Digital protective relaying systems

Claim 2

In a digital protective relaying device for protecting an electric power transmission system including an electric power transmission line having a first electric station and a second electric station at both ends thereof, each electric station including a circuit breaker, a disconnecting switch, a detector for detecting an electric value related to an input into the electric power transmission line, an A/D converter for converting an output of the detector into a digital value, a data transmitting and receiving terminal connected to receive the output of the A/D converter and to send the same to a data transmitting and receiving terminal in the other electric station through a data transmission line extending between the two data transmitting and receiving terminals, and a current differential protective relay connected to receive outputs of the two A/D converters for carrying out a relaying operation based on a vector sum of the two A/D converter outputs, one directly and the other through said data transmission line, the improvement wherein each current differential protective relay provided in said electric stations including a digital computer which, upon reception of a control condition from the other electric station, changes its data processing steps so as to neglect the output of said A/D converter in the other electric station and to operate the differential protective relay as an over-current protective relay solely according to the output of the A/D converter in the electric station receiving the control condition, said control condition representing one of tripping of the circuit breaker, opening of the disconnecting switch, and locking of the data transmitting and receiving terminal occurring in the other electric station.

Claim 3

A digital protective relaying device as set forth in claim 1 wherein another pair of data transmitting and receiving terminals are further provided at the first and the second stations, and a control condition occurring at either one of the stations is transmitted through a control condition transmitting line between said another pair of data transmitting and receiving terminals to the other station.

Claim 4

A digital protective relaying device as set forth in claim 1 wherein each of said control conditions originating in one of said stations is transmitted together with the output of the A/D converter of said one station in the form of serially arranged bits to the protective relay in the other station.

Claim 5

A digital protective relaying device as set forth in claim 1 wherein when a blind point fault occurs between said electric value detector and said circuit breaker in one of said stations, the circuit breaker is tripped by said differential protective relay of said one station for protecting said one station.

Claim 6

In a digital protective relaying device for protecting an electric power transmission system including an electric power transmission line having a first electric station and a second electric station provided at both ends thereof, said first electric station including a circuit breaker and a disconnecting switch provided for interrupting said power transmission line, a potential transformer means and a current transformer for detecting voltage and current of said power transmission line, an A/D converter for converting outputs of said potential transformer means and said current transformer into digital values, a signal receiving terminal for receiving a signal sent from the second electric station through a signal transmission line, and a distance protective relay connected to receive the outputs of said A/D converter and said signal receiving terminal; said second electric station including a power transformer, a differential protective relay for protecting said power transformer, and a signal transmitting terminal for transmitting a signal to the first electric station, the improvement wherein said second electric station further includes means cooperative with said differential protective relay for detecting an excitation current rush flowing into the power transformer from said electric power transmission line, and transmitting a control condition signal through said signal transmitting terminal toward the first electric station, said distance protective relay in said first electric station including a digital computer which, upon reception of said control condition signal sent from the second electric station, changes its data processing steps so as to increase a delay time or to decrease a protective distance of said distance protective relay.

Claim 7

In a digital protective relaying device for protecting an electric power transmission system including an electric power transmission line having a first electric station and a second electric station provided at both ends thereof, said first electric station including a circuit breaker and a disconnecting switch provided for interrupting said power transmission line, a potential transformer means and a current transformer for detecting voltage and current of said power transmission line, an A/D converter for converting outputs of said potential transformer means and said current transformer into digital values, a signal receiving terminal for receiving a signal sent from the second electric station through a signal transmission line, and a distance protective relay connected to receive the outputs of said A/D converter and said signal receiving terminal; said second electric station including a power transformer, a differential protective relay for protecting said power transformer, and a signal transmitting terminal for transmitting a signal to the first electric station, the improvement wherein said second electric station further includes means cooperative with said differential protective relay for detecting an excitation current rush flowing into the power transformer from said electric power transmission line, and transmitting a control condition signal through said signal transmitting terminal toward the first electric station, said distance protective relay in said first electric station including a digital computer which, upon reception of said control condition signal sent from the second electric station, changes its data processing steps so as to increase a delay time or to decrease a protective distance of said distance protective relay.