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Installation method and working principle of the TSI device probe 1 Sensor installation and calibration 1.1 Installation of the bearing vibration sensor probe Six eddy current probes with a diameter of φ8 mm and a sensitivity of 7.87 V/rnm are installed at bearings No. 1, No. 2, and No. 3 respectively. At each bearing, two probes are installed at 90° to each other and perpendicular to the bearing; the angle between these probes and the horizontal direction is 45°, allowing for the measurement of vibrations in the X and Y directions respectively. In general, for eddy current sensors, the range affected by eddy currents is approximately three times the diameter of the sensor coil; therefore, the measurement width corresponding to the sensor should be three times its diameter. Moreover, no other metal objects should be present within a 24 mm area around the sensor, as this can cause errors. The installation gap voltage should be set at the midpoint of the linear portion determined by the sensor’s output characteristic curve. For a probe with a sensitivity of 7.87 V/mm and a diameter of 8 mm, the installation gap voltage is around -9.75 V or 1.2 mm. Since the linear voltage range of the sensor **exceeds the measurement range, a larger deviation in the installation gap is acceptable, as long as the measurement range remains within the linear portion. However, to meet the requirements of fault diagnosis and reliability, the installation voltage is generally required to be 9.75 ± 0.2 V. 1.2 Installation of axial displacement and high/low pressure differential sensors: Axial displacement measures the axial movement of the thrust bearings relative to the cylinder. During the operation of the unit, this ensures that a certain axial gap exists between the moving and stationary components, thereby preventing friction and collision between the rotating and stationary parts inside the turbine. Two axial displacement sensor probes are installed at bearing No. 2, one on each side of the bearing; these probes are oriented in the direction of the low-pressure cylinder. The probe model used is type 7200 with a diameter of φ14 mm, and its sensitivity is 3.937 V/mm. The supply voltage for the preamplifier is -24V. The main shaft is set at its zero position with the thrust bearing resting on the working surface of the cylinder, relative to the design zero point of the cylinder. Before installing the axial displacement and low-pressure differential expansion sensors, the main shaft must first be pushed to zero position, and then the sensors should be installed as specified. The range of axial displacement is from -2 mm to +2 mm. The operating voltage is -9.75 ± 0.2 V. The relative dead point for the expansion of the turbine in the Zhanhua Power Plant is at bearing No. 2; the rotor of the high-pressure cylinder expands in the direction of the front casing, with bearing No. 2 serving as the relative dead point, while the rotor of the low-pressure cylinder expands in the direction of the generator, also with bearing No. 2 as the relative dead point. The high and low pressure differential expansion probe is an eddy current probe with a diameter of φ25 mm and no preamplifier; its sensitivity is 0.8 V/mm. Since the high and low pressure differential expansions are both installed in the direction of the generator, in order to keep the measurement ranges of these differential expansions within the linear range, the probe is positioned at the midpoint of its linear range, within a scale range of -2 to 10 mm. The installation voltage for the zero point of the probe can be calculated using the following formula: For high-pressure differential expansion probes, the installation voltage for the zero point is: Probe’s linear midpoint voltage (-6.95 V) – Probe sensitivity (0.8 V/mm) * 4. For low-pressure differential expansion probes, the installation voltage for the zero point is: Probe’s linear midpoint voltage (-6.95 V) + Probe sensitivity (0.8 V/mm) * 4. Therefore, the installation voltage for the zero point of high-pressure differential expansion probes is -11.10 V, while that for low-pressure differential expansion probes is -3.8 V. 1.3 Installation of the main shaft eccentricity sensor – The measurement of eccentricity is used to monitor the degree of bending of the main shaft. Direct eccentricity refers to the instantaneous eccentricity value, while peak-to-peak eccentricity represents the difference between the extreme value in the positive direction of shaft bending and the extreme value in the negative direction. The measurement of eccentricity is carried out using both an eccentricity probe and a phasor probe; both are eddy current probes with a diameter of φ8 mm and a sensitivity of 7.874 V/mm. The phasor probe monitors a groove on the shaft, and as the shaft rotates one full turn, a pulse voltage is generated in the probe, which provides the frequency needed to calculate the peak value of the eccentricity. The installation gap voltage for all probes is -10 V. Pay attention to the installation of the phase-probe; it should not be installed directly facing the slot. The phase shifter also provides a phase signal for the vibration, so as to analyze and study the vibration. 1.4 Installation of the speed probe: The turbine speed probe is also an eddy current probe with a diameter of φ8 mm and a sensitivity of 7.874 V/mm. It monitors a gear with 60 teeth on the main shaft; by converting the detected pulse voltage sequence into a frequency signal, the turbine speed can be determined. The recommended installation distance for this probe is 1.1 mm from the tip of the tooth, and it is convenient to use a feeler gauge for measurement during installation. 2 Brief description of the system: As the capacity of turbines increases, their safety monitoring and protection have become essential components of these turbines. At the same time, higher demands are placed on the accuracy and reliability of the operation of various safety devices in turbines. The safety monitoring system for steam turbines provides real-time monitoring of the turbine’s speed, bearing vibration, axial displacement, differential expansion between the high-pressure and low-pressure cylinders, cover vibration, eccentricity, and absolute expansion. When any of these parameters exceed the set limits, the monitoring system promptly issues an alarm or a shutdown signal to ensure the safe operation of the turbine equipment. The turbine safety monitoring system at Tengzhou Power Plant uses the Bentley 3500 monitoring system; its user-friendly software configuration and reliable hardware quality will provide strong support for the safe operation of the power plant. 3 System Structure 3.1 Instrument Framework Section The instrument framework section includes: 1 power input module, 1 framework interface module, 1 two-channel phase monitoring module, 4 four-channel eddy current displacement sensor or velocity/acceleration sensor monitoring modules, 2 four-channel differential expansion or axial displacement monitoring modules, and 1 two-channel rotational speed monitoring module. 2 four-channel relay modules. 3.2 On-site sensor section The sensor section mainly includes various eddy current monitoring probes and velocity probes, extension cables, preamplifiers, and signal wires. 3.3 Computers and Software The 3500 software package includes: framework configuration software; data acquisition/server software; operator display software. The internal settings of various monitoring modules can be adjusted by connecting a computer equipped with framework configuration software to the RS232 interface as well as the dedicated configuration interface of the framework interface module. The parameters for each module are set on the computer and then applied to those modules, allowing for the configuration of the measurement ranges, alarm points, probe types, and relay outputs for each monitor. Zhanhua Power Plant has not ordered any operator display software; therefore, various measurement values are sent to the DCS system via 4-20mA signals in order to enable display of the data. 3.4 Monitoring principles of eddy current sensors and velocity sensors: Eddy current sensors operate on the principle of the eddy current effect. The coil L of an eddy current sensor is connected in parallel with a capacitor C, forming a parallel resonant circuit. It is excited by a stable high-frequency current supplied by a crystal oscillator inside the preamplifier, which generates a high-frequency alternating magnetic field around the coil. When the spindle under test approaches this alternating magnetic field, eddy currents are generated on the surface of the spindle; these eddy currents in turn produce a new alternating magnetic field that opposes changes in the main magnetic field. This process consumes energy, thereby causing a change in the Q value of the coil. As the gap d between the spindle under test and the sensor changes, the Q value of the sensor coil also changes. In a circuit, the relationship between the Q value of a coil and its inductance is given by: Q = XL/R, where L represents the inductance of the coil, and R represents the resistance in the circuit. The above equation shows that the inductance of the coil varies with the value of Q, that is, it varies with the gap d. And the change in the inductance of the coil causes a change in the output voltage U of the coil. In this way, the vortex current sensor converts changes in the gap d into voltage changes. After being amplified by the preamplifier, the signal becomes a 0–24VDC signal that is fed into the instrument frame. The principle of a velocity sensor is as follows: A piezoelectric velocity sensor is installed on the bearing housing or the machine casing. Mechanical vibrations generate pressure or tension on the crystal, and the crystal functions like a spring – it resists this pressure or tension. As a result, charge is generated in the crystal, and this charge is regulated by an integrated electronic circuit. The monitor provides power while obtaining signals from the sensors. Internal configuration settings of the 4Bentley 3500 instrument 4.1 Power module configuration The 350 monitoring system can accept three types of power supplies: AC power, high-voltage DC power, and low-voltage DC power. It is also possible to set single-power and dual-power operation modes. Based on the on-site installation conditions, the single-power supply mode and high-voltage AC power supply are selected. In the power supply module configuration, a connection password and a configuration password can also be set. It’s best not to set it, so as to avoid forgetting the password over time. You can leave the other settings at their default values. 4.2 Configuration of the vibration module: The 3500/42 card can be configured as per requirements into shaft vibration, bearing vibration, eccentricity, axial displacement, velocity, and acceleration modules. The 3500/42 card is divided into four channels; channels 1 and 2, as well as channels 3 and 4, are configured in pairs. It is possible to complete channel 1 first and then replicate the settings to channels 2, 3, and 4, thereby reducing the amount of work required for configuration. For the radial vibration configuration, bonded-phase or unbound-phase signals can be selected. When a keyed signal is selected, it is possible to choose the amplitude of lX (1x frequency), the phase lag angle of IX; the amplitude of 2X (2x frequency), the phase lag angle of 2X; amplitudes other than 1X; and the amplitude of Smax (the maximum value for a single peak). All of these provide a basis for analyzing unit accidents; it is also possible to select a clamping value, whereby the voltage of a channel is clamped at a set value in the event of a failure in that channel or sensor, with zero as the default value. The output of the recorder is the amplitude of the vibration frequency, and this output is set to 4-20 mA. The delay time for the relays can use the default settings: 3 seconds for alarm levels and 1 second for critical levels. The type of radial vibration sensor can be an eddy current sensor with a diameter of φ8 mm. Both the alarm and critical relay modes are set to locking mode. The probe should be installed with its tip facing forward, without any safety barriers, and the alarm amplification factor is set to 1. 4.3 Configuration of axial displacement and differential expansion: Axial displacement and differential expansion are programmed using 3500/45 clips. The 3500/45 cartridge can perform axial displacement, differential expansion, inclined-plane differential expansion, and compensatory differential expansion functions. Tengzhou Power Plant’s 3500/45 cartridge: Channels 1 and 2 are for axial displacement, channel 3 is for high-pressure differential expansion, and channel 4 is for low-pressure differential expansion. The range of the axial displacement measurement is from -2 mm to +2 mm. The voltage at the probe’s zero position is -9.75 V. The sensor used is of type 7200 with a diameter of φ14 mm, and both channels are set to consider values that are positive when they are far apart. The differential expansion range for high and low pressures is set at -2 mm to +10 mm; the zero voltage is selected according to the installation requirements. The high-pressure differential expansion is set with a positive direction, while the low-pressure differential expansion is set with a positive direction when moving away. After the probe is installed, if an inaccuracy is observed on the DCS display screen, the zero adjustment screen can be opened to adjust the zero setting voltage; however, the range of adjustment is limited by the measurement range and the acceptable range for that channel. 4.4 Configuration of the speed channel: The speed channel uses a 3500/50 card, which is a dual-channel card. The speed range is set at 0–5000 revolutions per minute; the threshold voltage is set to automatic, the hysteresis voltage is 1 VDC, the signal polarity is recessed, and the number of events per revolution is 60, meaning 60 pulse voltages per revolution. It is also possible to set the output of the recorder and the output of the alarm relay. When configuring the speed channel, it is important to set the threshold voltage to automatic; this value is the midpoint between the positive and negative peaks of most input signals, and it changes as the input signals vary. The minimum amplitude of the signal required for the automatic threshold is 1 V peak-to-peak, and the minimum frequency is 0.0167 Hz. If the threshold is set to manual, it can be adjusted between +9.9 and -23.6; for a manual threshold, the amplitude of the minimum signal required is 500 mV peak-to-peak. 4. Configuration of 4.5-channel alarm and relay outputs: Each channel provides two alarm points; it is possible to set alarms for values above or below a certain threshold. It is also possible to determine whether the alarm should be active or inactive as needed. After setting the alarm points for each analog channel, the relay output channels can be configured. The relay outputs make use of the 4-channel relay modules available in the 3500/32 card set. The output of each relay can be programmed using AND or OR operators. The alarm drive logic for each relay can use the alarm inputs from any monitor channel in the frame. For example: Channel 1 of the relay is used for high vibration alarms; it can be configured to generate 6 vibration alarms, or the results of such calculations can be output from Channel 1 of the relay. In this way, both channels are saved and the maintenance workload for the plant’s thermal control staff is reduced, something that the previous 3300 system could not achieve. Each relay can be set to normally open or normally closed. All configurations must take effect after the software is installed. 5 Differences between the Bentley 3500 system and the 3300 system 5.1 Different configuration methods: The 3300 system’s cards are separate systems based on electronic circuit integration; the configuration is achieved by using short-circuiting elements in the circuits to enable the cards to perform various functions. In this way, every time the card settings are changed, the card has to be inserted and removed, which can easily damage the electronic circuits. The 3500 system cards form a network structure based on a bus system, and the functions of these cards can be configured via software through the computer’s RS232 interface. It is both convenient and fast, without damaging the card holder. 5.2 Different ways of displaying data: The real-time data of the 3300 system is shown through a rod-shaped LCD display on the front panel of the card. Bar charts exhibit lower data accuracy, and it is inconvenient to change the range and scales. The 3500 system does not have a display screen in its monitoring framework; therefore, operator display software is installed on the operator’s computer. This software enables the display of unit diagrams, bar charts, current values, trend charts for selected event periods, sequences of alarm events, a list of system events, and computer logs. The software’s powerful monitoring capabilities ensure that operators can have a better understanding of the unit’s operating status. Data monitoring can also be achieved by transmitting 4-20 mA outputs from the monitoring frame to the DCS system, and Zhanhua Power Plant uses this method. 5.3 Differences in communication methods: The 3300 system communicates with program controllers and distributed control systems through Bentley’s communication processors or the 3300 serial interface; this method of communication is generally not used, as hardwired connections are typically employed in the field to establish communication with other systems. In addition to having the 3300 communication functions, the 3500 allows communication between the host and the frame via the RS232 interface; it also enables communication between several frames through the RS422 port. The 3500 system can furthermore facilitate remote communication between frames and between hosts using modems. The significant difference in the communication methods between 3500 and 3300 is that the 3500 offers **improved support for networks**. 6 Problems encountered during debugging and solutions (1) One day after the installation of the high-pressure differential expansion probe and the low-pressure differential expansion probe, it was found that the high-pressure differential expansion value was 2 mm off from zero, while that of the low-pressure differential expansion probe was 0.5 mm off. It was determined on-site that there was slight heating in the low-pressure cylinder; however, the deviation of the high-pressure differential expansion probe was too large, which is an abnormal situation. The possible reasons for this are: first, the probe is not installed firmly enough, resulting in looseness; second, a shift in the zero position of the main shaft. In the end, it was decided to open the upper cover of the front box in order to inspect and adjust the high-pressure differential expansion probe. Upon inspection, it was found that the probe was not loose; the possible reason is that the main shaft moved during installation. After readjusting the installation zero point of the probe, the high-pressure differential expansion was 0.3 mm, returning to normal levels. (2) During the operation of the unit, it was found that one speed signal was unstable. When the actual speed of the turbine is 3000 revolutions per minute, the minimum displayed value is around 2000 revolutions per minute. After analysis, it is possible that there was interference at the site. Upon checking the signal shielding cable, it was found that the signal cable was not the required three-core shielded cable, but rather a multi-core cable, which could lead to interference between signals. Finally, by transferring some of the signals on the multi-core wire to other spare cores, the rotation speed returned to normal. Overall evaluation of the 7 Bentley 3500 system: The fully software-based configuration interface makes the 3500 system more intuitive and user-friendly during debugging and installation compared to the 3300 system. Reliable hardware quality provides a solid guarantee for the long-term stable operation of power plants. Furthermore, to improve the accuracy of measurements taken by the 3500 system, it is essential to be meticulous when installing the probes, striving to minimize zero-point errors. It is worth noting that when installing axial displacement and the differential expansion between the upper and lower cylinders, the zero position of the main shaft must be unified to avoid measurement errors caused by inconsistencies in the main shaft’s zero position. The turbine safety monitoring system plays an important role during the operation of power units. With the advancement of science and technology and the improvement in the operating standards of these units, there are increasing demands for higher levels of safety in their operation. Therefore, further development and research on turbine safety monitoring systems are necessary.