ABB RES670 Technical Manual page 186

Section 8
Current protection
180
faultState
I3P
V3P
Mode Selection
ANSI05000740 V3 EN-US
Figure 51: Functional overview of OC4PTOC (51/67)
A common setting for all steps, NumPhSel, is used to specify the number of phase
currents to be high to enable operation. These settings can be chosen: 1 out of 3, 2 out
of 3 or 3 out of 3.
Using a parameter setting MeasType within the general settings for the function
OC4PTOC (51/67), it is possible to select the type of the measurement used for all
overcurrent stages. Either discrete Fourier filter (DFT) or true RMS filter (RMS) can
be selected.
If the DFT option is selected, only the RMS value of the fundamental frequency
component of each phase current is derived. The influence of the DC current
component and higher harmonic current components are almost completely
suppressed. If the RMS option is selected, then the true RMS value is used. The true
RMS value includes the contribution from the current DC component as well as from
the higher current harmonic in addition to the fundamental frequency component.
In a comparator, the DFT or RMS values are compared to the set operation current
value of the function (I1>, I2>, I3> or I4>) for each phase current. If a phase current
is larger than the set operation current, outputs START, STx, STL1, STL2 and STL3
are activated without delay. Output signals STL1, STL2 and STL3 are common for all
steps. This means that the lowest set step will initiate the activation. The START signal
is common for all three phases and all steps. It shall be noted that the selection of
dirPhAFlt
Direction
Element
dirPhBFlt
dirPhCFlt
Harmonic
harmRestrBlock
Restraint
Element
enableDir
enableStep1-4
DirectionalMode1-4
1MRK 511 408-UUS A
4 step overcurrent
element
One element for each
step
ANSI05000740-3-en.vsdx
Phasor measurement unit RES670 2.2 ANSI
Technical manual
faultState
PICKUP
TRIP
M12883-16 v11