Toshiba GR 200 Series, Instruction Manual

Page: 49 / 1563

6F2S1915 (0.46)
GRZ200 (Soft 031 & 032)
- 28 -
𝑉
𝑎
= 𝑍
1
× 𝐼
𝑎
′
(2.1-14)
That is, the positive-sequence impedance Z
1
up to the fault point can be obtained from
the simple ratio of voltage Va to compensated current Ia' according to equation (2.1-14).
Obtaining the compensated current according to equation (2.1-13) is called "zero-
sequence compensation." Note that in this implementation of zero-sequence compensation, the
compensation coefficient
𝑍
0
− 𝑍
1
𝑍
1
and
𝑍
0𝑚
𝑍
1
are not real numbers, but complex numbers. The distance protection function has a
configuration that allows this compensation coefficient to be set as a complex number and
setting the coefficient correctly makes it possible to measure exactly the distance to the fault
point.
In equations (2.1-7) to (2.1-9), the fault resistance is ignored. Since the measurement of
the distance up to the fault point, based on equation (2.1-14) is carried out using the reactance
component, in principle there is no influence on the voltage component due to the fault
resistance. However, under real operating conditions, distance measurement errors are
introduced because of the fault resistance combined with the power flow or the current flowing
into the fault point from the remote terminal opposite to the relay location.
Figure 2.1-3 Equivalent circuit of single-phase earth fault
V1
Z2
Z1
Z0
V1F
V2F
V0F
Positive-sequence circuit
Negative-sequence circuit
Zero-sequence circuit
ZG
I1
I2
I0
V2
V0