Negative Sequence Overcurrent Protection - ABB REB670 Applications Manual

1MRK 505 337-UUS -
10.1.3.2
Application manual
If required, this CVGAPC function can be used in directional comparison protection
scheme for the power line protection if communication channels to the remote end of this
power line are available. In that case typically two NegSeq overcurrent steps are required.
One for forward and one for reverse direction. As explained before the OC1 stage can be
used to detect faults in forward direction. The built-in OC2 stage can be used to detect
faults in reverse direction.
However the following shall be noted for such application:
• the set values for RCADir and ROADir settings will be as well applicable for OC2
stage
• setting DirMode_OC2 shall be set to Reverse
• setting parameter PickupCurr_OC2 shall be made more sensitive than pickup value
of forward OC1 element (that is, typically 60% of OC1 set pickup level) in order to
insure proper operation of the directional comparison scheme during current reversal
situations
• pickup signals from OC1 and OC2 elements shall be used to send forward and reverse
signals to the remote end of the power line
• the available scheme communications function block within IED shall be used
between multipurpose protection function and the communication equipment in
order to insure proper conditioning of the above two pickup signals
Furthermore the other built-in UC, OV and UV protection elements can be used for other
protection and alarming purposes.

Negative sequence overcurrent protection

Example will be given how to use one CVGAPC function to provide negative sequence
inverse time overcurrent protection for a generator with capability constant of 20s, and
maximum continuous negative sequence rating of 7% of the generator rated current.
The capability curve for a generator negative sequence overcurrent protection, often used
world-wide, is defined by the ANSI standard in accordance with the following formula:
Section 10
Multipurpose protection
263