Page 43 - CARILEC CE Industry Journal_Oct_2019

Another extremely important and valuable attribute of It is extremely difficult and rare for utilities to acquire new
replacing a conventional cross-arm with the transmission right of way (ROW) routes today. As a result, it is
line TIF design is that it creates increased vertical line challenging to erect new lines. However, in some cases
clearance to the ground or underbuilt facilities as there may be a possibility to use this additional clearance
illustrated in Fig. 10. afforded by transmission TIF systems to install a second
and new circuit positioned lower down on the structure
(Fig. 11). Such additional lines would become new utility
assets and increase the value of that transmission line.

Fig. 10 - Transmission TIF Clearnace Increase
One means of exploiting this clearance increase is to
allow increased conductor sag, which permits an increase
in line operating current and thus an increase in line
capacity. This is achieved when the TIF arm is installed
at the existing or conventional cross-arm position on the
poles. Installing the TIF H-Frame system on existing
transmission lines offers an opportunity to gain an
increase in vertical clearance equivalent to the length of a
suspension insulator string. For example, when replacing
the cross-arm on a 115 kV line it is possible to gain Fig. 11 - Transmission TIF Double Circuit Structure
approximately one meter in clearance while about two
meters can be gained for 230 kV lines. When constructing a new transmission line using the TIF
system it is possible to erect shorter poles than for a
The example in TABLE I. demonstrates the potential for conventional two pole cross-arm framed line design. This
increasing the conductor capacity of an existing 115 kV creates a new opportunity for cost savings in transmission
transmission line when installing the TIF system. line designs.

TABLE I - EXAMPLE: OPERATING CURRENT INCREASE Also, since fixed positioning of the conductors on a TIF
framing eliminates the need for suspension insulators, it
also then eliminates insulator swing under transverse wind
System Voltage: 115 kV conditions. The elimination of this component of conductor
Span: 200 meters
displacement (Fig. 12) permits use of narrower ROW width
Ampacity @ 50°C : 160 A requirements. The benefits of this feature are the capability
Sag @ 50°C : 5.01 m (16.42’) to use existing ROW more efficiently or reducing land or
Ampacity @ 127°C : 861 A easement acquisition costs if constructing new lines.
Sag @ 127°C : 6.02 m (19.74’)
Ampacity increase : 538%
Sag Difference : 1.01 m

The above example illustrates the significant line load
capacity increase that is possible when replacing
conventional cross-arms with the transmission TIF designs.

Alternatively to using the new extra clearance to add
increased ampacity as noted above, transmission TIF
systems may also offer new opportunities to add
completely new second circuits to existing or new two Fig. 12 - Conventional Framing Insulator Swing/Displacement
pole structure systems.

CE INDUSTRY Journal 41