Negative Sequence Overcurrent Protection - Hitachi Relion 670 Series Applications Manual

Section 11
Multipurpose protection
• 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.
11.1.4.2

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
I
ç
è
EQUATION1740-ANSI V1 EN-US
where:
t is the operating time in seconds of the negative sequence overcurrent IED
op
TD is the generator capability constant in seconds
I is the measured negative sequence current
NS
I is the generator rated current
r
By defining parameter x equal to maximum continuous negative sequence rating of the generator in
accordance with the following formula
=
x 7%
EQUATION1756-ANSI V1 EN-US
Equation
negative sequence inverse overcurrent IED:
TD
=
t
op
æ
ç
x I
è
EQUATION1741-ANSI V1 EN-US
176
TD
2
ö
NS
÷
I ø
r
=
0.07 pu
87 can be re-written in the following way without changing the value for the operate time of the
1
×
2
x
2
ö
I
NS
÷
×
ø
r
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1MRK511407-UUS Rev. N
(Equation 87)
(Equation 88)
(Equation 89)
Phasor measurement unit RES670
Application manual
M13088-5 v5