Hitachi Relion 670 Series Applications Manual page 94

Section 7
Impedance protection
7.1.4 Setting guidelines
The parameters for automatic switch onto fault logic, voltage- and current-based function ZCVPSOF
are set via the local HMI or Protection and Control Manager PCM600.
The distance protection zone used for instantaneous trip by ZCVPSOF has to be set to cover the
entire protected line with a safety margin of minimum 20%.
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 is used to select GBASVAL for reference of base values.
Operation: The operation of ZCVPSOF is by default set to On. The parameter must be set to Off if
ZCVPSOF is not to be used.
IPh< is used to set the current level for the detection of a dead line. IPh< is, by default, set to 20% of
IBase. It shall be set with a sufficient margin (15–20%) below the minimum expected load current. In
many cases, the minimum load current of a line is close to zero and even can be zero. The operating
value must exceed the maximum charging current of an overhead line when only one phase is
disconnected (mutual coupling in the other phases).
UPh< is used to set the voltage level for the detection of a dead line. UPh< is, by default, set to 70%
of UBase. This is a suitable setting in most cases, but it is recommended to check the suitability in
the actual application.
AutoInitMode: automatic activating of ZCVPSOF is, by default, set to DLD disabled, which means the
dead-line logic detection is disabled. If an automatic activation of the dead-line detection is required,
the parameter AutoInitMode has to be set to either Voltage, Current or Current & Voltage.
When AutoInitMode is set to Voltage, the dead-line detection logic checks that the two-phase
voltages are lower than the set UPh< level.
When AutoInitMode is set to Current, the dead-line detection logic checks if the two-phase currents
are lower than the set IPh< level.
When AutoInitMode is set to Current & Voltage, the dead-line detection logic checks that both two-
phase currents and two-phase voltages are lower than the set IPh< and UPh< levels.
Otherwise, the logic is activated by an external BC input.
tSOTF: the drop delay of ZCVPSOF is, by default, set to 1.0 seconds, which is suitable for most
applications.
tDLD: The time delay for activating ZCVPSOF by the internal dead-line detection is, by default, set to
0.2 seconds. It is suitable in most applications. The delay shall not be set too short to avoid
unwanted activations during transients in the system.
Mode: The operation of ZCVPSOF has three modes for defining the criteria for tripping. The setting
of Mode is, by default, UILevel, which means that the tripping criterion is based on the setting of IPh<
and UPh<. The choice of UILevel gives a faster and more sensitive operation of the function, which is
important for reducing the stress that might occur when energizing onto a fault. However, the voltage
recovery can be slow in some systems when energizing the line. Therefore, if the timer tDuration is
set too short, ZCVPSOF can interpret this as a fault and release a trip.
When Mode is set to Impedance, the operate criterion is based on the BC input (breaker closing),
which can be the start of the overreaching zone from the impedance zone measurement. A
nondirectional output signal should be used from an overreaching zone. The selection of the
Impedance mode gives increased security.
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