how to connect 220kv supply to 380kv grid?
I'm sure that your generators do not generate at 220 kV. In reality you will have GSU (Generator Step-Up) transformers that connect the generators to the transmission system. The actual generators might actually be rated at something in the range of ...
high voltage equipment?
It is possible to reverse the input and output of a standard transformer in some cases and create high voltages. This is dangerous but I know that it has been done.Some projects that have been done:
Do stepdown transformers have any adverse effects on equipement?
All transformers do is change voltage. As long as the equipment you are using is rated for the output voltage of the transformer, there shouldn't be any problems. There is a small possibility that you might get a little bit of humming and line noise ...