Various cross current compensators (CCC) are used to restrain wattless cross current which flows between generators connected parallel in such as the Ship's A. C. power system.
When load power factor is low, these CCC's generally reduce the bus voltage, and thus the effect of CCC's opposes to the effect of the automaticvoltage regulator (AVR) . This means that the more cross current compensation is intended, the worse becomes the regulation of the main bus voltage, and the regulation will be larger than that at single operation.
We have used the differential current transformer (DCT) for these CCC circuits, and have confirmed by experiments on the marchant ship that the voltage drop at the parallel operation are remarkably reduced.
We also confirmed that the analytical results of the effects of the DOT Constant coincide to the experimental results.
The DCT can be used for any AVR system and the voltage regulation of the bus can be kept within ± 1 % in both cases of single and parallel operation by using the DCT.

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Ever growing engine size and power have renewed such crankshaft trouble as axial or coupled torsional-axial vibration. For the former mode some empirical methods have been proposed to calculate its natural frequencies, but are not so reliable as ones for torsional vibration. For the latter it seems to have been dealt with nothing but an experimental, scale-model method.
In this paper, (1) a new equivalent system of crankshaft is supposed ro as to tolerate 4 degrees of freedom : axial, torsional and two kinds of lateral vibration. (2) Theoretical, not empirical equations for calculating stiffness values of the shafting are derived, so that a design-stage forcast of the modes of shaft vibration is possible. (3) Equations of motion are written in matrices, transformed into eigen value problems and solved with the Jacobi-rotation method on a digital computer, not iteratively but directly. (4) The solution gives every mode and frequency on one chart, including coupled torsional-axial modes which have never been correctly explained before.
Two kinds of shafting were investigated, and their solutions showed fairly good agreements with the measured data on board.
The authors recommend to apply this new matrix method not only to coupled systems as above, but also to simple systems without coupling—pure torsional or pure axial—in place of Holzer method for convenience in digital computation.

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