True or False?
a. Zero-sequence currents do not exist in the delta windings of a three-phase transformer when the other windings are connected in wye.
I believe the correct answer to this is another question or it depends. Are the wye windings grounded, either solidly or through an impedance? Zero-sequence currents will flow (circulate) in the delta windings of a transformer if and only if a grounded-wye set of windings exists in the transformer. Any wye-configured transformer I have dealt with (either small dry type or large pad-mount) has been grounded, either solidly or through an impedance. Therefore my engineering judgment would lead me to assume a grounded-wye configuration if not stated explicitly for selection a. The solutions call selection a true. Although selection b may be more false (I apologize for not including in the post), if more false is even reasonable. This sort of question troubles me and I would like some feedback regarding the sorts of assumptions that may be required for the exam.
a. Zero-sequence currents do not exist in the delta windings of a three-phase transformer when the other windings are connected in wye.
I believe the correct answer to this is another question or it depends. Are the wye windings grounded, either solidly or through an impedance? Zero-sequence currents will flow (circulate) in the delta windings of a transformer if and only if a grounded-wye set of windings exists in the transformer. Any wye-configured transformer I have dealt with (either small dry type or large pad-mount) has been grounded, either solidly or through an impedance. Therefore my engineering judgment would lead me to assume a grounded-wye configuration if not stated explicitly for selection a. The solutions call selection a true. Although selection b may be more false (I apologize for not including in the post), if more false is even reasonable. This sort of question troubles me and I would like some feedback regarding the sorts of assumptions that may be required for the exam.
