Section 4 1MAC309294-MB FProtection functions220 RER620Technical ManualThe module calculates the start duration (START_DUR) value which indicates thepercentage ratio of the start situation and set operate time (DT). The start duration isavailable according to the selected value of the Operation mode setting.Table 235: Start duration valueThe combined start duration START_DUR indicates the maximum percentage ratio of theactive protection modes. The values are available via the Monitored data view.Blocking logicThere are three operation modes in the blocking functionality. The operation modes arecontrolled by the BLOCK input and the global setting “Configuration/System/Blockingmode” which selects the blocking mode. The BLOCK input can be controlled by a binaryinput, a horizontal communication input or an internal signal of the relay program. Theinfluence of the BLOCK signal activation is preselected with the global setting Blockingmode.The Blocking mode setting has three blocking methods. In the “Freeze timers” mode, theoperate timer is frozen to the prevailing value. In the “Block all” mode, the whole functionis blocked and the timers are reset. In the “Block OPERATE output” mode, the functionoperates normally but the OPERATE output is not activated.4.4.1.5 ApplicationThe frequency protection function uses the positive phase-sequence voltage to measure thefrequency reliably and accurately.The system frequency stability is one of the main principles in the distribution andtransmission network maintenance. To protect all frequency-sensitive electrical apparatusin the network, the departure from the allowed band for a safe operation should beinhibited.The overfrequency protection is applicable in all situations where high levels of thefundamental frequency of a power system voltage must be reliably detected. The highfundamental frequency in a power system indicates an unbalance between production andFreq> OR df/dt A parallel operation between the protection methods is enabled. The START output isactivated when either of the measured values of the protection module exceeds its setvalue. A detailed information from the active module is available at the STR_OFRQ andSTR_FRG outputs. The shortest operate delay time from the setOperate Tm Freq orOperate Tm df/dt is dominant regarding the OPERATE output. The time characteristic isaccording to DT. The characteristic that activates the OPERATE output can be seenfrom the OPR_OFRQ or OPR_FRG output. If the frequency gradient restores before themodule operates, the reset timer is activated. If the timer reaches the value set by theReset delay Tm df/dt setting, the operate timer resets and the STR_FRG output isdeactivated. If the frequency restores before the module operates, the reset timer isactivated. If the timer reaches the value set by theReset delay Tm Freq setting, theoperate timer resets and the STR_UFRQ output is deactivated.Operation mode in use Available start duration valueFreq< ST_DUR_UFRQFreq> ST_DUR_OFRQdf/dt ST_DUR_FRGOperation mode Description
