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Generator Fiber Temperature Measuring System

Introduction:

      Operating temperature of generating unit, especially the temperature of stator bar and loop tube, is an important indicator of the operation status of hydro generator. So far, the methods adopted to measure relevant temperatures of hydro generator include thermal-resistance temperature measurement, the thermocouple temperature measurement and the infrared temperature measurement ll'21. Both thermal resistance and thermocouple need metal wires to transmit the signal. Since the insulating stability of the metal wires cannot be guaranteed, we cannot measure the temperatures of stator bar and copper loop tube directly, but the temperature of insulation layer. As for infrared temperature measurement, it is a kind of non-contact temperature measurement, which can only measure the surface temperature of equipment prone to environmental temperature and surrounding electromagnetic interference, and can only be realized through manual operation rather than online measurement. Moreover, the space inside the hydro generator is too narrow to install infrared temperature probe. Therefore, with the development of optical fiber temperature measurement technology, it is possible to be adopted to measure the temperature of the water turbine generator. According to the “DL/T 1163-2012 Non-salient Pole Generator Online Monitoring Device Configuration Guide”, large number of resistance thermometers and thermocouple thermometer should be pre-embedded in the generator depending on measuring positions and generator design. As optical fiber temperature measurement technology develops and enjoys great advantages in anti-interference ability, fast response and high precision, optical fiber temperature sensors have been increasingly used for measuring internal temperatures of generator.

      Optical fiber sensing technology is a kind of new sensing technology, which is developed accompanying the development of optical fiber and optical fiber communication technology. It is one of the fastest developing technologies in the world since the mid 1970s. FOS FIBER OPTICAL SENSOR is different from power-based sensor in nature. Optical fiber sensor uses light as the carrier of the sensitive information, and optical fiber as the medium for transmitting sensitive information. It is widely used because of its unique characteristics. Optical fiber sensor is used to measure temperature. Fiber temperature measuring can be divided into many types based on the optical fiber sensors used and the measuring principles adopted. At present, Fiber Bragg Grating temperature measurement, distributed cable temperature measurement and fluorescence optical fiber temperature measurement are the main types of fiber temperature measurement mainly used in power industry. Among them, fluorescence optical fiber temperature measurement uses sensor smallest in size, which makes it suitable for measuring the temperatures of generator and transformer windings.

Principle of Fluorescence Temperature Measurement：

      The fluorescent temperature sensing probe is made up of ordinary multimode fiber and the fluorescent substance (coating) on top. Here is the temperature measurement principle: having accepted optical excitation of a certain wavelength, the fluorescent material would be stimulated and eradiate fluorescence energy. When optical excitation disappears, the persistence of the fluorescent luminescence is determined by the characteristics of the fluorescent substance, environmental factors, and the lifetime of the excitation state. This kind of excited fluorescence usually decays exponentially, and the time constant of decay is called fluorescence lifetime or fluorescence decay time (NS). Because fluorescence lifetime varies under different at different ambient temperatures, the ambient temperature can be known by measuring the length of the fluorescence lifetime.

Product introduction：

      AWDS-770 fluorescent optical fiber temperature measuring instrument is a temperature measurement system based on the principle of fluorescence fiber temperature measurement. This product is particularly developed for the power industry to meet the requirement online monitoring of generator temperature. It can realize online monitoring and control of the temperatures at the measuring points within generator, with high accuracy, stability and reliability, and even under special industrial environment of high voltage, high current, strong electromagnetic interference. The system enjoys intrinsic inherent safety under high pressure, electromagnetic environment.

      The system consists of a host thermodetector and multiple thermodetector expansion boxes. The host thermodetector is connected with thermodetector expansion boxes through RS485 or optical fiber, forming a temperature measurement system. For a single system, its capacity could be expanded to cover 250 of measurement points. And several systems could be connected through web server, forming a larger system whose capacity could be expanded to cover arbitrary number of temperature measurement points. The host thermodetector has functions of temperature display, temperature forewarning/alarm, system fault monitoring, alarm settings, communication settings, historical data storage, temperature calibration, PC communication etc.