4.2.4.2
Function block
Figure 212: Function block
4.2.4.3
Functionality
The admittance-based earth-fault protection function EFPADM provides a selective
earth-fault protection function for high-resistance earthed, unearthed and
compensated networks. It can be applied for the protection of overhead lines
as well as with underground cables. It can be used as an alternative solution
to traditional residual current-based earth-fault protection functions, such as
the IoCos mode in DEFxPDEF. Main advantages of EFPADM include a versatile
applicability, good sensitivity and easy setting principles.
EFPADM is based on evaluating the neutral admittance of the network, that is, the
quotient:
Yo
Io
Uo
=
−
/
(Equation 25)
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.
The function 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.
4.2.4.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of EFPADM can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
1MRS757644 H
Protection functions
620 series
Technical Manual
429
