A metering system for electric utility power line measurements includes voltage and current signal inputs that are randomly sampled and converted to binary representations. A system sequence controller and calculator provides programmed control for processing digital control and data signals and for producing digital calculations of electric energy parameters from the binary representations of the instantaneous signal values. Memory registers totalize and accumulate digitally calculated values for producing visual displays and output signals that correspond to electric energy parameters to be measured.

Digital processing and calculating ac electric energy metering system

Digital distance relaying of a three-phase electric power transmission line depends on accurate estimation of the postfault voltage and current phasors during the first postfault electrical cycle, when the line voltages and currents are corrupted by noise and transients. The digital relay herein responds to each postfault sample as it arrives and recursively electronically estimates the postfault phasors before the next sample arrives. The method involves a powerful state variable approach which for the voltages provides at least two state variables per voltage, and for the currents provides at least three state variables per current. Parallel processing of the samples equalizes computer burden, and an additional processor classifies the fault, computes faulted line resistance and reactance, relays the fault by tripping a circuit breaker, and documents the fault including its distance. Numerical results of part of the powerful estimation procedure which can be performed offline are prestored in the system, to permit the balance of the estimation procedure to occur in real-time, with slower inexpensive processing hardware. Relaying is expected within the first half of the first postfault electrical cycle for most Zone 1 faults.

Recursive estimation in digital distance relaying system

Method and apparatus that provide a response to the negative sequence current demands during a disturbance of the grid system connected to power-generating equipment, such as a wind turbine system, provide for tracking components in the grid signal, orienting at least a portion of the signal, and injecting the oriented portion. Controlled injection of negative sequence current provides for extending small-signal control response, and also provides for modifications of the apparent impedance to the grid interconnect of the power conversion equipment.

Method, apparatus and computer program product for injection current

A monitoring and control system for use in conjunction with a pulsation type welder which utilizes a computer to calculate the impedance characteristics of a weld and compare these characteristics to a preselected set of characteristics to determine if a quality weld has been made. The system then controls the heat and cool time to increase or decrease the temperature of the weld and thus control the size of the weld nugget. The monitoring control system is utilized in conjunction with a standard pulsation welding control system, which standard system provides a series of heat impulses each followed by a cool interval, this cycle being repeated for a preselected number of cycles. The monitoring and control system senses the voltage and current in the welding load and feeds this data to a computer which, in turn, calculates the impedance of the weld. This calculation is then compared to a predetermined set of standards which are evolved as a result of processing a preselected number of previous welds, and corrections are made to assure the weld quality. If the weld is not developing sufficiently, the number of cycles in the cool portion of the impulse, and thus, the cool time, is reduced until the weld meets the set standards. On the other hand, if the weld exceeds the standard, the number of heat cycles, and thus the heat time, is reduced.

Welding monitoring and control system

A gas turbine power plant is provided with an industrial gas turbine which drives a rotating brushless exciter generator coupled to a power system through a breaker. One or more of the turbine-generator plants are operated by a hybrid digital computer control system during sequenced startup, synchronizing, load and shutdown operations. The program system for the computer and external analog circuitry operate in a multiple gas turbine control loop arrangement. Automatic synchronization is achieved with a hybrid subsystem which includes the programmed computer and external phase detection circuitry. An automatic synchronization program for the computer is divided into rough speed and voltage matching, fine speed matching and breaker closure subprograms.

System and method employing a digital computer with improved programmed operation for automatically synchronizing a gas turbine or other electric power plant generator with a power system

A method of controlling the operation of a breaker in a transmission line by first monitoring the current and if the current exceeds a prescribed limit, measuring a sampling of the voltage on the line when the current is at zero and dividing this value by the maximum current on the line to obtain a first quantity which is added to a second quantity obtained by measuring a sampling of the voltage when the current is at its maximum value and dividing this voltage by the maximum current. The previous calculations will provide a measure of impedance since the voltage when the current is zero is equal to Vm sin phi while the voltage when the current is at maximum is equal to Vm cosine phi and impedance in a rectangular coordinate representation is: z R jX Vm cosine phi /Im + j(Vmsin phi /Im). This apparent impedance is then compared against relay characteristics which are implemented in a programmed general purpose computer and in the event the apparent impedance lies within the relay characteristic zone, the associated breaker is tripped.

Durbeck Robert C

Papers

Power system protective relaying by time-coordinated sampling and calculation