ABB Relion REC670 Applications Manual page 124

Section 7
Current protection
In many applications several steps with different current operating levels and time delays are
needed. EF4PTOC can have up to four, individual settable steps. The flexibility of each step of
EF4PTOC is great. The following options are possible:
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 earth-fault protection in meshed and effectively earthed
transmission systems. The directional residual overcurrent protection is also well suited to
operate in teleprotection communication schemes, which enables fast clearance of earth
faults on transmission lines. The directional function uses the polarizing quantity as decided
by setting. Voltage polarizing is most commonly used, but alternatively current polarizing
where currents in transformer neutrals providing the neutral source (ZN) is used to polarize (IN
· 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.
Table 16:
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)
It is also possible to tailor make the inverse time characteristic.
Normally it is required that EF4PTOC 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.
For some protection applications there can be a need to change the current operating level for
some time. Therefore there is a possibility to give a setting of a multiplication factor
118
Time characteristics
1MRK 511 358-UEN A
INxMult
Application manual