5-406 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUALTRANSDUCER INPUTS/OUTPUTS CHAPTER 5: SETTINGS5The base unit for current (see the FlexElements section in this chapter for additional details) is:Eq. 5-56The minimum and maximum power values to be monitored (in pu) are:Eq. 5-57The following settings are entered:DCMA OUTPUT H2 SOURCE: “SRC 1 Ia RMS”DCMA OUTPUT H2 RANGE: “4 to 20 mA”DCMA OUTPUT H2 MIN VAL: “0.000 pu”DCMA OUTPUT H2 MAX VAL: “1.260 pu”The worst-case error for this application can be calculated by superimposing the following two sources of error:• ±0.5% of the full scale for the analog output module, or ±0.005 x (20 - 4) x 6.3 kA = ±0.504 kA• ±0.25% of reading or ±0.1% of rated (whichever is greater) for currents between 0.1 and 2.0 of nominalFor example, at the reading of 4.2 kA, the worst-case error is max(0.0025 × 4.2 kA, 0.001 × 5 kA) + 0.504 kA = 0.515 kA.Example: Voltage monitoringA positive-sequence voltage on a 400 kV system measured via source 2 is to be monitored by the DCmA H3 output with arange of 0 to 1 mA. The VT secondary setting is 66.4 V, the VT ratio setting is 6024, and the VT connection setting is “Delta.”The voltage is to be monitored in the range from 70% to 110% of nominal.The minimum and maximum positive-sequence voltages to be monitored are:Eq. 5-58The base unit for voltage (see the FlexElements section in this chapter for additional details) is:Eq. 5-59The minimum and maximum voltage values to be monitored (in pu) are:Eq. 5-60The following settings are entered:DCMA OUTPUT H3 SOURCE: “SRC 2 V_1 mag”DCMA OUTPUT H3 RANGE: “0 to 1 mA”DCMA OUTPUT H3 MIN VAL: “0.404 pu”DCMA OUTPUT H3 MAX VAL: “0.635 pu”The limit settings differ from the expected 0.7 pu and 1.1 pu because the relay calculates the positive-sequence quantitiesscaled to the phase-to-ground voltages, even if the VTs are connected in “Delta” (see the Metering Conventions section inchapter 6), while at the same time the VT nominal voltage is 1 pu for the settings. Consequently the settings required in thisexample differ from naturally expected by the factor of .The worst-case error for this application could be calculated by superimposing the following two sources of error:• ±0.5% of the full scale for the analog output module, or ± 0.005 x (1-0) x 254.03 kV = ±1.27 kV• ±0.5% of readingFor example, under nominal conditions, the positive-sequence reads 230.94 kV and the worst-case error is0.005 × 230.94 kV + 1.27 kV = 2.42 kV.
