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Negative sequence overcurrent protection (OCN)
Negative-sequence overcurrent protection (OCN) function has both time characteristic and
directional elements. Four stages (elements) are available in the OCN function. The user can
select various features using the scheme switches provided. The elements are named OCN1,
OCN2, and others; and they operate independently.
To simplify the description, only OCN1 is discussed but is applicable to the other OCNs;
hence, read the expression for OCN1 as OCN2, OCN3, and OCN4 at each stage unless a special
explanation or instruction has been provided.
Relay polarity
2.5.1
The user can choose either non-directional OCN or directional OCN for each OCN stage. In
addition, the user can further select either the forward or the direction for each of the
directional OCN elements selected.
Characteristic of a non-directional OCN
(i)
The characteristic of the non-directional type (non-directional OCN) is a circle at the origin. A
setting and a scheme switch is used to configure each non-directional OCN element; i.e., the
user can set the threshold value of non-directional OCN element for state 1 using setting
[OCN1], provided time characteristic is required for define time delay (DT) described in
Chapter 2.5.2(i). NonDir is set for the scheme switch [OCN1-Dir].
Characteristic of directional OCN in the forward
(ii)
As shown in Figure 2.5-1, the characteristic of the directional-OCN elements in the forward
direction is a semi-circle based upon the borderline; the hatched area shows the operating
region of the directional-OCN.
- 90 -
6F2T0207 (0.01)
GRE200 (5,6)
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