WO2017045044A1

WO2017045044A1 - Adaptive control method for three-phase reclosure of compensated lines with inner faults

Info

Publication number: WO2017045044A1
Application number: PCT/BR2016/000093
Authority: WO
Inventors: Maria Cristina Dias Tavares; Patricia Mestas Valero
Original assignee: Universidade Estadual De Campinas - Unicamp
Priority date: 2015-09-17
Filing date: 2016-09-15
Publication date: 2017-03-23
Also published as: BR102015023940A2; BR102015023940B1

Abstract

The present invention relates to a method for identifying the fault clearance instant and the subsequent optimum instant for three-phase reclosure of a transmission line with shunt reactor compensation after an inner, single-phase fault condition. The optimum reclosure instant corresponds to the region of minimum beat frequency of the voltage between the contacts of the circuit-breaker after fault clearance. In this condition, reclosure reduces reclosure overvoltages and shortens the line out-of-service time if the optimum reclosure instant is shorter than the preset dead time. In addition, the present method increases the reliability of the three-phase reclosure operation in that it prevents reclosure while the fault is still present.

Description

"ADAPTIVE CONTROL METHOD FOR TRIPTOTE RELIGATION OF COMPENSED NAILS SUBMITTED TO INTERNAL FAULTS"

FIELD OF INVENTION

[1] The present invention relates to a method capable of identifying the fault extinction instant and the subsequent optimum instant for three-pole reclosure of a shunt reactive compensated transmission line after a single-phase fault condition, reducing overvoltages and increasing the safety and reliability of the maneuver.

[2} The method is applicable in the area of electric power, with a focus on power transmission systems and especially in the occurrence of faults and three-pole reclosing operations on extra long and ultra high voltage transmission lines. Applies to overhead, underground or mixed transmission lines, all with shunt reactive compensation.

BACKGROUND OF THE INVENTION AND TECHNICAL STATE

[3] Traditionally two distinct modes of automatic reclosing of the extra and ultra-voltage alternating current-fed transmission lines are used: monopolar reclosing and three-pole reclosing. In the monopolar reclosing scheme, the elimination of single phase defects is achieved by opening only the missing phase (monopolar opening). To conclude the maneuver, after the fixed dead time has elapsed, only the phase that was effectively switched off is reclosed. During the period of monopolar maneuver, the healthy phases of the circuit remain in service without the total interruption of the power flow in the line. In the three-pole reclosing scheme, the defect elimination in one or more phases occurs as a function of the opening of the three phases of the transmission line (three-pole opening). After a predetermined fixed dead time elapses, the maneuver is completed by energizing the three lead terminal phases and subsequent closing of the follower terminal.

[4] Alternating current, high and extra high voltage transmission lines, specifically long lines, generate large amounts of capacitive reactive power when operating under no load or light load conditions. This energy The reactive system must be controlled, as it can cause large permanent overvoltages at the terminals of equipment connected to the power system. Bypass reactors compensate capacitive reactive power and reduce overvoltages during light and no load conditions.

(5] When the line is compensated with bypass reactors, the degree of compensation has an important effect on the voltage waveform between the circuit breaker contacts due to the circuit formed between the line transverse capacitance and the inductance of the bypass reactors. , the voltage between the breaker contacts takes on an oscillatory (beat) form by composing the system fundamental frequency on one side of the breaker contact with the natural line frequency and compensating equipment on the other side of the breaker contact.

[6] Three-line relay of transmission lines occurs as a function of system conditions, which can be in two ways: when the breaker contacts open without a fault in the line, ie due to an external fault, or an operation due to a faultless opening, and when opening occurs after a transmission line fault.

[7] Faultless three-pole opening or external fault conditions are common when high switching overvoltage values can be mistakenly interpreted as missing by some protective relay, resulting in line output. Another example occurs in the case of dual loop transmission lines when the switching transients of one line may engage the other line, which may also lead to incorrect operation of the guard. This condition may also be due to a load shedding followed by the line shutdown or during recomposition of the electrical system after a large area shutdown. Although modern protective devices are designed to handle these situations, failures often occur and controlled switching allows for higher system quality and reliability, resulting in increased transmission line availability. In cases of three-pole tripping without internal defect, the voltage between the breaker contacts has a definite beat and the waveform is similar for all three phases, with the same period and no phase lag. [8} Depending on these conditions and taking into account the dead time for actuation of the protection, the optimal region of the voltage waves between the breaker poles to restart the breaker corresponds to the first smaller amplitude ranges of the voltage beat. This problem has been addressed in the prior art, as can be evidenced by US8680713B2, indicated for reclosing lines after single opening due to external defects. The same topic falls within US4724391, US7616419B2 and US7723872B2 which determine the reclosing instant based on zero crossing and the voltage gradient of the source side.

[9] In particular, document BR200804330A2 refers to a method that identifies the optimal region for three-pole reclosing of shunt compensated transmission lines without internal fault. Identification is based on the waveform between the breaker contacts. The method allows to control the transient overvoltages and adjust the reclosing dead time.

[10] In the second condition of reclosure, after an internal fault in the transmission line, the voltage waveform between the breaker contacts has an irregular appearance, and the same strategy of reclosure without fault does not fit.

[11} After an internal fault occurs on the transmission line, the protection will proceed to the three-pole opening, ie the three phases of the line, isolating the missing section. As the vast majority of faults that reach the transmission lines are not permanent, after a predefined time the protection will restart the open line stretch to ensure the continuity of the power supply. If the line is rewired before the line has been extinguished and the breaker contacts close when the voltage between their contacts is at maximum beat, the transient overvoltage will be increased.

112] When line opening occurs due to a single-phase ground fault on the transmission line, the sequence of events for three-pole reclosure includes the occurrence of the fault, line opening in the three phases to isolate the missing section, timeout. for extinction of the lack and finally rewiring the transmission line. In this case the missing phase influences the signal from the other two healthy phases, so the signals obtained are very complex and the expected beat is distorted, being impossible to apply the method developed for reclosing without fail.

[13] US8462474B2 refers to a system for fast reclosing of transmission lines based on the use of protective relays with reclosing function located at both terminals of the transmission line. The relays are configured to send the breaker close command when the missing phase satisfies the previously established reclosing condition. The method described by US8744637 detects fault extinction by analyzing the missing phase transient signature. With the same effect, US 2012/0176712 Al detects arc extinction based on the harmonic component contained in the missing phase voltage wave. In turn, US 2008/0030912 Al detects the fault extinction time by comparing the induced amplitude and stress angles in the open phases with predetermined adjustments. The documents mentioned show the ability to identify the moment when the fault is extinguished, but not the ability to determine the optimal moment to cool off.

[14] It should be noted, therefore, that there is no evidence in the state of the art of documents dealing with the problem of determining the optimum reclosing time after a fault has elapsed, at the very least of the voltage beating between the breaker contacts, proving the importance of the present invention.

BRIEF DESCRIPTION OF THE INVENTION

[15J The present method refers to optimizing three-pole reclosing on transmission lines by performing the maneuver after the single-phase fault within the line has been eliminated. Additionally, the method issues the command to restart at the optimum time, thereby reducing the amplitude of the overvoltages resulting from the maneuver. Additionally the present method increases the reliability of the three-pole reclosing maneuver by preventing reclosing under fault.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 - Diagram showing the electrical system configuration, including the general steps for identifying the optimum reclosing instant. Figure 2 - Flow diagram of the procedure before and after verification of fault extinction.

Figure 3 - Line side voltage of the fault phase showing the fault extinction moment.

Figure 4 - Block diagram showing the steps for reclosing at the optimal time.

Figure 5 - Voltage waveform between breaker contacts or reference signal.

Figure 6 - Effective value waveform of the reference signal.

Figure 7 ~ Waveform after filtering the effective value of the reference signal.

Figure 8 - Identification of the growth and decay moments of the filtered reference signal after the circuit breaker opening.

Figure 9 - Reference signal free from inconvenient incomplete cycles.

Figure 10 - Identification of growing cycles;

Figure 11 - Identification of the first half cycle

Figure 12 - Graph showing the duration time of the first semi-circle

DETAILED DESCRIPTION FOR THE INVENTION

[16] The present method concerns the optimization of three-pole reclosing on transmission lines by performing the three-pole reclosing maneuver after the internal single-phase fault in the line has been eliminated. Additionally, the method issues the command to reconnect the phases at the optimum time, thereby reducing the amplitude of the overvoltages due to the maneuver.

[17] The method comprises the following steps:

A. Identification of single-phase fault extinction by identifying the start of the beat on the phase-to-ground voltage waveform of the faulted phase; B. Obtain the voltage waveform between the breaker contacts considered as the reference signal as a result of the difference between the source side voltage and the line side voltage;

C. Obtain the effective value of the reference signal by digital processing;

D. Treat the effective value of the reference signal by digital filtering;

E. Identify the growth and decay times of the filtered signal after the circuit breaker opens;

F. Obtain a free signal from inconvenient incomplete cycles;

G. Apply a function that allows only the growing cycles to be considered;

H. Identify the first half-cycle after fault extinction and calculate the duration of the first half-cycle of the filtered signal;

I. Duplicate the value of the half cycle and obtain the duration of the full beat period; and, j. Set the reclosing time to a high value and order the replacement of the predetermined reclosing time by the period from the defect extinction time to the end of the first beat.

[18] To illustrate the invention, an equivalent of the electrical system is shown in Figure 1, which comprises an ideal three-phase source 11, single-phase circuit breakers 12A, 12B, 12C respectively installed for each transmission line phase 13A, 13B, 13C respectively. 13, and compensation reactor 14. The voltage of the source path is constantly monitored and reduced to convenient values by Potential Transformers (TPs) 15A, 15B> 15C. Similarly, line side voltage is reduced by TPs 16A, 16B, 16C The identification of the optimum instant for reclosing each phase is summarized in section 100, which includes steps 17, 18 and 19,

[19] The proposed method first identifies the instant of fault extinction in the affected phase. Figure 2 shows the process flow diagram. When a single-phase fault occurs (21), the faulted phase is monitored by line path voltage (VLF). (22). This signal in turn is compared with a predetermined signal (23). The extinction of the fault is verified (24). If the fault is not extinguished within the set dead time, the automatic reclosing block (25) proceeds. If the fault is extinguished, the optimum reclosing time is determined (100).

[20] Fault extinction is verified by the appearance of the beat on the phase-to-ground voltage waveform of the faulted phase line, as can be seen in Figure 3, Shortly after a predetermined time of fault occurrence in one of the phases (31), the three phases open simultaneously to isolate the defect (32). The moment in which the voltage waveform of the faulty phase appears appears corresponds to the moment of fault extinction (33). This instant is the same for all three phases.

[21] The algorithm for determining the optimum reclosing moment is detailed by the diagram of the bios shown in Figure 4. Note that as the voltage between the breaker contacts has different and lagged beats for the three phases, the algorithm developed should be applied to each phase independently.

[22] From the diagram in Figure 4 the explanations of the following steps are made:

A. Obtain the voltage waveform between the circuit breaker contacts considered the reference signal as a result of the difference between the source-side voltage and the line-side voltage of the healthy phases. This waveform appears after automatic tripping that occurs after a predetermined period of fault occurrence identification. (Figure 5)

B. By digital processing obtain the effective value of the reference signal. (Figure 6)

C. Treat the effective value of the reference signal by digital filtering. (Figure 7)

D. Next identify the times of growth and decay of the filtered signal after the breaker opens. (Figure 8)

E. Get a signal free of inconvenient incomplete cycles. The instant the fault is extinguished is random and can correspond to any point in the voltage wave between the breaker contacts. Due to this fact may appear eidos with short periods that prevents starting a logic based on the periods of increase and decay. (Figure 9)

F. Apply a function that allows you to consider only growing cycles. The resulting cycles may be growing or decaying. When the first cycle is growing _> indicates that the beat is beginning, and when the first cycle is decaying, it indicates that the beginning of the cycle corresponds to the maximum of the beat. (Figure 10)

G. identify the first half-cycle after the fault has been extinguished (Figure 11). With this result the duration of the first half-cycle of the filtered signal can be calculated after the fault has been extinguished. (Figure 12).

H. Next, the value of this half cycle is doubled to obtain the duration of the complete beat period. The end of the first beat corresponds to the optimal time for reclosing.

I. Immediately after opening the breaker contacts, the reclosing time should be set to a high value, such as 5 s. The instant the fault duration identification logic signal is completed, an order is provided for the reclosing time to be replaced for the period from the breaker opening to the end of the first beat. This value must be obtained for each healthy phase and repeated for the missing phase.

[23] Thus, applying the proposed method in the reclosing maneuver achieves:

- Detection of the fault extinction instant aiming to ensure that the reclosing maneuver does not occur under defect and is successful.

- Determination of the optimum instant for reclosing after the fault has been cleared, reducing the transient overvoltages resulting from the maneuver.

- Reduction of dead time if the reclosing time at the optimum time is less than the predetermined dead time. - Have a time frame to operate the breaker as the minimum region detection occurs with several fundamental frequency cycles in advance,

- Automatic reclosing lock if fault does not go out within the set dead time, which indicates the occurrence of a very long transient fault or a permanent fault.

- The optimal reclosing method should be applied to each phase independently.

[24] Figures 4 to 12 are the result of PSCAD simulations that prove the method works.

{25} The waveform analysis process for determining whether the fault has gone is shown in figure 2. The process for determining the optimal moment is shown in figures 4-12.

[26] The decision to reclose occurs after the gap is extinguished (Figure 3) and from that moment at the minimum of the beat _* This can occur before the normally predetermined dead time. The invention described herein is not limited to this embodiment and those skilled in the art will appreciate that any particular feature introduced therein should be understood solely as something that has been described for ease of understanding and cannot be realized without departing from the concept. inventive described. The limiting features of the object of the present invention are related to the claims that are part of this report.

Claims

1. Method for the reduction of transient overvoltages during three-pole reclosure following single-phase faults characterized by the following steps:

A. Identification of single-phase fault extinction by identifying the start of the beat on the phase-to-ground voltage waveform of the faulted phase line;

B. Obtaining the voltage waveform between the phase-breaker contacts is considered the reference signal as a result of the difference between the source-side voltage and the line-side voltage;

C Obtain the effective value of the reference signal by digital processing;

0. Treat the effective value of the reference signal by digital filtering;

F. Get a signal free of inconvenient incomplete cycles;

6. Apply a function that allows you to consider only growing cycles;

H. Identify the first half cycle after the taper has extinguished and calculate the duration of the first half cycle of the filtered signal;

1. Duplicate the value of the semi-cell and obtain the duration of the full beating period; and,

J, Set the reclosing time to a high value and order the reclosing time to be replaced by the period from the breaker opening to the end of the first beat for each healthy phase;

K. Repeat this value for the reclosing of the missing phase.

Method according to claim 1, characterized in that the waveform of the stress bias of the potential difference between circuit breaker terminals and from this signal the first half cycle of the beat will be determined to calculate the optimum reclosing time for each phase.