Toshiba GRZ100 B Series, Instruction Manual

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2.5.8 Negative Sequence Directional Elements DOCNF and DOCNR
There are two types of negative sequence directional element, the forward looking element
(DOCNF) and reverse looking element (DOCNR). They are used to detect faults during a power
swing. Their characteristics are shown in Figure 2.5.8.1.
Both the DOCNF and DOCNR use negative sequence current and voltage and determine a fault
direction based on the phase relationship between the current and voltage.
The operation decision is made using the following equation.
DOCNF
Z
k
I
2
2 −
V
2
I
2
sin
φ ≥
V
2k
|
I
2
|
I
2
≥
I
2k
DOCNR
Z
k
I
2
2
+ V
2
I
2
sin
φ ≥
V
2k
|
I
2
|
I
2
≥
I
2k
where,
I
2
= negative sequence current
V
2
= negative sequence voltage
φ
= lagging angle of I
2
to V
2
I
2k
= 0.267
×
rated current (fixed)
V
2k
= 6 V (fixed)
Z
k
= 2.5 ohm (1A rating, fixed) / 0.5 ohm (5A rating, fixed)
Figure 2.5.8.1 Negative Sequence Directional Element
I2
φ
DOCN-F
0
DOCN-R
V
2k
−
ZkI
2
−
(V
2k
−
ZkI
2
)