Mechanical Lugs for Medium Voltage?

Not sure what you are, or where you are, but in the 40 years of being in the electrical trade, I have never retorqued an electrical connection. I know aluminum conductors will eventually be cut by a rettorquing program. They will reach an equilibrium between the squeeze of the connector and the cold flow of the aluminum.

I once had a six month job in a large switchyard (250 KV)changing out compression connectors on the jumpers between buss and switchgear to mechanical connectors. Water had got in the compression lugs and froze, splitting them.

I believe that compression lugs are used because they are cheaper and faster to install than mechanical.

If in doubt hire an engineer, and if a problem develops, it is his fault. That is why he get paid so much.

How did the telephone discussions on this topic with both the transformer manufacturer and the medium voltage installers go?

If these are lugs with shear off bolts, one cannot re-torque the bolts. Also. if this an Ali core, the more one tightens the bolt the more loose the lug will become as the pressure causes the ali core to flow away from the compression point. Resulting in another loose connection which creates a hot spot and termination failure and load problems.

If you use a crimped lug, it is far better and the compaction of the core resuts in a really water tight electrically sound connection. On Ali use a bathtub or indent crimp, and on copper use a hex crimp. The lull out strength on a hex crimp on copper is very high and the indet/bathtub crimp on ali reduces the flow effect. If possible, do a crimp on a spare core, cut the lug across the lug barrel at the crimp and have a look at the compaction of the core after crimping. It should almost look like a solid core if compaction/crimp had been achieved. Crimping tool pressure, crimp dies and lug barrel thickness all affect the final crimp achieved.

But re-torquing, OH lines this can be done, and can happen..... on cable terminations?????