If I hadn’t paid only 100 euros in taxes, I would be a criminal. If AC 6-35 kV networks are being massively built all over the world (for example, to connect windfarms to the grid), where each cable line has tens and thousands of euros of useless power losses in screens, then this is called a “Green Transition”. Let’s talk about it.

There are 3 ways to detect the problem with currents in the cable screens:
1️⃣ Thermal inspection.
At the point where the screen goes out of the termination, the termination body is exposed to three sources of heating at once: from the core, the screen inside the termination, and the screen outside. This is one of the reasons why a lot of damage to terminations is known.

2️⃣ Measurements.
The measurement of currents in the screens, regardless of the voltage class of the line, can be performed with basic low-voltage clamp meter (since there is no voltage on the solidly grounded screen). It is important to set the current measuring range of at least 100 A.

3️⃣ Calculations.
Such a calculation should be a MANDATORY section of the design documentation of any AC line made with single-core cables. The calculation can be performed using numerous software, but in fact you can entrust such calculations even to your children – see the example.

You need basic data on the cable line:
✅ The cross-section of the core (Fc), and its material (Cu, Al);
✅ The cross-section of the screen (Fs), and its material (usually Cu);
✅ The average distance (S) along the route between phases A,B,C.

The methodology is to find:
➡️ the approximate outer diameter (d) of the cable from the catalogue;
➡️ the diameter of the screen (ds), using the typical thickness of the outer sheath (3-5 mm);
➡️ the ratio S/ds;
➡️ the ratio (Di = Is/Ic) of the currents in the screen and core (using graph);
➡️ the ratio (Ps/Pc) of losses in the screen and core (and a summary of losses, Psum = Pc + Ps).

Generally, if the loss ratio Ps/Pc exceeds 0.2, then:
♨️ losses in the screens noticeably heat up the XLPE insulation (in addition to the heat from the core), and you reduce the cable’s ampacity, or if you do not want to reduce the current in the core, simply damage the cable insulation along its entire cable line length;
♨️ taxpayers pay for such excessive losses (in one of posts I showed that over 30 years the cost of losses in screens can reach 1 million euros).

If you arrange the phases A,B,C in a row, then for sure you will have Ps/Pc > 0.2 (in the post’s example, 0.78). If you arrange the phases in a closed triangle (trefoil), then most likely you will have Ps/Pc < 0.2, and you can sleep more or less peacefully.

A cable line will become “a hole in the budget” if it has a combination of two factors at once:
❌ cables are in a row;
❌ screens are solidly bonded.

Please see Part 3 of the book (hardcopy is available).