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United States Patent
US005982595A [ii] Patent Number:  Date of Patent:
 REDUNDANT COMMUNICATIONS IN A PROTECTIVE RELAY
 Inventor: Marzio Pozzuoli, Maple, Canada
 Assignee: General Electric Company,
 Appl. No.: 09/092,030  Filed: Jun. 5, 1998
 Int. CI. 110211 3/00
 U.S. CI 361/62; 361/64; 361/66;
 Field of Search 361/62, 64, 66,
361/115, 68, 69, 59
 References Cited
U.S. PATENT DOCUMENTS
3,725,818 4/1973 Nurmohamed et al 330/124
REDUNDANT COMMUNICATIONS IN A
FIELD OF THE INVENTION
The present invention relates generally to intelligent, 5 networked protective relays. More particularly, the present invention provides a redundant communications scheme for network communication of protective relay data.
BACKGROUND OF THE INVENTION 10
To further enhance protective control of electrical power distribution systems, intelligent protective relay devices have been developed which are provided with communication capabilities to communicate protective relay data. To date, network communication capabilities have been imple- 15 mented using data rates of less than 1 Megabits per second, and using RS-485, RS-232, fiber optic asynchronous serial interfaces, or UART interfaces. Typically, communication among networked protective relays has been implemented using "master-slave" protocols, in which certain network 20 devices are prioritized. For example, U.S. Pat. No. 4,972, 290 to Sun et al. discloses an electrical power distribution system with remote monitoring and control of protective relays. The disclosed system includes slave stations which continuously monitor activity of analog protective relays, 25 and a master station which communicates with the slave monitoring stations and stores network relay data. The Sun patent also discloses communication of relay data via RS-232 communication channels.
While the desire for protective relays having communi- 30 cations capabilities has been recognized, there are shortcomings associated with known schemes for communicating protective relay information. For example, known relay communication schemes do not adequately address potential problems relating noise (e.g., due to electromagnetic 35 interference) and communication line faults, and do not adequately provide high speed (greater than 1 Mbps) communication capability. Further, the environment in which intelligent protective relays operate is subject to severe conditions, including relatively wide temperature variations, 40 which presents design challenges for potential solutions to the problem of providing a reliable, fault-tolerant, highspeed communications scheme for protective relays.
SUMMARY OF THE INVENTION 45
The present invention solves the above-mentioned problems, and achieves additional advantages, by providing for a redundant communications scheme for a networked control device in a power distribution system. According to exemplary embodiments of the invention, a digital protec- 50 tive relay is provided with a redundant communications circuit which can communicate relay information with peer devices over a network using a primary ethernet communication channel. The communications circuit is capable of detecting the presence of a fault or failure on the primary 55 communication channel, and of switching the communication from the primary channel to a secondary channel. The circuit performs the detection and switching in a manner which is transparent to the main relay processing circuitry. Preferably, the primary communication channel type can be 60 selected by a user without reprogramming the relay. Further, the communications circuit is industrially hardened to withstand operating conditions associated with electric utility substations, which can include a temperature range of approximately -40° C. to approximately +85° C. The com- 65 munications circuit advantageously provides multiple fiber communications ports on a single card.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be understood more clearly upon reading the following Detailed Description of Preferred Embodiments in conjunction with the accompanying drawings, in which:
FIG. 1 is a block diagram of a communication circuit for a protective relay according to an embodiment of the present invention; and
FIG. 2 is a flow chart describing an exemplary transmission scheme in accordance with the present invention.
Referring now to FIG. 1, a communication circuit 10 for a digital protective relay is shown. The circuit includes a serial interface adaptor/transceiver 12 which receives a plurality of control signals on lines TXD, RXD, TENA, RENA, CLSN, TCLK, and RCLK via an interface connector 16, which is electrically connected to an associated digital protective relay. The serial interface adaptor/transceiver 12 includes first and second ports 14a and 14b for transmitting and receiving protective relay data. According to one embodiment of the present invention, the communication circuit 10 is implemented as a daughter card, and the interface connector 16 interfaces the serial interface adaptor/ transceiver 12 with a mother board of the digital protective relay. The serial interface adaptor/transceiver 12 can be implemented by a Motorola MC68160 Enhanced Ethernet Interface circuit, or other suitable component.
The data ports 14a and 14b provide primary and secondary communication capabilities. The data ports can transmit and receive data according to the same or different communication protocols. According to an exemplary embodiment, the first data port 14a provides primary communications capabilities over a user-selected ethernet communication channel, as will be described in more detail below. According to an exemplary embodiment of the present invention, the second data port 14b conforms to IEEE standard 802.3 for an Access Unit Interface (AUI) port, and first data port 14a conforms to IEEE standard 802.3 for a lOBaseT Twisted Pair (TP) interface port.
The first data port 14a interfaces, to pulse transformers and filters 18, which provides isolation and noise filtration for data to be transmitted to, or received from, a primary communication channel which is connected to a network including some number of protective relay devices. The primary communication channel can include a plurality of user-selectable communication channels. In the example shown in FIG. 1, the twisted pair interface TPTX+, TPTX-, TPRX+, and TPRX- connect the pulse transformers/filters 18 to a bank of isolation transformers 20, and to a protocol converter 22. The isolation transformers 20 are connected to a first primary communication channel interface 24, which can be a lOBaseT ethernet interface, and the protocol converter 22 is connected to a second primary communication channel interface 26. The first primary communication channel interface 24 can include a RJ45 connector, or other suitable connector, for connection to the network, and the second primary communication channel interface can include a fiber optic transmitter and receiver 26a and 26b. The protocol converter 22 converts communication signals between a first and a second communication protocol (e.g., between lOBaseT and lOBaseFL ethernet protocols). It should be appreciated that the use of multiple primary channel interfaces allows a user to determine the type of primary channel interface. It should also be appreciated that the configuration shown in FIG. 1 allows an installer to