CHAPTER 2: PRODUCT DESCRIPTION PILOT CHANNEL RELAYINGL30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 2-72Figure 2-2: Communication paths2.2.2 Channel monitorThe L30 has logic to detect that the communications channel is deteriorating or has failed completely. This can provide analarm indication and disable the current differential protection. Note that a failure of the communications from the masterto a slave does not prevent the master from performing the current differential algorithm; failure of the communicationsfrom a slave to the master prevents the master from performing the correct current differential logic. Channel propagationdelay is being continuously measured and adjusted according to changes in the communications path. Every relay on theprotection system can be assigned a unique ID to prevent advertent loopbacks at multiplexed channels.2.2.3 Loopback testThis option allows the user to test the relay at one terminal of the line by looping the transmitter output to the receiverinput. At the same time, the signal sent to the remote does not change. A local loopback feature is included in the relay tosimplify single ended testing.
