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The results of T-Line Traveling Wave Fault Location is easily influenced by the wave arrival time and traveling wave propagation velocity; it proposes that the traveling wave uses wavelet transform to extract the modulus maxima of breakdown voltage, to confirm the time of the traveling wave reaching the three-terminal line. The speed of the traveling wave reaching three terminals is confirmed by the structural parameters of the transmission line. We apply the arrival time and propagation velocity to the T-type traveling wave fault location algorithm. Different transmission line distance select the corresponding algorithm, excluding the impact of fault branches and in some cases ranging accuracy, the failure dead zone will not appear. After MATLAB simulation analysis, the algorithm analysis is clear; the range accuracy is high, so that it can meet the requirements of fault location.

In the long-distance transmission system, T-connection transmission lines are a mode of connection which is a higher transport power and heavier load. Once the line fails, there will be a large area power outage, resulting in greater overall social economic losses. Therefore, when the malfunction occurs, we need to identify the fault slip and fault point quickly, and then restore the power, minimize the economic loss and social benefits.

According to the characteristics of T-junction, two aspects of the fault location can be concluded: the judgment of fault slip and the confirmation of failure points. Method One: inject the signal in one end of the circuit; confirm the position of the fault by the start time of the injected signal and the time of signal returns after reaching the point of malfunction. This method has great difficulties of processing data, and the traveling wave in the process of transmission will weaken the signal; the return time of signal is inaccurate [

The new proposed algorithm has the following advantages: using the voltage traveling wave, eliminating the effects of electrical traveling waves, selecting the appropriate wavelet transform applied to deal with the traveling wave signal [

Since the 1990s, the wavelet transform and its engineering applications aroused more and more attention of mathematicians and engineers of various countries, especially in the analysis of power system transient signals, in recent years it has been very good development, and has shown great advantage and potential applications, especially has been a very good development in the electrical equipment fault diagnosis of power quality disturbance signal analysis applications, protection, fault location.

In all of the wavelet transform, continuous wavelet transform, dyadic wavelet transform, orthogonal wavelet transform, semi-orthogonal wavelet transform, different wavelet transform has different characteristics. And in the power transient signal analysis, the wavelet transform is the most important wavelet choice. This paper analyzes the dyadic wavelet transform to select the voltage traveling wave signal.

In the wavelet transform, if

In the formula:

In the continuous wavelet transform, only the scale parameter do discrete binary (

The wavelet transform is called binary wavelet transform, the corresponding wavelet called binary wavelet, binary wavelet is allowable the wavelet (it satisfies allowable conditions

The function of the stability condition is to ensure the existence of dual wavelet Fourier transform, that is always possible to find a stable dual wavelet reconstructed [

T-connection as shown in _{1}, L_{2}, L_{3}. After a certain point line failure, traveling wave spread to the A, B, C three-terminal, at the measurement point 1, 2, 3 measured traveling wave arrival time of T_{1}, T_{2}, T_{3}. We choose the shortest distance observation point of three observation points as the reference distance point, assuming L_{1} is the shortest, we choose observation point 1 as a reference observation points. The following discussion is according to the different transmission line distance.

(1) When the three branches are equal, i.e., L_{1} = L_{2} = L_{3}. Because traveling wave velocity is equal under the same circumstances, according to T_{1}, T_{2}, T_{3}, we have:

① If T_{1} = T_{2} = T_{3}, we can see the point of failure in T node;

② If the time T is equal to the smallest of the three, we can see the fault in time T corresponds to the observation point branch circuit.

(2) When the two branches are equal, assuming TA < TB = TC, we have:

① If the fault happens in slip TA (including node T), it exists time T_{1} < T_{2} = T_{3};

② If the fault happens in slip TB, we choose the observation point 1 as a reference point, we calculate the distance on the line AB and AC fault line distance away from the observation point 1, assuming the distance of the point of fault to the observation point is X, the distance to the node of T is X', according to the same principles of traveling wave velocity [

So, we have:

So, we have：

where in_{1}, due to TB = TC, it is possible that the point of failure is in the TB, is also possible in the TC, then only need to determine the size of T_{2} and T_{3} from traveling wave to the observation point of time 2, 3.

When T_{2} < T_{3}, the failure points on the line TB; when T_{2} > T_{3}, the fault on the line TC.

(3) When the two branches are equal, assuming TA > TB = TC, we can know:

① If the fault slip is on TA (including node T) on the existence of time T_{2} = T_{3}

② If the fault slip is on TB or TC, the algorithm with the (2) ②.

(4) When the three branches are not equal, random selecting L_{1} < L_{2} < L_{3}, and we choose the shortest distance observation point of three observation points as the reference distance point. We calculate the distance on the line AB and AC fault line distance away from the observation point 1, assuming the distance of the point of fault to the observation point is X, we have:

① If the fault slip is on TA (including node T), we calculate on the line AB and AC, by Equation (4), we can be obtained:

So X_{1} = X_{2}, the fault slip is on TA (including node T).

② If the fault slip is on TB, assuming the distance of the point of fault to the node T is X , we calculate on the line AB, by Equation (4) ,we can be obtained:

We calculate on the line AC, by Equation (6), we can be obtained:

So X > L_{1,} the fault slip is on TB.

③ If the fault slip is on TC, assuming the distance of the point of fault to the node T is X , we calculate on the line AC, by Equation (4) ,we can be obtained:

We calculate on the line AB, by Equation (6), we can be obtained:

So X > L_{1}, the fault slip is on TC.

The algorithm only need to select the appropriate line, find the corresponding algorithm can quickly find fault branch, and quick and easy calculate, the algorithm simulation process is shown in

To validate the algorithm proposed in this paper, and using MATLAB/Simulink establish 220 KV three-terminal power system model shown in _{1} = 0.01273 Ω/km; R_{0} = 0.3864 Ω/km; L_{1} = 0.9337 × 10^{−3} H/km; L_{0} = 4.1264 × 10^{−3} H/km; C_{1} = 12.74 × 10^{−9} F/km; C_{0} =

7.751 × 10^{−9} F/km; velocity of traveling wave is

1) When the line length is AT = L_{1} = 120 km, BT = L_{2} = 100 km, CT = L_{3} = 100 km, after phase-mode trans- formation and the extraction of maximum modulus by wavelet transform, the simulation diagram of the fault voltage shown in

The calculation results of fault at AT, BT, CT showed in

The data in

2) When the line length is AT = L_{1} = 110 km, BT = L_{2} = 150 km, CT = L_{3} = 150 km, after phase-mode transformation and the extraction of maximum modulus by wavelet transform, the simulation diagram of the fault voltage shown in

The calculation results of fault at AT, BT, CT showed in

The data in

3) When the line length is AT = L_{1} = 120 km, BT = L_{2} = 150 km, CT = L_{3} = 200 km, after phase-mode transformation and the extraction of maximum modulus by wavelet transform, the simulation diagram of the fault voltage shown in

The calculation results of fault at AT, BT, CT showed in

The data in

Fault slip | The distance from endpoint | The time of the first wave arrive(s) | Judgment | Calculate the distance | Error | |
---|---|---|---|---|---|---|

AT | 25 km | T_{1} = 0.010086 T_{2} = 0.010674 T_{3} = 0.010674 | T_{2} = T_{3} | 25.224954 | 0.065 | |

BT | 40 km | T_{1} = 0.010622 T_{2} = 0.010138 T_{3} = 0.010553 | X = 180.166 L_{1} = 120.002 X > L_{1}; T_{3} > T_{2} | 40.011996 | 0.011 | |

CT | 30 km | T_{1} = 0.010657 T_{2} = 0.010588 T_{3} = 0.010104 | X = 190.189 L_{1} = 120.002 X > L_{1}; T_{2} > T_{3} | 30.153968 | 0.153 |

Fault slip | The distance from endpoint | The time of the first wave arrive (s) | Judgment | Calculate the distance | Error |
---|---|---|---|---|---|

AT | 35 km | T_{1} = 0.010121 T_{2} = 0.010777 T_{3} = 0.010777 | T_{2} = T_{3} | 35.082982 | 0.082 |

BT | 55 km | T_{1} = 0.010708 T_{2} = 0.010190 T_{3} = 0.010846 | X = 205.094 L_{1} = 109.994 X > L_{1}; T_{3} > T_{2} | 55.08898 | 0.088 |

CT | 45 km | T_{1} = 0.010743 T_{2} = 0.010881 T_{3} = 0.010156 | X = 215.097 L_{1} = 109.994 X > L_{1}; T_{2} > T_{3} | 45.230952 | 0.230 |

Fault slip | The distance from endpoint | The time of the first wave arrive (s) | Judgment | Calculate the distance | Error | |
---|---|---|---|---|---|---|

AT | 30 km | T_{1} = 0.010104 T_{2} = 0.010829 T_{3} = 0.011002 | X_{1} = 29.8 X_{2} = 29.8 X_{1} = X_{2} | 30.153968 | 0.153 | |

BT | 60 km | T_{1} = 0.010726 T_{2} = 0.010207 T_{3} = 0.011002 | X = 210.239 L_{1} = 119.988 X > L_{1} | 60.017994 | 0.017 | |

CT | 70 km | T_{1} = 0.010864 T_{2} = 0.010967 T_{3} = 0.010242 | X = 250.171 L_{1} = 120.067 X > L_{1} | 70.165964 | 0.165 |

Analysis by the introduction of traveling wave fault location method decided by two main parameters: one is the arrival time of traveling wave, the other is propagation velocity of traveling wave. The traveling wave propagation velocity is determined by parameters of line. In actual measurement may produce certain error, when find out fault branch and calculate the distance between fault point and end point, it can also produce some small error because of inaccuracy of line measurement. The arrival time of traveling wave caused by sampling precision. Under this paper proposed sampling frequency and the calculation of wave velocity, the resulting error is in the allowable range of engineering.

Fault location method based on wavelet transform was propose in this paper. In practical application, we can choose different calculation methods of different line lengths. Traveling wave velocity can be directly determined by parameters of line, while the accuracy of arrival time about voltage traveling wave is improved after wavelet transform; when it had malfunction, the traveling wave arrival time can be obtained and the fault branch can be accurately judged. There is no misjudgment so that the ranging error can meet the needs of practical engineering.

Although this algorithm proved to be feasible by the simulation, it exists limitations in practical application. First, the algorithm is only for T-type transmission network, not for the power transmission system to other networks; second, we should transplant the algorithm to DSP microprocessor to verify the practical feasibility.

PenggaoWen,HongSong,ZhitingGuo,QuanPan, (2015) Study on Fault Location in the T-Connection Transmission Lines Based on Wavelet Transform. World Journal of Engineering and Technology,03,106-115. doi: 10.4236/wjet.2015.33012