Abstract: For use in conjunction with a system for producing, at a transmitter location, time division multiplexed (TDM) frames having a plurality of channels of information signals and framing signals, communicating the frames from the transmitter location to a receiver location, and, at the receiver location, deframing the received frames to obtain frame timing signals and a bitstream of information signals which are coupled with a plurality of operating units. A technique for responding very quickly, upon loss of the TDM signal, to prevent misoperation of the operating units, including: at the transmitter, inserting a preselected pattern of bits in a timeslot of the information signals; at the receiver, detecting, in the deframed bit stream, the absence of the preselected pattern of bits, and producing a control signal in response; and producing override information signals that are coupled to the operating units when the control signal is present.

Abstract: A protective relay communication interface includes a transformer having primary windings arranged as, at least two, sets of opposed windings. The interface is connected to a local relay sensing a current at that point on a power line to be protected. The interface is also connected to a communication link to a remote relay sensing the current at a remote position on the power line. It is by this communication link that signals representative of the sensed currents are transmitted from each relay to the other. A local signal from the local relay is passed through part of, but not all of, the primary windings inducing a corresponding signal in the secondary windings of the transformer which is transmitted to the remote relay via the communications link. A received remote signal from the remote relay is passed via at least two mutually opposed sets of the primary windings to the local relay.