随着我国经济的发展，居民和工业用电需求越来越大，我国开始大力发展高电压直流输电系统，实现远距离、大容量输电，以解决我国东西部地区电能供需之间的矛盾。在直流输电系统中，接地极作为系统中的关键设备其工况的好坏对直流输电系统的正常运行有很大的影响。另外，接地极上在一定的情况下会持续流过大电流，引起电磁、热力和电化效应等现象，会影响周边设备的正常工作，甚至造成设备的损坏及人身安全的危害。所以实时监测接地极的运行情况，对于分析系统运行状态，保证整个高压直流输电系统的稳定运行和防止因接地极故障造成的安全问题具有重要的现实意义。 本文首先分析了直流输电系统运行方式与接地极电流的对应关系，以预防性监测为目标，结合接地极的运行要求，以确定接地电流的监测对象及其范围。其次，设计了一种直流输电接地极在线监测装置。监测装置以MSP430超低功耗单片机作为主控芯片，集合了太阳能供电、滤波电路、时钟电路和监控电路组成了主控单元，采用开环穿芯式霍尔传感器采集接地极上的电流，利用CYB500D系列水位水温传感器采集水位和水温，经过屏蔽导线送入在线监测装置；利用TC35i工业通讯模块以短消息为载体完成数据的无线通信传输。对装置硬件的屏蔽、抗干扰、系统功耗、元件布局等方面进行优化设计，保证了系统的稳定可靠工作。编写了相应的信号采集、数据处理、无线传输和控制程序。最后，针对两种典型的运行情况，进行了监测装置整体测试，对测量数据的误差进行分析和校准，以满足对接地极在线监测的精度要求。 测试结果表明，测试装置能够有效的测量电流、水位和水温，实现数据无线传输，并通过对数据的误差校正，使其精度满足接地极在线监测的要求，做为判断直流输电系统运行方式和接地极工作状态的重要数据依据，验证了设计的正确性，达到了高压直流接地极监测的目的，为进一步发展直流输电在线监测应用提供了参考。

With the development of our country's economy, industry and residents' demand for power is more and more. In order to solve the contradiction between supply and demand of electric power in the eastern and western areas in China, China began to develop the high-voltage direct current(HVDC) transmission system, realize the long distance and large capacity of power transmission. Earth electrode is a key equipment in HVDC systems, the working condition of the good or bad for the normal work of the HVDC system has a great influence. he stand or fall of its working conditions have great influence on the normal work of the DC transmission system. In addition, the large current will continue through earth electrode in a certain cases. It caused the phenomenons such as the electromagnetic effect, thermal effect and galvanic effect, will affect the normal work of the peripheral equipments. seriously, it will cause the damage of the equipments or endanger the personal safety. So, real-time monitoring the earth electrode operation situation has important practical significance for analysis system running status and ensure the stability of the HVDC transmission system in operation and prevent caused by earth electrode fault safety problem . This paper based on the corresponding relationship between HVDC system operation mode and grounding current of earth electrode, Combined with the operation requirements of earth, and selected monitoring objects and value range for the purpose of preventive monitoring. We design a HVDC earth electrode online monitoring device.This monitoring device adopts MSP430F149 ultra-low power micro controller unit as the master control chip, with the solar power supply , filter circuit, clock circuit and control circuit form the main control unit. We adopted open-loop wear core type Hall sensor gathering the earth electrode current, using CYB500D series water-level temperature sensor to collect water level and temperature. The hielding wires be used to transfer water level and temperature singal to online monitoring device. Monitoring device adopts industrial GSM communication module TC35i short message as the carrier to complete the wireless transmission of data. We optimized the device design of shielding anti-interference, power consumption component placement of device hardware, to ensure that the system is stable and reliable working, and make up the signal acquisition, data processing, wireless transmission and control program. Finally, in view of the two kinds of typical operation conditions, we overall test the monitoring device, and analyzes the error of the measured data and calibration, to satisfy the requirement of the docking the ends of the earth electrode online monitoring precision. Test results show that the test device can effectively measure the current, water level and water temperature data, and transfer these data by wireless transmission, and make its precision satisfy the requirements of earth electrode online monitoring through the data error correction program. It’s an important data basis to judge DC transmission system operation mode and the working state of earth electrode. The results validate the correctness of the design, to achieve the purpose of monitoring for HVDC earth electrode. The research provides reference for the further development of HVDC on-line monitoring application.