How big is the transformer and how many residences are sharing it? It’s probably stencil painted on the enclosure.

I’ve seen half a dozen houses on a single 7.2kV -> 240V 25kva transformer which can lead to problems given the available current on the secondary side is only 104A. As the transformer overheats you get voltage drop, as you’ve noticed ;)

Your supply voltage should be +/- 5% of nominal, 115-125V line to neutral and 230-250V line to line, appliances are generally OK with +/- 10% from nominal voltage.