Research Of On-line Temperature Monitoring System For High-voltage Switchgear

With widespread of dyadic handcart switchgear recently, it often happened that the switch contact temperature rising, even burning down to power failure owing to the touch head poor contact and the increasing contact resistance. This situation is more common in switchgear with large current. Therefore, it has very important project significance to monitor switch contact temperature in switchgear online. Normal temperature measurements cannot be applied in this area because of the issues of high voltage insulation and strong electromagnetic interference. In the thesis,a light / electric hybrid temperature measurement system has been designed,taking advantage of characteristics of optical fiber transmission to achieve high voltage isolation, a low-power sensor circuit has also been designed, so it is impossible to solve the problems that cannot get power supply from buried wires external in the high voltage situation by using a lithium battery to supply power enduring.The basic characteristics of optoelectronic devices have been analyzed at first, choosing the optical fiber,light source,photo detectors and the coupling between each of two ,and an effective optical fiber transmission system is designed.In the temperature acquisition system, thermistors were used in the system and the micro-power CMOS integrated chip was used for low-power design in the whole temperature sensor circuit. The complete temperature sensor circuit includes temperature Pulse-Frequency modulation circuit, pulse width modulation circuit and the light source drive circuit. In the end, the power loss of entire sensor circuit is calculated in the thesis.In the temperature monitoring measuring system, the photodiode pre-amplification electric circuit has been designed, and fiber optic transmission's light signal has been transformed into the same frequency voltage signal. Then the frequency voltage signal is sent to the monolithic integrated circuit to count through six-channel switching circuit which can control the signal channel, and the temperature is displayed via liquid crystal display, overtemperature alarm is realized. In software aspect, subroutines of he data acquisition, liquid crystal display, warning temperature upper limit, data linearization have been programmed for temperature gathering.This article also paid much attention to system's reliability under high voltage and strong electromagnetic field environment, and the effective insulation and anti-jamming measures have been proposed.The temperature gathering and the optical fiber transmission system designed in this thesis has been conducted pilot testing under the laboratory existing condition, and the temperature measurement system have been rectified by setting the temperature of the thermostat. The testing results showed that the temperature online measuring system for measuring the temperature of switch contacts in the switchgear under high voltage has accurate warning for temperature arising over set limit, fast channel conversion and response speed.