Motorized control rod drive

Claim 1

Motorized variable speed drive for nuclear reactor control rod, comprising a synchronous motor having a rotor with unidirectional field excitation means and having stator windings, multiphase current supply means and direct current supply means, means for selectively connecting said stator wind-ings to said multiphase supply means for relatively rapidly moving the control rod and to said direct current supply means for stepwise and relatively slowly moving the control rod, said stator windings being connectible to the direct current supply means by said connecting means in a selective sequence and direction and at a selective winding-switching frequency, a blocking detent device blockingly engageable with the drive to then prevent inadvertent upward travel of the control rods, said device having electromagnetic release control means connected to said selective connecting means and controllable thereby to temporarily disengage said device with each switching of current from said direct current supply means by said connecting means, and a magnetically saturable pulse transformer interposed between said electromagnetic release control means and said selective connecting means for passing to said release control means a short pulse to effect the temporary disengagement of said detent device.