The longest single span of an individual catenary length on the model is set at 39.73m.

Die längste Einzel spannweite einer einzelnen Oberleitungslänge des Modells ist auf 39,73 m festgelegt.

Add just 5mm to that length and the centre of the catenary "pops up", requiring an additional support.

Fügen Sie dieser Länge nur 5 mm hinzu und die Mitte der Oberleitung "springt auf", was eine zusätzliche Unterstützung erfordert.

Is there a reason for this, like a physical limit in the program? Because in real life, a single span can be up to 65m, possibly longer.

Gibt es dafür einen Grund, wie zum Beispiel eine physikalische Grenze im Programm? Denn im wirklichen Leben kann eine einzelne Spannweite bis zu 65 m betragen, möglicherweise länger.

Google Earth Satellite view, line drawn between two catenary pylons.

Google Earth Satellitenansicht, Linie gezogen zwischen zwei Oberleitungsmasten.

Is there a way to turn off this "pop-up", because it is impossible for me to put the correct number of pylons on the model to make it as accurate as possible?

Gibt es eine Möglichkeit, dieses "Pop-up" auszuschalten, weil es mir unmöglich ist, die richtige Anzahl von Pylonen auf das Modell zu setzen, um es so genau wie möglich zu machen?

Addendum:

By placing two "Tunnel end" catenaries end to end it is possible to get 79.46m and by adding "tunnel" lengths, one can extend the span indefinitely....

Nachtrag:

Indem zwei "Tunnelend"-Oberleitungen Ende an Ende platziert werden, ist es möglich, 79,46 m zu erhalten, und durch Hinzufügen von "Tunnel"-Längen kann man die Spannweite unbegrenzt verlängern ....

Only as an explanation for the seemingly odd value of the maximum length:

It's a straight number in H0 scale, which is the base measurement in the studio.

The actual limit is (to my knowledge) set by the model designer. And one reason for the set distance may be the behaviour in curves, with respect to the unnaturally tight curves in model railway layouts.

That makes sense, yes. (both answers).

Having messed around for half an hour it is possible to get a straight contact wire between two hangers using two start-tunnel catenaries, but it's a pain!

Either you pit one at each end and meet them in the middle, which if the track is not straight puts a kink in the wire that basically would not be there without a support, or what I did was stretch a single catenary for the correct length, check it's "width" (y-distance, which for some reason is the length) and halve it, then move the catenary away from everything and line it to z=0°. Then add another one to the end using the + icon. Change both to "Tunnel Anfang" and set whichever one is the wrong way around to z=180°. Then group them together.

With auto-align turned off I put it on the track and with trial and error and a technique known as binary-chop searching (learned from my days as a programmer) I managed to line it up correctly