10.3.3.7 Settings for two step residual overvoltage protection
Operation: Off or On
UBase (given in GlobalBaseSel) is used as voltage reference for the set pickup values.
The voltage can be fed to the IED in different ways:
1. The IED is fed from a normal voltage transformer group where the residual
voltage is calculated internally from the phase-to-earth voltages within the
protection. The setting of the analog input is given as UBase=Uph-ph.
2. The IED is fed from a broken delta connection normal voltage transformer group.
In an open delta connection the protection is fed by the voltage 3U0 (single input).
Section Analog inputs in the Application manual explains how the analog input
needs to be set.
3. The IED is fed from a single voltage transformer connected to the neutral point of
a power transformer in the power system. In this connection the protection is fed
by the voltage UN=U
0
(single input). Section Analog inputs in the Application
manual explains how the analog input needs to be set.
ROV2PTOV will measure the residual voltage corresponding to the nominal phase-
to-earth voltage for a high-impedance earthed system. The measurement will be based
on the neutral voltage displacement.
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: This is to enable/disable operation of step n.
Characteristicn: Selected inverse time characteristic for step n. This parameter gives
the type of time delay to be used. The setting can be, Definite time or Inverse curve A or
Inverse curve B or Inverse curve C or Prog. inv. curve. The choice is highly dependent
of the protection application.
Un>: Set operate overvoltage operation value for step n, given as % of residual
voltage corresponding to UBase:
IECEQUATION2290 V1 EN
(Equation 247)
The setting depends on the required sensitivity of the protection and the type of system
earthing. In non-effectively earthed systems, the residual voltage cannot be higher
than three times the rated phase-to-earth voltage, which should correspond to 100%.
In effectively 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.
tn: time delay of step n, given in s. The setting is highly dependent on the protection
application. In many applications, the protection function has the task to prevent
damage to the protected object. The speed might be important, for example, in the case
1MRK 502 071-UEN - Section 10
Voltage protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 417
Application manual
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