Operation Principle - ABB RED615 Technical Manual

Section 4
Protection functions
4.2.4.4
312
Yo Io = − / Uo
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The measured admittance is compared to the admittance characteristic boundaries
in the admittance plane. The supported characteristics include overadmittance,
oversusceptance, overconductance or any combination of the three. The
directionality of the oversusceptance and overconductance criteria can be defined
as forward, reverse or non-directional, and the boundary lines can be tilted if
required by the application. This allows the optimization of the shape of the
admittance characteristics for any given application.
EFPADM supports two calculation algorithms for admittance. The admittance
calculation can be set to include or exclude the prefault zero-sequence values of Io
and Uo. Furthermore, the calculated admittance is recorded at the time of the trip
and it can be monitored for post-fault analysis purposes.
To ensure the security of the protection, the admittance calculation is supervised by
a residual overvoltage condition which releases the admittance protection during a
fault condition. Alternatively, the release signal can be provided by an external
binary signal.
The function contains a blocking functionality. It is possible to block function
outputs, timers or the function itself, if desired.

Operation principle

The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of the admittance-based earth-fault protection can be described using
a module diagram. All the modules in the diagram are explained in the next sections.
Io
Neutral
admittance
calculation
Uo
RELEASE
BLOCK
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Figure 156: Functional module diagram
Neutral admittance calculation
The function can operate on the measured or calculated residual quantities. The
residual current can be selected with the Io signal Sel setting. The selectable
options are "Measured Io" and "Calculated Io". Respectively, the residual voltage
can be selected with the Uo signal Sel setting. The selectable options are
"Measured Uo" and "Calculated Uo".
Timer
Operation
t
characteristics
Blocking
logic
1YHT530004D05 D
(Equation 15)
OPERATE
START
615 series
Technical Manual