Hitachi Relion 670 Series Applications Manual page 195

1MRK506375-UEN Rev. N
9.3.2 Application
The residual voltage will increase in case of any single phase earth-fault occurred in isolated or
compensated two-phase railway supply systems. Depending on the type of fault and fault resistance,
the residual voltage will reach different values. The highest residual voltage, equal to two times the
phase-to-earth voltage, is achieved for a solid single phase-to-earth fault. The residual voltage
increases approximately to the same level in the whole system and does not provide any guidance in
finding the faulted component. Therefore, ROV2PTOV is often used as a backup protection or as a
release signal for the feeder earth-fault protection.
9.3.3 Setting guidelines
All the voltage conditions in the system where ROV2PTOV performs its functions should be
considered. The same also applies to the associated equipment, its voltage withstand capability and
time characteristic.
All voltage-related settings are made as a percentage of a settable base voltage, which shall be set
to the primary nominal voltage (phase-phase) level of the power system.
The time delay for ROV2PTOV is seldom critical, since residual voltage is related to earth faults in a
high-impedance earthed system, and enough time must normally be given for the primary protection
to clear the fault. In some more specific situations, where the residual overvoltage protection is used
to protect some specific equipment, the time delay is shorter.
Some applications and related setting guidelines for the residual voltage level are given below.
9.3.3.1 High impedance earthed systems
In high impedance earthed systems, an earth fault on one phase will cause a voltage collapse in that
phase. However, the other healthy phase voltage will raise to full phase-to-phase voltage value. The
residual voltage sum 2U
9.3.3.2 Solidly earthed systems
In solidly earthed systems, an earth fault on one phase is indicated by voltage collapse in that phase.
The other healthy phase will still have normal phase-to-earth voltage. The residual sum 2U
the same value as the remaining phase-to-earth voltage.
9.3.3.3 Settings for two step residual overvoltage protection
Parameters for ROV2PTOV application function are set via the local HMI or Protection and Control
Manager PCM600.
Common base IED values for primary current (IBase), primary voltage (UBase) and primary power
(SBase) are set in the global base values for settings function GBASVAL.
GlobalBaseSel: To select GBASVAL function for reference of base values.
Operation: For residual overvoltage protection Off/On.
UBase (given in GlobalBaseSel) is used as voltage reference for the set pickup values. UBase shall
be set equal to rated phase-to-phase voltage. Note that the set value for UBase will be multiplied by
factor 0.5 within the ROV2PTOV function. The voltage can be fed to the IED in different ways:
1. The IED is fed from two VTs connected phase-to-ground, where the residual voltage 2U
calculated internally within the protection.
2. 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
Railway application RER670
Application manual
will raise to the same phase-to-phase value during earth fault.
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Section 9
Voltage protection
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