Abstract
This paper is the further research about "Charging of the Transmission Line and SelfExcitation of Alternators, " for which subject the author described on the Journal of the Institute of Electrical Engineers of Japan, July, 1924. In the former paper the balanced three phase and single phase phenomena are chiefly discussed and the author introduced an accurate graphical method for obtaining the voltage and current due to self-excitation of alternators from experimental data. In general for unbalanced three phase load, the alternator voltage and current can be obtained by the superposition of balanced three phase vector and single phase vectors.
The author applied this principle of superposition to the unbalanced three phase condensive load and obtained the method for the velt-ampere charging characteristics (Fig. 10) and the saturation curve excited by unbalanced armature leading current by using his formerly introduced method (Fig. 11.)
The self-excitation of alternators for unbalanced condensive load may be clearly explained by the intersection of these two curyes. In actual such a condition occurs when one line of isolated three phase trans nission system is grounded at the charging condition.
We experienced an abnormal veltage rise due to self-excitation of an alternator at Ryushima Power Station, Keihin Electric Power Company at such a condition during the test under the Ministry of Communications. The author applied above characteristics to this case and has given numerical values for voltage and current. (Fig. 20)
The Petersen earth coil is also recommendable for the avoidance of such an abnormal condition of self excitation, not merely for the use of the suppression of arcing ground.
This paper includes the following topics:-
(I) Introduction.
(II) Unbalanced condensive lead and characteristics of alternators.
(1) Unbadanced load and principle of super osition.
(2) Volt-ampere characteristics for unbalanced condensive load.
(3) Saturation curve excited by unbalanced armature leading cu rent.
(III) One line ground of three phase transmission system and self-excitation of alternators.
(1) One line ground of isolated three phase system.
(2) One line ground in the case of Petersen earth c il is used.
(IV) Numerical example.
(V) Conclusion.
Appendix.
