Energy and Power Engineering, 2013, 5, 941-944
doi:10.4236/epe.2013.54B180 Published Online July 2013 (http://www.scirp.org/journal/epe)
New Method of Measuring the Positive-sequence
Capacitance of T-connection Transmission Lines
Yuansen Zhang1, Demin Cui1, Qingtao Cao1, Yongqiang Chai1, Peng Liu1, Xiaobo Li 1,
Zhijian Hu2, Chuanqi Li2, Chengxue Zhang2
1Dezhou Power Supply Company, Shandong Electric Power Group Co., Dezhou, China
2School of Electrical Engineering, Wuhan University, Wuhan, China
Email: zhijian_hu@163.com
Received February, 2013
ABSTRACT
A novel method of measuring the positive-sequence capacitance of T-connection transmission lines is proposed. The
mathematical model of the new method is explained in detail. In order to obtain enough independent equations, three
independent operation modes of T-connection transmission lines during the line measurement are introduced. The digi-
tal simulation results and field measurement results are show n. The simulation and measurement results hav e validated
that the new method can meet the needs of measuring the positive-sequence capacitance of T-connection transmission
lines. This method has been implemented in the newly developed measurement instrument.
Keywords: T-connection Transmission Lines; Line Parameter; Positive-sequence Capacitance; Measurement
1. Introduction
With the rapid development of power systems, line cor-
ridors become more and more crowed. In order to reduce
synthetic cost of the line construction and limited objec-
tive conditions, T-connection transmission lines are al-
ways applied in HV/EHV. The reliable operation of
power systems depends on the correct operation of re-
laying protection devices [1].
It is well known that the computation for parameters of
T-connection transmission lines is derived from Carson
formula [2]. It is influenced by many practical factors,
such as the resistance of earth, the equivalent depth of the
lines and, etc. So the parameters should be practically
measured rather than theoretically calculated.
There are many related literatures discussing about
measuring the impedance parameters of T-connection
transmission lines [3-5]. The capacitance parameters are
always ignored. But the capacitance is very important for
transmission line protection. When it exceeds certain
length, because the numerical value of capacity current is
big, the current flow on both sides of the lines and phase
relation will change according with the increase of ca-
pacity current value. Especially, when load current and
short-circuit current are small, it can lead to the malop-
eration of high frequency protection [6, 7]. If we use the
traditional method to measure the capacitance of T-con-
nection transmission lines, it can only calculate parallel
values of three branches. When the parameters of three
branches are different, the traditional method no longer
works. So, new measurement method needs to be found
out for the positive-sequence capacitance of T-connec-
tion transmission lines.
In this paper, a new method of measuring positive-
sequence capacitance of T-connection lines is proposed.
The method has been applied to the newly developed
measurement instrument.
2. The Theory of the Measurement Method
Usually, the length of T-connection transmission lines is
less than 50 km. So it can use the lumped parameter
model. Each branch can be equivalent to T-form circuit.
The lumped parameter model of T-form equivalent cir-
cuit is shown in Figure 1.
When the length and impedance of transmission lines
are known, the susceptance can be calculated. Three
phases end is opening circuit, , the susceptance y
is as follows, 20I
1
2
/2z/2z
1
U
2
U
ygjb
Figure 1. The lumped parameter model of T-form equiva-
lent circuit.
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