CHAPTER 5: SETTINGS PRODUCT SETUPB90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-1255Figure 5-58: Interlocking bus protection scheme via direct inputs/outputsIn this application, apply the following settings. For UR-series IED 1:DIRECT OUTPUT DEVICE ID: “1”DIRECT I/O CH1 RING CONFIGURATION: “Yes”DIRECT I/O CH2 RING CONFIGURATION: “Yes”For UR-series IED 2:DIRECT OUTPUT DEVICE ID: “2”DIRECT I/O CH1 RING CONFIGURATION: “Yes”DIRECT I/O CH2 RING CONFIGURATION: “Yes”For UR-series IED 3:DIRECT OUTPUT DEVICE ID: “3”DIRECT I/O CH1 RING CONFIGURATION: “Yes”DIRECT I/O CH2 RING CONFIGURATION: “Yes”For UR-series IED 4:DIRECT OUTPUT DEVICE ID: “4”DIRECT I/O CH1 RING CONFIGURATION: “Yes”DIRECT I/O CH2 RING CONFIGURATION: “Yes”Message delivery time is approximately 0.2 of power system cycle (at 128 kbps) times number of ‘bridges’ between theorigin and destination. Dual-ring configuration effectively reduces the maximum ‘communications distance’ by a factor oftwo.In this configuration the following delivery times are expected (at 128 kbps) if both rings are healthy:IED 1 to IED 2: 0.2 of power system cycleIED 1 to IED 3: 0.4 of power system cycleIED 1 to IED 4: 0.2 of power system cycleIED 2 to IED 3: 0.2 of power system cycleIED 2 to IED 4: 0.4 of power system cycleIED 3 to IED 4: 0.2 of power system cycleIf one ring is broken (say TX2-RX2) the delivery times are as follows:IED 1 to IED 2: 0.2 of power system cycleIED 1 to IED 3: 0.4 of power system cycleIED 1 to IED 4: 0.6 of power system cycleIED 2 to IED 3: 0.2 of power system cycleIED 2 to IED 4: 0.4 of power system cycleIED 3 to IED 4: 0.2 of power system cycleA coordinating timer for this bus protection scheme could be selected to cover the worst case scenario (0.4 of a powersystem cycle). Upon detecting a broken ring, the coordination time is adaptively increased to 0.6 of a power system cycle.The complete application requires addressing a number of issues, such as failure of both the communications rings, failureor out-of-service conditions of one of the relays, and so on. Self-monitoring flags of the direct inputs and outputs featureprimarily are used to address these concerns.
