IEEE Proof IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 1 Model, Design, and Testing of Field Mill Sensors for Measuring Electric Fields Under High-Voltage Direct-Current Power Lines 1 2 3 Yong Cui, Haiwen Yuan, Xiao Song, Member, IEEE, Luxing Zhao, Yumeng Liu, and Liwei Lin 4 Abstract—High-voltage direct-current (HVdc) transmis- 5 sion lines have been implemented in many countries, in- 6 cluding Australia, Brazil, China, and Sweden, and the safety 7 concerns as the result of the high electromagnetic-radiation 8 underneath the HVdc lines have garnered increased public 9 attentions. Here, we report on the model, design, and test- 10 ing of field-mill electric field sensors to measure the electric 11 field at the ground level under the HVdc transmission lines. 12 This study utilized a finite-element analysis method to es- 13 tablish numerical simulation results based on the electrical 14 and mechanical parameters to achieve optimal designs with 15 experimental calibrations. Afterward, these sensors were 16 successfully tested and utilized at the national high-voltage 17 test base. Q1 18 Index Terms—Electric field sensors, field mill, finite- 19 element analysis, high-voltage direct-current (HVdc) trans- 20 mission. 21 I. INTRODUCTION 22 C OMPARED with a high-voltage alternating current 23 (HVac) transmission system, the high-voltage direct- 24 current (HVdc) scheme is a better choice for long-distance 25 bulk power transmission to send vast amounts of electricity 26 over a very long distance with fewer power losses and envi- 27 ronmental impact [1]. Several ±800 kV and ±1000 kV HVdc 28 transmission systems are now in commercial operation in some 29 Manuscript received January 26, 2017; revised April 24, 2017; ac- cepted May 24, 2017. This work was supported in part by the China Aviation Science Foundation under Grant 2015ZD51051, in part by the National Natural Science Foundation of China under Grant 61273165, and in part by the SGCC Science and Technology Project of China under Grant GY71-16-010. (Corresponding author: Xiao Song.) Y. Cui is with the Berkeley Sensor and Actuator Center, University of California Berkeley, Berkeley, CA 94720 USA (e-mail: yongcui@ berkeley.edu). H. Yuan and X. Song are with the Automation School, Beihang Uni- versity, Beijing 100191, China (e-mail: yhw@buaa.edu.cn; songxiao@ buaa.edu.cn). L. Zhao is with the China Electric Power Research Institute, Beijing 100192, China (e-mail: zhaolx@erpi.sgcc.com.cn). Y. Liu is with the Department of Mechanical Engineering, University of California Berkeley, Berkeley, CA 94720 USA (e-mail: yumengliu@ berkeley.edu). L. Lin is with the Department of Mechanical Engineering and the Berkeley Sensor and Actuator Center, University of California Berkeley, Berkeley, CA 94720 USA (e-mail: lwlin@berkeley.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2017.2719618 countries [2]. According to the planning of some grid cooper- 30 ation, about 30 HVdc transmission projects will be constructed 31 by 2020 in the world. 32 With the large-scale implementations of HVdc transmission 33 lines, the environmental impacts due to electromagnetic waves 34 have become a focus of public attention in the following techni- 35 cal parameters: electric field, ion current density, space charge 36 density, radio interference, audible noise, etc. [3]–[11]. In con- 37 trast to the HVac transmission lines, the electric field under 38 HVdc lines is greatly enhanced when a corona discharge occurs 39 and an accurate and efficient measurement method is needed 40 to assure the system follows the electromagnetic environmen- 41 tal standard. Many techniques have been proposed to measure 42 this electric field, including microelectromechanical systems 43 [12]–[14], optics [15]–[17], and field-induced charges [18]– 44 [20]. Specifically, two types of the field-induced charges sensor 45 are widely used under the HVdc transmission lines: the vibrat- 46 ing electrode field meter and the rotating-vane-style electric 47 field meter or “field mill.” The field mill sensor employs an 48 earthed rotor to periodically modulate the dc electric field by 49 alternately exposing and covering the sensor electrode to the 50 external electric field. For example, the field mill sensors have 51 been used at the Hydro-Qu´ ebec’s Research Institute and NASA’s 52 Jet Propulsion Laboratory, whereas the vibrating electrode field 53 meters have been used by the Bonneville Power Administration 54 [21]–[23]. In general, the field mill is less affected by the poor 55 weather situations and normally operated at the ground plane 56 to measure an electric field at the ground level. Besides the 57 applications in the power systems, field mill sensors have also 58 been widely used in measuring atmospheric quasi-static electric 59 fields for applications, such as lightning hazard warning [24], 60 radioactive pollution detection [25], earthquake prediction [26], 61 and electrostatic nature of volcanic plumes [31]. 62 The structure of the field mill has many types in the sensing 63 plate, sensing area, height, etc. For example, Batemen [21], 64 Fort [27], and Tant [28] have used two open sensing plates and 65 Chubb [19] and Maruvada [30] have employed four and six open 66 sensing plates, respectively, while Mendez [31], Kaplan [32], 67 and Bai [33] have the design of eight; Soula [34] has the design 68 of ten; and Zou [3] has the design of 16 open sensing plates. None 69 of these previous reports have provided detailed analyses, such 70 as the effect of the gap distance between the rotating and sensing 71 electrodes, which is adjustable by the fabrication and assembly 72 processes. In this paper, a numerical model for the field mill 73 0278-0046 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.