HVDC入地电流对地电场的影响规律及入地极定位

doi:10.3969/j.issn.0253-4967.2022.03.010

摘要/Abstract

摘要：

高压直流输电(HVDC)换流站的入地电流造成了地电场观测中的显著干扰, 通常在入地极附近数百千米范围内会引起很大的阶变。但判断阶变来源于某个换流站的入地电流是较为困难的, 一般需要借助高压直流线路对地磁场的影响数据来识别。文中以海驻线(海南藏族自治州—驻马店)、扎青线(扎鲁特—青州)和宝德线(宝鸡—德阳)为例, 获取了3次典型干扰的响应数据, 对3条线路周边58个地电场台站的数据展开分析, 并使用山东大山台极低频数据作为对比案例。首先, 解释了不同位置的台站对入地电流有不同的响应方式, 即台站分别位于1个入地极附近、两极中间以及两极之间靠近一侧入地极这3种情况时, 对应的3类响应分别为台阶状阶变、脉冲状响应和脉冲+半台阶状响应。然后, 采用日变化幅度对高压直流输电干扰的阶变量进行校正, 基于多台的电位差具有方向性的原理对入地极进行定位, 判断入地电流的来源和换流站的大致位置。定位结果对海驻线、扎青线和宝德线的入地极位置都有较好的指向, 结合多台的阶变合成矢量能够判断换流站的位置; 此外, 经日变化校正后的阶变幅度能显示入地极所在, 可对定位结果进行补充。进一步建立入地电流的定量扩散电流模型, 展示大电流入地时电位差的分布规律, 判断入地电流的干扰范围和台站响应的阶变量。基于58个地电场台站和1个极低频台站的观测数据, 文中给出了入地电流对周边地电场台站干扰的特点, 可将其应用于实际观测中对HVDC干扰的数据校正。

关键词: 高压直流输电, 入地极, 地电场, 多台定位, 极低频

Abstract:

The grounding current of HVDC(high voltage direct current)converter station causes the most significant interference in the observation of geoelectric field, which usually causes a step change as 0.5~100mV/km within a range of hundreds of kilometers near the grounding pole. However, it is difficult to determine which converter station’s grounding current causes the step change. Taking Hainanzhou-Zhumadian line, Zhalute-Qingzhou line and Baoji-Deyang line as examples, we obtain the response data of three typical disturbances, and calculate the step change using the data of 58 geoelectric stations around these three lines. To compare the interference situation, we referred the extremely low frequency data of Dashan station for comparison with their original curves.

First, we explained the different response modes of the stations at different locations to the ground current. This means that when the stations locate near a ground electrode, in the middle of the two poles and near to one side of the ground electrode between the two poles, the corresponding three response types are: step response, pulse response and pulse+half step response, respectively. In particular, stations located in the middle of two poles but close to one pole are mainly affected by the near pole and less importantly affected by the other pole. Consequently, step response appears in the near pole stations, step recovery appears in the far pole stations, and the final result is in the form of step+pulse.

Then, we use daily variation amplitude to correct the order variable of HVDC interference and locate the position of grounding pole by the principle that the potential difference of multiple stations has directivity, and then determine the source of grounding current and the approximate location of converter station. The step change after diurnal change correction shows a certain trend, which is shown as the quadratic attenuation of the source-station distance. The fitting of the step change observed by a wide range of geoelectric stations confirms this trend. The locating results have good directive effect on the grounding poles’ positions of the Hainanzhou-Zhumadian line, Zhalute-Qingzhou line and Baoji-Deyang line, and by combining the step change synthesis vector of multiple stations, we can simultaneously determine the approximate location of the converter station. In addition, the amplitude of step change after daily variation correction can suggest the site of the ground electrode, which can supplement the locating results.

Furthermore, we build the quantitative diffusion model of the grounding current to show the law of potential distribution of large input current, and determine the interference range and the variation trend. The simulation results show that the potential difference decreases rapidly within 50km near the grounding pole; the potential difference reduction effect is not strong in far-field exceeding 200km and basically maintains a gentle trend. Based on observation data of 58 geoelectrical stations and another station of extremely low frequency, the response characteristics of grounding current to the surrounding stations are identified, which may serve for the data correction of HVDC interference in the future.

Results of the influence of grounding current on geoelectric and geomagnetic field can be further extended to the study of seismic electromagnetic signal. Electromagnetic stations are usually set up near the active fault zone in an attempt to detect electromagnetic signals generated by strong earthquakes. Relying on the observation data, researchers can present a preliminary prediction of strong earthquakes under certain conditions, and provide a spatial range and time scale of the earthquakes. However, the explanation of how the electromagnetic signal near the source propagates to the observation stations is not very satisfactory. In particular, there are anomalies appearing in some distant stations, while no anomalies appear in the nearby stations. It means the differential response is obvious. Moreover, some prediction is generally not logical and physical, which means the abnormal signal may not come from earthquake activity but some other sources. Therefore, it is necessary to study how the signal propagates from the source to the station and why it causes differential response.

Key words: HVDC(high voltage direct current), grounding current, geoelectric field, locating grounding poles, extremely low frequency

中图分类号:

P315.722

章鑫, 范晔, 叶青, 钱银苹. HVDC入地电流对地电场的影响规律及入地极定位[J]. 地震地质, 2022, 44(3): 718-735.

ZHANG Xin, FAN Ye, YE Qing, QIAN Yin-ping. THE INFLUENCE OF HVDC TRANSMISSION ON GEOELECTRIC FIELD AND LOCATING THE GROUNDING POLES[J]. SEISMOLOGY AND GEOLOGY, 2022, 44(3): 718-735.

图/表 12

图 1 高压直流线附近的台站分布和构造要素 a ±800kV海驻线的台站分布; b 宝德线入地极的位置和台站分布; c 扎青线入地极的位置和台站分布。红色三角为被干扰台站, 蓝色为区域内其他台站, 黑色箭头表示输电端和受电端的方向

Fig. 1 Distribution of stations and faults near HVDC lines. The red triangle represents the disturbed stations, and the blue ones represent other stations in the area.

表1 台站信息及阶变量计算结果

Table 1 Station information and partial results of step changes

海驻线台站	S_EX /mV·km^-1	S_EY /mV·km^-1	与入地极的距离 /km	宝德线、扎青线台站	S_EX /mV·km^-1	S_EY /mV·km^-1	与入地极的距离 /km
蒙城	9.153 7	62.681 3	203	成都	-6.153 3	-20.881 7	63
嘉山	-2.528 7	6.031 8	374	江油	7.305 5	10.827 2	80
南京	-1.68	14.5	499	固原	-2.585	0.495	175
新沂	0.106 7	2.473 3	397	乾陵	-18.646 7	-24.438 3	93
高邮	0.071 7	1.561 7	485	宝鸡	-4.146 7	-8.598 3	55
海安	-0.258 3	0.54	583	周至	-0.512 8	-2.419 3	110
郯城	8.47	3.061 7	425	凤翔	-197.721 7	-32.876 7	88
菏泽	8.636 7	2.538 3	223	延庆	2.19	-0.42	475
大山	0.488 3	0.995	605	静海	2.547	-1.431	289
邹城	6.195	2.738 3	340	徐庄子	1.491	-0.255	247
洛阳	-13.948 3	-7.683 3	219	宝坻	4.218	-1.78	348
周口	17.44	4.671 7	51	昌黎	5.748	-3.697	341
应城	-21.27	-11.71	270	大柏舍	2.29	-1.27	338
仙女山	-1.58	-2.08	748	兴济	0.78	-2.945	247
红池坝	-0.28	-1.57	488	肥乡	1.252	-0.865	316
乾陵	2.87	-2.76	579	新城子	10.47	-4.35	348
合阳	-1.59	-0.52	433	锦州	13.078 3	-3.535	297
凤翔	-4.65	-1.79	646	阜新	75.128 5	-13.203	231
平凉	-3.14	-9.25	499	三岗	-0.458 3	-3.648 3	373
山丹	-1.14	-1.02	309	四平	3.591 7	-1.22	354
武威	-1.09	-0.64	245	榆树	1.67	-2.341 7	517
松山1	-1.53	-1.39	263	德都	-4.44	-2.19	673
松山3	-1.03	-0.78	264	林甸	-1.63	-1.2	502
古丰	-9.67	-3.80	234	王奎	-0.83	-1.36	553
黄羊	1.44	0.68	246	肇东	-0.44	-3.07	498
玛曲	0.83	-1.29	239	通河	1.72	15.85	650
都兰	-1.99	2.67	254	安丘	-3.008 3	3.523 3	75
大武	34.49	26.45	179	菏泽	-0.976 7	-0.14	328
金银滩	-5.30	0.38	110	大山	0.631 7	-0.07	173

图 2 不同位置的台站受到海驻线影响的结果 a 代表性响应台站及其位置示意图; b—d 都兰台、凤翔台和大山台受影响的观测曲线; 图b为第1类响应, 只受到一侧极的影响; 图c为第2类响应, 同时受到两侧极的影响且影响几乎相当; 图d为第3类响应, 受到两侧极的影响且以一侧极为主。干扰发生的时间为2020年7月11日和2020年4月23日

Fig. 2 Results of different stations that are affected by Hainanzhou-Zhumadian line.

图 3 大山台地电场观测数据与极低频观测数据对高压直流的响应比较 a 地电场EX分量; b 地电场EY分量; c大山台极低频电场的观测值; d、 f D1、 D2时段的放大图; e、 g E时段的放大图。LEX表示极低频电场的EX分量, LEY表示极低频电场的EY分量; 图 3d—g 表示截取典型响应的台阶(或脉冲)时段。 D1和D2 表示2个独立的干扰阶段, E表示扰动时段同时存在于地电场观测与极低频观测中

Fig. 3 Comparison of the responses of geoelectric field data and extremely low frequency data to HVDC at Dashan station.

图 4 按照距离排列的驻马店入地极附近台站EX分量的阶变情况(a)及阶变延迟信息(b、 c)

Fig. 4 The EX order variables that are arranged by distance of stations near the Zhumadian ground electrode(a)and step delay information(b, c).

图 5 驻马店入地极附近台站的阶变量、日变化幅度(a)及两者比值(b)

Fig. 5 The step changes, daily variation range, and their ratio of stations near the Zhumadian grounding electrode.

图 6 海南藏族自治州入地极附近台站的阶变量、日变化幅度(a)及两者比值(b)

Fig. 6 The step changes, daily variation range, and their ratio of stations near the Hainanzhou grounding electrode.

图 7 高压直流的电位方向性响应及电位方向差异定位原理 a 南京台短极距对三常线(三峡—常州, ±500kV)2020年5月9日的阶变; b 南京台短极距阶变的方向性响应;c 基于2个虚拟台站的电位方向差异的定位原理示意图

Fig. 7 Potential directional response of HVDC and the principle of locating by potential direction difference of HVDC.

图 8 海驻线阶变比的矢量归一化定位结果

Fig. 8 The locating result of Hainanzhou-Zhumadian line by using composite vector of step changes.

图 9 阶变量合成矢量归一化的方向 a 扎青线入地极的定位结果; b 宝德线入地极的定位结果

Fig. 9 Direction of composite vector of step changes.

图 10 阶变比值的强度排序 a 海驻线电流开始注入阶段; b 海驻线电流恢复阶段

Fig. 10 Intensity rank of step change and diurnal variation ratio of Hainanzhou-Zhumadian line.

图 11 理想导电状况下的电位分布及电位差衰减 a 2个入地极附近的电位取对数(log10)的分布, 单位为mV; b、 c 对图a中沿y轴求电位差的结果, 在-800~-100km范围每隔100km取1条线, 单位为mV/km; d、 e 对图a中沿y轴求电位差的结果, 在-20~50km范围每隔10km取1条线, 除通原点的线, 单位为mV/km。入地电流强度为4 000A, 电阻率为150Ω·m, 埋深100m

Fig. 11 Potential distribution and difference attenuation under ideal conduction condition.

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