便携式电容电流测试仪----硬件部分.docVIP

便携式电容电流测试仪----硬件部分 摘 要 国内现有的高压小电流接地系统普遍采用中性点不接地系统，单相接地电流主要为线路对地电容产生的电容电流。因此电容电流是小电流接地系统重要参数，也是系统运行方式改造的重要依据。传统的电容电流测量方法有直接法和间接法，测量时接线复杂，与高压一次侧接触，且测量对电网有冲击，人员与设备安全得不到保障，测量工作效率低。 本文设计了一种基于注入法的电容电流测试仪，采用直接数字频率合成技术(DDFS)产生变频电流信号，运用傅氏算法，在不影响电网正常工作的情况下，对中性点非直接接地系统的电容电流进行测量，具有较高的精度，使用方便、灵活。 设计的电容电流测试仪采用80C196KC为核心，硬件电路设计基于模块化思想，由单片机最小系统、注入变频电源发生电路、采集系统、通信电路、键盘显示电路构成。本设计采用了软硬件结合的滤波方法和32点采样的傅氏算法，兼顾了测量精度和硬件电路最简化。 关键词：电容电流； 测试仪； 注入法； DDFS ABSTRACT At present, the domestic high voltage system with small current grounded mostly adapts the mode of neutral non-gruounded, when single line grounded, the current is just the capacitave current brought by the capacitance between the line and ground. Therefore, capacitave current is an important parameter of the small current system, and the basis of the running mode of system restruction. Traditionally, the capacitive current could be measured directly or indirectly. However, the operation and connection were complex and inefficient, and it is dangerous for personnel and the equipment. This paper designs the capacitive current measuring instrument base on the thoery of signal injection. The design makes use of Direct Digital Frequency Synthetics (DDFS) to produce various frequency currents. By Fourier , a high measurement precision is achieved. So it can be applied to all kinds of neutral non-valid grounded systefinish the measurement of capacitive current while doesn’t affect normal running of the system, it has high presicion and is used conveniently and neatly. This design has take the chip of 80C196KC as the core, and the hardware is designed based on the thought of module. This design is composed of SCM system、frequency conversion supplying circuit、signal gathering system、communicating circuits、keyboard and display circuits etc.. Software and hardware are combined to filter the unwanted signals, and 32 points signals for sampling control is used. The presicion and the predigestion of the circuit are both given attention to.