Effective TLSA Installations
Installations that adhered to good industry practice and where no improvements were deemed necessary were identified on 5 lines having 6 different configurations. These included arresters mounted across insulators that were horizontally as well as vertically mounted. The fifth installation was unique and not typical. While some of these installations might be considered unconventional, they were nonetheless rated operationally acceptable both for the in-service condition and should the arrester fail. Included here were two installations that are more than 40 years old and that, while still in-service, might no longer function as intended (see Figs. 10 & 11).
The first installation type was on 69 kV lines where all three phases are supported by horizontally mounted polymeric post insulators (see Figs. 2 & 3). Examples include one line that does not have a static wire and with underhung mounted arresters on all three phases (Fig. 2) and another line having a static wire where the arrester is installed only on the bottom phase (see Fig. 3).
The second installation type evaluated was on a 69 kV line with woodpecker wrap (see Figs. 4 & 5). A vertical polymeric post insulator supports the top phase and two horizontally mounted back-to-back polymeric post insulators support the lower phases. The top phase has a vertically mounted arrester while the bottom two phases have side mounted arresters. Higher insulation value insulators were used for the bottom phases to maintain adequate climbing space between phases.
The third installation type was on a 138 kV line with no shield wire in this section (see Fig. 6). The top phase wire in this example is supported by a vertically mounted polymeric post insulator and horizontally mounted back-to-back polymeric post insulators support the bottom two phases. The top phase has a vertically mounted arrester while the bottom two phases have side mounted arresters.
The fifth installation type involved a 138 kV line with two shield wires (see Figs. 7 & 8). In this case, arresters are installed on all three phases of both circuits over the entire length. The installation on this line is unique in that it is a double dead-end structure utilizing horizontal line post insulators to support arresters for the top and middle phases. Bottom phase arresters are hung from the phase conductor jumper.
The sixth installation type involved a 69 kV line with a single shield wire (see Fig. 9). For this line, a standoff ground is used in the wire zone to increase effective BIL of the structure and arresters are installed only on the bottom phase. Due to the standoff ground, an 88 MCOV arrester was used for the additional length needed to bridge the distance between phase wire and a lower point on the structure ground.
