In the process of serving many power plants, we often encountered various problems at the scene. At first we thought that these problems existed in small and medium-sized hydropower plants. Later, we found that these problems also existed in large foreign power units such as the Three Gorges, Guangzhou Storage, and Xiaolangdi. So these problems have some commonalities across the industry. Here we list these issues for analysis and try to solve them. Particularity of hydropower plants For temperature measuring resistors, the operating environment of hydropower plants is very special, which is different from other industrial fields. If industrial temperature measuring resistors are used in hydropower plants, it is definitely a problem. These particularities are expressed as: 1. Long running time and difficult to maintain. The Wawen temperature measuring resistor is installed in a place where the space is small and it is not suitable to maintain the replacement sensor. Generally, it is only necessary to maintain the temperature measuring resistor during overhaul. Now, due to technological advances, the overhaul cycle is getting longer and longer, which requires long-term stable operation of the temperature measuring resistor. 2. High degree of importance. The thrust bearing is one of the key devices of the generator set, and the temperature measuring resistor is the only means to monitor the running state of the thrust tile. Moreover, the thrust tile temperature measuring resistor generally requires protection, and the importance is self-evident. The general industrial sector is not as important as this. 3. The operating environment is bad. Take the thrust tile temperature measuring resistor as an example. The sensor and its wire are immersed in the high temperature turbine oil for a long time, and always bear the impact of the oil flow and the vibration of the unit. In such an environment, few sensors and wires can withstand up to five years of testing. 4. The intensity of electromagnetic interference is quite large. In general, the power of generators in hydropower plants is very large, and the strong electric field generated by the generator, especially the strong magnetic field generated by magnetic flux leakage, has a great interference to the upper guide bush and the thrust tile temperature measuring resistor. This requires a high level of immunity to the sensor and its conductors. Pervasive problem It is precisely because of the special environment of the temperature measuring resistors used in hydropower plants that the temperature measuring resistors of hydropower plants generally have the following problems. 1. Poor long-term stability and low reliability. In fact, the accuracy requirements of thermoelectric power plants for temperature measuring resistors are not high, but the long-term stability and reliability requirements of sensors are very high. Many power plants have long-term stability and poor temperature resistance. After several years of operation, there will be a lot of false alarms, jumps and no readings, which makes it difficult for engineers to judge the problem of the unit itself. It is also a problem of temperature measuring resistors. If the above problems occur in the thrust tile temperature measuring resistors, it will cause a jump and cause a major accident. 2. The cable is broken or the skin is cracked. The cable is broken at the roots in almost every power plant. The cable is immersed in the flowing turbine oil for a long time. If it is not treated specially, the wire will be disconnected at the root of the sensor for a long time. The failure of the root breakage accounts for about half of the fault of the temperature measurement resistor, which should be taken seriously. In addition, the cable sheath will also crack in high temperature and corrosive turbine oil environments. 3. The sensor and wires are not shielded or shielded but not connected. Many power plants do not effectively shield the temperature measuring resistors, so that the strong electric field and strong magnetic field of the generator interfere with the temperature measuring resistors and introduce the interference signals into the temperature measuring circuit, resulting in inaccurate temperature measurement. We have seen that the thrust tile temperature measuring resistor induces a magnetic flux leakage signal of 110V. This makes the measurements meaningless and can cause damage to other devices in the loop. The temperature measuring resistor and the whole temperature measuring circuit have many wires and long wires, and there are many wiring links. The shielding requirements must be reliably shielded in the whole link. As long as there is a problem in one link, the shielding will be invalid. 4. The sensor installation is not standardized. Generally, when installing the wattage resistor, the sensor is required to be rigidly connected with the tile body, preferably by screw connection, and the wire inside the tile should be reliably fixed, especially the root wire should be fixed on the same rigid body as the sensor. However, we have seen that some power plants are simply placed in the hole when installing the bearing temperature measuring resistor, and some are filled with epoxy resin in the hole. These are all irregular installations, and such installations do not effectively protect the wire roots. 5, wire system and wiring problems. The wire system is the lead wire method of the temperature measuring resistor, such as: 4-wire system, 3-wire system and 2-wire system. The wire system determines the influence of the resistance of the sensor wire on the measurement result. Among them, the 4-wire system and the 3-wire system can minimize the influence of the wire resistance on the measurement results, while the 2-wire system can. Taking a 20-meter cable as an example, the resistance of the wire is 3 ohms, and the temperature value is 6 ° C. This error is very large. The three-wire wiring method is also a 20-meter wire. Only 0.1 ohm is added to the system, which produces an error of 0.2 °C. This error is acceptable, which means that the wire resistance hardly affects the measurement result. If measured in a four-wire system, the effect of wire resistance can be completely ignored. We have seen that many power plants use 2-wire temperature-measuring resistors, or 3-wire systems are connected to 2-wire systems, or they are connected to a 2-wire system at a certain intermediate point. In any case, this will produce a big error. Some people may compensate for this on the back-end temperature module, but it is not a good idea to compensate for different types of wires of different lengths. 6, the sensor tail structure problem. The sensor tail structure is completely sealed and has a connector difference. At least half of the power plants are using the structure of the tail connector. The advantage of this structure is that it is easy to disassemble. Once the sensor has a problem, it can be used without moving the wire. The sensor is replaced. However, such a structure is only suitable for installation in a water-cooled water cooler or an air cooler, and temperature monitoring of the bearing bush is not suitable. For example, in the thrust bearing, the sensor is completely immersed in the turbine oil, and the turbine oil is constantly flowing. In addition to the vibration of the bearing bush, the tail connector is very easy to leak oil or the contacts are disconnected, thereby reducing the sensor's Long-term stability. In fact, if the sensor itself has high long-term stability, it should be little or no maintenance at all. 7, Pt100 and Cu50 problems. This is the problem of the temperature measurement resistance index. Pt100 and Cu50 are the most commonly used temperature measurement resistors in power plants, and basically 99% of hydropower plants are in use. Pt100 uses platinum as the sensitive component and Cu50 uses copper as the sensitive component. The comparison between Cu50 and Pt100 has several disadvantages: firstly, copper has a lower resistance than platinum, and requires a long copper wire to be wound into a sensitive component, and platinum is relatively short. Generally, the longer the thinner the material, the lower the reliability of the material. Second, platinum resistance is the mainstream temperature measuring resistor. Large manufacturers, especially German manufacturers, produce Pt100 chips by photolithographic sputtering process, which is very mature and reliable. Almost no manufacturer produces Cu chips, so if you want to use Cu50 products, you only need to coil yourself to make sensitive components, and the reliability is greatly reduced. This is why the Cu50 temperature measuring resistors used in some power plants are often bad. 8, very good sensor. In power plants such as the Three Gorges and Xiaolangdi, because they are VOITH and ALSTON units, the sensors are Swiss or German sensors. The sensor itself is very good, but because it is not a sensor made for a specific use environment, there are often problems with the results. Such as: the problem of the sensor structure, the problem of the wire disconnected at the root. Different power plants have different characteristics, and the requirements for temperature measuring resistors are also different. Up to now, we have not found a hydropower plant with the same temperature measuring resistance. For a particular power plant, the temperature-measuring resistors are not designed to be targeted, and even the best sensors will still have problems. Solution Every effort is made to improve the long-term stability and reliability of the temperature measuring resistor. This requires efforts in the manufacture and installation of temperature measuring resistors. 1. Use high quality Pt100 chip. As mentioned above, the platinum resistance is superior to the temperature resistance of other materials, and the quality of the platinum resistance chip is also very different. The Pt100 chip should be fabricated by sputtering lithography, and the accuracy requirement is up to Class A. These chips have low drift, long-term stability, and resistance to shock and vibration. The chip leads are made of platinum-nickel alloy. This is also a weak link because the chip leads are ultimately soldered to the core of the wire or armor wire, which can easily cause the metal material to become brittle and break. Platinum-nickel alloy on the chip leads to ensure the mechanical properties of the leads after soldering and to prevent the wires from breaking inside the sensor. 2. Use special wires. The long-term immersion of the wire in the oil appears to be hard and brittle due to the unreasonable selection of the outermost insulating layer material of the wire. For example, the outer skin material of the wire is PVC material, and its oil resistance and temperature resistance are relatively poor. At higher temperatures, its oil resistance will be greatly reduced and the service life will be much shorter. After immersing in a higher temperature oil for a long time, the wire will become hard and brittle. We use oil resistant and temperature resistant wire materials. We chose polyperfluoroethylene propylene (TEF), abbreviated as F-4, which is a copolymer of tetrafluoroethylene and hexafluoropropylene, and is a modified material of polytetrafluoroethylene. It has excellent oil, corrosion and heat resistance and can be used for a long time at -250 to 250 °C. In addition to high temperature and high pressure, fluorine and molten alkali metals corrode it. Others such as strong acids (including concentrated nitric acid and aqua regia), strong alkalis, strong oxidants, oils, ketones, ethers, alcohols, etc., even at high temperatures Does not work for it. In addition, its crack resistance is also very prominent, which can completely solve the problem of cracking of the wire in the oil for a long time. 3. Add a protection device at the joint of the wire and the temperature measuring resistor. Introduction: Thermal power plant thermal resistance faults and solutions for thermal power plants Hydrothermal power stations are the most important sensors in hydropower plants. The operation of temperature measuring resistors in hydropower plants directly affects whether the generating units can operate safely. In the hydropower industry, the unstable performance of the temperature measuring resistor and the poor reliability are very common, mainly solving the problem of wire breakage at the root of the wire. According to the situation on the spot, choose different protection forms, such as conical spring protection tube, bellows and armor wire extension protection. In particular, the method of extending the armor wire is emphasized. The armor wire inside the sensor is extended all the way, so that the part of the wire that is impacted by the oil flow is all armored wire. In fact, the armor wire is a stainless steel wire that can be bent at will. The corrosion resistance, shock and vibration properties are very good, which completely solves the problem of oil corrosion and impact on the wire. Longer service life and more reliable performance. 4. Integrated mesh shielding of temperature measuring resistor and its wire. In theory, the magnetic field is more difficult to shield than the electric field. For the interference of strong magnetic fields, mesh shielding is the most effective solution. Since the thrust and the upper guide bearing are closest to the generator, the mesh shielding of the thrust and the temperature measuring resistor of the upper guide is particularly important. The temperature measurement system has many wires and long, and there are many intermediate links. It is especially careful when wiring. It is required to reliably connect the shielded wires of the wires to the common ground at each link. 5. Wiring method above three-wire system. We recommend using a three-wire system. The sensor itself must be made into a three-wire system. Each link in the temperature measurement system must be wired in a three-wire system to ensure accurate measurement accuracy. It is especially emphasized here that the two-wire connection must not be used. 6, packaging process and structure. Full armor packaging process, using armored wire produced by German specialized chemical plant. This armored wire is finished by high-purity magnesium oxide filling, high-temperature drying, drawing, rolling and annealing. It is characterized by long life and response. Fast speed, high mechanical strength and good insulation. The temperature measuring resistors used for the temperature of the tile and the oil in the tile must not use the structure of the tail connector. 7, custom temperature measuring thermal resistance. For a specific power plant, the temperature measuring resistor must be designed and manufactured in a targeted manner. 8. At present, there are many manufacturers of oil-resistant (oil tank) cable, which can achieve oil-resistant and temperature-resistant lead. The three-core resistance is very low. Three-wire 20-30 meters wire, each conductor wire resistance is only 0.01 ohm, three leads The resistance must be the same as 0.01 ohms. This connection of Pt100 thermal resistance can reach the A-class standard. Specially designed for thermal resistance, silver-plated shielded lead cable specifications. Model: Oil-resistant and temperature-resistant cable (oil tank dedicated) KHFRP21 type with Pt100 thermal resistance three core, four core, six core shield silver plated wire, P100 thermal resistance special extension line, compensation line. The thermal resistance indexing number is: CU50.CU100. G53. Pt100. Pt500. Pt1000 core number: 2 cores, 3 cores, 4 cores, 6 cores, 8 cores Wire core specifications are 3*7/0.15|3*7/0.20|3*19/0.15|3*19/0.16|3*19/0.18|6*7/0.15|6*7/0.20|6*19/ 0.15|6*19/0.16|6*19/0.18| Core insulation color: two red one white or two white one red or other requirements Outer diameter insulation layer: white transparent imported oil-resistant and temperature-resistant PTFE, blue imported oil-resistant and temperature-resistant PTFE, red imported oil-resistant and temperature-resistant PTFE, or other colors. Insulation material: Imported oil-resistant PTFE TEF (260 ° C), TEF (200 ° C), PVC material (106 ° C), silicone rubber cord. The shielding layer is: silver plating layer / copper wire layer / tin plating layer Overall outer diameter: 2.8mm-6.5mm Solar On and Off Grid Inverter Grid Tie Inverter,Solar Pump Inverter,On Grid Solar Inverter,On And Off Grid Inverter Jinan Xinyuhua Energy Technology Co.,Ltd , https://www.xyhenergy.com