Assessing the influence of frequency-controlled asynchronous electric drives on the operation of ship power plants and their elements

   The paper shows that the use of energy-saving frequency-controlled asynchronous electric drives in ship power plants instead of traditional ones (contactor-induction motor) makes it possible to reduce electricity consumption in fractional modes several times and significantly expand the functionality of the equipment. Ho-wever, during the operation of a frequency-controlled electric drive, higher current harmonics are emitted into the supply network, and voltage harmonics are supplied to the asynchronous electric motor along with the main harmonic. Current harmonics, propagating through the power supply system, lead to a decrease in the efficiency of the elements of ship power plants in which they are part of. It has been found that in all modes of operation of the electric drive, there are large values of the consumed reactive power. With a large number of frequency-controlled asynchronous electric drives on a ship, diesel generators will not be able to fully load them in terms of active power. During the operation of a frequency-controlled electric drive, current harmonics that are multiples of three are emitted into the supply network. These harmonics are zero sequence currents. Since the ship's network does not have a neutral wire, the third harmonic current from one phase is closed through the wires of the other two phases. This current creates a zero-sequence field in electrical machines with the ensuing consequences. Of greatest interest are the results of experimental studies of the vibration spectrum at 10 % load on the shaft of an asynchronous motor: at a frequency close to 20 Hz, which may indicate asymmetry of the poles of the asynchronous motor under study, at a frequency of 300 Hz from the interaction of moments of the fifth (reverse sequence) and seventh (positive sequence) harmonics, at a frequency of 50 Hz, due to the influence of the main harmonic.

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