In 110-500 kV networks with a grounded neutral, cable line lengths from 0.6 to 1.2 km are considered as “bad”. The reasons are simple – for lines more than 0.3-0.6 km, single-end screen grounding can no longer be used (due to the dangerous voltage Us induced on the screens during a single-phase short circuit external to the line), but it is too early to make a full cross-bonding cycle (because the typical cable drum length is 0.4-0.6 km, and for the screen cross-bonging, three segments are needed, that is, the line must be at least 3*0.4=1.2 km). So, let’s talk what to do if our 110-500 kV line is less than 1.2 km. There are three main options.

1️⃣ Single-end screen grounding (for a line up to 0.3-0.6 km).
2️⃣ If the line is longer than 0.3-0.6 km, then it probably has one joint dividing the line approximately in half. Then, for each of the halves of the line length, it is necessary to make a single-end screen grounding.
3️⃣ Single-end screen grounding and equipotential conductor.

In option (1), the length limit (0.3 or 0.6 km) depends on the magnitude of the single-phase short circuit current, as well as on what induced AC 50 Hz voltage Us on the screen is considered acceptable. Usually, for the time of a short circuit, it is assumed that the acceptable AC 50 Hz voltage on the screen is up to 5-7 kV (RMS). If the voltage does not exceed the specified values, standard surge arresters (sheath voltage limiters, SVL) with the continuous operating voltage of 6 kV can be installed in the screens, which perfectly protect the outer sheath of the cable from impulses (lightning and switching).

In option (2), everything is done in the same way as option (1), but only half of the line should be substituted for the voltage Us calculations. The problem is that link boxes with SVLs inside have to be placed in manholes. They can be flooded, vandalized, and subjected to theft of boxes. They also require good grounding (for electrical safety needs), with an impedance of 0.5 Ω, which is practically impossible to provide out of switchgear, and this turns a manhole into a place dangerous for personnel and for third parties.

In option (3), due to the conductor laid along the line, the area of the contour formed by the screen and the ground is reduced, and this reduces the voltage Us that is induced on such a contour in case of single-phase short cirtuit mode. However, the question arises of what material to make a conductor and what should be the cross-section. The best effect does not exceed a 40% reduction in induced voltage Us (K=1/1.4=0.7), and to have this we need a copper bus with a cross-section of at least 185 mm2. It means, we will increase the length of the line, for which single-end screen grounding is possible, from 0.3-0.6 km (option 1) to 0.45-0.90 (40% longer).

I can’t recommend options 2 and 3. They have a lot of problems. If you can avoid building a 0.6-1.2 km line, it is better to do so.