In the operation system of steam turbine, accurate measurement of actuator displacement is of great significance to ensure stable and efficient operation of steam turbine. With its excellent performance, displacement sensor HTD-300-5 has become a powerful assistant in the field of displacement measurement of steam turbine actuator.

Working principle

Displacement sensor HTD-300-5 belongs to LVDT (Linear Variable Differential Transformer) displacement sensor. Its structure mainly includes a primary coil, two secondary coils and an axially movable iron core. When the AC excitation signal is passed into the primary coil, an alternating magnetic field is generated. Under the influence of this magnetic field, the two secondary coils will generate induced electromotive force. Under normal circumstances, the iron core is in the middle of the two secondary coils. At this time, the induced electromotive force of the two secondary coils is equal in magnitude and opposite in direction, and the output voltage is zero. Once the actuator moves and drives the iron core to move, breaking the balance, the induced electromotive force of the two secondary coils differs, the output voltage is no longer zero, and the magnitude and polarity of the output voltage are directly related to the displacement of the iron core. By detecting the output voltage, the displacement information of the actuator can be accurately obtained. For example, when the actuator pushes the valve to open and drives the iron core to move, the output voltage of the sensor changes. After processing by the supporting circuit, the displacement value can be converted.

Performance characteristics

1. High-precision measurement: In the scenario of turbine actuator displacement measurement, accuracy is crucial. The displacement sensor HTD-300-5 can achieve an accuracy of 0.1% FS or even higher. Taking a 300MW steam turbine as an example, if the stroke range of its actuator is 0-300mm, the measurement error of the sensor can be controlled within 0.3mm, ensuring that the control system controls the actuator based on accurate displacement data, ensuring accurate control of the steam intake of the steam turbine, and maintaining stable speed and load.

2. Strong reliability: Made of high-quality materials, such as stainless-steel shell, it not only has good mechanical strength, can resist vibration and impact during turbine operation, but also effectively prevent external water vapor, dust and other internal precision components from eroding. The internal circuit has been specially designed and processed to have excellent anti-interference ability. It can also stably output accurate measurement signals in complex electromagnetic environments to avoid measurement errors or signal fluctuations caused by interference.

3. Wide temperature adaptability range: When the turbine is running, the working environment temperature of the actuator changes greatly. The operating temperature range of HTD-300-5 is usually – 50℃ – +150℃, and some special specifications can reach – 50℃ – +280℃. Whether it is the start-up phase of the unit in cold winter or the high temperature full load operation in summer, it can work normally to ensure the stability and accuracy of displacement measurement.

4. Rapid dynamic response: The actuator moves quickly, requiring the sensor to respond quickly. The dynamic frequency of the sensor can reach 0-200Hz (3db), which can track the displacement changes of the actuator in real time and output measurement signals in time. Under conditions such as sudden changes in turbine load and emergency load shedding, ensure that the control system obtains displacement information in time, quickly adjusts the action of the actuator, and ensures safe and stable operation of the turbine.

Technical parameters

1. Range: “300″ in the model indicates that its range is 0 – 300mm, which can meet the displacement measurement requirements of most steam turbine actuators. Of course, there are other range specifications for different steam turbine designs.

2. Output signal: Common output signal types include voltage type, such as 0 – 5V, 0 – 10V, ±5V, etc.; current type, such as 4 – 20mA. Different output signals are easy to adapt to different interfaces and modules in the steam turbine control system to achieve stable data transmission and processing.

3. Excitation power supply: The excitation power supply frequency is generally a sine wave or square wave, ranging from 1 to 5KHz. The primary excitation voltage is commonly 3Vrms, and can also be adjusted between 1 – 5Vrms according to actual applications to ensure that the sensor works stably and outputs accurate signals.

Zero voltage: The zero voltage is less than 0.5% of the full-scale output, ensuring that the output signal error is extremely small when the core is in the initial equilibrium position, thereby improving measurement accuracy.

4. Sensitivity drift: zero drift is less than 0.02%/℃, full-scale drift is less than 0.03%/℃, which means that when the temperature changes, the sensor sensitivity remains stable and the measurement accuracy is less affected by temperature.

Application in turbine actuator

1. Actuator stroke monitoring: real-time monitoring of the actuator piston displacement, and continuous transmission of displacement data to the turbine control system. Operators can intuitively understand the working status of the actuator through the control system interface, judge whether it is acting according to the command, and whether the stroke is within the normal range, providing a key basis for the evaluation of the turbine operation status.

2. Valve opening control: closely related to the turbine steam inlet valve, by accurately measuring the displacement of the actuator, the valve opening is indirectly and accurately controlled. When the turbine load is adjusted, the control system adjusts the displacement of the actuator according to the set load and actual speed and other parameters, and the sensor feeds back the displacement information in real time to ensure accurate adjustment of the valve opening, control the steam inlet volume, and achieve stable control of the turbine speed and load.

3. Fault diagnosis and early warning: During the continuous monitoring of the displacement of the actuator, if there is abnormal fluctuation in displacement or it exceeds the normal range, the output signal of the sensor will also be abnormal. After the control system captures the abnormal signal, it can trigger the alarm in time to remind the staff to check the actuator and related equipment, check whether there are problems such as component wear, jamming, hydraulic system failure, etc., prevent the expansion of faults in advance, and ensure the safe operation of the steam turbine.

The displacement sensor HTD-300-5 plays an irreplaceable role in the displacement measurement of steam turbine actuators with its unique working principle, excellent performance characteristics and key technical parameters. With the continuous development of steam turbine technology, the requirements for sensor performance are increasing day by day. HTD-300-5 will also continue to be optimized and upgraded to provide a more solid guarantee for the safe and efficient operation of steam turbines.

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