Error 1) when status of first AC branch is 0 2) if transformer is present but R and X are set to zero

[jay-dave]

The program is not able to find a key when the status of the first AC grid branch is set to zero.

[jay-dave]

Also when a transformer is set to be present in mpc.convdc input data, but its R and X are set to zero, the solution status is :Error. Not sure if there should be a warning message for this.