Xi'an Metro Line 3, known as the most beautiful subway in Xi'an, has a theme color of è—•è·è‰², which is a subway line that makes girls girls burst into heart. However, the subway used to inferior cable incidents that had been raging in the past time pushed it to the forefront. Today we analyze the hidden dangers of cable events from another perspective, power quality. The subway, as an increasingly important means of transportation for a city, carries the safety of millions of people every day. Take the Xi'an subway as an example, its maximum single-day passenger flow is 2,051,100. As shown in Figure 1, it is the Xi'an Metro Line 3. Figure 1 Xi'an Metro Line 3 Some time ago, the problem of using inferior cables in Xi'an subway has made it a hot topic for discussion. There are serious problems in the 400V auxiliary cable and 120V signal control cable used. For the subway, in addition to the use of cables and other factors that affect its operational safety, power quality also affects its safety as a major factor. Below, we analyze the impact on safety from the classification of cables to the quality of power. About cables, they can be seen everywhere in daily life, as shown in Figure 2, which is a common cable. Figure 2 common cable But for the classification of cables, everyone is not necessarily clear. According to their use, they are roughly divided into the following categories: · Bare wire: The product is a conductor without insulation layer, such as steel core aluminum stranded wire for overhead transmission line; · Power cable: A cable product used to transmit and distribute high-power electrical energy in the backbone of a power system. In the power system, it plays the role of power transmission, power distribution and power supply, and the current is large; · Wire and cable for electrical equipment: The variety is the most diverse, accounting for about 60% of the total. From the power station's substation, the electrical energy is directly transmitted to the cable products for the power connection lines of various electrical equipment or instruments, the electrical installation lines in various industrial and agricultural equipment, and the cable products for control signals. Such as control cables, wires, etc.; · Communication cable and fiber optic cable: mainly used for transmitting audio, digital signals and analog signals; · Electromagnetic wire (winding wire): A wire that cuts a magnetic induction line in an electromagnetic field to generate a current or generate a magnetic field in a current in the form of a winding, and is used for winding coils in various transformers and motor magnetic field generators. The problem cable of Xi'an Metro Line 3 mainly has 400V auxiliary cable and 120V signal control cable part, which has nothing to do with the locomotive traction 1500V DC power system. It is mainly two types of power cables and wire and cable for electrical equipment in the above types. As with common air and water, there are certain quality indicators for cable. The most important indicators for measuring wire and cable are the following: · Measurement of wire DC resistance; · Testing of insulation resistance; · Measurement of capacitance and loss factor; · Insulation strength test; · Partial magnification measurement; · Aging and stability tests. As we all know, harmonics mean that the frequency contained in the current is an integer multiple of the fundamental wave. Usually harmonic generation comes from three aspects: the power quality is not high, the harmonics are generated, the harmonics are generated by the transmission and distribution system, and the harmonics are generated by the electrical equipment. The third point is the main cause of harmonics, such as non-linear loads such as rectifiers, switching power supplies, UPS, inverters, inverters, etc. As shown in Figure 3, the harmonics generated by the device. Figure 3 Harmonics generated by the device The harmonics generated by the above three points have a serious impact on our electrical equipment. For the Xi'an subway cable mentioned at the beginning of this article. We will focus on the hazards of harmonics on cables. Harmonic pollution will cause the dielectric loss of the cable, the transmission loss to increase, the leakage current to rise, the temperature rise to increase, and the partial discharge of the dry cable to increase, which increases the possibility of single-phase ground faults. Since the distributed capacitance of the power cable amplifies the harmonic current, when the system load is low, the system voltage rises and the harmonic voltage increases accordingly. The higher the rated voltage rating of the cable, the greater the risk of harmonics causing instability of the cable medium and the greater the risk of failure. As shown in Figure 4, the cable is burned by harmonics. Figure 4 Harmonic cable burning For the problem cable of Xi'an subway, the influence of harmonics will be more prominent. Unqualified cables and heat caused by harmonics are prone to accidents. This is even more serious in a relatively closed and crowded subway station. Of course, the problem with the problem cable is not just about harmonics. Therefore, for all aspects of our transportation, we must not only request the transmission medium, but also the quality of the electricity source. At this time, a device is needed to accurately capture various parameters of the measured power quality and then analyze it to promptly check for potential safety hazards. As shown in Figure 5, it is the E6500 power quality analyzer. Figure 5 E6500 Power Quality Analyzer It is the world's exclusive power quality analyzer with oscillating function. It can capture common power quality problems such as harmonics, voltage fluctuations, flicker, power and three-phase unbalance at the fault site. It also has transient measurement and oscillography analysis. , inverter testing, energy consumption statistics, demand statistics, pollution assessment and other advanced features. As shown, the current waveform and voltage transient graph of the elevator are captured by a testing agency in Guangzhou. Figure 6 Current original waveform and voltage dip curve It can accurately locate the causes of excessive temperature and abnormal operation of electrical distribution equipment such as switchboards, switch boxes, transformers, breakers, contactors, fuses, cables, generators, winding equipment, oil pillows, and UPS. It is an indispensable professional measurement and analysis tool for smart grid, new energy, electrified railway and large industrial power quality. Capacitive Membrane Switches,Waterproof Flexible Membrane Switches,Remote Control Membrane Switch,Flexible Membrane Switch Assembly KEDA MEMBRANE TECHNOLOGY CO., LTD , https://www.kedamembrane.com
