30 minutes seems harsh. Give them a simple 1 minute the first, and double your time every time you consecutively get kicked off. This way if you get kicked as a troll, its only 1 minute and you cannot complain. If you get kicked twice because of a troll, highly unlikely but its only 2 minutes. If you get kicked 3 times, then you wait 4 minutes, and after 3 I feel like you're doing something wrong.
For those of you verbally challenged, consecutively means games in a row, not every time you get kicked. I know some of you will read that wrong.