ABB Relion 611 Series, Technical Manual

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4.5.5.2 Function block
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Figure 130: Function block
4.5.5.3 Functionality
The positive-sequence undervoltage protection function PSPTUV is used to detect
positive-sequence undervoltage conditions. PSPTUV is used for the protection of
small power generation plants. The function helps in isolating an embedded plant
from a fault line when the fault current fed by the plant is too low to start an overcurrent
function but high enough to maintain the arc. Fast isolation of all the fault current
sources is necessary for a successful autoreclosure from the network-end circuit
breaker.
The function starts when the positive-sequence voltage drops below the set limit.
PSPTUV operates with the definite time (DT) characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
the definite timer or the function itself, if desired.
4.5.5.4 Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of PSPTUV can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
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Figure 131: Functional module diagram. U
1
is used for representing positive
phase sequence voltage.
Level detector
The calculated positive-sequence voltage is compared to the set Start value setting. If
the value drops below the set Start value , the level detector enables the timer. The
Relative hysteresis setting can be used for preventing unnecessary oscillations if the
1MRS757454 D
Section 4
Protection functions
611 series 277
Technical Manual