Synchronizing transients and synchronizers for large machines

H. T. Seeley (General Electric Company, Philadelphia, Pa.): The authors are to be complimented on their thorough analysis of the dependence of transient current magnitudes upon the differences in voltage magnitude, phase, and frequency, during synchronizing onto the sending bus of a transmission system, but the calculations and the design seem to be based on a maximum voltage difference of 8 per cent between machine and bus. This will almost certainly be exceeded during system emergency conditions, especially in the case of the first machine to be connected to the bus, and it is under just such conditions that prompt synchronizing is most needed. Allowance for operation at system voltages down to 80 per cent of normal has long been considered standard for control equipment in unattended installations; the synchronizer described by the writer in 1934 (see reference 4 of the paper) was designed to operate under such conditions, and will operate with voltage differences exceeding 30 per cent of rated voltage.