Page 40 - Energize September 2021 HR

TECHNICAL

Figure 6: EGLA installation

grounding wire and strike a phase conductor. When such shielding
failures occur, the lightning current is not significantly high and the
load generated by such lightning is not considered so severe.
Consequently, to sum up, while larger lightning may strike
the shielding wire, only smaller lightning can impact the phase
conductor, meaning the current following through the arrester unit is
expected to be small.
This explains why the compact type EGLA (Class Y2) can be
applicable and ensure the reliability of transmission systems. With
analysis of the lightning phenomena and long term experience of
EGLA applications in Japan, the compact type EGLA (Class Y2)
became a reality and a satisfactory experience was achieved.
The lightning current and subsequent current following
through the arrester unit may be significantly larger under certain
transmission system conditions, such as shielding conditions, Structures
footing resistance, etc. Arresters with much larger lightning The Toshiba EGLA arrester unit consists of the ZnO column, which
withstand capability must be provided to protect such systems. is directly moulded with silicone rubber, helping reduce the size
Toshiba can also supply heavy duty type EGLA (Class Y3 and Class and weight of the arrester unit. The silicone material has excellent
Y4) with sufficient lightning withstand capability. weatherproof and hydrophobic characteristics, meaning the
Toshiba EGLA boasts an extended service life. Toshiba EGLA is
Ratings mounted to the hardware of insulator strings, rather than directly
- Toshiba EGLAs comply with IEC 60099-8: 2017 to the power conductors. Direct installation to the power lines
- The “TMLRG series and RVLRG series units are suitable for could damage the conductor, due to the load, vibration and torsion
systems of up to 362kV. For up to 550kV, the “RVLRC series” are caused by the wind to which the line arrester is exposed, or arcing
applicable. Concerning the EGLA type selection, please contact movements along the conductor.
Toshiba for information on EGLA application.
- Notes: The other ratings are available based on users’ requests. Installation
The Toshiba EGLA can be easily installed to the hardware of the
insulator strings. Typical installations are shown in the figures.
Mounting the arrester unit to the horn holder is typical and the
easiest installation method. Even if mounting the arrester unit to
other hardware, the mounting parts can be modified to fit to the
latter. Setting the external series gap distance is vital for EGLA,
because of the need to consider the following items:
● The series gap must withstand switching over-voltage and
power frequency
● The series gap must be designed to coordinate the arcing horn
against any lightning impulse

The gap horn is designed to be adjustable in order to fix the series
gap distance correctly.

Verification tests
Toshiba tested the EGLA in its own excellent testing facilities using
Table 1: Comparison between EGLA and gapless type arresters Both newly revised testing methods. The EGLA’s excellent performance
are 120 kV rated for a 145 kV system as an example has been confirmed in all test areas.

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