As power supply reliability becomes of more concern each year, utilities are carrying out diagnostics of their lines and insulation in order to avoid unforeseen failures. Inspecting insulators has been recognized to be very difficult to do with porcelain (buzzing each unit...), and is sometimes impossible with composite insulators. For both these types of insulator a visit to each pylon by a ground crew is necessary, using specialised equipment. On the other hand with toughened glass insulators, which cannot be punctured nor be internally cracked, a simple glance at the string gives a complete and reliable assessment of the condition of the insulation. This means that a crew in a helicopter can inspect 100 kilometres of line, or more, per hour.

As cost is also being scrutinized sharply year after year, utilities are considering with great interest the possible savings in the cost of maintenance of their power lines. The first step is the inspection cost. In fact, it is a double folded question. The real question would be: how to ensure the best level of evaluation of the lines at the cheapest cost. The periodicity or frequency of inspection, the level of confidence in the inspection work itself, are important factors to add to the overall cost of inspection of a line.

Several studies have been performed worldwide. Each time, toughened glass insulators were proven to provide the cheapest and most dependable inspection results.

A study published by Stattnet* showed the following relative global inspection costs per km:

* "Recent experience and future plans for the newest generation of Insulators and arresters on the Statnett AC and DC Networks" from Kjell Halsan Diarmid Loudon - Statnett, Norway.
Published in Insulator 2000 – World Congress on Insulator Technologies for the Years 2000 and beyond, Barcelona November 14-17 1999.