5–54 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
S4 ELEMENTS CHAPTER 5: SETPOINTS
1. With energization sensing by current enabled, all currents dropping below the
minimum energization current indicates de-energization; any current exceeding the
minimum energization current indicates energization. This method is the least reliable
method of detecting energization, since an energized and unloaded transformer will
be detected as being de-energized if this method is used alone.
2. With energization sensing by voltage enabled, the voltage dropping below the
minimum energization voltage indicates de-energization; any current exceeding the
minimum energization current indicates energization.
3. With ‘b’ auxiliary contacts from all switching devices (which can be used to energize
the transformer) connected in series to a logic input and assigned to the
BREAKERS
ARE OPEN
setpoint, the contacts closed indicates de-energization; any current
exceeding the minimum energization current indicates energization.
Energization inhibit settings are put in service upon detection of de-energization. Upon
energization, the energization inhibit duration timer is initiated and the settings are
removed from service when the time delay elapses. The energization inhibit feature may
also be put in service during sympathetic inrush. The onset of sympathetic inrush is
detected via a close command to the parallel transformer switching device connected to a
logic input, assigned to the
PARALL XFMR BRKR CLS setpoint. Energization inhibit settings
are put in service when the contact closes. Upon signal removal, the energization inhibit
duration timer is initiated and the settings are removed from service when the time delay
elapses.
In a breaker-and-a-half scheme, where current can be present in the CTs without being
present in the transformer winding, it may be necessary to use the parallel transformer
breaker close contact to initiate energization inhibit.
• ENERGIZATION INHIBIT PARAMETERS: Select “2nd” to compare the 2
nd
harmonic
current against
HARMONIC INHIBIT LEVEL. Select “2nd + 5th” to use the RMS sum of
the 2
nd
and 5
th
harmonics.
• HARMONIC AVERAGING: Select “Enabled” to use the three-phase average of the
harmonic current against the harmonic inhibit setting.
• ENERGIZATION INHIBIT LEVEL: Enter the level of harmonic current (2
nd
or 2
nd
+ 5
th
)
above which the percent differential element is inhibited from operating. This setting
will often need to be set significantly lower than the
HARMONIC INHIBIT LEVEL,
especially when used with the “Parallel Xfmr BkrCls” logic input function for
sympathetic inrush.
• ENERGIZATION INHIBIT DURATION: Enter the time delay from the moment of
energization (or the end of the parallel breaker close command) before the
energization inhibit feature is removed from service.
• ENERGIZATION SENSING BY CURRENT: Select “Enabled” to detect de-energization by
the level of all currents dropping below the minimum energization current.
• MINIMUM ENERGIZATION CURRENT: Enter the current level below which the
transformer is considered de-energized (energization sensing by current enabled), and
above which the transformer is considered energized (any energization sensing
enabled).
• ENERGIZATION SENSING BY VOLTAGE: Select “Enabled” to detect de-energization by
the level of the voltage dropping below the minimum energization voltage. This
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