ABB REU 610 Technical Reference Manual

Also see for REU 610: Installation manual Technical reference manual Operator's manual Technical reference manual Operator's manual

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ABB REU 610 Technical Reference Manual Manual pdf 26 page image

The settable drop-off/pick-up ratio enables the voltage protection tosatisfactorily work with a voltage regulator, for instance, such as a tapchanger. The tap changer step is often 1.67%, which is less than thedrop-off/pick-up ratio of voltage relays. This can cause a situationwhere the voltage protection remains active even though the tapchanger already has changed the voltage.Overvoltage protection based on negative phase-sequencevoltageWhen the calculated negative phase-sequence voltage value U 2s exceeds the set startvalue of the stage U 2>, the stage generates a start signal after a 50 ms' start time.When the set operate time at definite-time characteristics or the calculated operatetime at IDMT characteristics elapses, the stage generates a trip signal. The stage isreset in 70 ms after the calculated negative phase-sequence voltage value has fallenbelow the set start value of the stage.The negative phase-sequence voltage is calculated as follows:U 2s = + × + ×U a U a U12223 313 (1)a = 1∠ 120°a2 = 1∠ -120°The negative phase-sequence value is scaled to the amplitude of the measuredvoltage. On a network with a reverse phase order, the calculated negative phase-sequence value has the same amplitude as the measured voltage signal.Stage U2 > can be set to be blocked when one of the measured phase-to-phasevoltages falls below 0.15 × U n . The selection is made in SGF4.Stage U2 > has a fixed drop-off/pick-up ratio of 0.96.5.1.4.3. Undervoltage protectionThe undervoltage protection can be based on either conventional voltagemeasurement or the calculated positive phase-sequence voltage.The low-set undervoltage stage U< is based on conventional voltage measurement.The low-set stage can also be used for alarm purposes.The high-set undervoltage stage U<< can be set to be based on either:* Conventional voltage measurement ( U<< mode selected) or* Calculated positive phase-sequence voltage ( U 1< mode selected).26REU 610 Voltage RelayTechnical Reference Manual1MRS755769