Abstract: In a superconducting energy storage apparatus including an AC-DC converter unit, a superconducting coil, a quench protection unit and a mechanical type persistent current switch, a self-firing type thyristor switch is connected in parallel to the mechanical type persistent current switch to be first operated in the event of an occurrence of trouble in an associated electric power system, and a control unit generates an ON instruction signal for turning on the persistent current switch so as to immediately establish a persistent current mode.

Abstract: A superconducting coil system includes an excitation power source, a superconducting coil, a DC circuit breaker connected in series between the excitation power source and the superconducting coil to disconnect them when quenching occurs, a protective resistor connected in a parallel manner to the superconducting coil for dissipating the energy accumulated in the superconducting coil when the quenching occurs, and a switch provided as a bypass of the DC circuit breaker, the switch being closed during the normal operation to pass the energy from the excitation power source to the superconducting coil through a resistor and being opened when the quenching occurs.

Abstract: A servo system for use in a video signal recording and playback apparatus to control rotation of an electric motor which drives a recording medium for the composite video signal. A reference signal generator generates a reference signal having a period equal to an integral multiple of the horizontal synchronizing period of the composite video signal. A servo control circuit controls the rotation of the electric motor in response to any phase difference between the reference signal and a rotational speed signal sensed from and corresponding to the speed of the electric motor.