Abstract: In a digital protective relaying device for protecting electric power transmission line including an electric station at each end thereof, and each electric station including at least one circuit breaker to be tripped by a protective relay for protecting the own station, a digital protective relay provided with a computer is further provided at each end so as to receive electrical data in digital form from the electric stations for operating in an ordinary protective operation. As a control condition occurs in one station, the condition is sent to a digital protective relay provided at the other end of the transmission line, thereby changing the operational steps of the computer included in the protective relay.

Abstract: An input setting method for a protective relaying apparatus including an input setting switch for setting data, a digital operational device for carrying out a relaying operation utilizing the data, and a memory device for storing the data, the method comprising the steps of setting the data by the input setting switch, storing the data thus set in the memory device, comparing the set data with the stored data, carrying out the relaying operation utilizing the data when the compared data are found equal, and issuing an alarm signal when the compared data are found to be unequal.

Abstract: In a protective system which operates in response to a plurality of state quantities, for example voltage and current, one of which being a digital code signal having a long code length and transmitted over a transmission circuit, the density of the code errors of the digital code signal is detected. A plurality of state quantities are processed by a processor including first means responsive to the digital code signal and second means not responsive to the digital code signal. Either one of the first and second means is selected according to the density of the code errors.

Abstract: Provided is a digital fault-location calculation system which comprises first means for obtaining data including voltage and current information of a power transmission system subjected to fault-location calculation, a computer, and second means coupled between the first means and the computer for transferring the obtained data to the computer from the first means. The computer has at least two functions, one of which is the detection of occurrence of a faultin the transmission line and the other is the calculation of distance from the point of installation of the system to the fault point, in response to the data transferred through the second means and in accordance with predetermined processes. The distance to the fault point is computed by the other function of the computer only upon the detection of occurrence of a fault in the transmission line by the one function of the same.