Six fiber-optic grating temperature sensor measurement at the same time involves the multiplexing of the optical path, fiber-optic grating sensor multiplexing can use wavelength division multiplexing (WDM), space division multiplexing (SDM) or time division multiplexing (TDM), the system is using space division multiplexing and wavelength division multiplexing method. As shown in Figure 2, with 1′8 coupler to achieve the sensor air division multiplexing, so as to avoid the disadvantages of a single WDM, that is, multiple sensors in series on an optical fiber, in which a sensor damage will affect the transmission of other sensor signals; at the same time, the choice of the sensor wavelength of operation on the use of WDM, used to improve the system's measurement speed, namely A single scan cycle for wavelength demodulation allows for simultaneous measurement of six sensors.

In Figure 2, A, B, C three phases of the six fiber optic grating temperature sensors in the high-voltage side, respectively, installed in the static contact aperture, while the coupler, wavelength demodulator, controller and data processing circuitry are on the ground potential side, installed in the control room, using long-distance fiber optic transmission to achieve the high-voltage side of the insulation isolation. Figure A1, B1, C1, A2, B2, C2 is a fiber-optic grating temperature sensor designed in this paper, respectively, distributed on the upper and lower side of the isolation contacts A, B, C three phases, at room temperature sensor wavelengths of 1548.5nm, 1550.1nm, 1551.6nm, 1553.5nm, 1555.5nm, 1557.1nm, respectively. Sensitivity is 0.011nm/°C, 0.013nm/°C, 0.011nm/°C, 0.010nm/°C, 0.011nm/°C, 0.012nm/°C, and the measurement range is 0"110°C; coupler is

By a combination of seven 3dB coupler 1′8 coupler; wavelength demodulator for the use of piezoelectric ceramic drive standard to achieve the wavelength scan, the operating wavelength range of 1548"1558nm, covering six sensors at 0"110 ℃ temperature changes in all wavelength bands; controller under the control of the data processor to achieve wavelength Demodulator scan.

During the operation of the high-voltage switchgear, the contacts, bus, current transformer, and cabinet constitute multiple heat sources, and the high-voltage switchgear and internal components form a complex thermal resistance network [14]. In this system, it is difficult to deduce the mathematical relationship between the contact temperature rise and the temperature rise of the fiber-optic grating sensor through theory, so this paper establishes a mathematical model between them through experimental methods.

The temperature rise experiment is conducted in 10kV high-voltage switchgear, when the three-phase contact normal contact, work rated current of 1kA, room temperature of 25 ℃. Figure 3 is on the isolated contact B phase temperature rise process curve, can be seen that the fiber grating sensor temperature rise change than the actual temperature change of the contact slower, but their change trend is the same, about 3h after the temperature field changes tend to stabilize. The difference between the measured temperature and the actual temperature is due to the sensor uses a non-contact way to measure temperature, it relies on the static contact radiation to transfer heat. Table 1 shows the measured temperature rise.

It can be seen in the switchgear contacts contact normal, stable temperature change after the actual temperature rise of each contact DTC and the corresponding sensor temperature rise DTS of the proportional relationship between the value of 1.43 near, take the average as a test result, can be established between the actual temperature of the contact and the measured temperature of the sensor mathematical relationship formula for TC="K"(TS-T)+T (3) where K="1".43;TS is the temperature value measured by fiber-optic grating temperature sensor; T is the high-voltage switchgear. Ambient temperature