For coordination, the IEEE Buff book would be an excellent reference.
Assuming that by medium voltage you mean 1kV to 35kV, there are different methods for arc flash. The IEEE standard 1584-2002 contains the equations for calculating incident energy, arc flash boundary, etc. for 3 phase voltages from 208V to 15kV. This is a good document to have and read if you are going to be doing arc flash hazard analysis. A good book is Complete Guide to Arc Flash Hazard Calculation Studies by Jim Phillips. He also has a very good forum for arc flash, arcflashforum.com
Above 15kV, you starting to get into the realm of utility voltages and equipment. OSHA 1910.269 Appendix E contains information on performing arc flash analysis at these voltage levels. Analysis at these levels typically utilize a program called ArcPro which is noted in OSHA as a preferred method.
If you are just starting to do this work, it would be beneficial to do it under the tutelage of an engineer experience in these studies as there are nuances to them.