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Functions
2.35
Inadvertent Energization (ANSI 50, 27)
General
2.35.1 Functional Description
Criteria
230
The inadvertent energizing protection serves to limit damages by accidental
connection of the standing or already started, but not yet synchronized generator by a
fast actuation of the mains breaker. A connection to a standing machine corresponds
to the connection to an inductivity. Due to the nominal voltage impressed by the power
system, the generator starts with a high slip as asynchronous machine. In this context,
impermissibly high currents are induced inside the rotor which may finally destroy it.
The inadvertent energizing protection only intervenes if measured quantities do not
yet exist in the valid frequency working area (operational condition 0 in case of the
standing machine) or if an undervoltage below the nominal frequency is present
(machine already started, but not yet synchronized). The inadvertent energizing
protection is blocked by a voltage criterion on exceeding a minimum voltage, in order
to avoid that it picks up during normal operation. This blocking is delayed to avoid that
the protection is blocked immediately by the time of an unwanted connection. Another
pickup delay is necessary to avoid an unwanted operation in case of high-current
faults with a heavy voltage dip. A dropout time delay allows for a measuring limited in
time.
As the inadvertent energizing protection must intervene very quickly, the
instantaneous current values are monitored over a large frequency range already in
operational condition 0. If valid measured quantities exist (operational condition 1), the
positive phase-sequence voltage, the frequency for blocking the inadvertent
energizing protection as well as the instantaneous current values are evaluated as
tripping criterion.
Figure 2-111 illustrates the logic diagram of the inadvertent energizing protection. This
function can be blocked via a binary input. For example, the existence of an excitation
voltage can be used as addition criterion. As the voltage is a necessary criterion for
tripping the inadvertent energizing protection, the voltage transformers must be
monitored by the Fuse–Failure–Monitor (FFM). If it detects a voltage transformer fault,
the voltage criterion of the inadvertent energizing protection is deactivated.
7UM62 Manual
C53000-G1176-C149-3
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