1 、油雾保护系统
1.1 工作原理
油雾保护系统的主要保护元件是油雾探测器，它能及时检测出有否因轴承过热或活塞环损伤造成过量漏气等故障而导致在曲轴箱内形成油雾，从而监视柴油机的主要运行部件——曲轴和气缸的工作状况是否正常。在柴油机运行过程中它通过采样管系不停地抽出曲轴箱内的油气，并送至一个灵敏且准确的浓度测量装置。该浓度测量装置包括一个红外线发射二极管和对侧一个光电接收二级管。光电二级管感受红外线产生的光强度，并将光强度信号转换为电信号送至电子鉴定装置。如果曲轴箱气体含有油雾（使得浓度测量装置测量通道的不透明度增加），部分红外线会在测量管内被吸收，光强度会减弱，因而电信号减弱。浓度越高电信号减弱越多，当电信号降低到一个最低限值时（即油雾浓度超过最大限值时），电子鉴定装置将发出“油雾探测器高油雾”警报并停机，同时阀箱指示出是哪一部分故障引起的高油雾，以供检修人员检查。
1.2 优缺点
该保护装置的快速性、灵敏性无可厚非，但经过几年的运行检修发现，由于外界或装置自身的原因，使得其选择性和可靠性大大降低。比如由于润滑油冷却器的泄漏（水进入并污染了润滑油），油雾探测器将会感受到由于水份的增加而引起的不透明度的增加，继而发生跳机。油雾探测器的电子元件属于高精度元件，但因其安装在柴油机本体上，温度高、振动大，工作环境极为恶劣，由此使得电子元件的老化加剧，产生温度漂移，跳机的灵敏度增加，误动率也增加。而且该保护有时出现指示灯全无指示，使得保护经常处于脱离状态等。频繁的保护误动及保护的无法就绪，不仅会造成因甩负荷而引起的材质疲劳，寿命缩短，而且会使生产人员产生麻痹心理，认为该装置不可靠，是误动，这样大大限制并误导了生产人员的思维，而在真正出现“高油雾”时就会发生事故。
1.3 common faults and Countermeasures
1.3.1 components aging, temperature drift and so on cause sensitivity changes.
According to the actual conditions of the power plant and with the consent of the relevant experts, the alarm threshold S switch is adjusted to level fourth (the original 4 units are all at level third), and the jump phenomenon has not occurred since the operation.
Failure of 1.3.2 electronic board
When the red and green indicator lights out of the oil mist detector, and when the 24VDC power supply is normal and the plug is not loose, the fault of the electronic board can be judged basically, and the electronic board for other units can be used to judge. If it is an electronic board failure, it should be overhauled or replaced in time.
The oil and gas of the 1.3.3 crankcase contain a lot of water
Because of the presence of moisture, the opacity of the measurement channel is greatly increased, resulting in false positives in electronic devices. This requires checking the moisture in the lubricating oil, the leakage of the lubricating oil cooler, the excessive humidity of the air system, and the normal operation of the heater in the oil mist detector floor. In recent years, through the analysis of high oil fog hopper events, it is found that the real high oil mist jumper is 0%, and the high water jumper is 98% (and the final inspection, 95% are caused by the leakage of the lubricating oil cooler), and the other faults are 2% (such as the electronic board failure, the relay misoperation, etc.). Therefore, if a highly sensitive water detection device is installed on the lubricating oil inlet pipe for alarm, the operator can be reminded in time when the water is too high to reduce the number of destructive hops and increase the stability of the power grid.
1.3.4 The basic purpose of installing the oil mist detector is to monitor whether the working condition inside the crankcase of the diesel engine itself has changed. For example, the piston ring failure (including spalling, abnormal wear, breaking) causes the cylinder liner to leak to the crankcase and form a high oil mist. The cylinder liner and piston ring should be checked, and the damage should be replaced. If the main axle bush or the connecting rod bush high temperature burning tile causes local high temperature, causing the oil mist concentration to increase and stop, it is necessary to open the explosion-proof door, carefully check whether the bearing and shaft of the connecting rod are burned, and change when necessary.
1.3.5 Oil mist detector itself has many types of faults, these faults will not cause jump, but will make the diesel engine lose important protection. According to the operation experience, the failure rate can be reduced to a minimum as long as the following points are done, and the rate of malfunction can be reduced greatly, and the first hand information is provided for the check after the jump.
(1) maintenance personnel should do a good job of maintenance. Replace the air filter, pressure relief air filter, remove the water from the condensing tube, clean the oil pollution of the valve box, clean the infrared probe with alcohol, blow the sampling tube, oil road and air road with compressed air, and do the necessary alarm test and the high oil mist protection action (the simplest way is to blow a cigarette smoke from the entrance of the sampling tube. " Fog in) test.
(2) during the operation of the unit, the operator should monitor the temperature of the bearing, the temperature of the lubricating oil and other relevant parameters, and observe the working condition of the oil mist detector, the indication of the concentration of oil mist, the difference of the U form differential pressure meter of the crankcase, the smoke of the crankcase ventilating device, the flameproof door of the crankcase, and the high pressure difference of the crankcase. There is no alarm and so on. In the case of high oil mist jumper, the concentration value, the case of the valve box, the difference between the crankcase differential pressure meter, the bearing temperature and the indication of the indicator light of the oil mist detector should be recorded as soon as possible.
2. Speed measurement and protection system
2.1 system composition and working principle
The speed is one of the most basic and most important parameters in the diesel generator equipment. The ignition speed, the speed adjustment during the operation, the parking protection in the overspeed, and even the size of the load can also be reflected from the size of the speed, so the speed measurement is the basis of the diesel generator supervision and protection. There are two ways to measure the speed of a diesel engine, one is the measurement of the speed of the main engine, and the other is the measurement of the speed of the turbocharger. Two.
(1) sensor. The sensor is a short-range inductive switch that works without contact. It consists of an oscillator, a trigger and an amplifier, and produces an alternating electromagnetic field through the coil of the oscillator circuit. When the metal conductor approaches the sensor, the alternating magnetic field will change, and the output voltage and frequency of the oscillator will change accordingly. There are 4 sensors for measuring the speed of the main engine. The 2 speed is measured, and the speed is displayed on the CMR or OCW disk, and the other 2 are used by the governor.
(2) speed transmitter. The frequency signal transmitted by the transducer is converted to a 4~20 mA current signal and transmitted to the tachometer.
(3) a tachometer. Show the speed.
2.2 advantages and disadvantages
This system has great advantages, especially the overspeed system has multiple protection functions. Its sensor (speed sensor) has no direct contact with the measured rotating object, so it is not worn, easy to repair and repair, and the unit can also repair and replace the probe when the unit is running, and the connection is convenient. The speed transmitter of the host also has the functions of 11P1 (generator bearing pre lubrication pump) control, excitation input, synchronous locking, electrical overspeed jumper (>565 r/min), speed governor (>575 r/min) and so on. At the same time, the mechanical overspeed protection (>595 r/min) system was also set up on the diesel engine, which ensured the safe and stable operation of the diesel engine (rated speed 500 r/min) to a large extent, and no flying car accident occurred. But at the same time, there are also some problems: the movement of the flywheel at high speed will cause the probe damage, the tachometer often fluctuates and even has no speed, electric overspeed protection misoperation and so on. There is also the frequent start and stop of the generator pre lubrication pump due to the fluctuation of the speed indicator (>100 r/min stop, <100 r/min), causing the burning of the generator. The condition of the bearing pre lubricating pump motor or its contactor coil.
2.3 common faults and Countermeasures
The distance between the 2.3.1 sensor and the flywheel is too far or too close. This distance is about 2.5+0.3 mm. Too far away is likely to be unable to sense the signal, which is too near to damage the working face of the sensor. As the flywheel runs in high speed, the radial (or axial) movement will occur, and the distance is too close to the safety of the sensor. It has been found that the working face of several probes has been scraped. According to practical experience, the distance is generally suitable for about 2 mm, and can be measured with feeler gauge.
2.3.2 Due to the vibration of the fixed frame mounted on the sensor, the measurement signal is inaccurate, and the alternating magnetic field produces irregular changes, resulting in the fluctuation of rotational speed indication. The method is to reinforce the support and weld it with the diesel engine body.
2.3.3 because the oil thrown off by the flywheel is stuck to the working face of the sensor, it has a certain effect on the measurement results. If the oil shield is installed on the flywheel, it will achieve good results.
The failure of the 2.3.4 speed transmitter makes the output signal unstable, resulting in the fluctuation of the speed indicator or even the speed indicator, and the electrical overspeed protection misoperation will be triggered because of the unstable work and the bad contact of the connection head. The frequency generator can input the frequency signal to verify the speed transmitter, and the terminal is fastened. Since the speed transmitter is controlled by PLC microcomputer, it may be readjusted or replaced if necessary.
2.3.5 sensor failure. After measuring the distance, the open disc machine looks at the red light emitting diode on the sensor. When the flywheel tooth passes, the luminance will obviously increase, or the non open car machine is close to or away from the sensor with the metal, and the brightness of the red LED is changed, if the brightness is not changed or there is no light at all, It is possible that the sensor is damaged and needs to be replaced. The CMR524 system starts with the "governor fault" of the times, most of which are sensor failures.
3, temperature and pressure protection system
3.1 system introduction
The control of temperature and pressure is very important in the operation of diesel engines.
If the lubricating oil pressure and fuel pressure are insufficient, the diesel engine will not be able to run. Most of the current high-power medium speed diesel engines have a relatively complete monitoring and detection system, which monitor some important parameters of the diesel engine such as temperature, pressure and so on. Once these parameters exceed the setting range, the sound and light alarm or automatic shutdown are carried out.
The diesel engine set has cylinder exhaust, turbine exhaust, main bearing, generator stator, cylinder liner water, lubricating oil and other temperature monitoring and pressure monitoring of fuel, starting air, lubricating oil, raw water, cylinder water, oil mouth water, air intake and so on. These temperature and pressure monitoring, alarm and safety shutdown systems are mainly composed of CMR424 and CMR524 units mounted on the control panel.
There are many temperature sensors in diesel engine, but they can be divided into two types: thermal resistance (PT100) and thermocouple (Ni-Cr/Ni-Al). Through the change of the resistance of the thermoelectric resistance sensor when the temperature changes and the change of the thermoelectric potential when the thermocouple sensor changes in the temperature change, the signal is transferred to the CMR424 system to be transformed, compared, printed, displayed and acted on the alarm or the hopper. The transmission of pressure is mainly transmitted through the field pressure transmitter to the CMR424 system for conversion, comparison, printing, display and acting on the alarm or hopper.
3.2 advantages and disadvantages
The system is small in size, small in components (each signal is converted by an independent circuit board), centralized in layout, easy to monitor, and a part of temperature (such as water temperature of cylinder liner, lubricating oil temperature and so on) is controlled by PLC microcomputers, and the degree of automation is high. The control of the lubricating oil pressure and the water pressure of the cylinder is directly driven by the pressure switch on the jumper. Nevertheless, the system still has some limitations. For the exhaust temperature, only the difference between the single cylinder and the average temperature alarm, there is no single cylinder temperature over the set value of the alarm, temperature can not be real-time display. Traditional automatic recorders require a large number of printing paper, printing interval is too long, many curves are not easy to distinguish, and can not be digitized. Several times the turbocharger was damaged because the valve was damaged because the temperature rising trend was not detected in time.
3.3 common faults and Countermeasures
3.3.1 temperature shows fluctuating and large amplitude, and sometimes shows -1 or 1 of the fault cause: first, the connection plug contact is bad, can be tightened, when the plug is loose, CMR424 display -1; second, the probe characteristic is bad, the probe can be replaced, especially when the thermal resistance probe short circuit CMR424 shows 1; third, electronic plate needs to be re adjusted. Whole.
3.3.2 temperature shows that electronic board failure or set temperature change can be checked by standard resistance box or milli generator set into a set of standard temperature signals, and a set of actual temperatures can be checked with a thermostat box. It is true that the failure of the electronic board should be replaced. A small change in temperature (less than 2%) is a normal condition and is a result of temperature drift.
