A switch failure treatment brings us enlightenment
switch failure process
one day in July 2001, the boiler operator of a power plant was stopping the operation of the pulverizing system. When the centralized control disconnected the switch of No. 1 coal mill, the green light of the switch was on, and the ammeter indicated 0, but the sound of coal mill operation was still faintly audible, reaching 0 M. the attendant reported: No. 1 7 End the experiment or carry out the next round of experiment. The pulverizer is still running, and the reason is unknown. The electrical foreman immediately sent watchmen A and B to 0 m for inspection. The on-site inspection found that No. 1 coal mill was indeed running and the motor sound was abnormal, but it was found in the power distribution room that the follow-up position indication of the 6 kV trolley switch mechanism showed that the switch was in the off position. A believes that if the green light of the switch is on, the current reaches 0, and the position indication is in the off position, it is impossible for three indications to fail at the same time, and the switch is definitely off. After reporting to the team leader, the team leader ordered to check the live indicator light of the switch again. After a while, Party B reported that the live indicator lights of phase A and C of the switch were on, and phase B was not on. The electrical foreman ordered to close the switch of No. 1 coal mill, immediately contact the steam turbine and boiler operators to switch or stop all loads on the 6 kV bus where No. 1 coal mill is located, then cut off the bus with the working incoming switch of the bus section, pull out the trolley switch of No. 1 coal mill, and then restore the power supply of the 6 kV bus
2 analysis of switch fault phenomenonit is necessary to test all castings or forgings
Figure 1 shows the wiring of the ammeter of No. 1 coal mill in the CT secondary circuit. When the ammeter indicates 0, it can only indicate that the B-phase current or the sum of the A and c-phase currents is 0, which cannot prove that the three phases are switched off in some cases; However, when the switch green light is on and the position indication is disconnected, it can only indicate that the switch mechanism is disconnected, and it cannot prove that the three-phase switch is indeed disconnected; However, the operation of the motor and the electrified indicator lights of phase A and C confirm that phase A and C are not disconnected. As for the reason, there may be a problem in the transmission part of the mechanism. Inspection results of switch: the connecting rod of camera mechanism a and C fell off
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Figure 1. The wiring of the ammeter of coal mill 1 in the CT secondary circuit
the enlightenment brought to us by the fault treatment of switch 3
(1) when analyzing abnormal phenomena, the electrical operators must break through the thinking formula of" not 1 is 0 "
it is generally recognized that the steam turbine and boiler operators operate the valves half open and half closed, while the electrical operation is different," not 1 is 0 " ", no regrets. This view emphasizes the logic of electrical operation and promotes the electrical operators to correct their operating attitude and seriously implement the" three second thinking ", but it restricts people's way of thinking to a certain extent, making many electrical operators unable to make correct judgments on mechanical faults. For example, the less experienced attendant a can't find out that" the current reaches 0, the position indication is off and the switch is not off " Reasons
(2) abnormal analysis of the market demand for non-ferrous metal products, which is difficult to see a significant increase, must grasp the key
in the process of this failure, the motor operation is a "key" phenomenon. Unlike other equipment, there is no such situation as "fan pneumatic, water pump hydraulic". It can operate, and there must be electricity. Only through the phenomenon can we find out whether the switch is three-phase or two-phase, why. If you can't grasp the key, you will be confused by the illusion of "current to 0, position indication off position"
(3) the operator must be familiar with the equipment structure and electrical secondary circuit
some operators believe that "the operation union can work, and it is useless to learn more". This view is extremely wrong. There is a great difference between good or bad learning and theoretical level in analyzing problems. To a certain extent, it is more difficult to analyze a small anomaly than to carry out a so-called "large-scale operation", and it is impossible without a solid theoretical foundation
(4) the implementation of "emergency stop regulations" should be "tight"
during the fault treatment, when it is judged that the switch a and C camera mechanisms are disconnected, someone said to stop the bus immediately, and the electrical team leader took corresponding measures, which is the real "tightness". The motor switch failure cannot be disconnected belongs to the scope of emergency stop, but we can't blindly make an article on the word "emergency". The motor is not in full phase operation for fear of overheating and damage; However, if the switch refuses to operate, it will cause the bus power switch to skip the level and trip in case of motor failure, which will affect the operation of the generator and boiler. At this time, immediately cutting off the bus power is the worst case. For the boiler with a single forced draft fan, it is impossible not to extinguish the fire. Therefore, it is correct to turn on the switch immediately to turn the motor into three-phase operation, and then take other measures. This also reminds the operators not to take drastic measures because they are too nervous
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