The glass gas discharge tube is also called Spark Gap Protectors (SPG) or a powerful discharge tube. SPG has the advantages of small size, low cost, and low junction capacitance(≤0.8PF), fast responding, high isolation（≥10^8Ω), zero leakage current,stable electrical characteristics over time, up to 3kA impulse discharge current, and is often used for lightning protection of communication lines.