How can i find the voltage in a high tension transmission line? is the rings are key to finding it?

Yes, You can find the Voltage from VT secondary Circuit and Calculate the trough Ratio of PRI & SEC voltage with measured Voltage.

Hi,
If you mean just to specify the estimated voltage by looking at a conventional T/L, you may find it out from the numbers of the insulators per string (suspension or tension).

Capacitive coupling can be used, to check the charge on the conductor from a distance, a kind of non contact sensor.

Puede ser un indicador bastante aproximado, pero hay que tener en cuenta si el aislador es vidrio o porcelana y si el ambiente es húmedo, seco o contaminado.
Estamos hablando de línea de fuga y de cm/ Kv en cada aislador.

In the UK the transmission line pylons have ID labels stating the voltage. Failing that you can calculate from the string insulator length
Below is a guide:
Line voltage
(kV) Discs
34.5 3
46 4
69 5
92 7
115 8
138 9
161 11
196 13
230 15
287 19
345 22

Standard disc insulators are rated at an operating voltage of 10-12 kV.

Mr.mohammad kordmahalleh,would u plz elaborate as an example that how would i find voltage of a transmission line from the insulator disc by counting the discs.is there any formula that's applicable everywhere?and which helps me make calculations easy?