BLOCK: blocks the START and TRIP outputsBLKTRIP: blocks the TRIP outputBLKREST: blocks the RESTORE outputIf the measured voltage level decreases below the setting of IntBlockLevel, both thePICKUP and the TRIP outputs are blocked.10.3.6.4 Design M14970-34 v7Rate-of-change frequency protection (SAPFRC, 81) measuring element continuouslymeasures the frequency of the selected voltage and compares it to the settingPUFreqGrad. The frequency signal is filtered to avoid transients due to power systemswitchings and faults. The time integrator operates with a definite delay time. Whenthe frequency has returned back to the setting of RestoreFreq, the RESTORE output isissued after the time delay tRestore, if the TRIP signal has earlier been issued. The signof the setting PUFreqGrad is essential, and controls if the function is used for raisingor lowering frequency conditions. The design of SAPFRC (81) is schematicallydescribed in figure 110.Section 10 1MRK 511 408-UUS AFrequency protection316 Phasor measurement unit RES670 2.2 ANSITechnical manual