ABB Relion 670 Series RES670, Technical Manual

Page: 187 / 888

component as well as from higher current harmonic. The selected current values are fed
to OC4PTOC (51/67).
In a comparator, the DFT or RMS values are compared to the set operation current value
of the function
(Pickup1, Pickup2, Pickup3, Pickup4) for each phase current. If a phase
current is larger than the set operation current, outputs PICKUP, PU_STx, PU_A, PU_B
and PU_C are activated without delay. 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:
_ _ ref AB A B dir AB A B
V V V I I I
= - = -
GUID-4F361BC7-6D91-47B5-8119-A27009C0AD6A V1 EN
(Equation 8)
_ _ ref BC B C dir BC B C
V V V I I I
= - = -
ANSIEQUATION1450 V1 EN
(Equation 9)
_ _ ref CA C A dir CA C A
V V V I I I
= - = -
ANSIEQUATION1451 V1 EN
(Equation 10)
Phase-ground short circuit:
Table continues on next page
1MRK 511 365-UUS A
Section 8
Current protection
Phasor measurement unit RES670 2.1 ANSI 181
Technical manual