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Low-Voltage Circuit Breaker Testing Strategies-Part 2 - High-Current Overloads and Ground Fault Detection

机译：低压断路器测试策略，第2部分-大电流过载和接地故障检测

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摘要

This three-part article addresses testing requirements, methods, and challenges for low-voltage circuit breaker testing strategies. High currents are those that exceed 200 percent of the breaker's rating and are segregated into short-time and instantaneous faults. Ground faults are characterized by an excessive amount of current flowing in the ground system. These types of faults are of the most concern in industrial and commercial applications and, therefore, these protection modes are often found on three-phase breakers. Part one of this series (Fall 2002) described the general technology of circuit breakers and how longtime overcurrent conditions are detected. This article will specifically focus on the sections of the trip unit dedicated to high currents and ground faults. Electromechanical trip units rely on the magnetic field generated by the fault current to activate what is essentially a relay armature. Closure of this magnetic circuit activates the tripping mechanism, and the breaker opens. For the instantaneous function, this action is not time delayed and normally happens within 200 milliseconds after the fault is initiated. Electrohydraulic mechanisms commonly respond in less than one second. Tripping times are shorter when the strength of the magnetic field generated by the current pulls the slug through the liquid at a faster rate. The higher the magnetic field, the shorter the trip time. Finally, electronic trip units implement all of these functions by measuring the actual current and comparing it to a reference table of values to determine the appropriate response.
机译：本文分三部分，介绍了低压断路器测试策略的测试要求，方法和挑战。高电流是指超过断路器额定值200％的电流，并且会被分为短时故障和瞬时故障。接地故障的特征是在接地系统中流动的电流过多。这些类型的故障在工业和商业应用中是最令人关注的，因此，这些保护模式通常出现在三相断路器上。该系列的第一部分（2002年秋季）描述了断路器的一般技术以及如何检测到长时间的过电流情况。本文将重点介绍脱扣单元专门针对大电流和接地故障的部分。机电脱扣器依靠故障电流产生的磁场来激活继电器电枢。该磁路的闭合激活了跳闸机构，并且断路器断开。对于瞬时功能，此操作没有时间延迟，通常在故障启动后的200毫秒内发生。电动液压机构通常在不到一秒钟的时间内做出响应。当电流产生的磁场强度以更快的速度将弹头拉过液体时，跳闸时间会更短。磁场越高，跳闸时间越短。最后，电子脱扣器通过测量实际电流并将其与参考值表进行比较以确定合适的响应，从而实现所有这些功能。

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