An RCD will trip when there's a difference between Live and Neutral of 30mA - the assumption being that the "missing" current is running to earth possibly through a person - it's for safety. RCDs of other ratings can be had but 30mA is typical.
Your oven has a leak to earth type fault - the heating element will be a very likely - probable cause.
An appliance engineer will be able to properly diagnose and repair it for you.
Good luck...
Peccavi
November 2009
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix electric cookers.