9.1.7 Operation principle M15326-3 v9Two-step undervoltage protection (UV2PTUV ,27) is used to detect low power systemvoltage. If one, two or three phase voltages decrease below the set value, acorresponding START signal is generated. The parameters OpMode1 and OpMode2influence the requirements to activate the PICKUP outputs: 1 out of 3, 2 out of 3, or 3out of 3 measured voltages have to be lower than the corresponding set point to issuethe corresponding PICKUP signal.UV2PTUV (27) has two voltage-measuring steps with separate time delays. If thevoltage remains below the set value for the chosen time delay, the corresponding tripsignal is issued. To avoid an unwanted trip due to the disconnection of the related high-voltage equipment, a voltage-controlled blocking of the function is available: if thevoltage is lower than the set blocking level, the function is blocked and no PICKUP orTRIP signal is generated. The time delay characteristic is individually chosen for eachstep and can be either definite time delay or inverse time delay.To avoid oscillations of the output PICKUP signal, a hysteresis has been included.9.1.7.1 Measurement principle M15326-6 v7Depending on the set ConnType value, UV2PTUV (27) measures either phase-to-ground voltage or phase-to-phase voltage and compares it against the set values,Pickup1 and Pickup2. The voltage-related settings are made in percentage of the basevoltage which is set in kV phase-to-phase voltage. This means operation for phase-to-ground voltage under:(%) ( )3Vpickup VBase kV< ×EQUATION1606 V1 EN-US (Equation 48)and operation for phase-to-phase voltage under:Vpickup (%) VBase(kV)< ×EQUATION1991-ANSI V1 EN-US (Equation 49)When the phase-to-ground voltage measurement is selected, thefunction automatically introduces division of the base value by thesquare root of three.Section 9 1MRK 511 408-UUS AVoltage protection276 Phasor measurement unit RES670 2.2 ANSITechnical manual
