Expediente Electrónico / SGDE

Two proposed adaptive single-phase reclosing methods, i.e., the angle-based and the phasor- based methods, have different structures, algorithms and logics and therefore, they will have different performance in different situation. However, using all simulated cases, both methods have had a successful operation and the difference is only in operation speed.

In term of structure of the methods, the angle-based method has a simpler structure as uses only the phase angle of the faulted phase while the phasor-based method uses the faulted phase voltage magnitude and derivatives of both magnitude and phase angle of the voltage.

In therms of fault type recognition, the logic of the angle-based method is based on imme- diate/late detection of temporary/permanent faults. In fact, the default fault type is permanent in this method and this is double checked throughout a predetermined time period of length of five power system cycles or 83ms after the first-angle-locked detection, while temporary faults can be detected anytime in that period of time. In fact, the average time needed for detection of a temporary/permanent fault including all simulated cases is 91/139ms for the angle-based

method. Therefore, the angle-based method has a faster fault type detection performance for temporary faults than permanent faults.

However, the phasor-based method has no default fault type and has has to wait until the end of its 100ms time period for the fault type recognition. But, the time period is shorter than the period used for the angle-based method. Therefore, for temporary faults, the angle-based method has had a faster performance while phasor-based method acts faster for permanent fault cases. But, the fault type recognition speed is more important for permanent fault cases than for temporary faults. The reason is that after the permanent fault detection, the next step is three-phase tripping while the recloser is to wait for the arc extinction for temporary faults. Therefore, the phasor-based method has a better performance in fault type recognition.

In terms of reclosing time delay, the angle-based method is able to detect the arc extinction 18 to 114 ms after the arc extinction while it is 32 to 91 ms for the phasor-based method. Therefore, the time delay values are more diverse for the angle-based method than the phasor- based. Considering all temporary fault simulated cases, the angle-based method has a reclosing time delay not longer than 59ms while the phasor-based method can do the same job not later than 80ms after the real arc extinction, in average. Therefore, when the fault is temporary, the phase-angel-based method acts faster at both fault detection and arc extinction detection.

As a comparison of the performances of the methods with the existing adaptive reclos- ing methods, two of the best existing methods were chosen, including one local and one communication-based method, using [62] and [56]. The local method was able to detect the arc extinction 70 to 160ms after the line isolation while the communication-based method was faster and could do the same job in 29 to 67ms. Therefore, the proposed methods, which are local, were faster than the local method, while they were slightly slower the communication- based method, in average. Therefore, the improvement is observed in their performances com- pared to the existing reclosing methods.

4.4

Summary

In this Chapter, two methods for adaptive single-phase reclosing in transmission lines were proposed. The first method, called the angle-based method, uses phase angle of the faulted phase, both to recognize the fault type, i.e., permanent or temporary, and to detect the arc extinction in case the fault is temporary. The second method, the phasor-based method, uses the first derivative of the faulted phase voltage magnitude for fault type recognition, and the first derivatives of both magnitude and angle of the faulted phase voltage, for arc extinction detection.

Both methods had successful performances for transmission lines with various transposi- tion configurations, including ideally-transposed, untransposed and partially-transposed. Com- pensation condition was not also an important factor to affect the performance of the methods. Both methods were evaluated using 550 different simulated cases as well as a real case study, and the results confirmed the capabilities of the methods. Both methods had a successful performances for all of the simulated cases. The angle-based method had a better performance for temporary fault cases while the phasor-based method acted better when the fault type was permanent. In terms of the structures of the methods, the angle-based method has a simpler structure and also, can be considered as the more reliable method as used the data itself and not the derivative of the data. Performances of the proposed methods was also compared with two of the best existing adaptive reclosing methods, one local and one communication-based. Methods had better performances than the local method while they were slightly slower than the existing communication-based method.

Arc Extinction Time Prediction

When single-phase reclosing function is considered, what normally happens for a temporary fault case is to open the faulted phase and reclose the circuit breaker after a delay. The tra- ditional single-phase reclosing uses a predetermined time delay to avoid arc restriking. This time delay must be chosen properly as reclosing the breaker when temporary fault has not been cleared yet can further damage the equipment and put the system stability at risk.

Adaptive single-phase reclosing methods have been proposed in the literature to identify the fault type including temporary and permanent, and then, to recognize if the arc is extin- guished [55]. However, all the proposed adaptive single-phase reclosing methods have to wait for the arc to be extinguished if the fault is temporary. The problem is that, in some cases, the arc extinction speed is too low and it is harmful for the system to serve with one phase open for a long time which leads to issues such as injection of negative sequence component to the system. Therefore, it would be beneficial to predict the arc extinction time for temporary faults well in advance to initiate three-phase tripping signal in case of a slow extinguishing arc. How- ever, prediction of the arc extinction time after breaker interruption has not been investigated in the literature.

In this Chapter, voltage magnitude of the faulted phase after single-phase isolation of the line is used to predict the arc extinction time for temporary faults. For this purpose, there are two methods proposed and the results are compared. The proposed methods are effective for both uncompensated and compensated transmission lines with shunt reactor and are consider- ably insensitive to transposition condition of the line.

5.1

Fundamentals of The Proposed Prediction Methods

To verify the special behaviors of the faulted phase voltage during arc extinction, six simulated temporary fault case studies are used in this Section. In all six simulated cases, a temporary single-phase-to-ground fault incepts at t = 0.2s. At t = 0.27s and t = 0.28s, breakers of Sides A and B isolate the faulted line by performing single-phase opening. Therefore, after t= 0.28s the faulted phase is fully isolated. For performing an easier and more clear comparison, similar to Chapter 4, Vsnand VsnDvariables are employed in this Chapter as well, as defined in (3.8).