Abstract: Circuitry for sensing frequency over time of a signal that has zero crossings. A first circuit commences generation of a periodic waveform in response to at least some of the zero crossings. A bistable circuit connected to the waveform commencing circuit produces a first electrical level in response to a zero crossing and, upon the occurrence of a predetermined change in the waveform, produces a second electrical level until a subsequent zero crossing occurs. A third circuit low-pass filters the electrical levels from the bistable circuit to produce an output which is a function of the frequency of the signal. Methods for sensing frequency over time of a signal that has zero crossings are also disclosed.

Abstract: Transfer apparatus for use with an AC generator having a field winding, the DC energization of which controls the output of the generator. Associated with the generator are first and second voltage regulators each including means for sensing the output of the generator and means for varying the DC energization of the generator field winding to regulate the output of the generator to a respective reference level for each voltage regulator. The transfer apparatus includes a circuit for generating a first signal as a function of the generator output as sensed by the first voltage regulator sensing means and a second signal as a function of the generator output as sensed by the second voltage regulator sensing means. Another circuit independently produces an additional signal to which the first and second signals ordinarily have a predetermined relationship. A further circuit selects the first or second voltage regulator to energize the generator field winding.

Abstract: Apparatus for use in an electrical power generating system including a generator for supplying an A.C. output voltage to a load on a set of lines and a circuit responsive to the A.C. output voltage for producing a regulating voltage, the generator having a winding the D.C. energization of which controls the A.C. output voltage. The apparatus controls the energization of the winding and includes a switching circuit adapted to be connected across a resistance and which when rendered conductive bypasses the resistance to couple the voltage regulating circuit to the winding with negligible loss of energy. The switching circuit is combined with a circuit that produces a signal when an increase in the A.C. output voltage exceeding a preselected parameter occurs, and with another circuit that renders the switching circuit nonconductive in response to the signal thereby causing the resistance to consume energy from the winding. Methods of operation of the apparatus are also described.

Abstract: A system for supplying power to a field winding to maintain excitation of an alternating current generator during excessive output current conditions, the generator having a plurality of output lines for supplying power to a load and the field winding being supplied during normal operating conditions by a shunt type voltage regulator responsive to the output voltage of the generator. The system includes a current transformer having a primary winding in series with an output line of the generator, a secondary winding, and a tertiary winding shunted by a capacitance. A rectifier circuit rectifies the voltage supplied by the secondary winding, the output terminals of the rectifier circuit being connected in series with the regulator output terminals to supply power to the field winding. A control circuit, connected to the output of the generator and responsive to output current conditions enables the rectifier circuit output during excessive output conditions.

Abstract: In a generating system having a shunt-type regulator for exciting the field of a generator during normal operating conditions, circuitry is provided for supplying voltage to a field winding to maintain excitation of the generator during excessive output current conditions. This circuitry senses the low voltage indicative of a fault or overload condition and in response boosts the field of the field winding during such an excessive output current condition an amount sufficient to maintain generator excitation during that particular condition. It does this by impressing a voltage, supplemental to that supplied by the regulator, upon the field winding during the condition. As a result the excitation of the generator is maintained.