Discussion of Paper No. 61-138

1. We object to the statement that among the several maintenance tests that are available, overpotential tests at power frequency have generally been accepted as the most significant for large HV machines. 2. The author´s theoretical analysis of voltage distribution within the slot parts for d-c 0.1 cps and power frequency is overly simplified and leads him to conclusions which are not supported by more critical analysis. 3. The analysis of the situation with respect to surface corona and voltage distribution is not valid for machine end windings, particularly where semiconducting stress relieving surface treatments or internal foil grading schemes are used. It further appears that from the standpoint of endwinding stresses, the 0.1-cps test would be less desirable than either the 60-cps or the d-c test. 4. Finally, even in the absence of theoretical objections, we would still have reservations concerning the proposed testing scheme because the circuit necessary to produce the 0.1-cps voltage seems too complicated. Those who have had extensive experience in the conduct of winding overpotential tests under field conditions will appreciate that sinmplicity and ruggedness of test equipment capable of withstanding shipping abuse and whose proper functioning may be easily verified, is a must if the possibility of serious errors in the application of test voltages are to be avoided. The apparent complexity of the circuit required to produce the 0.1 cps voltage appears to us to fall short in this very important requirement also. 5.