ABB ret650, Technical Manual

Page: 155 / 670

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.
Service value for individually measured phase currents are also available on the local
HMI for OC4PTOC 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:
1 2 1 2 1 2 1 2
= - = -
refL L L L dirL L L L
U U U I I I
EQUATION1449 V1 EN
(Equation 35)
2 3 2 3 2 3 2 3
= - = -
refL L L L dirL L L L
U U U I I I
EQUATION1450 V1 EN
(Equation 36)
3 1 3 1 3 1 3 1
= - = -
refL L L L dirL L L L
U U U I I I
EQUATION1451 V1 EN
(Equation 37)
Phase-earth short circuit:
1 1 1 1
= =
refL L dirL L
U U I I
EQUATION1452 V1 EN
(Equation 38)
2 2 2 2
= =
refL L dirL L
U U I I
EQUATION1453 V1 EN
(Equation 39)
3 3 3 3
= =
refL L dirL L
U U I I
EQUATION1454 V1 EN
(Equation 40)
1MRK 504 135-UEN A
Section 8
Current protection
149
Technical manual