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Voltage protection is based on nominal voltage. If 20000V is set to be the nominal voltage this equals
100% setting in voltage based protection functions. 120% trip setting in overvoltage stage equals to
24000V on primary level so 20% increase in this case would be 4000V.
Figure. 5.2.2. - 11. Voltage may be based on line to line voltage or line to neutral voltage. This selection is completed in
“Measured magnitude” –menu under each voltage protection stage separately. Availability of protection functions depends on
IED type.
After the settings are input to the IED scaling factors are also calculated and displayed for the user.
Scaling factor P/S tells the VT primary to secondary ratio. Per unit scaling factors to primary and
secondary values are also shown.
Triggering of voltage protection stage can be based on single, dual or all three fault loops. Fault loops
are either line to line or line to neutral according the “Measured magnitude” setting.
Figure. 5.2.2. - 12. Activation of one fault loop will trip the voltage protection stage as a default.
There are several different ways to use all four voltage channels. Most common voltage measurement
mode is the three from line to neutral voltages and measured zero sequence voltage 3LN+U0. For
further information see different voltage measurement mode examples below:
3LN+U4
3LL+U4
2LL+U3+U4
See below connection wirings for 3LL and 2LL connections.
AQ-T257
Instruction manual
Version: 2.00
25
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