ABB REG670 Applications Manual page 357

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
• Earth-fault and phase-phase short circuit protection of feeders in effectively
earthed distribution and subtransmission systems. Normally these feeders have
radial structure.
• Back-up earth-fault and phase-phase short circuit protection of transmission
lines.
• Sensitive earth-fault protection of transmission lines. NS4PTOC can have better
sensitivity to detect resistive phase-to-earth-faults compared to distance
protection.
• Back-up earth-fault and phase-phase short circuit protection of power
transformers.
• Earth-fault and phase-phase short circuit 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. NS4PTOC can have up to four, individual settable steps. The
flexibility of each step of NS4PTOC function 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 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 37: 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
Table continues on next page
Section 9
Current protection
351