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I
2
Forward
Operation zone
Characteristic of the directional-OCN element in the forward direction
Figure 2.5-1
Note: Directional characteristic angle (θ) forms the angle between the reference
quantity and the directional characteristic angle line. The half plane
represents the zone of operation bordered on one side by the borderline and
extending in the direction that contains both the reference (polarizing) and
operating quantities.
A setting and a scheme switch, as well as the non-directional OCN element, provide the
settings for the directional OCN element: for example, the user can set the threshold value
(I
) for stage 1 with the setting [OCN1] and Forward can be set for the scheme switch [OCN1-
OCN
Dir]. Setting of the sensing angle (θ) is configured by the setting [OCN1-Angle] with the value
of θ in the range of -90 – 90°. Figure 2.5-2 shows an example of an angle and a characteristic
using the θ.
The operation decision of OCN uses the following equation:
where
I 2
V 2
−V 2
Φ
θ
I OCN
OCN_Vpol = Setting value of the polarizing voltage ([OCN1-Vpol])
Note: The phase angle in the event of an internal fault is equal to the angle of the zero-
sequence impedance of the system; this value ranges approximately from 50° to
Reverse
Operation zone
Polarizing voltage (-3V
-θ
φ
Directional characteristic
angle line
��
2
��
× cos(φ − |θ|) ≥ 0
2
��
≥ ������_��������
2
= Negative phase sequence current
= Negative phase sequence voltage
= reference voltage (or polarizing voltage)
= lagging angle
= OCN setting angle ([OCN1-Angle])
= Setting value of OCN ([OCN1] and the others])
- 91 -
Forward
Operation zone
I
2
)
2
≥ ��
������
6F2T0207 (0.01)
Directional characteristic
angle line
φ
+θ
Polarizing voltage (-3V
Reverse
Operation zone
(2.5-1)
(2.5-2)
(2.5-3)
GRE200 (5,6)
)
2
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