| Insulating property of electrical equipment is an important parameter for safe operation. In order to avoid sudden breakdown and outage, power industry mainly adopts pretesting and checking methods. Insulating resistance (IR) testing is common for experimental projects. The dampness, aging or penetrating flaw can be detected in time by measuring IR. For large scale equipments, absorption or polarization index is used to judge the state of IR.This paper introduces the research and development of megohmmeter briefly which is used for measuring IR. According to the principle and method of IR testing, five modules are designed in the system, which are high voltage module, stabilized voltage module, communication module, measuring module and LCD displaying module. Firstly, the high voltage module is designed by driving MOSFET with square-wave circuit to control switching power supply. And push-pull mode of low-voltage generates the required high voltage in using voltage doubling rectifying circuit. For the stabilized voltage module, there is a constant voltage circuit which has the feature of over-current protection. Through the feedback of circuit, voltage can be controlled automatically. Secondly, the communication module is using the ISP of STC12C4052AD, CH341 and optical coupling chips to fulfill reliability of data. For the measuring module, dual-branch method of measuring IR is applied to eliminate the effect of power supply and 16-bit AD7705 is chosen in AD circuit because of the high resolution and strong anti-noise ability. And for the displaying module, all related parameters can be shown in LCD. This paper explains both hardware circuits design and software programs design. In addition, methods of signal processing and causes of dynamic error are analyzed.Through practical debugging and simulation, a system for insulating property testing is built by using single chip and switching power supply. It is valuable to spread digital megohmmeter and important to study insulating research. |
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