Study on Salt Tolerance of Distribution Equipment
- Reproduction test of Tracking Growth -

Half century ago, HEPCO commenced installing insulated wire onto high-voltage distribution lines and improved their reliability through sealing up live parts of them. We, however, faced a new problem "tracking", which is a kind of carbonization, because almost all of insulating material and a cover of electric wire are organic.

The possibility of service interruption due to contact of electric wire with a tree or a bird rises as tracking grows, because insulating material's durability of that weakens. We know that it glows in seaside area with heat and/or discharge, resulted from leakage current on the surface of electric wire's insulating material to which salty water adheres.

Therefore, we have been studying the method for reproduction of tracking growth.

We believe that tracking grows with various factors, and have carried out a number of test methods to reproduce that. In addition, we learned about the international standards of IEC61109 and IEC62217, and have been trying to apply multiple stresses onto distribution equipment, like nearby seaside area.

We have accomplished to reproduce repeatedly tracking growth in a test room as follows:

1. (a) to created a seaside-like environment by wind, rain and spray of salt fog;.
2. (b) to measure the quantities of these factors and make them controllable; and
3. (c) to charge high-voltage electricity to equipment and measure leakage current.

Fig.1 Measured leakage current at the test