外部ギャップ型避雷器
The Externally Gapped Line Arrester (EGLA) is a surge protection device consisting of a Series Varistor Unit (SVU) and an external spark gap. The device protects transmission line insulators from lightning-induced flashovers and switching surges in power systems ranging from 13.2kV to 230kV. When a surge occurs, the gap sparks over and channels the current through the SVU, which then limits and terminates the current flow before any power frequency follow current develops.
The EGLA comes in two configurations: IEC type for lightning-only protection and standard type for both lightning and switching surge protection. The Externally Gapped Line Arrester mounts directly on transmission lines and requires precise gap spacing calibration based on system voltage and environmental conditions. The device can be installed with either single or dual SVU configurations depending on voltage requirements.
主な特長:
– Zero power frequency losses during normal operation
– Self-resetting capability without circuit breaker intervention
– Guaranteed fail-open design preventing sustained system outages
– Reduced housing material requirements with 30% less creepage distance
– Minimal aging of metal oxide varistors due to external gap isolation
– Flexible mounting options for new installations or retrofits
Externally Gapped Line Arrester Drawing
よくある質問 (よくある質問)
How does an EGLA work?
The EGLA combines a well-coordinated gap and varistor that work together. When lightning strikes, the gap sparks over at a predetermined voltage, then the MOV elements conduct surge current to ground, limit follow current, and extinguish the external power arc, all without requiring circuit breaker operation.
What are the key components of an EGLA?
An EGLA consists of two main components: a Series Varistor Unit (SVU) that acts as the surge arrester part, and an external spark gap in series. The electrodes create durable arc landing points, allow gap spacing adjustment, and provide consistent flashover characteristics.
What happens if the gap spacing is incorrect?
If gap spacing is below minimum, risk of flashover during temporary overvoltage increases, potentially damaging the arrester. If above maximum, the insulator may flashover before gap sparkover, causing momentary or long-term outages.
What advantages does EGLA have over NGLA?
EGLA eliminates the need for disconnectors and corona rings, reduces size and weight, and prevents temporary overvoltage failures. The design is isolated from system voltage, eliminating thermal recovery concerns and hardware fatigue issues.
How does EGLA handle environmental conditions?
While gap performance may be affected by environmental conditions, the gap maintains its ability to flashover before the protected insulator in most weather conditions. しかし, EGLA cannot protect against severe pollution-induced flashovers at power frequency.
What is the role of lead management in EGLA?
Lead management is simpler with EGLA compared to NGLA because the electrodes are generally shorter than leads. This makes electrode management less challenging than managing the leads of an NGLA.
How does EGLA handle overload situations?
During overload situations, EGLA can be equipped with a disconnector or failure indicator. This configuration allows the electrode to move after overload, ensuring full Critical Flashover (CFO) recovery of the insulator.
What is the calculation basis for minimum gap distance?
The minimum gap setting is calculated based on the expected maximum switching surge. The gap is set wide enough to prevent sparkover during switching surges, using the equation: G = 39.37[e(SS/1080) – 1.46], where G is gap distance in inches.