Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.2.9.6
REX640
Technical Manual

Application

MFADPSDE provides selective directional earth-fault protection for high-impedance
earthed networks, that is, for compensated, unearthed and high-resistance earthed
systems. It can be applied for the earth-fault protection of overhead lines and
underground cables, regardless of the earth-fault type (continuous, transient or
intermittent) or the fault resistance value (low or high ohmic). MFADPSDE replaces
traditional sensitive directional earth-fault protection (such as Iocos) and transient
earth-fault protection (such as Wischer principle) combining the same functionality
into a single function block (see
Table 562: Comparison of the MFADPSDE functionality with traditional methods in resonant
earthed networks
Earth-fault type
Transient
Traditional
Iocos
Traditional x
Wischer
New x
MFADPSDE
As shown by numerous practical field tests, MFADPSDE provides better sensitivity
and selectivity compared with traditional methods with less complexity in settings and
configuration. MFADPSDE provides enhanced earth-fault protection performance,
especially in networks with cable feeders where distributed compensation coils are
applied and earth-fault type is typically intermittent. It is applicable in feeders with
distributed compensation regardless of the size or localization of distributed coils.
Selective protection can be achieved also in case of overcompensated feeders.
MFADPSDE operation is based on multifrequency neutral admittance measurement
using the cumulative phasor summing technique. This concept provides extremely
secure, dependable and selective earth-fault protection also when the residual
quantities are highly distorted and contain non-fundamental frequency components.
MFADPSDE is well-suited for compensated networks where measurement signals
may have such characteristics, for example, during intermittent earth faults.
MFADPSDE can operate with both low-ohmic and higher-ohmic earth faults, where
the sensitivity limit is defined with the residual overvoltage condition. This allows
earth faults with several kilohms of fault resistance to be detected in a symmetrical
system. The achieved sensitivity is comparable with traditional fundamental
frequency based methods such as the IoCos/IoSin (DEFxPTOC), Watt/Varmetric
(WPWDE) and neutral admittance (EFPADM).
MFADPSDE can detect faults with dominantly fundamental frequency content as
well as transient, intermittent or restriking earth faults. MFADPSDE can be used as an
alternative solution to transient or intermittent function INTRPTEF.
Table 562).
Continuous Restriking/
Intermittent
x
x
x x
Section 4
Protection functions
Low-ohmic High-ohmic
x x
x
x x
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