7SR210 & 7SR220 Description of Operation
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3.13 Voltage Protection: Phase Under/Over Voltage (27/59) -
7SR22
In total five under/over voltage elements are provided in the 7SR22 relay. Four elements are provided for the
‘Phase’ Voltages and one for the ‘Auxiliary’ input voltage.
The relay utilises fundamental frequency RMS voltage for this function. All under/over voltage elements have a
common setting to measure phase to phase (Ph-Ph) or phase to neutral (Ph-N) voltage using the Voltage Input
Mode setting.
Voltage elements can be blocked if all phase voltages fall below the 27/59 U/V Guard setting.
27/59-n (27/59-Vx) Setting sets the pick-up voltage level for the element.
The sense of the element (undervoltage or overvoltage) is set by the 27/59-n Operation (27/59-Vx Operation)
setting.
The 27/59-n O/P Phases setting determines whether the time delay is initiated for operation of any phase or only
when all phases have detected the appropriate voltage condition. An output is given after elapse of the 27/59-n
Delay (27/59-Vx Delay) setting.
The 27/59-n Hysteresis (27/59-Vx Hysteresis) setting allows the user to vary the pick-up/drop-off ratio for the
element.
Operation of the under/over voltage elements can be inhibited from: -
Inhibit 27/59-n A binary or virtual input, function key or remote data Comms.
27/59-n VTSInhibit: Yes Operation of the VT Supervision function.
27/59-n U/V Guarded Under voltage guard element.
Figure 3.13-1 Logic Diagram: Under/Over Voltage Elements (27/59)
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