ABB RELION REX640, Техническое руководство, Страница: 579 / 1960

Table 616: Comparison of the MFADPSDE functionality with traditional methods in
resonant earthed networks
Earth-fault type
Transient Continuous Restriking /
Intermittent
Low-
ohmic
High-ohmic
Traditional Iocos x x x
Traditional Wischer x x x
New MFADPSDE x x x x 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 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.
MFADPSDE supports fault direction indication in operate and non-operate
directions which can be used during fault location process. The in-built transient
detector can be used to identify restriking or intermittent earth faults, and
discriminate them from permanent or continuous earth faults.
The direction of MFADPSDE can be set as forward or reverse. The operation
characteristic is defined by a tilted operation sector, which is universally valid both
in unearthed and compensated networks. The tilt of the operation sector should
be selected based on the measurement errors of the applied residual current and
voltage measurement transformers.
The operating time characteristic is according to the definite time (DT).
The function contains a blocking functionality to block function outputs, timers or
the function itself.
MFADPSDE supports both tripping and alarming operation modes. For the alarming
earth-fault protection application, the function contains a dedicated operation
mode. MFADPSDE provides reliability and sensitivity of protection with a single
function. This enables a protection scheme implementation that is simpler than
1MRS759142 F Protection functions
REX640
Technical Manual
579