current can be set separately as a ratio of the injected current. For example, in a linewith three IEDs the return current from each remote IED is set to 50% of theinjected current. Current Iinjected, L1 is injected in phase L1 to get the followingdifferential and bias currents:Phase L1:1 1 , 1L L injected LIDiff IBias I= =EQUATION1458 V1 EN-US (Equation 1)Phase L2:2 2 , 1 1 240L L injected LIDiff IBias I= = × Ð °EQUATION1459 V1 EN-US (Equation 2)Phase L3:IDiffL3 = IBiasL3 = 0EQUATION1460 V2 EN-US (Equation 3)11.3.3.1 Verifying the settings GUID-6C24AEF3-CD9A-4F39-A696-0125081F4892 v21. Block the trip signal from all involved IEDs with local operation released (seestep 3).2. Set Test mode = On to test the L4CPDIF function.3. Release the local function with setting ReleaseLocal in local HMI underMain menu/Test/Line differential test/LineDiffLogic4. Set the factor of the return currents to 1/(number of current IEDs = 1).5. Inject a current in phase L1, and increase the current until L4CPDIF operatesfor phases L1 and L2. The injected operate current must correspond to the setIdMin. The service values for IDiffL1, IBiasL1, IDiffL2 and IBiasL2 must beequal to the injected current.6. Repeat the current injection in phases L2 and L3.7. Inject a symmetrical three-phase current, and increase the current untiloperation is achieved in all three phases. The injected operate current mustcorrespond to the set IdMin. The service values for IDiffL1, IBiasL1, IDiffL2,IBiasL2, IDiffL3 and IBiasL3 must be equal to the injected current.8. Read the transmission delay.9. Measure the operate time by injecting a single-phase current in phase L1. Theinjected current must be 4 x the operate current. Time measurement is stoppedby the trip output.Tripping time in this loop test includes sending local currentsto the remote end, and sending them back. This means thattripping time is double the time achieved with real faults or inbench testing.Section 11 1MRK 505 378-UEN ATesting functionality by secondary injection108 Line differential protection RED670 2.2 IECCommissioning manual
