Importance

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Abstract

There is disclosed a polyphase power line adapter for providing polyphase electric power to operate a motor at a speed less than rated speed particularly useful for pump motors and the like where it is undesirable to stop the motor. A bridge of from nine to eighteen thyristors, which is also conventially used in cycloconverters, connects the input terminals to the output terminals. A delta-to-Y transformer arrangement and a wave shaping circuit produces cyclic pulse control signals synchronized with the wave-forms of the respective phases of the polyphase power line input; one such signal is transmitted to a divider circuit with a maximum division factor (always an integer) corresponding to the factor, N, by which the frequency, and hence, motor speed is to be reduced. A plurality of logical 'and' circuits each has its inputs connected to receive one output from the divider circuit and cyclic pulse control signals are supplied to another of the inputs. The gates of the thyristors are supplied with the outputs of the logical 'and' circuits and the entire arrangement causes only each Nth half-wave of one phase from the power line to be transmitted to a respective pair of output terminals and then to input terminals of a motor. Specific circuits for dividing the frequency by a factor of 2, or 3, and of 4 are illustrated; extension of the concept of other factors of division is explained.

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First Claim