ABB RES670 Applications Manual page 148

Section 8
Current protection
142
clearance, the directional function can be necessary. This can be the case for
unsymmetrical fault protection in meshed and effectively earthed transmission
systems. The directional negative sequence overcurrent protection is also well
suited to operate in teleprotection communication schemes, which enables fast
clearance of unsymmetrical faults on transmission lines. The directional function
uses the voltage polarizing quantity.
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 operating time of the different
protections. To enable optimal co-ordination all overcurrent relays, 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.
Table 15: Inverse 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
IEC Definite Time
User Programmable
ASEA RI
RXIDG (logarithmic)
There is also a user programmable inverse time characteristic.
Normally it is required that the negative sequence overcurrent function shall reset
as fast as possible when the current level gets lower than the operation level. In
some cases some sort of delayed reset is required. Therefore different kinds of reset
characteristics can be used.
1MRK 511 407-UEN C
Phasor measurement unit RES670 2.2 IEC
Application manual