Abstract: After the units of Qingyuan Pumped-storage Power Plant are installed, separate tests of various auxiliary machines must be carried out before the operation test. The adjustment of the magnetic switch of the oil level gauge is one of the contents. The author introduced the adjustment method of the magnetic switch of the oil level gauge, analyzed some problems that appeared in the adjustment process and proposed solutions. Through adjustment, after Qingyuan Power Station is put into operation, the magnetic switch of the oil level gauge can send out an accurate alarm signal.PrefaceThe Qingyuan Pumped Storage Power Station is located in Taiping Town, Qingxin County, Qingyuan City. The total installed capacity of the power station is 1 280 MW, and 4 vertical-shaft single-stage reversible mixed flow generators with a single capacity of 320 MW (power generation conditions) are installed. After the power station is completed, it will be used as one of the backbone peak-shaving power sources to undertake tasks such as peak-shaving, valley filling, frequency modulation, emergency backup and other tasks of the Southern Power Grid. After the unit is installed, individual tests of various auxiliary machines shall be carried out before the operation test. The adjustment of the magnetic switch of the oil level gauge is one of the contents. The lower oil tank of Qingyuan Power Station has four alarm signals, namely, oil level ultra-low (LL), low (L), high (H), and ultra-high (HH). When the oil level of the oil tank changes and the oil level passes by the magnetic switch of the oil level gauge, the magnetic switch will send out a corresponding alarm signal. Whether the magnetic switch is adjusted in place is related to whether the oil level alarm signal can be accurately issued. This article introduces the adjustment method of the oil level indicator signal of Qingyuan Power Station.1 Oil level gauge pipeline structureAn auxiliary oil tank is set outside the annular foundation of the Qingyuan power station unit, and the auxiliary oil tank is connected to the lower oil tank through a connecting pipe. The oil level gauge is installed on the connecting pipe. According to the principle of the communicating device, the oil level of the oil level gauge is equal to the oil level in the lower oil tank, so that the oil level of the lower oil guide tank can be monitored by monitoring the oil level of the oil level gauge. A ball valve is installed between the oil level gauge and the connecting pipe to facilitate the disassembly and assembly of the oil level gauge during maintenance. The specific structure is shown in Figure 1.2 Structure and principle of oil level gaugeThe oil level gauge of the Qingyuan power station unit uses the Kopler BNA bypass magnetic turning column liquid level gauge. The level gauge is composed of flange, magnetic switch, bypass pipe, magnetic turning column, magnetic float, transmitter, sewage plug, etc. The specific structure is shown in Figure 2. The oil level gauge is connected with the pipeline to be tested through a flange. There is a magnetic float in the oil level gauge, which floats up and down with the oil level. In the process of floating up and down, the float drives the magnetic column level gauge to flip and trigger the magnetic switch through its own magnetic field. Magnetic turning column level gauge is turned over with different oil levels, so that it is convenient to observe the oil level height on-site. The switching value sent by the magnetic switch is sent to the monitoring terminal, and the unit can respond according to the preset logic. The transmitter outputs 4-20 mA analog quantity to the monitoring screen according to different oil level heights. The monitor screen can display the corresponding elevation according to the setting.3 Adjustment of the magnetic switch of the oil level indicator3.1 Calculate the elevation of each alarm signal magnetic switchWhen the oil level of the lower oil tank is stationary, extend the ruler into the oil tank to measure the actual distance h that the oil level exceeds the upper ring plate (measurement reference) of the lower frame, as shown in Figure 3. Read the display corresponding to the actual oil level from the monitor screen Elevation H. Find out from the drawing the distance h0 that the design oil level is higher than the measurement datum, Δh = h-h0 is the height difference between the actual oil level and the design oil level. With these data, the oil level display height on the monitoring screen corresponding to the designed oil level h0 can be calculated. H0 = H-Δh.Find out the elevation difference Δhi of each alarm signal trigger position relative to the designed oil level from the design data, and the monitor screen display elevation corresponding to each alarm trigger signal is Hi = H0 + Δhi. Refer to Table 1 for the triggering method and display elevation of the four groups of alarm signals.3.2 Confirm the magnetic switch corresponding to each alarm signalRemove the 4 sets of magnetic switches from the bypass pipe. Pick up the magnetic switch one after another, and move it up and down near the oil level against the bypass pipe (simulating oil level rise and fall), and observe which alarm signal is changing at the monitoring screen. This changing alarm signal corresponds to the magnetic switch, and a corresponding mark is made on the magnetic switch.3.3 Adjust the height of the magnetic switch corresponding to each alarm signalWhen adjusting the height of the magnetic switch, it is necessary to push the magnetic float up and down to simulate the up and down movement of the oil level in the oil tank. In the test process of Qingyuan Power Station units, two methods have been used: wire-top float and oil-driven float.3.3.1 Method of using steel wire top floatThe height adjustment of the magnetic switch is initially the use of a slender steel wire top magnetic float, as shown in Figure 4. During the test, close the ball valve between the connecting pipe and the oil level gauge, unscrew the drain plug, drain the oil in the oil level gauge, insert the thin steel wire into the oil level gauge through the drain hole, and push the float up and down. In actual operation, it was found that this method has the following problems:1) The bottom of the sewage outlet is close to the foundation, and it is difficult to insert the long steel wire into the oil level gauge;2) The top of the steel wire is easily stuck in the gap between the float and the inner wall of the bypass pipe and cannot move up and down. Therefore, in the subsequent adjustment of the unit, this method was abandoned.3.3.2 The method of using oil to drive the floatAccording to the height from low to high, adjust the four magnetic switches of super low (LL), low (L), high (H), and super high (HH) in sequence. Choose a welded pipe joint that has the same interface size as the drain plug. Put the non-threaded end of the pipe joint into the hose and tie it tightly with an iron wire. During the adjustment, screw the pipe joint with hose into the drain hole, and fill the oil level gauge with oil through the funnel and hose, as shown in Figure 5.The specific adjustment process is as follows:1) Close the ball valve between the connecting pipe and the oil level gauge, unscrew the drain plug, and drain the oil in the oil level gauge.2) Screw the pipe joint with hose into the drain hole.3) Fill the oil level gauge through the hose, and stop filling when the monitor screen shows that the oil level is near HLL.4) Put the ultra-low (LL) magnetic switch against the bypass pipe, move the hose upwards, and raise the oil level in the oil level gauge until the alarm signal disappears.5) Slowly move the hose down to lower the oil level in the oil level gauge. At the same time the ultra-low (LL) alarm is issued, record the oil level HLL' displayed on the monitoring screen.6) If the HLL' is within the range of HLL±5 mm, it means that the height of the magnetic switch has been adjusted in place, and the magnetic switch is fixed; otherwise, according to the height difference between HLL' and HLL, move the magnetic switch up or down, and then Repeat steps 4) and 5) until HLL' reaches the range of HLL±5 mm.7) Refer to steps 3) to 6) to adjust the elevation of the three magnetic switches of low (L), high (H) and super high (HH) in sequence.Using this method to adjust the height of the magnetic switch has the advantages: ①It is less affected by the installation space of the oil level gauge; ②The height control of the float is relatively simple. Subsequent unit adjustments have adopted this method.4 Problems encountered in adjustment and their treatment4.1 The magnetic turning column level gauge is out of orderThe disorder of the magnetic flip-column level gauge is shown in Figure 6(a). The magnetic flip-column level gauge that is submerged in oil is not flipped, or the magnetic flip-column that is not submerged in oil is flipped. In this case, the magnetic turning column is generally interfered by the external magnetic field, and a magnet can be used to move the magnetic turning column level gauge in one direction to drive the magnetic turning column level gauge to flip. After the magnetic turning column level gauge is turned normally, it is shown in Figure 6(b).4.2 There is no signal from the magnetic switchThere is no signal from the magnetic switch. Generally, there is an open circuit somewhere in the signal cable, or the connector at the cable connection is loose. Use a multimeter to check section by section, find the disconnected cable or loose connector, and then replace the cable or tighten the connector. If there is no problem with the cable, you can connect the cable to another magnetic switch at the oil level gauge end, or connect the cable to another module at the monitoring end, and then observe whether the alarm signal can be obtained at the monitoring screen. Through such a comparative test, confirm the damaged component and replace it.4.3 The magnetic switch signal is reversedFor example, a high (H) alarm signal should be issued when the oil level rises above the magnetic switch, and disappears when the oil level drops below the magnetic switch. If the high (H) alarm signal is sent out during the process of oil level falling and the rising process disappears, it means that the on and off values of the signal at this point are reversed, and the wiring needs to be reconnected from the correct position.4.4 Problems that should be paid attention toPay attention to keep the job site clean. Use oil to drive the float to adjust the magnetic switch. During the operation, oil may overflow. Therefore, during the operation, protective materials such as plastic film should be laid on the work site to prevent the oil from polluting the environment.5 ConclusionAfter Qingyuan Power Station is put into operation, the magnetic switch of the oil level gauge can send out an accurate alarm signal. Through the debugging of the four units of Qingyuan Power Station, the adjustment method of the oil level gauge magnetic switch has been continuously improved, and a set of successful experience has been summed up, hoping to provide a reference for the adjustment of similar oil level gauges in the power station in the future.
Post time: 21-09-21