ABB RELION REX640 Technical Manual page 529

1MRS759142 C
REX640
Technical Manual
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 558).
Table 558: Comparison of the MFADPSDE functionality with traditional methods in resonant
earthed networks
Earth-fault type
Transient
Traditional
Iocos
Traditional x
Wischer
MFADPSDE x
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 the 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.
The neutral point in compensated networks is earthed via a controllable centralized
arc suppression coil located typically in the primary substation. Additionally, (fixed)
distributed compensation coils can be used, which are installed in relevant locations
along the protected feeders.
In unearthed networks, the neutral point in the primary substation is not connected to
earth. However, in unearthed networks (fixed) distributed compensation coils can also
be used to compensate a part of the total capacitive earth-fault current. Typically, the
resulting compensation degree is less than 50 percent. Thus, unearthed networks with
or without distributed compensation coils are generally referred to as unearthed
networks in this manual.
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.
The sensitivity that can be achieved is comparable with traditional fundamental
frequency based methods such as IoCos/IoSin (DEFxPTOC), Watt/Varmetric
(WPWDE) and neutral admittance (EFPADM).
MFADPSDE can detect faults with dominantly fundamental frequency content as
well as transient, intermittent and restriking earth faults. The function can be used as
an alternative solution to transient or intermittent function INTRPTEF.
Continuous Restriking/
Intermittent
x
x
x x
Section 4
Protection functions
Low-ohmic High-ohmic
x x
x
x x
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