Hitachi Relion 670 Series Applications Manual page 196

Section 9
Voltage protection
(single input). Section Analog inputs in the Application manual explains how the analog input
needs to be set.
The setting parameters described below are identical for the two steps (n = step 1 and 2). Therefore
the setting parameters are described only once.
OperationStepn: To enable/disable operation of step n.
Un>: Set operate overvoltage operation value for step n, given as % of residual voltage
corresponding to UBase:

Un (%)
IECEQUATION050 V2 EN-US
The setting depends on the required sensitivity of the protection and the type of system earthing. In
high impedance earthed systems, the residual voltage can be at maximum rated phase-to-phase
voltage, which should correspond to 200%.
In solidly earthed systems, this value depends on the ratio Z0/Z1. The required setting to detect high
resistive earth faults must be based on network calculations. Typically it shall be lesser than 100%.
tn: time delay of step n, given in s. The setting is highly dependent on the protection application. The
time delay must be co-ordinated with other automated actions in the system.
190

UBase kV ( ) / 2
If the Programmable inverse curve is chosen for operation and
based on the set values, no TRIP signal is issued. However, START signal is set and
maintained as long as the measured quantity for operation is above the set start level of
step.
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1MRK506375-UEN Rev. N
(Equation 68)
Equation does not satisfy
Railway application RER670
Application manual