[Copyright notice]

IEEE Transactions on Power Apparatus and Systems is published monthly by The Institute of Electrical and Electronics Engineers, Inc., 345 East 47 Street, New York, NY 10017, and at 20th and Northampton Sts., Easton, PA 18042. Responsibility for the contents rests upon the authors and not upon the IEEE, the Group, or its members. Individual copies may be purchased at the following prices: IEEE members (one copy) $2.50; public libraries and colleges $3.75 in the USA and Canada, $4.25 elsewhere. Others $5.00 in USA and Canada, $5.50 elsewhere. Annual subscription price: IEEE members, dues plus Group fee. Price for nonmembers available on request. Abstracting is permitted with mention of source. All rights, including translation, are reserved by the IEEE. Requests for republication permission should be addressed to the IEEE Editorial Department, 345 East 47 Street, New York, NY 10017. Copyright (c) 1969 by The Institute of Electrical and Electronics Engineers, Inc. Printed in USA at Mack Printing Company, 20th and Northampton Sts., Easton, PA 18042. Secondclass postage paid at Easton, PA. IEEE Transactions on Power Apparatus and Systems are registered trademarks belonging to the IEEE.