LV transformer is a machine from IndustrialCraft 2. It can transform medium voltage (31-511 EU) into low voltage (31 EU and less).
If there is more than medium voltage leading into the LV transformer, it explodes, not leaving itself on the floor as an item.
When powered by a redstone signal, it transforms low voltage into medium voltage.
There are some dots on the machine. Three dots (on one side) mean medium voltage, one dot (all other sides) means low voltage. The place where the dots are can be changed with industrialCraft wrench.
Note that if medium voltage is leaded into normal IC2 machines, they explode. That's why you need low voltage.