Question

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2-5. Ground-fault current
Ground-fault current consists of any current which flows outside the normal circuit path. A ground-fault condition then, results in current flow in the equipment grounding conductor for low-voltage systems. In medium- and high-voltage systems, ground-fault current may return to the source through the earth. Ground-fault protection of medium-voltage and high-voltage systems has been applied successfully for years using ground current relays. Ground-fault protection of low-voltage systems is a considerable problem because of the presence and nature of low-level arcing ground faults. Ground-fault current on low-voltage systems may be classified as leakage, bolted, or arcing.

a. Leakage ground-fault current. Leakage ground-fault current is the low magnitude current (milliampere range) associated with portable tools and appliances. It is caused by insulation failure, and is a serious shock hazard. Personnel protection is accomplished by using ground-fault circuit interrupters (GFCI) in the form of GFCI-receptacles or GFCI-circuit-breakers.
b. Bolted ground-fault current. Bolted ground-fault current results when phase conductors become solidly connected to ground (i.e., the equipment grounding conductor or to a grounded metallic object). Bolted ground-fault current may equal or even exceed three-phase, bolted short-circuit current if the system is solidly grounded. Equipment protection is accomplished by using standard phase and ground overcurrent devices depending upon system voltage levels.
c. Arcing ground-fault current. Arcing ground-fault current results from a less than solid connection between phase conductors and ground. Because an arc is necessary to sustain current flow through the connection, the magnitude of arcing ground-fault current will be less than that of bolted ground-fault current. Depending upon the arc impedance, arcing ground-fault current may be as low as several amperes (low-level) or as high as 20-38 percent of three-phase, bolted short-circuit current (high level) on a 480V system. Considerable research has been conducted in the area of arcing ground-fault current magnitudes on low voltage systems. Some designers use the 38 percent value while others use the 20 percent figure. NEMA PB2.2 applies ground-fault damage curves instead of performing a calculation. Equipment protection is accomplished by using ground-fault protective (GFP) devices. Due to ionization of the air, arcing ground faults may escalate into phase-to-phase or three-phase faults.

Answer 1

2-5。接地故障电流
接地故障电流包括任何目前，不属于正常的电路路径流动。阿接地故障状态，然后，结果在接地的低电压系统导体设备电流。在中，高电压系统，接地故障电流可能返回到在地球的来源。接地故障保护的中压和高压系统已应用多年，在成功地使用接地电流继电器。接地故障的低电压系统的保护是因为存在和电弧接地故障的低级别的性质相当严重的问题。接地故障电流低电压系统可作为泄漏，螺栓，或电弧分类。

字母a.泄漏地面故障电流。漏电接地故障电流幅度的低电流（毫安范围）的便携式工具及相关设备。它是由绝缘失败，是一个严重的触电危险。人员的保护是通过使用地面的形式漏电开关电路断路器故障（漏电开关）的盛器或漏电开关，断路器。
湾螺栓接地故障电流。螺栓接地故障时相导体成为牢固连接到地（即设备接地线或接地的金属物体）当前结果。螺栓接地故障电流可能等于或什至超过三个阶段，螺栓短路电流，如果系统是坚实的基础。设备保障是通过使用标准的相位和地面设备的过电流取决于系统电压水平。
角电弧接地故障电流。电弧接地故障电流的结果从一间不到相导体和地面坚实的连接。因为一个弧要通过连接维持目前的流量，电弧接地故障电流的幅度将低于地面的螺栓故障电流。这取决于电弧阻抗，电弧接地故障电流可能高达数安培的低（低级别）或在20-38百分之三相栓短路电流（高的水平，在480V系统）高。相当多的研究已进行了的电弧接地面积故障低电压系统电流程度。一些设计师使用百分之三十八的价值，同时其他人使用20个百分点。类型NEMA PB2.2适用于地面断裂损伤曲线而不是执行计算。设备保障是通过使用接地故障保护（GFP）的设备。由于空气电离，电弧接地故障可能升级成为相接相或三相故障。