PR muni bonds

I’ve been taking a closer look at these since some of the bonds are trading at 20-30 cents on the dollar. I get why maybe GO and pension type bonds would trade there, but why the power authority bonds trade at such a steep discount seems a bit of a mystery. Also, why would a refunding bond series trade $0.66/dollar? Isn’t the principal amount held off in escrow?

http://www.municipalbonds.com/bonds/issue/74526QA51/

http://www.municipalbonds.com/bonds/issue/914811NK6/

Starting to get clearer now. PREPA (power) filed and the university system has had to shut down several schools.