ABB REG650 Technical Manual page 179

1MRK 502 043-UUS B
Technical Manual
overcurrent protection 3-phase output function OC4PTOC (51/67), it is possible to
select the type of the measurement used for all overcurrent stages. It is possible to
select either discrete Fourier filter (DFT) or true RMS filter (RMS).
If DFT option is selected then only the RMS value of the fundamental frequency
components of each phase current is derived. Influence of DC current component and
higher harmonic current components are almost completely suppressed. If RMS option
is selected then the true RMS values is used. The true RMS value in addition to the
fundamental frequency component includes the contribution from the current DC
component as well as from higher current harmonic. The selected current values are
fed to OC4PTOC (51/67).
In a comparator, for each phase current, the DFT or RMS values are compared to the
set operation current value of the function (Pickup1, Pickup2, Pickup3, Pickup4). If a
phase current is larger than the set operation current, outputs PICKUP, PU_STx,
PU_A, PU_B and PU_C are, without delay, activated. Output signals PU_A, PU_B
and PU_C are common for all steps. This means that the lowest set step will initiate the
activation. The PICKUP signal is common for all three phases and all steps. It shall be
noted that the selection of measured value (DFT or RMS) do not influence the
operation of directional part of OC4PTOC (51/67) .
Service value for individually measured phase currents are also available on the local
HMI for OC4PTOC (51/67) function, which simplifies testing, commissioning and in
service operational checking of the function.
A harmonic restrain of the function can be chosen. A set 2nd harmonic current in
relation to the fundamental current is used. The 2nd harmonic current is taken from the
pre-processing of the phase currents and the relation is compared to a set restrain
current level.
The function can be directional. The direction of the fault current is given as current
angle in relation to the voltage angle. The fault current and fault voltage for the
directional function is dependent of the fault type. To enable directional measurement
at close in faults, causing low measured voltage, the polarization voltage is a
combination of the apparent voltage (85%) and a memory voltage (15%). The
following combinations are used.
Phase-phase short circuit:
= -
V V V
ref _ AB A B
GUID-4F361BC7-6D91-47B5-8119-A27009C0AD6A V1 EN
= -
V V V
ref BC _ B C
ANSIEQUATION1450 V1 EN
Table continues on next page
= -
I I I
dir AB _ A B
= -
I I I
dir BC _ B C
Section 8
Current protection
(Equation 33)
(Equation 34)
173