Created on:2021-07-28 09:53

Fault analysis of abnormal trip caused by hydraulic oil system of steam turbine_ Analysis and inspection experiment

汽轮机液压油系统引起机组异常跳闸的故障_分析检查实验
Fault analysis of abnormal trip caused by hydraulic oil system of steam turbine_ Analysis and inspection experiment

(1)概述
(1) Overview

    某电厂2号机在运行过程中因推力瓦磨损检测液压装置的信号引起机组一系列异常动作并触发跳机。跳闸前机组带340MW负荷稳定运行且无任何操作。跳机报告如下。
During the operation of unit 2 in a power plant, a series of abnormal actions were caused by the signal of thrust pad wear detection hydraulic device, and the tripping was triggered. Before tripping, the unit operated stably with 340mw load without any operation. The trip report is as follows.

09:1 8:50 500 ms**TURBINE THRUST TRIP
09:1 8:50 500 ms**TURBINE THRUST TRIP

+00 00 145 TURBINE THRUST NORMAL
+00 00 145 TURBINE THRUST NORMAL

+o0 00 280 TURBINE THRUST TRIP
+o0 00 280 TURBINE THRUST TRIP

+00 00 405 TURBINE THRUST NORMAL
+00 00 405 TURBINE THRUST NORMAL

+00 01 005 IV (LEFT) FULLY CLOSE
+00 01 005 IV (LEFT) FULLY CLOSE

+00 01 055 ALL CVs FULLY CLOSE
+00 01 055 ALL CVs FULLY CLOSE

+00 01 260 IV (RIGHT) FULLY CLOSE
+00 01 260 IV (RIGHT) FULLY CLOSE

+00 07 220 MSV (LEFT) FULLY CLOSE
+00 07 220 MSV (LEFT) FULLY CLOSE

+00 1 1 675 MSV (RIGHT) FULLY CLOSE
+00 1 1 675 MSV (RIGHT) FULLY CLOSE

+00 1 1 695 ALL MSVs FULLY CLOSE
+00 1 1 695 ALL MSVs FULLY CLOSE

+00 11 755 MFT ACTION ON
+00 11 755 MFT ACTION ON

+00 1 2 055 MTS OPERATED
+00 1 2 055 MTS OPERATED

    在以往的跳机报告中,触发原因及保护动作过程一般都符合正常的动作顺序,而这次跳机报告不符合机组的任何一种常规保护设计逻辑,看上去非常混乱,存在很多疑问。因此,跳机原因不能立即下结论。针对这次跳机,当时及事后对各种可能原因进行了大量的试验研究。
In the previous trip reports, the trigger reason and protection action process generally conform to the normal action sequence, but this trip report does not conform to any of the conventional protection design logic of the unit, which seems very confusing and has many doubts. Therefore, the cause of the trip cannot be concluded immediately. In view of this trip, a large number of tests were carried out at that time and afterwards on various possible causes.

(2)跳机期间的分析检查及试验
(2) Analysis, inspection and test during tripping

    由于一时找不到对跳机过程的合理解释,于是进行各种可能性猜测,对各相关系统进行分析并在可能的条件下进行了一系列的试验和调查。
Because we can't find a reasonable explanation for the trip process at the moment, we speculated on various possibilities, analyzed the relevant systems, and carried out a series of tests and investigations under possible conditions.

    ①汽轮机推力瓦磨损检测液压装置 该汽轮机推力瓦磨损检测液压装置的工作原理如图F所示。当推力瓦发生磨损时,45。斜面凸轮将轴向移动,带动斜面喷嘴做上下同步移动,使活塞错油门的进出油口尺寸发生变化,从而使活塞内油压发生变化。通过与之相连的油压开关可以判断推力瓦的磨损状况。活塞套由内外两层结构组成,外活塞套相对汽轮机轴承座固定,内活塞套可以通过试验盘的螺纹进行上下移动,可等效模仿活塞的反向上下位移,即模仿汽轮机大轴的轴向位移。试验肘,通过试验开关解除跳闸联锁保护,并由试验灯观察试验状态。
① The working principle of the hydraulic device is shown in Fig. F. When the thrust pad is worn, 45. The inclined cam will move axially to drive the inclined nozzle to move up and down synchronously, which will change the size of the oil inlet and outlet of the piston's stagger throttle, thus changing the oil pressure in the piston. The wear condition of thrust pad can be judged by the oil pressure switch connected with it. The outer piston sleeve is fixed relative to the bearing seat of the steam turbine, and the inner piston sleeve can move up and down through the thread of the test plate, which can simulate the reverse up and down displacement of the piston, that is, the axial displacement of the main shaft of the steam turbine. The trip interlock protection is released by the test switch, and the test status is observed by the test lamp.

F.jpg

    跳机报告中显示汽轮机推力瓦磨损信号(带~号者)触发跳机,因此首先对推力瓦磨损检测液压装置进行了数次试验。未发现任何异常。令人不解的是,跳机报告中推力瓦磨损信号在不到半秒的时间内连续动作了2次,而且2次动作的持续时间很短,分别是145ms及125ms。如果汽轮机推力瓦真正发生严重磨损,那么就不会自动恢复正常,因此推断推力瓦本身没有问题,而短暂的脉动信号只是误动作。于是把推力轴承磨损信号当作直接触发跳机的原因。但很快发现,这样的假设与跳机报告中各保护的动作顺序不符。在对测量回路及控制盘内保护通道进行了检查、试验且均为正常后,又开始寻找其他的跳机原因。
The trip report showed that the turbine thrust pad wear signal (with No.) triggered the trip. Therefore, several tests were carried out on the thrust pad wear detection hydraulic device. No exception was found. What is puzzling is that the thrust pad wear signal in the trip report acted twice in less than half a second, and the duration of the two actions was very short, which were 145ms and 125ms respectively. If the thrust pad of steam turbine is seriously worn, it will not automatically return to normal. Therefore, it is inferred that there is no problem with the thrust pad itself, and the transient pulsation signal is only misoperation. Therefore, the wear signal of thrust bearing is regarded as the cause of tripping. However, it is found that this assumption is inconsistent with the action sequence of each protection in the trip report. After checking and testing the measuring circuit and the protection channel in the control panel, we began to look for other causes of tripping.

    ②汽轮机危急保安器试验电磁阀 跳机报告中,先是汽轮机蒸汽阀门关闭,然后是汽轮机主跳闸电磁阀(MTS)动作,那么这些由油动机带动的汽轮机蒸汽阀门又是什么原因导致关闭的呢?从汽轮机危急保安器系统分析可知,若试验电磁阀误动作,将会导致误跳机。经确认跳机后无人对危急保安器液压装置进行就地操作或复位,于是检查危急保安器液压装置的位置状态,发现试验电磁阀未引起跳机活塞杆动作,因此排除了该电磁阀误动的可能性。
② In the trip report of turbine emergency protector test solenoid valve, first the turbine steam valve is closed, and then the turbine main trip solenoid valve (MTS) acts. So what causes these turbine steam valves driven by hydraulic motor to close? According to the analysis of the emergency protector system of steam turbine, if the test solenoid valve misoperates, it will lead to mistripping. After confirming that no one operated or reset the hydraulic device of the emergency protector on site after tripping, the position state of the hydraulic device of the emergency protector was checked, and it was found that the test solenoid valve did not cause the tripping piston rod to act, so the possibility of the solenoid valve misoperation was ruled out.

    ③MTS连杆位置开关 是否MTS在蒸汽阀门关闭之前实际已经动作,只是因这个位置开关动作不灵敏,其信号送到计算机系统有延迟?经检查位置开关,未见异常,之后又进行了多次动作试验,也正常。
③ Is the MTS connecting rod position switch actually activated before the steam valve is closed, only because this position switch is not sensitive and its signal is sent to the computer system with delay? After checking the position switch, no abnormality was found. After several action tests, it was also normal.

    ④汽轮机功率负荷不平衡保护功能(PLU) MTS未动作而蒸汽阀门先被关闭,可能是PLU保护动作引起。这项保护是当电网设备故障、电厂机组瞬间大幅甩负荷时,为了防止汽轮机超速飞车而设计的。当PLU动作时会立即把汽轮机4个高压调门(CV)及2个中压调门(IV)关闭。用于这个保护回路中的中压缸进汽压力变送器、发电机输出功率变送器以及检测运算回路是否有误动的可能?据此对PLU进行了试验,未发现任何异常。若PLU动作,不应该关闭汽轮机高压主汽门(Msv),除非发电机逆功率保护动作,这与跳机报告也不符,因此也可以排除PLU误动作的可能。
④ If the MTS of the turbine power load unbalance protection function (PLU) does not act and the steam valve is closed first, it may be caused by the action of the PLU protection. This kind of protection is designed to prevent the turbine from speeding when the power grid equipment fails and the unit of the power plant suddenly loses load. When the PLU acts, the four high pressure control valves (CV) and two medium pressure control valves (IV) of the steam turbine will be closed immediately. Is there any possibility of misoperation of IP cylinder inlet pressure transmitter, generator output power transmitter and detection calculation circuit used in this protection circuit? Based on this, the test of PLU was carried out, and no abnormality was found. If the APU acts, the high pressure main steam valve (MSV) of the steam turbine should not be closed unless the reverse power protection of the generator acts, which is also inconsistent with the trip report. Therefore, the possibility of wrong operation of the APU can also be ruled out.

    ⑤汽轮机数字电液控制系统(DEH) 在跳机报告中,汽轮机阀门动作混乱。是否因为DEH汽轮机阀门控制电路板或就地控制设备出现异常?由于多个阀门几乎同时动作,可以排除各个相对独立的阀门控制通道发生故障的可能性。若是DEH主控制器(MC)或系统控制器(SC)中的某些电路板故障或者程序问题使阀门关闭,根据信号处理流程,不应该在跳机报告中出现推力瓦磨损触发信号。因此,对于整个DEH系统来说,除与现场油压开关相连的输入通道板外,其他软件及硬件设备触发故障的可能性均可排除。
⑤ In the trip report of DEH, the action of steam turbine valve is confused. Is it because of the abnormality of DEH steam turbine valve control circuit board or local control equipment? Because multiple valves act almost at the same time, the possibility of failure of each relatively independent valve control channel can be eliminated. If the valve is closed due to some circuit board fault or program problem in the main controller (MC) or system controller (SC) of DEH, the trigger signal of thrust pad wear should not appear in the trip report according to the signal processing flow. Therefore, for the whole DEH system, except for the input channel board connected with the field oil pressure switch, the possibility of other software and hardware triggering faults can be eliminated.

    ⑥外部电磁干扰对计算机的影响 在未对跳机报告进行合理解释的情况下,经与运行当班了解,在跳机前,机组及系统没有大功率设备操作,计算机也未记录到任何干扰或异常现象。根据十几年来计算机系统的运行表现,虽然这次跳机报告看上去很怪异,但是打印的动作结果不应该是一种虚假现象,因此还需要更深入地分析原因。在停机的几小时里,通过上述分析检查及试验后,仍未能找到一种合理的解释,因此又回到了推力瓦磨损检测回路,分析另一种可能性,即跳机不是由于磨损信号直接触发,而是由其间接引起。虽然这种猜测不符合正常的保护逻辑,但在极端的情况下能否发生,需要模拟产生毫秒级的脉冲信号进行验证。因此,决定在启机后进一步研究并准备相关设备进行试验。
⑥ The impact of external electromagnetic interference on the computer without reasonable explanation of the trip report, after understanding with the operator on duty, before the trip, the unit and system did not operate with high-power equipment, and the computer did not record any interference or abnormal phenomenon. According to the performance of the computer system over the past decade, although the report of this trip seems very strange, the printed action result should not be a false phenomenon, so we need to further analyze the reasons. In several hours of shutdown, after the above analysis, inspection and test, a reasonable explanation could not be found, so we went back to the thrust pad wear detection circuit to analyze another possibility, that is, the tripping was not directly triggered by the wear signal, but indirectly caused by it. Although this guess does not conform to the normal protection logic, whether it can happen in extreme cases needs to be verified by simulating the generation of millisecond level pulse signal. Therefore, it is decided to further study and prepare relevant equipment for test after startup.

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