Abstract: An apparatus for protecting an electrical power system supplying electrical power to an electrical load comprises a transformer for sensing an operating condition of the electrical power system and for producing an analog signal representative of the operating condition, and a microcomputer for periodically sampling the analog signal and for converting the analog signal into a series of digital signals. The microcomputer includes circuitry for deriving a digital value representative of a square root of the series of digital signals and circuitry for processing the digital value over time to determine a processed value which is a function of both the sensed operating condition and time. A circuit breaker is responsive to the microcomputer for disconnecting the power system from the load in the event that the processed value is not within preset limits.

Abstract: An apparatus for monitoring phased currents in a first winding and a second winding of a transformer and for disconnecting the transformer from a power source supplying the transformer when a difference between the magnitude of the current in the first winding and the magnitude of the current in the second winding exceeds a predetermined amount to indicate a fault condition is disclosed. The apparatus is used in combination with circuitry for generating first and second current signals each having a phase and magnitude which is a function of the phase and magnitude of the phased currents in the first and second windings, respectively.

Abstract: A reclosing relay for use in an electrical power system with a circuit breaker for clearing line faults by tripping and reclosing. The breaker has auxiliary contacts defining the state of the circuit breaker as open or closed. The reclosing relay includes a circuit responsive to the auxiliary contacts for producing a first signal representative of the state of the breaker and another circuit for generating a second signal when a loss of power to the reclosing relay is anticipated.

Abstract: Protective relay for use in an electrical power system having electrical conductors which are energizable with an AC voltage. The protective relay includes a circuit for sensing the AC voltage to produce an AC output that has zero crossings and a time period between zero crossings, a circuit for supplying an electrical signal representing a preselected pickup value of volts-per-Hertz for the relay, and a circuit responsive to the AC output and to the electrical signal for generating an electrical level as a function of both the time period and the pickup value and for producing an output signal for the relay when the AC output exceeds the electrical level. In this way, the output signal is produced when a volts-per-Hertz value of the AC voltage exceeds the preselected pickup value of volts-per-Hertz for the relay. Other protective relay apparatus and methods are also disclosed.

Abstract: A protective apparatus for use in an A.C. electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors that are electrically energizable, the conductors normally having a negligible phase difference of electrical energization when the circuit breaker is closed, and the circuit breaker having auxiliary contacts defining the state of the circuit breaker as open or closed. The protective apparatus includes a circuit responsive to the auxiliary contacts for producing a first signal representative of the state of the breaker as open or closed and another circuit connected to the circuit for producing the first signal and operable when the breaker is closed for generating a second signal when the phase difference of electrical energization of the first and second electrical conductors exceeds a predetermined value. A further circuit provides an indication of malfunction of the circuit breaker when the second signal occurs.

Abstract: Apparatus for the activation of a remotely located device, such as a lamp or bell, under the control of telephone subscriber tip and ring lines. The apparatus of the present invention is located in the general vicinity of a called telephone subscriber station and is operated to activate and power a remotely located annunciator as a function of detecting ringing signals initiated by a calling telephone subscriber station. The apparatus plugs into a wall outlet for providing actuating power to the remote annunciator(s).