Application of PLC in Temperature Measurement of Generator Rotor
Whether in a hydroelectric or thermal power plant, the generator is the main equipment of the plant, and any shutdown failure will cause the power plant to fail to generate electricity, so monitoring the main components of the generator is critical. The stator and rotor of the generator are the core components of the generator. The temperature of the PT100 is embedded in the core of the stator. By connecting these components to the monitoring equipment, the stator temperature can be monitored in real time. Since the rotor of the generator is a rotating component, such as a temperature measuring resistor embedded in the rotor, a small number of small carbon brushes are required to take out the signal, which brings hidden troubles to the operation of the generator, and the process is also difficult to implement. Especially for high-speed thermal power generators, the temperature of the rotor of the generator can only be measured by the indirect method. The indirect method measurement is to detect the relevant parameters of the generator rotor, and the rotor temperature is determined by analyzing and calculating these parameters.
1 Temperature detection principle The rotor coil of the generator is made of copper wire. The resistance of the copper wire is different at different temperatures. When the generator is in normal operation, the generator rotor has a large excitation current, which causes the temperature of the rotor coil to rise, resulting in a large resistance of the copper coil. Through the measurement of the current and voltage of the rotor winding, and analysis and calculation, the resistance value of the rotor winding can be derived. The calculation of the generator rotor temperature is based on calculating the resistance of the coil of the generator rotor. The calculation formula is as follows: coil winding reactance, Ub is the DC component of the collector voltage of the collector ring, Rb is the resistance of the carbon brush, and Rl is the resistance of the DC busbar between the magnetic field voltage measurement point and the collector ring carbon brush. Based on the calculation result of the resistance value of the magnetic field winding, the temperature of the winding can be calculated according to the following formula. Therefore, the voltage and current quantity of the generator rotor are collected, and the rotor temperature value of the generator is output through the analysis and calculation of the data, which is the basic design idea of ​​the detecting device. .
2 Configuration of the detecting device 2.1 Hardware configuration of the device The detecting device is composed of three parts.
Voltage Transmitter, Current Transmitter Rotor current conversion is accomplished by a 2 ~ 20mA current transducer in the rotor loop. The rotor voltage is measured directly by the voltage transmitter, and the ratio of the detector to the control box is the core of the device. In order to ensure the reliability of the device, the detector adopts the FP0 type small PLC of Matsushita Co., Ltd., which is small in size (the cross-sectional area is only the size of the business card), light in weight and easy to install. And it can perform 32-bit floating-point operations, and the operation speed is fast (0.9 / step), and the filtering and calculation accuracy are greatly improved. This part consists of regulated power supply A (for controller), regulated power supply B (for touch screen), CPU module, analog/digital and digital/analog conversion modules. The detector accepts the signal measured from the voltage and current transmitter, and after calculation, sends a 4~20mA rotor temperature signal or an over-temperature alarm signal, and also transmits it to the human-machine interface through the RS232 serial port COM2, as shown.
The principle block diagram of the rotor temperature measuring device The human-machine interface-touch screen man-machine interface adopts the touch screen, and the industrial-level human-machine interface of HITECH company is selected. It can replace the traditional control panel function, save PLC I / O module, button switch, digital settings, indicators, etc., and display important information at any time. According to various interfaces that need to be edited, real-time detection can be displayed through page conversion and system parameters can be set through the setting interface.
2.2 Software composition of the device Signal filtering, calculation and logic relationship are completed by PLC and programmed in the FPGR software environment of NAIS; /O selection, historical data storage, curve drawing, etc. are completed by HITECH man-machine interface, and programmed in SADP3 software environment.
2.2.1 Signal filtering Since the magnetic field voltage of the generator is the DC-side output of the thyristor, it contains interference signals such as higher harmonics and arc-switching voltage. If no filtering is performed, the temperature measurement output will fluctuate by 5 to 20 degrees. Composite filtering using inertial filtering and de-amplitude averaging filtering.
Inertial filtering: The low-pass filter transfer function is G(S)=Y(S)/X(S)=V(TdXS sample value; m is the filter coefficient; Td is the operation cycle corresponding to software.
Inertial filtering is used to eliminate higher harmonics in the voltage signal.
Go to the extremum average filtering method: continuously sample N times, find the maximum and minimum values ​​at the same time, and then average the N-2 samples. This method is used to eliminate interference from arcing voltage spikes.
2.2.2 Numerical calculations To ensure accuracy, 32-bit floating point calculations are used. Since the input and output of the PLC are both 0 ~ 4000, the conversion should be performed at the input and output, and the calculation sequence should be arranged reasonably to prevent the value from overflowing.
If the value overflows, the PLC may crash, so some special conditions are considered during programming.
Face and debug interface, and set different levels of passwords. The user interface is mainly used to display data, historical temperature records and over-temperature event records. The debugging interface is used to set generator parameters, PLC I/O, A/D and D/A checksum simulation tests.
3 program debugging and device test 3.1 HITECH man-machine interface measurement temperature and temperature history curve, a temperature history data display p ship switch, then the heart machine and touch screen encounter RS232 pass i message first compile the program on the PC Perform the simulation operation, check the function block of each interface and the display of Chinese characters and the switching of each interface, to avoid the endless loop of interface switching. After the above functions are adjusted normally, follow the instructions of HITECH to set the application technology line connection on the back side of the touch screen to download the program. If there is a fault during the download process, you must download it again. Otherwise, the HMI will malfunction after running.
3.2 Human-machine interface and PLC communication 3.3PLC software debugging Select an excitation device to connect its thyristor output with a large resistance analog rotor load, and input the voltage signal into the PLC through the transmitter. Use FpwinGR software Timechartmonitor observes the waveform after software filtering, and constantly adjusts the values ​​of Td and m (Equation (2), Eq. (3)) to select the best setting.
Simulate the generator rotor voltage and current values ​​under different operating conditions, and calculate the theoretical rotor temperature, compare it with the actual displayed temperature, and minimize the deviation by adjusting the relevant parameters.
Use a copper wire of the same material as the generator rotor (thin wire diameter), wind a high-resistance coil (R=344n), apply a constant current to the coil, and place the coil into the incubator. Gradually increase the temperature of the incubator, compare the temperature of the incubator with the actual displayed temperature, and adjust the value of a (formula (1)) in the software so that the display temperature is close to the actual temperature. After adjustment, the measurement results are shown in Table 1. Table 1 Adjusted Measurement Results Actual Temperature Display Temperature Actual Temperature Display Temperature 4 Conclusions 72h simulation test and on-site operation instructions Designed with NAIS PLC and HITECH human-machine interface It can fully meet the requirements of the site, and has the advantages of friendly display interface and high reliability. Since all the hardware of this device adopts mature products, there is no need to make a PCB board. It is only necessary to change the software for different applications. This paper has certain reference significance.
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