32.5
伝送線路: 過渡動作
絶縁協調とは、電気機器の絶縁強度と保護装置の特性を一致させて、機器を予想される過電圧から保護するプロセスです。この選択は、エンジニアリングの判断とコストに基づいて行われます。機器は一般に、短時間の高過渡過電圧に耐えることができますが、同じ波形で繰り返し試験を行うと、一貫性のない結果が生じる可能性があ…
家庭の配線に見られるように、電気絶縁は安全のために重要であり、導電性材料をプラスチックやゴムなどの絶縁材料で覆うことにより、感電や短絡を防ぎます。
機器の絶縁強度は時間とともに変化しますが、短寿命であれば、高い過渡過電圧に耐えることができます。
絶縁強度の試験には、標準的なインパルス電圧波が使用されます。この波形は、電圧がピークに達し、ピーク値の半分に減衰するのにかかる時間によって定義されます。
このピーク値によって、基本断熱レベル(BIL)が定義されます。標準BILを満たす機器は、絶縁不良なしに標準波形の繰り返し適用に耐えることができます。
架空送電線の絶縁など、一部の機器は短絡後に自己修復されますが、内部の変圧器の絶縁は故障時に修理または交換が必要です。
各相からアースに機器と並列に接続された保護装置は、BILを超える過電圧から機器を保護し、保護マージンを提供します。
保護装置の簡単な例は、指定された過電圧でスパークオーバーするように設計されたロッドギャップです。
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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.