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1MRK 505 370-UEN D
16. Set
17. Set
18. Set
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
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
•
setting
•
setting parameter
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
•
start 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 start signals
Furthermore the other built-in UC, OV and UV protection elements can be used for other
protection and alarming purposes.
10.1.3.2
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:
=
t
op
æ
ç
è
EQUATION1372 V1 EN-US
where:
t
op
k
I
NS
I
r
By defining parameter x equal to maximum continuous negative sequence rating of the
generator in accordance with the following formula
Busbar protection REB670
Application manual
typical value) of measured
settings within the same function shall be done:
EnRestrainCurr to On
RestrCurrInput to PosSeq
RestrCurrCoeff to value 0.10
RCADir and ROADir settings will be as well applicable for OC2 stage
DirMode_OC2 shall be set to Reverse
StartCurr_OC2 shall be made more sensitive than pickup value of
k
2
ö
I
NS
÷
I
ø
r
is the operating time in seconds of the negative sequence overcurrent IED
is the generator capability constant in seconds
is the measured negative sequence current
is the generator rated current
PosSeq current in the power line. To do this the following
NegSeq overcurrent steps are required. One for forward
Section 10
Multipurpose protection
M13088-5 v4
(Equation 76)
231
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