ABB REC650 Applications Manual page 113

1MRK 511 286-UUS A
Application manual
Non-directional/Directional function: In some applications the non-directional
functionality is used. This is mostly the case when no fault current can be fed from the
protected object itself. In order to achieve both selectivity and fast fault clearance, the
directional function can be necessary. This can be the case for ground-fault protection in
meshed and effectively grounded transmission systems. The directional residual
overcurrent protection is also well suited to operate in teleprotection communication
schemes, which enables fast clearance of ground faults on transmission lines. The
directional function uses the polarizing quantity as decided by setting. Voltage polarizing
(3V or V ) is most commonly used, but alternatively current polarizing (3I
0 2
currents in transformer neutrals providing the neutral (zero sequence) source (ZN) is used
to polarize (IPol · ZN) the function. Dual polarizing where the sum of both voltage and
current components is allowed to polarize can also be selected.
Choice of time characteristics: There are several types of time characteristics available
such as definite time delay and different types of inverse time characteristics. The
selectivity between different overcurrent protections is normally enabled by co-
ordination between the operate time of the different protections. To enable optimal co-
ordination all overcurrent protections, to be co-ordinated against each other, should have
the same time characteristic. Therefore a wide range of standardized inverse time
characteristics are available: IEC and ANSI. The time characteristic for step 1 and 4 can
be chosen as definite time delay or inverse time characteristic. Step 2 and 3 are always
definite time delayed and are used in system where IDMT is not needed.
Table 9: Time characteristics
Curve name
ANSI Extremely Inverse
ANSI Very Inverse
ANSI Normal Inverse
ANSI Moderately Inverse
ANSI/IEEE Definite time
ANSI Long Time Extremely Inverse
ANSI Long Time Very Inverse
ANSI Long Time Inverse
IEC Normal Inverse
IEC Very Inverse
IEC Inverse
IEC Extremely Inverse
IEC Short Time Inverse
IEC Long Time Inverse
Table continues on next page
Section 6
Current protection
or I ) where
0 2
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