Source: Polaris Thermal Power People
Part 1 EH Oil System
1. Concept
The EH oil system is the steam turbine speed control oil system, also known as the high-pressure anti-fuel system, mainly because the speed control oil system and the lubricating oil system of the steam turbine are independent, using high temperature anti-fuel (EH oil), and using high oil pressure to control the main valves and speed control valves of the steam turbine, so it is also known as the steam turbine EH oil system.
2. System composition
The EH oil system is divided into three parts according to its function, the EH oil supply system, the actuator part, and the critical blocking part:
1) The function of the oil supply system is to provide high pressure fuel resistance, and it drives the servo actuator, while maintaining the normal physical and chemical characteristics and running characteristics of the hydraulic oil.
2) The actuator responds to the electrical command signal sent from DEH to adjust the opening of each steam regulating valve of the steam turbine;
3) The critical cut-off system is controlled by the cut-off parameters of the steam turbine, and when these parameters exceed its operating limit value, the system closes all the steam turbine inlet valves or only closes the speed-regulating valves.
3. EH oil supply system
The EH oil supply system consists of EH oil tank, EH oil pump, entrance and exit door, filter screen, control block, relief valve, accumulator, EH oil supply and return pipe, oil cooler, and a set of self-circulating oil filtration system and self-circulation cooling system.
After EH oil is sent from the oil tank to the actuator and the critical blocking system through the oil pump inlet door, inlet strainer, EH oil pump (high-pressure variable piston pump), EH oil control block (including outlet strainer, check valve, outlet door, and overflow valve), through the high-pressure accumulator and the high-pressure oil supply mother pipe HP, and the oil return of the system actuator is returned to the oil tank through the pressurized oil return mother pipe DP, the oil return filter screen, and the oil return cooler; The oil return of the critical blocking system is returned to the oil tank through the non-pressure oil return mother pipe DV. During the normal operation of the unit, the oil return in the non-pressure oil return mother pipe is the oil discharge after the emergency blocking oil in the AST critical blocking control block passes through the two throttle holes, and two pressure switches are installed between the two throttle holes to monitor and test the working and action of the AST solenoid valve.
4. Executive agency
The actuator consists of an oil motor, which is opened by anti-fuel and closed by spring force. The oil engine is connected to a control block, on which a shut-off valve, a quick unloading valve and a check valve are installed, plus different accessories, to form two basic forms of actuators - regulating type and switching type. Except for the reheat main valve is a switch type, it is an adjustment type. The position of each steam valve is controlled by its own actuator.
The regulated actuator is fitted with an electro-hydraulic converter (servo valve) and two linear displacement transmitters, LVDTs, which allow the corresponding steam valves to be controlled in any intermediate position and the steam intake is proportional to the demand.
5. Critical blocking system
The critical blocking system is mainly composed of membrane valve, AST solenoid valve, air guide valve, critical blocking test device, critical blocking device, critical blocking spool valve and security control device for remote reset.
As long as the security oil pressure in the mechanical overspeed and manual shutdown mother pipe disappears, such as the action of the critical cut-off or the manual movement of the trip lever, resulting in the release of the security oil pressure, it will cause the opening of the membrane valve, and the shutdown will be caused by the release of high-pressure anti-fuel.
There are six solenoid valves on the critical shut-off control block, four of which are automatic shutdown shut-off solenoid valves AST and two overspeed protection solenoid valves OPC. There is an air guide valve below the critical shut-off control block, which is used to control the exhaust backstop door and the high-discharge backstop door of each section.
Part 2 EH Oil System Courseware
Part 3 Typical Faults and Handling of EH Systems
1. EH oil pressure fluctuation
2. Resistance to increased fuel acid value
3.EH The oil temperature increases
4. Oil motive swing
5. Tubing vibration
6. ASP Oil pressure alarm
1. EH oil pressure fluctuation: EH oil pressure fluctuation means that under the condition of normal operation of the unit (non-valve large adjustment), the range of EH oil pressure fluctuation is greater than 1.0MPa.
The two main oil pumps configured in the EH system are constant pressure variable pumps. The constant pressure variable pump is to automatically adjust the output flow of the pump through the change of the outlet pressure of the pump to achieve the purpose of constant pressure, so theoretically speaking, the constant pressure pump has a certain pressure fluctuation. However, if the pressure fluctuation range exceeds 1.0MPa, we consider the pump to be a regulation failure. Of course, if the minimum output pressure of the pump is greater than 11.2MPa at this time, it will not affect the operation of the unit. When the pressure of the EH oil system fluctuates greatly, most of them are caused by the inflexible action of the regulating device of the main oil pump, and on the other hand, the accumulator is defective and has poor stability.
The regulating device is divided into two parts: the regulating valve and the pushing mechanism. The regulating valve is installed in the upper part of the pump, which feels the change in the outlet pressure of the pump and converts it into the thrust of the pushing mechanism, and the adjustment screw on it is used to set the system pressure. The gap between the spool of the control valve is very small, about 0.02~0.03mm, if the impurity particles in the EH oil enter the pressure regulator with the oil, the gap will be blocked, resulting in jamming. When the regulating valve core appears jammed, can not be converted into the thrust of the pushing mechanism in time, according to the position of the valve core jamming, the oil pressure may drop lower and lower, may also rise higher and higher, the valve core is rushed to a new position, thereby causing the pump output pressure to fluctuate greatly. Due to the frequent operation of the regulator, long-term operation will lead to wear and tear of the valve core and valve sleeve, and the gap will increase. This will make the pressure oil enter the regulating oil port from the pressure port through the gap, and cause the variable oil cylinder to be unable to move back, and the output flow rate and pressure of the pump are low. The pushing mechanism is inside the pump body, and the driving force generated by the piston overcomes the spring force to determine the inclination angle of the pump swash plate. When the pushing piston is jammed or the friction increases, the change of the pressure signal output by the regulating valve cannot be converted into the change of the inclination angle of the swash plate (i.e., the output flow rate of the pump) in time, so that the output pressure of the pump fluctuates. In this case, it is necessary to clean the relevant parts of the pushing mechanism and check the surface quality of the pushing piston. Because this part of the mechanism is installed in the pump body, it is best to be completed by the professional and technical personnel appointed by the pump manufacturer.
2. Resistance to elevated fuel acid value:
The influence of temperature on the increase of acid number is (1) the influence of temperature: the local temperature in the oil system is too high or a certain section of the oil pipeline is very close to the steam pipeline, so that the temperature of the oil pipeline is affected by radiant heat and the temperature increases, resulting in the aging and decomposition of the oil and the production of a large number of organic acids. If there is a problem with the cooling device, such as the scaling of the cooler pipeline, the cooling effect is not good, resulting in a long-term high oil temperature, and the acid value of the oil will also increase during operation.
(2) The influence of additives in oil: In order to prevent the accelerated deterioration of oil products during operation, a certain dose of additives is usually added to the oil, such as rust inhibitors, demulsifiers, etc. Different types of additives added, or different dosages of the same type of additives, will affect the acid value of the oil. Therefore, before adding additives to the oil, a small test must be done, the purpose of which is to ensure that the anti-deterioration effect is achieved, and does not affect the performance indicators of the oil, especially the acid value of the oil. When meeting the above requirements, it is advisable to choose the minimum amount of additives.
(3) The influence of moisture in the oil: for the anti-fuel oil of phosphate lipids, the increase of water content will cause hydrolysis, the generation of acidic phosphate and phenol, and further reaction to generate low molecular acid and high molecular aging products, and the resulting acid products will catalyze the further decomposition of the oil, resulting in the continuous increase of the acid value of the oil.
(4) The influence of microorganisms and environmental pollution: There are a large number of microbial communities in the oil, and under the condition of suitable oil temperature and pH value, microorganisms can multiply in large quantities, and their metabolites will increase the acid value of the oil. In addition, some microorganisms can also promote the oxidation and decomposition of oils, producing acidic substances.
At present, the influence of microorganisms on oil quality has been widely paid attention to abroad, and the influence of microorganisms on transformer oil dielectric loss has also been found in China. In addition, the increase of the acid number of the oil will also be affected by the content of a certain medium in the air, the strength of the surrounding electric field and other factors, which will also promote the change of the acid value of the oil under certain circumstances. The internal factor that affects the increase of the acid value of the oil is the internal basic molecular structure of the anti-fuel, but this has been determined in the oil production process and cannot be changed by the user. The acidity index of the new oil resistance is 0.03 (mgKOH/g), and when the acidity index exceeds 0.1, we consider the acid resistance to fuel oil to be too high, and high acidity will lead to problems such as sedimentation, foaming and air spacing in the fuel resistance. There are many factors that affect the acidity of the fuel, but for the EH system we use, the main factors that affect the acidity of the fuel are local overheating and excessive water content, with local overheating being the most common. Because the EH system works on the steam turbine, accompanied by high temperature and high pressure steam, it is inevitable that some components or pipelines are in a high temperature environment, and the increase in temperature accelerates the anti-fuel oxidation, and the oxidation will increase the acidity of the anti-fuel and darken the color.
Therefore, when designing and installing an EH system, we should pay attention to:
1) EH system components, especially pipelines, should be kept away from high-temperature areas;
2) Increase ventilation and reduce ambient temperature;
3) Increase the flow of anti-fuel and try to avoid dead oil cavities. Due to the reliability design of the oil cooler, there are few examples of water leakage in the oil cooler to resist fuel, and most of the water in the oil cooler is caused by condensation in the fuel tank. Water is hydrolyzed in the fight against fuel, and the hydrolysis produces phosphoric acid, which in turn is a catalyst for hydrolysis. Therefore, a large amount of moisture will increase the acid value of fuel resistance. When the acid number of the fuel rises to an additional level, it must be continuously put into the regeneration unit. The diatomaceous earth filter in the regeneration unit effectively reduces the acidity of the fuel resistance. When the acidity of the fuel resistance is close to 0.1 (e.g. greater than 0.08), it should be put into a regeneration unit, at which point the acidity will drop very quickly. When the acidity of the fuel resistance exceeds 0.3, it is difficult to reduce the acidity with diatomaceous earth. When the anti-fuel acidity exceeds 0.5, it is no longer operational and needs to be changed.
3. EH oil temperature rises: The normal working oil temperature of the EH system is 43.3~54.4°C, when the oil temperature is higher than 57°C, it will be automatically put into the cooling system. If the oil temperature is consistently above 50°C when the cooling system is already in operation and working properly, we consider the system to generate too much heat and the oil temperature is too high. The high oil temperature excludes environmental factors, mainly due to the internal leakage of the system and the oil cooler.
Due to system design reasons:
1) At this time, the return oil does not pass through the oil cooler, and the temperature of the return pipe will rise, so that the temperature of the oil tank will rise.
2) The overpressure overflow of the oil pump also does not pass through the oil cooler, and the temperature of the return oil pipe will rise, so that the temperature of the oil tank will rise.
3) The normal leakage of the system is reduced, so that the cooling medium is reduced, and the cooling effect cannot be achieved.
4. Oil engine swing: Under the condition that the input instruction is unchanged, the oil engine feedback signal changes periodically and continuously, which we call the oil engine swing. The amplitude of the oil motor swing is large and small, and the frequency is fast and slow.
The main reasons for the oscillation of the oil motor are as follows:
1) Thermal signal problem. When the output signal of the servo power amplifier card contains an AC component, and when the servo valve signal cable is grounded at a certain point, the oil engine swing phenomenon will occur. LVDT signal fluctuations or failures.
2) Servo valve failure. The servo valve is jammed, reducing the response frequency of the servo valve, after the servo valve receives the command signal, the servo valve adjustment can not meet the requirements of the command signal, resulting in hysteresis causing the oil motor to swing.
3) Changes in output instructions caused by sudden valve jumps. When a certain valve works at a specific working point, due to the action of steam force, the main valve suddenly jumps from the bottom dead center of the door stem to the upper dead center of the door rod, resulting in an increase in the flow rate, and according to the power feedback, DEH issues a command to close the valve. In the process of valve closing, also under the action of steam force, the main valve suddenly jumps from the upper dead center of the door stem to the bottom dead center of the door rod again, resulting in the decrease of flow rate, and DEH issues the command to open the valve again. This repetition causes the oil engine to swing. The DEH is powerless to deal with the oscillation of the oil engine due to the sudden jump of the valve, and the only way to move the common operating point away from this position is to modify the characteristic curve of the valve.
5. Tubing vibration: EH tubing has high-frequency oscillation, especially the part close to the oil motive, with an amplitude of more than 0.5mm, which is called EH tubing vibration, of which HP pipe is the most. Tubing vibration can cause joints or clamps to loosen, resulting in leakage and, in severe cases, pipeline breakage.
The main causes of tubing vibration are as follows:
First, the unit vibrates. The oil motor is connected with the valve body, such as the medium pressure valve of the unit, the oil motor is in the uppermost part of the cylinder, when the vibration of the unit is larger, it is bound to cause the oil motor to vibrate greatly, and the oil pipe vibration connected with it is also bound to be large.
Second, the pipe clamp is not well fixed. The pipe clamp must be fixed reliably, if the pipe clamp is not fixed well, it will cause the tubing to vibrate.
Third, the servo valve is faulty, which generates an oscillation signal and causes the tubing to vibrate.
Fourth, the control signal entrains the AC component, so that the pressure in the HP tubing alternates to produce the tubing vibration. It is possible to determine which cause of the vibration is caused by the test. When vibration occurs, the valve is slowly placed in the fully closed position by a forced signal, the inlet throttle is closed, the servo valve is unplugged, and the vibration is measured. If the vibration decreases significantly at this time, it means that the servo valve or control signal is a problem; If the vibration persists, it means that the unit is vibrating. For the former case, open the inlet throttle, use the servo valve test tool to open the valve to the original position by the method of external signal, if there is no vibration at this time, it means that it is a control signal problem, which is handled by thermal inspection; If the vibration increases, it means that the servo valve is faulty, and the servo valve should be replaced immediately.
6. ASP Oil Pressure Alarm: ASP oil pressure is used to test AST solenoid valves online. ASP oil pressure is generated by AST oil pressure through the orifice and then through the orifice to the return oil. The ASP oil pressure is usually around 7.0MPa. When the AST solenoid valve 1 or 3 acts, the ASP pressure rises and the ASP1 pressure switch acts; When the AST solenoid valve 2 or 4 acts, the ASP pressure decreases and the ASP2 pressure switch acts. If the AST solenoid valve is not operating, the ASP1 or 2 pressure switch is acting, or the pressure switch does not reset after the AST solenoid valve is reset, there is an ASP oil pressure alarm. ASP oil pressure alarm should first check the solenoid valve fault, such as ASP oil pressure greater than 9.3 means AST solenoid valve 1 or 3 failure, ASP oil pressure less than 4.2 means AST solenoid valve 2 or 4 fault. However, if the oil quality problem causes the throttle to become blocked, it will also cause an ASP oil pressure alarm. Of course, ASP oil pressure alarm, after the alarm, the first thing to determine is which solenoid valve is faulty, which can be determined by replacing the position of the solenoid valve. For example, an ASP high alarm indicates that AST solenoid valve 1 or 3 is faulty. The solenoid valve 1 and the solenoid valve 2 can be swapped positions, if it is still a high alarm at this time, it means that solenoid valve 3 is faulty, if it becomes a low alarm at this time, it means that solenoid valve 1 is faulty. If a faulty solenoid valve is found, it can be dealt with by overhauling or replacing it.