Equivalent electricity ~ road talk about outdoor grounding device ground fault protection Yu Yuelan 1 problem in China for the Olympic Games, the World Expo built stadiums, convention centers and other buildings (structures), it is necessary to use a large number of outdoor lighting Device. These outdoor lighting devices are Class I electric shock protection devices, and the metal rods and casings of the lamps are often in a range accessible to the human body. When they have a ground fault and the metal rod and casing of the luminaire exhibit a fault voltage, the human body will contact with it and endanger the personal safety. Article 1.0.1 of the "Design Specification for Low-Voltage Power Distribution" (GB50054-95) states that the design of the distribution system should ensure personal safety and reliable distribution. Since the ground fault is the most common fault of the distribution line, it is a non-negligible link to ensure the safety and reliability of the power supply of the outdoor lighting device to ensure the safety and reliability of the power supply.
At the time, the author believes that the outdoor lighting device has the characteristics of being exposed to the outdoors, often affected by wind, frost, rain and snow, load dispersion, long line, large leakage current, and difficulty in implementing equipotential bonding. The installation is complex and deserves more attention and reflection from electrical designers.
2 Selection of the grounding system type of the outdoor lighting device The setting of the grounding fault protection of the electrical device is related to the type of the grounding system. Therefore, to discuss the ground fault protection of outdoor lighting devices, the grounding system type should be correctly selected first.
Common outdoor lighting devices are: facade floodlights, lawn lights, garden lights, buried lights, mast lights, etc. There have been many discussions about the safety of the landscape lighting of the fountain, and the specifications are also clearly defined, so I will not repeat them here. According to the situation of the power supply, and considering the possibility of eliminating the fault voltage introduced by the power supply system, the power distribution mode of the outdoor lighting device and the corresponding grounding system are generally of the following four types, see the construction of the power supply to the public power grid or the residential transformer. The distribution method of outdoor lighting devices such as facade floodlights and garden lights is generally as shown or shown; the distribution method of outdoor lighting devices such as facade floodlights and garden lights of buildings with transformer substations Generally, such as the voltage r,.
As shown in the above; the lighting pattern of the high-lights, lawn lights, garden lights, buried lights and road lighting of the square lighting is generally as shown below. The grounding fault current () and the expected contact voltage on the exposed metal components (Chapter 15 Section 3 "Electrical Safety in Special Environments" requirements for the safety of parking lots and farm animals facilities).
3 Outdoor lighting device grounding protection measures IEC standards and China's specifications stipulate that for the Class I electric shock protection class equipment, the two main measures of ground fault protection: one is to install overcurrent protection appliances (fuse) , low-voltage circuit breakers or leakage protectors quickly cut off the fault circuit; the second is to rely on equipotential bonding to reduce the contact voltage. The two measures should be combined with each other and complement each other. However, the outdoor lighting device can not implement the equipotential bonding because the load is dispersed outside, and the ground fault protection can only rely on the overcurrent protection device or the leakage protector to quickly cut off the fault circuit (for mast lights and stadium tower lights, Combined with the foundation concrete pier for local equipotential bonding, it will not be discussed here).
3.1 Outdoor lighting device using TT system (including local TT system) ground fault protection When the outdoor lighting device of TT system (including local IT system) has a ground fault, its ground fault current is very small, generally ampere level (such as , 2, 3 calculation of the current value), it is difficult to make the overcurrent protection device operate within a specified time. Therefore, the earth leakage protector should be used for ground fault protection.
3.2 Ground fault protection when the outdoor lighting device adopts TN system When the outdoor lighting device of the TN system has a ground fault, since it is mostly a metallic short circuit, the ground fault current is large, generally a hundred-ampere level (such as the calculated current/d value). ). The condition that the overcurrent protection can also be used as the ground fault protection in the TN system is that the action characteristics of the overcurrent protection device can meet the action characteristic relationship of the ground fault protection of the TN system: the ground fault protection of the outdoor lighting device Yu Yuelan Z, grounding The impedance of the fault circuit, that is, the phase-preserving impedance, consists of the impedance of the line, the transformer, and the busbar; /* The protective device automatically cuts off the current of the faulty loop within the agreed time. The value is related to the setting value of the overcurrent protection device.
For example, in the case of a three-phase floodlight (metal halide lamp) branch, the equipment capacity P, = 18 kW, the power factor cs = 0.95, then calculate the current / fl = 32 A. Select the gas discharge lamp circuit The setting of long delay and instantaneous overcurrent release: It can be seen that in the area where the soil resistivity is as high as 5 (mm), a 2.5m long 0 steel pipe or a current round steel is hit vertically toward the ground (top ground) Ping 0.8m), the grounding resistance values ​​are 151Q and 186fl. It can be seen that the above grounding resistance is less than 25n, which is very easy to achieve. It only costs a 2.5m long post steel pipe or 丨20. Round steel. In sand or rock areas with higher soil resistivity, measures such as adding a grounding electrode or adding a resistance reducing agent may be adopted, so that the grounding resistance is less than the above calculation. Several advantages: the expected contact voltage will be greatly increased. For example, the R value will be close to 220V. However, the fault voltage will not be transmitted to other outdoor lighting devices outside the fault point, and the fault surface will be reduced. The feature is that when the RCD refuses to move Indirect contact with electric shock Accidents are limited to a minimum to improve the level of electrical safety of outdoor lighting.
When grounding occurs, it is easy to find the fault point and facilitate maintenance and repair.
The distribution box of the outdoor lighting device can be directly installed in the building for easy management.
It can be seen that the outdoor lighting device adopts the power distribution scheme proposed by the author, and only needs to increase a small part of the cost, but has the above various advantages, and therefore is suitable for popularization and application in engineering practice.
5 Conclusion In summary, with the continuous improvement of China's modernization construction, a large number of outdoor lighting installations are deployed in newly built stadiums and convention centers, and are widely visible in squares, streets, parks, roads, and residential quarters, and are closely related to people's living environment. Related. Therefore, the electrical safety and distribution reliability of outdoor lighting devices is an important issue that cannot be ignored. Moreover, due to the particularity of the power consumption of outdoor lighting devices, the ground fault protection is worthy of more attention and consideration.
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