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Authors: Wang Qian, Zheng Hongyan, Zhang Yingli (Xuansteel Power Plant, Hebei Iron and Steel Group, Zhangjiakou, Hebei). When reproducing this article, please cite the authors’ copyright. 【Abstract】Against the backdrop of the renovation of the liquid level monitoring device for the hot well of a turbine blower, this paper outlines the application of magnetic flip-top level gauges (magnetic float level gauges) in such monitoring systems. By comparing magnetic flip-top level gauges with electric contact level gauges, it explains the working principle of these magnetic float level gauges as well as their measurement capabilities, and demonstrates the role that this renovation plays in ensuring the stable operation of production processes. 1 Introduction The hot well level is one of the important monitoring parameters for steam turbine blowers. It determines the stability of the water circulation system in these blowers, and constitutes a key parameter for the smooth operation of the steam turbines. The magnetic float level gauge is one of the commonly used level measurement instruments. Xuansteel Power Plant of Hebei Iron and Steel Group primarily uses it as a device for measuring the liquid level in the hot wells of steam turbine blowers. In recent years, the newly installed AV71 and AV80 blowers have also employed magnetic float level gauges in combination with level switches to achieve automated control of the liquid level in these hot wells; the control performance is good, and the accuracy of the monitoring data is high. 2 Background of the project: The 3650 fans installed in the power plant at its initial construction used electric contact level gauges, whose control performance was not very satisfactory. The working principle of these electric contact level gauges relies on the contact between electrodes and water, which enables the electrodes to conduct electricity; once the electrodes conduct electricity, the corresponding green light on the display indicates the current liquid level. Electrocontact level gauges are suitable for measuring in environments with clean water quality. However, due to the long-term operation of turbine equipment, the water inside such gauges becomes turbid; these impurities adhere to the electrodes, interfering with their contact with the water and thus affecting their conductivity, which prevents the display instrument from showing the accurate level of the liquid in the hot well. The solution to this problem is to add clean water into the measuring cylinder; the fluidity of the water helps to wash away the turbidity adhering to the electrodes, thereby ensuring their conductivity for a short period of time. This method requires frequent addition of water and can only solve the problem for a short period of time; therefore, during equipment operation, the improvement in poor electrode conductivity is not significant ； Moreover, every time water is added, it is necessary to frequently open and close the ball valve located in front of the electric contact level gauge; frequent opening and closing of this ball valve can lead to poor sealing, which in turn affects the vacuum level of the turbine and poses a risk to its safe operation. To address the above issues, the hot well level detection device was replaced, switching from an electric contact level gauge to a magnetic float level gauge with a level transmission output. The magnetic float level gauge with a transmitter output (magnetic float level meter) includes an on-site display in addition to the electric contact level gauge; it allows for the display of the level directly at the site, and it also enables the level signal to be transmitted to control instruments, so that operators can view the level status intuitively without having to be on site. The most important thing is that the magnetic float level gauge is not affected by the quality of the water inside the measuring tank when detecting the liquid level. 3 Working Principle and Performance Characteristics of Magnetic Flip Column Level Gauges (Magnetic Float Level Gauges) 3.1 Structural Characteristics of Magnetic Flip Column Level Gauges (Magnetic Float Level Gauges) A magnetic flip column level gauge (magnetic float level gauge) consists of three components: the basic unit, an on-site level indication and alarm device, and a remote level transmission system. The basic design is developed based on Archimedes’ principle, which states that a magnetic float generates buoyancy in a liquid, as well as the property that like magnets repel each other while opposite poles attract. Based on the above principle, the change in liquid level is linearly transmitted magnetically to the on-site indicator; the liquid level is indicated by white and red colors, with the dividing point representing the liquid level height. The level alarm uses magnetic material to act through a contactless switch, causing the relay contacts to operate according to the set level value. The liquid level remote transmission device uses magnetic materials to convert changes in liquid level into a DC current signal of 4–20 mA in a linear manner, which is then sent to secondary instruments for the remote transmission, measurement, control, and recording of the liquid level. 3.2 Working Principle: The basic model is installed on the side of the container via upper and lower process connection flanges. Based on the principle that the weight of the float equals the weight of the volume of liquid displaced by it, the float equipped with permanent magnets floats within the medium being measured, moving up and down as the liquid level or interface changes. Magnetic stones inside the float drive the flip plates; when the liquid level rises, they turn so that the red side faces outward, and when the liquid level drops, they turn so that the white side faces outward. Each flip plate is spaced 10 mm apart, and every 9 plates there is a number marked on them, allowing for an easy reading of the liquid level. The alarm consists of an alarm switch and a converter, and is installed on the outside of the float. It is driven by the magnet inside the float, and has a memory function that keeps the alarm active as long as the fault persists. The converter is installed in the control room; it supplies power to the alarm switch and simultaneously converts the signal generated by the operation of the alarm switch into relay contact actions (three normally open, three normally closed) as output signals. The alarm switch operates without contacts, with a operating voltage of 220VDC. When the liquid level is within the normal operating range, the contactless switch remains in the off state; the current flowing through it is 1 mA at this time. The transistor BG inside the converter is in the cut-off state, and the relay J0 does not operate. When the liquid level exceeds the upper (lower) control point, the contactless switch closes, and the current flowing through it becomes 10 mA. At this current level, the transistor BG inside the converter turns on, the coil of relay J0 is energized, causing the relay to activate and thus enabling liquid level alarm. The working principle of the alarm is shown in Figure 1. http://www.huoyumi.com/d/file/zhishi/2016-10-09/ea17fc90af9f11870f5b79dc125dcbca.jpg The remote transmission device consists of two circuits: a sensing circuit and a conversion circuit. Changes in liquid level cause a corresponding change in the resistance value of Rx in the sensing circuit. For example: when the liquid level is at zero, the magnetic force of the magnet inside the float causes JG1 to be attracted, resulting in the highest Rx value (4 mA of output). As the liquid level rises, JG1 loses its magnetism and stops being attracted, while JG2 becomes magnetized and gets attracted; thus Rx = R_total – R1. Consequently, as the float rises, the resistance Rx decreases linearly as the liquid level increases, and at the highest point, Rx = 0 (20 mA of output) ； If the liquid level drops, the opposite is true. A constant current source 1H is provided by the conversion circuit, which generates a linear voltage at Rx; this voltage then enters the conversion circuit where it is converted into a 4–20 mA signal. The working principle is shown in Figure 2: http://www.huoyumi.com/d/file/zhishi/2016-10-09/f49095c5105a09ad8d8610041941f034.jpg. The key technologies and advantages of the magnetic flip-column level gauge (magnetic float level gauge) are as follows: This type of level gauge uses a magnetic float as the sensing element; through the magnetic coupling between the magnetic float and the magnets in the display column, it enables measurement of the liquid level or interface being monitored. The magnetic flap level gauge (magnetic float level gauge) operates on the principle of a communicating tube, ensuring that the liquid level in the container being measured is equal to that in the measuring tube. As the float in the measuring tube changes in height in accordance with the liquid level, the magnet inside the float interacts with the magnets in the color columns on the display panel, causing these columns to flip. White indicates no liquid present, while red indicates the presence of liquid, thereby allowing for the direct display of the liquid level. The selection of the zero point for a magnetic float level gauge: the zero point displayed locally by the gauge must be identical to the zero point transmitted as a signal, and it must also correspond to the actual zero point of the liquid level in the hot well, in order to ensure accurate measurement. The locally displayed magnetic flap level gauge (magnetic float level gauge) features intuitive and prominent display, a wide viewing angle, a compact and rational design, safety and reliability, no issues with leakage, low maintenance requirements and low repair costs. Its local indication function does not require additional power supply; thus, even in the event of a power failure, level monitoring is not affected, making it an ideal instrument for level measurement. 5 Conclusion Through the modifications, not only is maintenance made easier and the amount of maintenance work reduced, but it also enables the personnel on duty to monitor the liquid level in the hot well at any time, thereby ensuring the stable operation of the steam turbine blower’s water circulation system. More importantly, the accuracy and timeliness of measuring the liquid level in the hot well are improved; there is no need to frequently open and close valves or add water to the measuring tank, which reduces the impact on the vacuum level of the blower and contributes to its smooth operation.