Abstract: Apparatus for the supervision of a sudden pressure relay (SPR) system which protects a power system network transformer having a plurality of windings associated with each phase of the power system network. This apparatus overcomes the difficulties associated with previous overcurrent supervision of the SPR system for multiple-winding transformers. The apparatus utilizes a maximum restraint signal selection network which offers a discriminating differentiation between high and low current levels in all of the transformer windings and accomplishes this in one embodiment with a single measuring unit per phase of the power system network. For each phase, when the selected maximum restraint signal exceeds a predetermined level, the supervisory unit blocks the SPR from operating the breakers which isolate the power transformer from the power system network. This blocking condition is relieved after a predetermined time period from when the selected restraint signal falls below the predetermined level.

Abstract: A directional comparison relaying system includes forward looking pilot relays at each terminal of a protected line segment and monitors which detect predetermined incremental changes in line currents and voltages indicative of a fault. These predetermined incremental changes in current or voltages, which can be detected before the pilot relays respond, generate local blocking signals which are transmitted to the other terminal as remote blocking signals over a two-way communications channel. Trip signals for tripping circuit breakers at the associated terminals are generated from forward fault signals produced by the pilot relays but are blocked by the presence of either a local or remote blocking signal. However, the forward fault signal cancels the local blocking signal and the corresponding remote blocking signal at the other terminal so that when both pilot relays see an internal fault, the circuit breakers at the two terminals are tripped simultaneously.

Abstract: Loss-of-potential supervision for a distance relay controlling a circuit breaker in a poly-phase electric power transmission system is provided by blocking circuit breaker trip signals in the presence of a low voltage condition and the absence of an increase in current of more than a predetermined amount. Overblocking is prevented for weak feed conditions, a circuit breaker closing on a fault, transients induced by replacement of a fuse, and sequencing caused by tripping of a remote breaker.

Abstract: A transformer differential relay which includes apparatus for speeding up the detection of a power transformer internal fault condition to initiate breaker action which interrupts current through the transformer is disclosed. Presently, conventional transformer differential relays include a unit for each phase of the power transformer for detecting a potential internal fault in a respective transformer phase winding and for generating a signal to operate a set of breakers. This breaker operation is inhibited for current inrush conditions of the transformer. However, a processing time is associated with the detection of such a current inrush condition. Accordingly, the breaker operating signal must be delayed for at least this processing time in order for the inhibition to be effectuated. For the case in which there is no current inrush condition, the breakers remain delayed in operation from the inception of a true internal fault.

Abstract: An echo-keyed directional comparison blocking system for protecting an electrical power transmission path in a power system network against internal faults is disclosed. The system includes a terminal unit disposed at each end of the transmission path for measuring characteristics representative of the power at its corresponding end and for activating a corresponding circuit breaker when an internal fault of the transmission path is detected. Each terminal unit includes a transmitter and a receiver for communicating transmit and receive signals with each other through a communication medium and additionally includes at least one forward-looking pilot relay, at least one over-current relay, and a plurality of circuits.

Abstract: An apparatus and method for detecting a single-phase-to-ground fault on a three-phase electrical power system and for identifying the faulted phase conductor. Each phase conductor is monitored by evaluating three phasor signals associated therewith, i.e., the zero sequence current of the electrical power system, the negative sequence voltage on the phase conductor rotated 90 electrical degrees counterclockwise (or the negative sequence current on the phase conductor), and the quadrature phase voltage for the phase conductor rotated 30 electrical degrees counterclockwise. The coincidence of these three signals for a predetermined time indicates the occurrence of a single-phase-to-ground fault on the monitored phase conductor.