32.5
Líneas de transmisión: funcionamiento transitorio
La coordinación del aislamiento es el proceso de hacer coincidir la resistencia del aislamiento del equipo eléctrico con las características del dispo…
El aislamiento eléctrico, como se ve en el cableado doméstico, es crucial para la seguridad, ya que evita descargas eléctricas y cortocircuitos al cubrir los materiales conductores con materiales aislantes como el plástico o el caucho.
La resistencia del aislamiento del equipo varía con el tiempo, pero puede soportar altas sobretensiones transitorias, siempre que sean de corta duración.
Para probar la resistencia del aislamiento, se utiliza una onda de voltaje de impulso estándar. Esta forma de onda se define por el tiempo que tarda el voltaje en alcanzar su pico y decaer a la mitad de su valor máximo.
El valor máximo de esto define el Nivel Básico de Aislamiento, o BIL. Los equipos que cumplen con los BILs estándar pueden soportar aplicaciones repetidas de la forma de onda estándar sin fallas de aislamiento.
Algunos equipos, como el aislamiento de la línea de transmisión aérea, se restauran automáticamente después de un cortocircuito, mientras que el aislamiento interno del transformador requiere reparación o reemplazo en caso de falla.
Los dispositivos de protección, conectados en paralelo con el equipo desde cada fase hasta el suelo, protegen el equipo contra sobretensiones que excedan su BIL, proporcionando un margen de protección.
Un ejemplo simple de un dispositivo de protección es el espacio de la varilla, diseñado para generar chispas a sobretensiones especificadas.
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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.