Page 39 - Energize September 2021 HR

an external series gap and is fitted with insulation between the
arrester unit and insulator strings.
As a result of this, an EGLA has advantages over gapless
type transmission line arresters. An EGLA can be downsized
compared to station type surge arresters and hence handled very
easily. Moreover, ZnO disks are not normally energised, and would
therefore not deteriorate when used under normal circumstances,
eliminating the need for maintenance and/or monitoring for current
leakage.

How can the compact type be applicable?
In the case of a shielded system, when lightning strikes the
grounding wire or tower structure, the lightning current will decline
as it traverses the grounding wire and tower structure, thus
significantly reducing the load to which the EGLA body is exposed.
EMTP analysis has shown that the following current through the
arrester unit is decreased to approximately 10% or less of the
lightning current.
The shielding distance from the grounding wire depends on the
lightning current. Smaller lightning current may pass close to the

Figure 4: EGLA for suspension type insulator strings

Figure 3: Schematic Diagram of the Lightning Strike Event Figure 5: EGLA for tension type insulator strings

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