ABB Relion 670 series, Technical Manual

Page: 467 / 1432

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-US
(Equation 119)
_ _ ref BC B C dir BC B C
V V V I I I
= - = -
ANSIEQUATION1450 V1 EN-US
(Equation 120)
_ _ ref CA C A dir CA C A
V V V I I I
= - = -
ANSIEQUATION1451 V1 EN-US
(Equation 121)
Phase-ground short circuit:
_ _ ref A A dir A A
V V I I
= =
ANSIEQUATION1452 V1 EN-US
(Equation 122)
_ _ ref B B dir B B
V V I I
= =
ANSIEQUATION1453 V1 EN-US
(Equation 123)
_ _ ref C C dir C C
V V I I
= =
ANSIEQUATION1454 V1 EN-US
(Equation 124)
The polarizing voltage is available as long as the positive-sequence voltage exceeds 4% of the set
base voltage
VBase. So the directional element can use it for all unsymmetrical faults including
close-in faults.
For close-in three-phase faults, the V1
AM
memory voltage, based on the same positive sequence
voltage, ensures correct directional discrimination.
The memory voltage is used for 100 ms or until the positive sequence voltage is restored.
After 100 ms, the following occurs:
1MRK 502 066-UUS B Section 8
Current protection
461
Technical manual