32.5
输电线路:瞬态运行
绝缘协调是将电气设备的绝缘强度与保护装置特性相匹配以保护设备免受预期过电压影响的过程。此选择基于工程判断和成本。设备通常可以承受短时间的高瞬态过电压，但使用相同波形进行重复测试可能会产生不一致的结果。因此，使用标准脉冲电压波形进行测试，该波形由电压达到峰值并衰减至峰值一半的特定时间定义。
基本绝缘水…
电气绝缘，例如家庭电线中的绝缘措施，对于安全至关重要，它通过用塑料或橡胶等绝缘材料包裹导电材料，防止触电和短路。
设备绝缘的强度随时间变化，但只要持续时间短暂，便能够承受较高的瞬态过电压。
测试绝缘强度时，采用标准冲击电压波形。该波形由电压上升至峰值所需时间以及衰减至峰值一半所需时间来定义。
该峰值定义了基本绝缘水平（Basic Insulation Level，BIL）。符合标准BIL的设备能够承受多次标准波形的冲击而不发生绝缘失效。
某些设备，例如架空输电线路的绝缘体，在短路后具有自恢复能力，而变压器内部绝缘在发生故障后则需要维修或更换。
与每相设备并联连接至地的保护装置，可防止设备承受超过其基本冲击绝缘水平（BIL）的过电压，从而提供保护裕度。
一种简单的保护装置示例是保护间隙，其设计可在特定过电压下发生火花放电。
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Q1: What is the Basic Insulation Level and how is it determined?
The Basic Insulation Level, or BIL, is the peak value of a standard impulse voltage waveform used for testing equipment insulation strength. This waveform is defined by specific times for voltage to reach its peak and decay to half that peak value. Equipment meeting standard IEEE-defined BILs can withstand repeated applications of this waveform without insulation failure.
Q2: Why do protective devices need to limit voltage during overvoltages?
Protective devices limit voltage to protect equipment from overvoltages exceeding its insulation capacity. Connected in parallel between each phase and ground, these devices must provide high impedance during normal operation and low impedance during surges. This voltage limiting prevents insulation breakdown and equipment damage while maintaining system stability.
Q3: What is the protection margin in insulation coordination?
The protection margin is the difference between the equipment's breakdown voltage and the protective device's ceiling voltage. This margin ensures the protective device operates before equipment insulation fails. A proper protection margin is essential for reliable equipment operation and is determined through engineering judgment and cost considerations during insulation coordination design.
Q4: How do rod gaps function as protective devices?
Rod gaps are simple protective devices designed to spark over at specified overvoltages, creating a conduction path that diverts excess voltage to ground. They operate by providing high impedance during normal conditions and transitioning to low impedance when overvoltage thresholds are exceeded, protecting connected equipment from voltage surges.
Q5: What is the difference between self-restoring and non-restoring insulation?
Overhead transmission line insulation is self-restoring after a short circuit, automatically recovering its insulating properties. In contrast, internal transformer insulation requires repair or replacement upon failure. This distinction affects maintenance strategies and equipment design choices in power system protection planning.
Q6: How does insulation coordination protect power systems from overvoltage damage?
Insulation coordination matches equipment insulation strength with protective device characteristics to prevent overvoltage damage. By ensuring protective devices limit voltage below equipment withstand capacity, coordination maintains system stability and equipment longevity. This process involves analyzing lossy lines and overvoltages to select appropriate protective measures.
Q7: What characteristics must surge arresters have to be effective?
Effective surge arresters must provide high impedance during normal operation to minimize losses, low impedance during surges to limit voltage, and effectively dissipate or store surge energy. After the surge passes, they must return to open-circuit conditions. Common types include air-gap designs with resistors and gapless surge arresters.