We need a typical method of directly measuring geomagnetically induced current (GIC) to compare data for estimating a potential risk of power grids caused by GIC. Here, we overview GIC measurement systems that have appeared in published papers, note necessary requirements, report on our equipment, and show several examples of our measurements in substations around Tokyo, Japan. Although they are located at middle latitudes, GICs associated with various geomagnetic disturbances are observed, such as storm sudden commencements (SSCs) or sudden impulses (SIs) caused by interplanetary shocks, geomagnetic storms including a storm caused by abrupt southward turning of strong interplanetary magnetic field (IMF) associated with a magnetic cloud, bay disturbances caused by high-latitude aurora activities, and geomagnetic variation caused by a solar flare called the solar flare effect (SFE). All these results suggest that GIC at middle latitudes is sensitive to the magnetospheric current (the magnetopause current, the ring current, and the field-aligned current) and also the ionospheric current.

我们需要一种直接测量地磁感应电流（GIC）的典型方法，以比较数据以估算由GIC引起的电网潜在风险。在这里，我们概述了已发表论文中出现的GIC测量系统，记录了必要的要求，报告了我们的设备，并展示了我们在日本东京附近的变电站中进行测量的几个示例。尽管它们位于中纬度，但可以观察到与各种地磁干扰有关的GIC，例如由行星际震荡引起的风暴突然开始（SSC）或突然脉冲（SI），地磁风暴​​，包括由强行星际磁场突然向南转弯而引起的风暴与磁云有关的磁场（IMF），高纬度极光活动引起的海湾干扰，由太阳耀斑引起的地磁变化称为太阳耀斑效应（SFE）。所有这些结果表明，中纬度地区的GIC对磁层电流（磁层顶电流，环形电流和场对准电流）以及电离层电流都敏感。