ABB REU 610 Technical Reference Manual

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ABB REU 610 Technical Reference Manual Manual pdf 25 page image

255.1.4.3. Undervoltage protectionThe undervoltage protection can be based on either conventional voltagemeasurement or the calculated positive phase-sequence voltage.The low-set undervoltage element 27P-1 is based on conventional voltagemeasurement. The low-set element can also be used for alarm purposes.The high-set undervoltage element 27P-2 can be set to be based on either:* Conventional voltage measurement (27P-2 mode selected) or* Calculated positive phase-sequence voltage (27D mode selected).The selection between these modes is made either by using HMI or parameterS7, the default setting being conventional measurement. Element 27D (PPS)and 47 (NPS) cannot be used at the same time.The undervoltage elements can be set to be blocked when one of themeasured voltages fall below 0.15 × U n (VT). The blocked element is resetafter the set resetting time. This feature can be used to avoid unnecessarypickups and trips during, for example, an auto-reclose sequence. In addition,the tripping of element 27P-1 can be set to be blocked by the element 27P-2pickup. The selection is made in SGF4.Element 27P-2 can be set out of operation in SGF3/2. This state is indicatedby dashes on the LCD and by 999 when the set pickup value is read via serialcommunication.It is possible to block the tripping of an undervoltage element byapplying a digital input signal to the relay.Undervoltage protection based on conventional voltagemeasurementBoth the low-set and the high-set undervoltage element can independently beset to pickup and trip when one of the three voltages or all the voltages fallbelow the set pickup value. By default, the low-set undervoltage elementoperates when one of the three voltages fall below the set pickup value andthe high-set undervoltage element operates when all the voltages fall belowthe set pickup value. The selection is made in SGF4/7 and SGF4/8.When the phase-to-phase voltage values fall below the set pickup value of thelow-set element, 27P-1, the element generates a pickup signal after a ~ 80 ms’pickup time. When the set operate time at definite-time characteristic or thecalculated operate time at IDMT characteristic elapses, the element generatesa trip signal.1MRS755972 Voltage RelayTechnical Reference Manual - ANSI VersionREU 610