CHAPTER 5: SETTINGS TRANSDUCER INPUTS/OUTPUTSL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-4275The base unit for power (refer to the FlexElements section in this chapter for additional details) is:Eq. 5-53The minimum and maximum power values to be monitored (in pu) are:Eq. 5-54The following settings are entered:DCMA OUTPUT H1 SOURCE: “SRC 1 P”DCMA OUTPUT H1 RANGE: “–1 to 1 mA”DCMA OUTPUT H1 MIN VAl: “–1.247 pu”DCMA OUTPUT H1 MAX VAL: “1.247 pu”With the above settings, the output will represent the power with the scale of 1 mA per 20.65 MW. The worst-case error forthis 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 (1-(-1)) x 20.65 MW = ±0.207 MW• ±1% of reading error for the active power at power factor of 0.9For example at the reading of 20 MW, the worst-case error is 0.01 × 20 MW + 0.207 MW = 0.407 MW.Example: Current monitoringThe phase A current (true RMS value) is to be monitored via the H2 current output working with the range from 4 to 20 mA.The CT ratio is 5000:5 and the maximum load current is 4200 A. The current is to be monitored from 0 A upwards, allowingfor 50% overload.The phase current with the 50% overload margin is:Eq. 5-55The 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.
