Megger and Hi-Pot Test

You could try here. http://www.maintenancegeeks.com/forums/23-motors-a-generators/269-how-to-understand-a-megger-reading#269 there is a download area with a book that explains this. I think it is called A Stitch In Time

First of all, Megger is not the correct technical name. Please say it as, Insulation resistance test. Megger is the company which manufacture testers.

Coming to your question, hi pot test will be conducted to stress the insulation whether it could withstand the voltage higher than its rated. Insulation resistance tests are conducted to check the condition of the Insulation resistance. Hi pot is one of the special tests that are not conducted frquently and readily. Insulation resistance tests can be conducted for any electrical equipment for troubleshooting, pre commissioning, maintenance and it will be first step to test an equipment before conducting the equipment specific tests.

I am posting this using my knowledge I acquired from my testing & commissioning career.

Megger do the testing with DC voltage and objective of test is to measure the resistance of insulation that is between winding and all other parts,on other hand HI-pot is done with AC voltage of rated frequency and objective is to see if insulation is not braking down at specified voltage,total current (resistive, inductive and capacitive) is with in the specified range,No body to coil sparks is observed,

Actually, hipot test could be DC, AC (at rated frequency) or Very Low Frequency (VLF) AC. It depends on the specific apparatus being tested, such as MV or HV cables, circuit breakers, etc., and what tests are specified or selected for the apparatus. But you are generally correct in saying that the test is looking to see if the insulation breaks down (leaks current or flashes over) at the test voltage.