Toshiba GR 200 Series, Инструкция по эксплуатации

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6F2S1915 (0.46)
GRZ200 (Soft 031 & 032)
- 25 -
2.1.1
Principle of distance measurement
(i)
Phase-to-phase fault
The distance protection function used to detect phase-to-phase faults measures the impedance
from the relay to the fault point using delta voltage and current. The positive-sequence
impedance is used to represent the line impedance.
Figure 2.1-1 provides an illustration of the power system for the condition of a phase-to-
phase fault. The impedance from the relay to the fault is the same in phase-B and phase-C,
the self-impedance is Zs and the mutual impedance between phases is Zm. If the voltages and
currents of phase-B and phase-C are Vb, Vc, Ib and Ic and the fault point voltage is VF, then
Vb and Vc are given by the following equations.
𝑉
𝑏
= 𝑍𝑠 × 𝐼
𝑏
+ 𝑍𝑚 × 𝐼
𝑐
+ 𝑉𝐹
(2.1-1)
𝑉
𝑐
= 𝑍𝑠 × 𝐼
𝑐
+ 𝑍𝑚 × 𝐼
𝑏
+ 𝑉𝐹
(2.1-2)
From equations (2.1-1) and (2.1-2), the following equation is obtained.
𝑉
𝑏
− 𝑉
𝑐
= (𝑍𝑠 − 𝑍𝑚) × (𝐼
𝑏
− 𝐼
𝑐
)
(2.1-3)
where,
Zs: Self impedance
Zm: Mutual impedance
Since the effect of the phase-A current is small, and hence negligible in equation (2.1-3),
there is no need to introduce it in equations (2.1-1) and (2.1-2).
When each phase of the line is symmetric with the other, the positive-sequence and zero-
sequence impedances are Z
1
and Z
0
according to the method of symmetrical components. Z
1
and Z
0
are defined by the following equations, using the self-impedance Zs and the mutual
impedance Zm:
𝑍
1
= 𝑍𝑠 − 𝑍𝑚
(2.1-4)
𝑍
0
= 𝑍𝑠 + 2𝑍𝑚
(2.1-5)
where,
Z
1
: Positive-sequence impedance
Z
0
: Zero-sequence impedance
Equation (2.1-3) can be rewritten as follows: