Another transmission line question...

Hi Bill,

The towers have six lines - three phases on one side, three phases on the other. The three on one side were with insulators different diameter but same length than the three on the other side.

In that case it probably is two different circuits at two different voltages.

I suppose another possibility is that the towers were erected to take two circuits (six lines) but only one circuit was installed at the time. Later they installed a second circuit with insulators from a different manufacturer, perhaps of a better material that allows them to be a smaller diameter.

Same sized conductors on either side?

Its possible that either side was reconductored or otherwise upgraded at different times and the insulator change reflects a better or just different specification or technology available at the time.

For some reason the insulators that are different are for the same voltage rating but are Polymer vs the older style porcelain insulators. More and more of these will be seen as they do have some advantages. The reason for this is unknown to all but the people who designed the line. Are all insulators on the one side the same from tower to tower? If so, I would suggest that these were a cautious experiment at the time the line was built - otherwise, it may be a replacement of a faulty or damaged insulator string.

Sorry, I missed the details in your first paragraph. The second 3 phase line with the polymer insulators was added to the towers at a later date than the first 3 phase line as indicated by Paul- who knows his stuff.

I'll guess (and that's what it is) that the length of the insulators is a function of the voltage; but the smaller diameter has to do with the forces on them.

Tomsic

Nice discussion -- didn't know that polymers were able to replace porcelain for such insulators.

Tomsic

See

They have been around for some time and have some advantages/disadvantages. By the way the diameter of a porcelain insulator is simply to provide the necessary surface leakage distance- the string is made up of multiple units and the load bearing region is between the metal top cap and the metal bottom pin If a unit is damaged or broken, it can be replaced. Tempered glass insulators are made the same way-- an advantage is that if it is damaged, structural strength is retained but the skirts disappear so it is easy to spot damage. On the other hand some utilities in Western Canada and USA don't use them as they are too tempting to people with 22's who shoot at them- and see them explode- great fun! With porcelain insulators, the shooter may not even know if he hit the insulator-boring!