10.4.6 Monitored dataTable 324:FTAQFVR Monitored dataName Type Values (Range) Unit DescriptionFREQ REAL - Hz Measured frequencyvalueACCTIME REAL - s Accumulated time forfrequency band limitsLASTEVTD REAL - - Accumulation time forlast event of frequencywithin band10.4.7 Operation principleFrequency time accumulation protection function FTAQFVR is used to protect theturbine against an abnormal frequency operation. During the startup and shutdown ofthe turbine-generator set, FTAQFVR is blocked to avoid unnecessary accumulationof time or tripping of generator. FTAQFVR is also blocked when the system positive-sequence voltage magnitude deviates from the given voltage band limit, which can beenabled with the EnaVoltCheck setting. The overall logic of FTAQFVR is explainedin Figure 270.The frequency of the measured input voltage is monitored continuously and comparedto the set frequency band limits FreqHighLimit and FreqLowLimit. When themeasured system frequency is above the FreqLowLimit setting and below theFreqHighLimit setting, the FREQOK and START signals are activated. The STARTsignal is controlled by the measured current and voltage input magnitude and thestatus of the circuit breaker position.FTAQFVR function will block START signal activation and Accumulation of timeunder two following conditions even if the system frequency falls within set bandlimits.• When the generator is not synchronized as indicated by the CBOPEN signal input:Generator currents are considered to detect whether the generator is supplying itsunit auxiliary supply transformers or not. FTAQFVR function will be blockedwhen the measured current magnitude drops below the setting CurrStartLeveland CBOPEN input is high. FTAQFVR remains blocked until the generatorreturns to the operation condition. It can be verified by using the CBCLOSEsignal. Generator's start and stop detection logics for the START output can beignored by disabling the CBCheck setting.• When the positive-sequence voltage of the measured input voltage is outside theband limit.The START output will be blocked if the EnaVoltCheck setting is enabled and thesystem positive sequence voltage is not within the voltage band limits.Section 10 1MRK502052-UEN BFrequency protection560Technical manual
