Toshiba GR200 Series Instruction Manual page 115

Principle of distance measurement
2.10.1
Phase-to-phase fault
(i)
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 2.10-1 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 V b , V c , I b and I c and the fault point voltage is VF, then
V b and V c are given by the following equations.
From equations (2.10-1) and (2.10-2), the following equation is obtained.
where,
Zs: Self impedance
Zm: Mutual impedance
Since the effect of the phase-A current is small, and hence negligible in equation (2.10-3),
there is no need to introduce it in equations (2.10-1) and (2.10-2).
When each phase of the line is symmetric with the other, the positive-sequence and zero-
sequence impedances are Z
and Z are defined by the following equations, using the self-impedance Zs and the mutual
0
impedance Zm:
where,
Z : Positive-sequence impedance
1
Z : Zero-sequence impedance
0
Equation (2.10-3) can be rewritten as follows:
�� = ���� × �� + ���� × ��
�� ��
�� = ���� × �� + ���� × ��
�� ��
= ( ���� − ���� ) × ( ��
�� − ��
�� ��
and Z according to the method of symmetrical components. Z
1 0
�� = ���� − ����
1
�� = ���� + 2����
0
- 92 -
+ ����
��
+ ����
��
)
− ��
�� ��
6F2S1914 (0.49)
(2.10-1)
(2.10-2)
(2.10-3)
1
(2.10-4)
(2.10-5)
GRL200 (Soft 033 & 037)