift occurs, the potential of the exposed conductive part of the street lamp rises, which may lead to the danger of contact between the maintenance personnel. Therefore, foreign regulations have not allowed the power supply and distribution in the TN-C system. Ground fault current protection is set on the line.
Therefore, for lighting lines with a line length within a small range, a TN-C grounding system can be used without leakage protection. Urban road lighting usually has a long line. It is recommended to adopt TN-S system. The length of road lighting line of industrial and mining enterprises exceeds a certain range. The grounding adopts TN-S system. The protection requirements are as mentioned above. It should be noted that if the line is exploding In the danger zone 1 or the fire danger zone 10, only the TNS system can be used to set the leakage protection of 1=300 mA; while the residential buildings, shopping malls, hotels and other civil buildings have relatively short road lighting, and can pass appropriate large lines. The cross-section improves the single-phase ground fault current value, which usually meets the requirements of over-current protection and ground fault protection. However, considering the low installation height of this type of lighting and neglecting maintenance management during operation, it is recommended to use TN-S system to set up lAN. =300mA leakage protection.
It should be emphasized that the ground fault protection ground protection appliance automatically cuts off the fault circuit to meet the protection requirements. Except for the quality of the protection appliance itself, any error in the design, construction and maintenance management work may lead to protection failure and leakage protector action. Sensitive, but also the possibility of misoperation, refusal and failure, so this type of protection is not a reliable electrical safety measure, and can not prevent the intrusion of external dangerous voltage. When there is a low-voltage overhead power line in the road lighting outlet, a lightning arrester should be installed on the phase line of the TNS system, the neutral line of the neutral line and the TNC system. Therefore, various safety measures should be combined and used to achieve maximum safety.
3 control system street lamp control mainly uses photoelectric control and quartz clock, time switch control, the former has the possibility of misoperation, and then adjust the time with the season. The new street lamp control relay can meet the control requirements of road lighting. The input terminal has switching quantity and analog quantity, and the output circuit is 4-12. It can contact 4 to 12 three-phase/single-phase street light circuit according to photoelectric signal. The device can be controlled according to its internal clock and four timer output loops, and the operation mode is extremely flexible. The control relay has strong anti-interference ability and small volume, and can be installed in the distribution box. The external wiring is simple and the control logic can be directly modified on the liquid crystal display of the relay. For road lighting control, it is a simple, economical and reliable method.
In summary, China's electrical standard specifications are gradually in line with TEC standards, but there are still problems such as imperfect content, low safety level, and inconsistent standard specifications. In the design of power supply and distribution systems, in addition to strictly complying with the requirements of the regulations In addition, according to the specific conditions of road lighting, electrical safety and investment savings should be considered in order to make the most reasonable design.
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|IC Programming||JHYPCB's Fab|
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loctite solder pastePhysicochemical and process property of solder paste directly impact SMT soldering quality. Solder paste printing is applicable for placing appropriate amount solder paste onto PCB pads, in order to ensure good circuit connection between SMT components and PCB pads and their mechanical strength. Solder paste printing is the critical process of SMT. Metal template printing is conventionally applied so far. According to related statistics, 60%~70% quality problems are caused by solder paste printing in premise of quality guarantee of components and printed circuit board. Requirements of solder paste printing:
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|No.||Types Of Assembly||File Format||Component Footprinr||Component Package||Testing Produres||Produres||Others|
|1||SMT ASSEMBLY||Gerber RS-274X||0201,0402,0603-||Reels Package||Visual Inspection||Lead-Free(Rohs)||Custom Reflow Profile|
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