modification of superconducting_wire

I've created a modification of "superconducting_wire" from model library (AC/DC Module --> Other Industrial Applications) with two superconducting cores. It works properly, but when I try to simulate situation with reversed current in one of cores, model crashes.
To make current reversed I've define variable Ez_sc for second core as:
-E0*((Jz_sc-Jc)*flc2hs(Jz_sc-Jc-dJ,dJ)/Jc)^alpha