Intrusion Path Ⅰ～Ⅲ of Lightning Surge into Power System

Protection by Surge Isolation Transformer

Entry Point	Equipment at Input (Power Supply) Side	Equipment at Output (Load) Side
Input (power supply) side	× Equipment cannot be protected as it receives lightning surge directly.	○ Lightning surge voltage is reduced (to 1/1000 or less) by the transformer.
Output (load) side	○ Lightning surge voltage is reduced by the transformer. However, the amount of reduction is smaller compared to the case when surge enters from the primary side and flows to the secondary side.	× Equipment cannot be protected as it receives lightning surge directly.
Ground	△ When the ground potential rises, the shield potential of the transformer increases, and static electricity is transferred to the power supply side.	△ Equipment can withstand the ground potential rise with the insulation of the transformer by performing equipotential grounding between the transformer and the load equipment.

Installation Precautions

• The main point is to perform equipotential grounding between the Surge isolation transformer and the electric equipment (i.e. load equipment which is a target of protection).
• It is necessary to have a specialist perform “an examination of the grounding system”.

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