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Coal-fired power plants hydropower station temperature measuring thermocouple failure and solutions _ instrument

by:JVTIA     2020-10-29
The particularity of hydropower station for temperature measuring thermocouple, the operation of the power plant environment is very special, it is different from other industrial sectors, if the general industrial use of temperature measuring thermocouple to hydropower is sure to go wrong. The particularity of: 1, long running time, not easy to maintain. Tile temperature measuring thermocouple temperature should not be installed in a narrow space maintenance replacement sensor, generally in the overhaul have the opportunity to maintain temperature measuring thermocouple. Now due to technical progress, overhaul cycle longer and longer, which requires the temperature resistance and stable operation for a long time. 2, the important degree is high. Thrust bearing is one of the key device of generator sets, and the temperature measuring thermocouple and the means of monitoring of running status of thrust tile. Temperature measuring thermocouple and thrust tile temperature, general requirements to protect, importance is self-evident. While the importance of the industry is not so high. 3, operation conditions. Or thrust tile temperature measuring thermocouple, for example, sensors and lead long soak in the turbine oil temperature is higher, and time of oil flow under shock and vibration of the unit. In such an environment there is very little sensors and wire has withstood the test of 5 years, only the thermocouple can meet the requirements. 4, the intensity of the electromagnetic interference is quite large. General hydropower generator power is very big, generator produce strong electric field especially strong magnetic field produced by the magnetic flux leakage on the guide shoe and thrust tile temperature resistance interference is very big. It has a high requirement on the sensor and its anti-interference ability of the wire. Common problem, it is because of the particularity of hydropower station temperature resistance using the environment, temperature resistance makes hydropower plants generally exist the following problems. 1, poor stability and low reliability for a long time. Actually hydropower station of temperature measuring thermocouple accuracy is not high, but very high demand for long-term stability and reliability of the sensor. Many power plants with long term stability of temperature resistance, in the unit operation for several years, there will be a lot of problems such as false positives, jump and no prescription, make the engineering personnel is difficult to determine what is the problem that the unit itself or temperature resistance, if thrust tile temperature measuring thermocouple appear afore-mentioned problems, can cause dance machine, a major accident. 2, cable broken or sheath craze. Cable in the root fracture phenomenon in almost every power plant, cable soaked in flow turbine oil for a long time, if you don't do special processing, after a long time will in sensor root disconnect thermocouple wire. Temperature resistance is the root of bolt failure accounted for about half of the failure, and should be taken seriously. In addition, the cable sheath under high temperature and corrosion resistance of the turbine oil environment will craze. 3, sensors and wires without blocking, or have good shielding but not answered. Many power plants are not implement effective shielding for temperature measuring thermocouple, the generator of strong electric field and magnetic field on the temperature resistance interference and the interference signal import temperature measurement circuit, caused by temperature is not allowed. We have seen, thrust tile temperature measuring thermocouple induction magnetic flux leakage signals of 110 v. This makes the measurements without any significance, but also can lead to other devices in circuit damage. Temperature measuring thermocouple and the temperature measurement circuit, wire is much and long, connection link, shielding requirements should have reliable shielding in the link, as long as there is a link to appear problem, shielding will be invalid. 4, sensor installation specification. Thermocouple sensor and requests in the installation tile tile body rigid connection, the better is threaded connection, Vanessa wires also want reliable fixation, especially the root wire with sensor is fixed on the same rigid body. But we see some power plant when installing bearing shell temperature measuring thermocouple is simply placed in the hole, and also some of them are with epoxy potting in the hole. These are all non-standard installation, the installation mode can effectively protect wires roots. 5, wire and connection problems. Wire is temperature measuring thermocouple lead way, such as: 4 wire, three wire system and 2 wire, wire system determines the resistance of the sensor wire effects on measurement results. Four wire and 3 wire system can reduce the wire resistance on the result of measurement to lower, whereas the 2 wire system could. 20 meters cable, for example, the resistance of the conductor for 3 ohm, converted to temperature is 6 ℃, the error is very big. Three wire connection mode, the same is 20 meters wire, only 0. One ohm is added into the system, produce 0. The error of 2 ℃, the error is acceptable, this suggests that the conductor resistance almost does not affect the measurement result. If measured with four wire system, the influence of the thermocouple wires can be completely neglected. We see a lot of power plant adopts 2 wire temperature measuring thermocouple, or take 3 wire into 2 wire system, or in the middle a link into 2 wire system. No matter how this will have a lot of error. May be someone in the back end temperature compensate for this module, but in the face of different types of different lengths of wire to compensate, it is not a good way. 6, sensors, tail structural problems. Sensor tail has fully sealed structure and take the difference between the connector and now there are at least half of the power plant in the use of the rear of the connector structure, this structure has the advantage of convenient disassembly, once there is something wrong with the sensor can be in the case of without moving wire sensors in down. But the structure is only suitable for installation in the oil and water cooler or air cooler place, for the bearing temperature monitoring is not appropriate. Such as sensors in the thrust bearing is totally immerse in the turbine oil, turbine oil and is constantly moving, and the vibration of the bearing, the tail connector is very easy to leak or contact release, which reduces the long-term stability of the sensor. Indeed, if the sensor itself high long term stability, should be to maintain few or no need maintenance.
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