Discussion on Safety Automatic Protection System of Diesel Generator Set

Oil mist speed measurement Temperature monitoring pressure monitoring In order to solve the shortage of power supply in the grid, to ensure the shortage of power grids in the case of peak load of the power grid or unit failure in the large power grid, and to alleviate the pressure on the power grid, diesel generator sets have emerged. The diesel generator set has the outstanding advantages of high comprehensive reliability, good peak shaving performance and excellent maneuverability. However, diesel power plants have relatively high investment costs, expensive spare parts, relying on foreign imports, mechanical load and heat load, sports parts, and sudden accidents. At present, most high-power medium-speed diesel engines are equipped with a fairly advanced safety automatic protection system to stop the operation of the equipment in a timely, effective and safe manner when it is not suitable for the safe operation of the equipment. The safety automatic protection system for diesel engines in Xiamen Power Plant can be roughly classified into three categories, namely oil mist protection system, speed measurement protection system, temperature and pressure monitoring and protection system.

1 Oil mist protection system working principle The main protection component of the oil mist protection system is the oil mist detector, which can detect in time whether there is a fault caused by overheating of the bearing or excessive leakage of the piston ring, resulting in oil mist in the crankcase. In order to monitor the main operating components of the diesel engine, whether the working condition of the crankshaft and the cylinder is normal. During the operation of the diesel engine, it continuously extracts the oil and gas in the crankcase through the sampling pipe system and sends it to a sensitive and accurate concentration measuring device. The concentration measuring device includes an infrared emitting diode and a photoelectric receiving diode on the opposite side. The photodiode senses the intensity of the light generated by the infrared light and converts the light intensity signal into an electrical signal for transmission to the electronic identification device. If the crankcase gas contains oil mist (so that the opacity of the channel is measured by the concentration measuring device), some of the infrared rays are absorbed in the measuring tube, the light intensity is weakened, and the electrical signal is weakened. The higher the concentration, the more the electrical signal is weakened. When the electrical signal drops to a minimum limit, the oil mist concentration exceeds the maximum limit.) The electronic identification device will emit “oil mist detector high oil mist”.

The alarm is stopped and the valve box indicates which part of the fault is caused by high oil mist for inspection by the service personnel.

1.2 Advantages and Disadvantages The rapidity and sensitivity of the protection device are understandable. However, after several years of operation and maintenance, it is found that the following functions and effects have been achieved for the safety status of the nuclear power plant due to the establishment of the original indicator system of the outside world or the device itself. Description to facilitate a more specific understanding of the overall situation. Target values ​​are set for these indicators in the annual industrial safety program, and the Industrial Safety Section reports monthly to the various departments of the power station through the actual values ​​of these indicators. By comparing actual and target values, leaders and employees have a clear understanding of the gaps in industrial safety controls.

Indicator analysis provides a basis for developing accident prevention strategies.

After the establishment of the indicator system, the Industrial Safety Section analyzes and compares the indicators on a quarterly basis, finds the main problems in management, proposes targeted countermeasures, and reports to the Industrial Safety and Radiation Protection Committee of the power station.

Through the analysis of the indicators of the previous year, the main problems in management are found, and the basis for the formulation of the annual management improvement plan project and the annual work outline of the power plant industrial safety is provided.

The industrial safety management system has played a good role in the industrial safety management of power stations. In recent years, the industrial accident rate of power stations has shown a steady downward trend. The rate of three consecutive injuries has not exceeded 0.14, far below the intermediate value of WAN 0.

5 Insufficient indicators management system The scope of the anomaly indicators is not comprehensive. There are still some undetermined anomalies that are not included in the definition. There are only human experience components in the process of index definition, and the accuracy of judgment is inconsistent, indicating that the indicator definition remains to be Further actualization and standardization in actual work.

Because of this, its selectivity and reliability are greatly reduced. For example, due to the leakage of the lubricating oil cooler (water entering and contaminating the lubricating oil), the oil mist detector will feel the increase of opacity caused by the addition of moisture, and then the machine will trip. The electronic components of the oil mist detector are high-precision components, but because they are mounted on the diesel engine body, the temperature is high, the vibration is large, and the working environment is extremely harsh, thereby causing the aging of the electronic components to be intensified, causing temperature drift, and the sensitivity of the tripping machine plus The mismotion rate is also increased. Moreover, the protection sometimes has no indication of the indicator light, so that the protection is often in a disengaged state or the like. Frequent protection misoperation and unprepared protection will not only cause material fatigue caused by load shedding, but also shorten the service life, and will cause paralysis of the production personnel. It is considered that the device is unreliable and misplaced, which greatly limits and misleads. The thinking of the production staff, and an accident will occur when there is a real "high oil mist."

1.3 Common faults and countermeasures to improve the countermeasures 1.3.1 Component aging, temperature drift and other sensitivity changes combined with the actual situation of the power plant and agreed by the relevant experts, the alarm threshold S switch is adjusted to the fourth level (the original 4 units are in the third level ), there has been no tripping since the operation.

1.3.2 Electronic board failure When the oil mist detector shows that the red and green indicators are all extinguished, and the 24VDC power supply is normal and the plug is not loose, it can basically be judged as an electronic board failure, and other units can be replaced. The electronic board to judge. If it is a malfunction of the electronic board, it should be repaired or replaced in time.

1.3.3 Crankcase oil and gas contains a large amount of water due to the presence of moisture, which makes the opacity in the measurement channel greatly increased, causing false alarms in the electronic device. This requires checking whether the lubricant contains moisture, whether the lubricant cooler leaks, whether the air system is excessively humid, and whether the heater in the oil mist detector floor is working properly. In recent years, through the analysis of the high oil mist jump event, it is found that the real high oil mist jumper is 0%, and the high water jump machine is 98% (and the final inspection, 95% is due to the leakage of the lubricating oil cooler) Caused by, the remaining fault is 2% (such as electronic board failure, relay malfunction, etc.). Therefore, if a high-sensitivity moisture detecting device is installed on the lubricating oil inlet pipe for alarm, the operator can be reminded in time when the water is too high, and the number of destructive tripping machines can be reduced, and the grid is stabilized. Sex.

1.3.4 The basic purpose of installing the oil mist detector device is to monitor whether the working condition inside the crankcase of the diesel engine itself has changed. For example, piston ring failure (including spalling, abnormal wear, breaking) causes the cylinder liner to leak into the crankcase and form a high oil mist. At this time, check the cylinder liner and piston ring. If it is damaged, replace it. Another example is the high temperature caused by the high temperature burnt tile of the main bearing bush or the connecting rod bearing bush, which causes the oil mist concentration to be large. When the machine is shut down, the explosion-proof manhole door should be opened, and the big end bearing and the shaft of the connecting rod should be carefully inspected for burns and replaced if necessary.

1.3.5 The oil mist detector itself has many types of faults. Although these faults will not cause a trip, it will cause the diesel engine to lose important protection. According to the operating experience, as long as the following points are achieved, the failure rate can be reduced to a minimum, and the false alarm rate can be greatly reduced, and first-hand information is provided for the inspection after the trip.

Maintenance personnel should be regularly maintained. Regularly replace the air filter and the decompressed air filter, drain the moisture from the condenser, clean the oil in the valve box, clean the infrared probe with alcohol, purge the sampling tube, oil circuit and gas path with compressed air, and do the necessary alarm test. And the high oil mist protection action æ’® simple method is to blow a cigarette from the inlet of the sampling tube into the test).

When the unit is running, the operating personnel should carefully monitor the bearing temperature, lubricating oil temperature and other relevant parameters, and regularly observe the working condition of the oil mist detector, the indication of the oil mist concentration, the difference of the U-shaped differential pressure gauge of the crankcase, and the ventilation of the crankcase. Whether the device has smoke, whether the crankcase explosion-proof door is hot, whether the crankcase high-pressure difference has an alarm or not. If a high oil mist jump occurs, the concentration value, the valve box flop, the difference of the crankcase differential pressure gauge, the abnormality of the bearing temperature, and the indication of each indicator of the oil mist detector should be recorded as soon as possible.

2 Speed ​​measurement and protection system system composition and working principle Speed ​​is one of the most basic and important parameters in diesel generator equipment. The ignition speed at start-up, the speed adjustment during operation, the parking protection during overspeed, and even the load Can be reflected in the size of the speed, so the speed measurement is the basis of diesel generator monitoring and protection.

Generally, the speed of the diesel engine is measured in two places, one is the measurement of the main engine speed, and the other is the measurement of the speed of the turbo compressor.

sensor. The sensor is a proximity sensor that works without contact. It consists of an oscillator, a flip-flop and an amplifier that generates an alternating electromagnetic field through the coil of the oscillator circuit.

When the metal conductor approaches the sensor, the alternating magnetic field changes, the output voltage of the oscillator changes, and the frequency changes.

There are 4 sensors for measuring the speed of the main unit. Two measuring speeds are displayed by the speed transmitter on the CMR or 0CW disc, and the other two are used by the governor.

Speed ​​transmitter. The frequency signal transmitted from the sensor is converted into a current signal of 420 mA and transmitted to the tachometer.

2.2 Advantages and Disadvantages This system has great advantages, especially the overspeed system has multiple protection functions. Its sensor (speed probe) and the rotating object being measured are not in direct contact, so there is no wear, easy to disassemble and repair, and the probe can be repaired and replaced when the unit is running, and the wiring is convenient. The speed transmitter of the main engine also has 11P1 (generator bearing pre-lubrication pump) control, excitation input, synchronous lockout, electrical overspeed tripping (>565r/min), governor overspeed tripping (>575r/min), etc. Features. At the same time, the mechanical overspeed protection (>595r/min) system is also installed on the diesel engine body, which ensures the safe and stable operation of the diesel engine (rated speed 500r/min) to a large extent, and there will be no flying accidents. However, there are also some problems: the flywheel will cause damage to the probe during high-speed operation, the tachometer often fluctuates or even has no speed, the electrical overspeed protection is malfunctioned, etc., and the generator pre-lubrication pump frequently starts due to the fluctuation of the speed indication. Stop (>100r/min stop, <100r/min open), causing the generator bearing to pre-lubricate the pump motor or its contactor coil.

2.3 Common faults and countermeasures for improvement 2.3.1 The distance between the sensor and the flywheel is too far or too close to sense the signal. Too close may damage the working surface of the sensor.

Due to the high-speed operation of the flywheel, radial (or axial) turbulence occurs. The distance is too close to pose a great threat to the safety of the sensor. It has been found that several working faces of the probe have been scraped. According to practical experience, the distance is generally about 2mm, which can be measured with a feeler gauge.

2.3.2 Due to the vibration of the sensor mounting bracket, the measurement signal is inaccurate, and the alternating magnetic field produces irregular changes, causing the speed indication to fluctuate. Treatment method: Reinforce the bracket and weld it to the diesel engine body.

2.3.3 Because the oil from the flywheel sticks to the working surface of the sensor, it will have a certain impact on the measurement results. If you install an oil hood on the flywheel, it will work well.

2.3.4 The speed transmitter is faulty, which makes the output signal unstable, causing the speed indication to fluctuate or even no speed indication, and it may trigger the electrical overspeed protection malfunction due to its unstable operation and poor contact of the terminal. For this purpose, the frequency generator can be used to input the frequency signal to verify the speed transmitter and the terminals are tightened. Since the speed transmitter is controlled by a PLC microcomputer, it can be readjusted or replaced if necessary.

2.3.5 Sensor failure. After measuring the spacing, open the car to observe the red LED on the sensor. When the flywheel teeth pass, the brightness of the flywheel will be obviously strong, or the metal object of the disc drive machine will be close to or away from the sensor, and the brightness of the red LED is observed. Change, if the brightness does not change or does not shine at all, the sensor may be damaged and needs to be replaced. The CMR524 system reports "speed governor failure" at start-up, mostly sensor failure.

3 Temperature and pressure protection system 3.1 System introduction Temperature and pressure control is very important in diesel engine operation.

The lubricating oil pressure and fuel pressure are insufficient and the diesel engine will not operate. At present, most high-power medium-speed diesel engines have a relatively complete monitoring and detection system to monitor some important parameters of the diesel engine (such as temperature, pressure, etc.). Once these parameters exceed the set range, the sound and light alarm or automatic shutdown.

The diesel power plant of Xiamen Power Plant is equipped with cylinder exhaust, turbine exhaust, main bearing, generator stator, cylinder liner water, lubricating oil and other temperature monitoring and fuel, starting air, lubricating oil, raw water, cylinder water, nozzle water, Pressure monitoring such as intake air. These temperature and pressure monitoring, alarm and safety shutdown systems are mainly composed of CMR424 and CMR524 units mounted on the control panel.

Diesel engines have many temperature sensing elements in operation, but they can be roughly classified into two types: thermal resistance (PT100) and thermocouple (Ni-Cr/Ni-Al). The thermal resistance sensor changes the resistance value during temperature change and the thermoelectric potential change of the thermocouple sensor during temperature change, and transmits the signal to the CMR424 system for conversion, comparison, printing, display and action on the alarm or trip. The pressure is transmitted through the on-site pressure transmitter to the CMR424 system for conversion, comparison, printing, display and action on the alarm or trip.

3.2 Advantages and Disadvantages This system is small in size, few components (each signal is converted by a separate circuit board), centralized layout, easy to monitor, and some of the temperature (such as cylinder water temperature, lubricant temperature, etc.) control PLC microcomputer control, the degree of automation is relatively high. The control of the lubricating oil pressure and the water pressure of the cylinder liner directly uses the pressure switch to act on the jumper. Despite this, the system still has some limitations. For the exhaust temperature, only the difference between the single cylinder and the average temperature is alarmed. There is no alarm that the single cylinder temperature exceeds the set value, and the temperature cannot be displayed in real time. Conventional automatic recorders require a large amount of printing paper, and the printing interval is too long, and the various curves are crowded together and difficult to discriminate, and cannot be digitized. A few times the damage of the turbine is because the temperature rise is not detected in time and the valve is damaged and the turbine is damaged. 3.3 Common faults and countermeasures for improvement 3.3.1 Temperature display fluctuations and large amplitude, sometimes showing -1 or 1 The causes of the fault are: First, the connection plug is not in good contact and can be tightened. When the plug is loose, CMR424 shows -1; Second, the probe characteristics deteriorate, the probe can be replaced, especially when the thermal resistance probe is short-circuited, CMR424 shows 1; third, the electronic board needs to be re-adjusted.

3.3.2 Temperature display electronic board failure or set temperature change Deng Yi bypass generation main switch operation protection configuration impact on system safety Chen Chaoming Sun Plain (Jiangxi Jiujiang Power Supply Bureau Jiujiang 332000) explained the bypass switch generation When the main transformer switch is running, the problem of the main transformer protection blind zone and its harm to the stability of the system appear, and the scheme of eliminating the blind zone is proposed.

Switching bypass main transformer relay protection blind zone In the high voltage power grid where the neutral point is directly grounded, the main transformer switch of the power must sometimes exit the system due to abnormalities such as mechanism failure. In order to ensure continuous power supply of the transformer, the bypass switch is used to replace the main transformer. run. However, during this period, the bypass switch protection usually exits from operation, posing a safety hazard to the stable operation of the power grid.

1 Large main transformer and bypass loop current transformer (CT) and protection configuration Large-scale main transformer and bypass loop CT configuration diagram To facilitate the explanation of the wiring principle, the number and coil of each CT are simplified, only listed Representative number, the function is explained below.

1LH (main transformer switch CT) is mainly used for transformer differential protection, zero sequence direction protection, bus differential protection, metering, etc.; direction overcurrent, zero sequence overcurrent protection and power and current measurement; 3LH (bypass switch CT) Used for busbar protection and line (distance, zero sequence, high frequency) protection.

2 Problems existing in the current configuration 2.1 When the bypass switch is operated in the main transformer, the operation of the protection is actually working. When the bypass switch is used to operate the main transformer, the main principle of the main transformer protection wiring must be adopted. The protection is changed without the use of a bypass switch protection device. However, with the change of the operation mode, the protection range and configuration of the main transformer protection device have also undergone corresponding changes, mainly in the following: the main transformer switch is replaced by the zero-sequence direction of the generation side to disable the main transformer differential protection current loop. 1LH is transferred to 2LH. The second point is automatically realized by the wiring principle, and the third point needs to be completed by manual switching, and the main variable differential protection needs to be withdrawn during the switching process, and the range of differential protection is also reduced accordingly.

When the main change switch is faulty between the lead bushing and the bypass switch CT lead (see the fault point), it can be seen from the analysis that the short circuit point is in the blind zone of the main transformer differential protection, and the fault point is not in its scope. within. Therefore, the main transformer differential protection cannot cut the fault point.

Since the fault point is also outside the range of the busbar protection, the busbar protection cannot operate to remove the faulty point.

The short-circuit current generated by the fault can cause the bypass protection to operate and remove the fault. However, since the general practice is to test the bypass switch distance by using a standard resistance box or a millivolt generator to input a set of standard temperature signals, it is also possible to input a set of actual temperatures for verification using an oven. It is true that the failure of the electronic board should be replaced. A small change in the set temperature (within 2%) is a normal condition and is a result of temperature drift.

Preventive management is an advanced management mode. The advanced automatic protection system does not make the operation management staff sit back and relax. Only by correctly understanding, maintaining and utilizing such a system to prevent accidents can the reliable operation of the diesel engine be provided. Foundation.

4 Conclusion

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