The EV-Transformer is used to convert Insane Voltage (IV) to Extreme Voltage (EV), and back. Note that this block is mostly useless without any addons, as no IC2 machines or generators (except the reactor) require EV to function.
Note that when using any Transformer, the 3-dotted side means higher voltage and the 1-dotted sides mean lower voltage. You can change the direction the 3-dotted side is facing by right-clicking a 1-dotted face with a Wrench.
To convert IV to EV place the input cable (IV) next to the 3-dotted side. They should connect, and run your output cable (EV) next to any 1-dotted side connecting to your machines, or energy storage units.
To convert EV to IV you must apply a redstone signal to the transformer or change the setting in the GUI, and place the input cables next to any 1-dotted side, and the output cable next to the 3-dotted side.