ABB REG670 Applications Manual page 345

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
• Earth-fault protection of feeders in effectively earthed distribution and
subtransmission systems. Normally these feeders have radial structure.
• Back-up earth-fault protection of transmission lines.
• Sensitive earth-fault protection of transmission lines. EF4PTOC can have better
sensitivity to detect resistive phase-to-earth-faults compared to distance
protection.
• Back-up earth-fault protection of power transformers.
• Earth-fault protection of different kinds of equipment connected to the power
system such as shunt capacitor banks, shunt reactors and others.
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 the 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 for IEC and ANSI.
Table 36: 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
Table continues on next page
Section 9
Current protection
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