KR100637619B1 - Method and apparatus for protecting shunt capacitor banks based on voltage difference - Google Patents

Abstract

High-accuracy faults such as arcs that occur inside capacitor banks can be used to accurately identify faults, and can accurately distinguish between high-resistance faults inside banks and external harmonics such as nonlinear loads. A method and apparatus for protecting a parallel capacitor bank system without fear of malfunction are proposed.

The method of protecting a parallel capacitor bank system of the present invention includes a first capacitor bank and a second capacitor bank, in which one or more unit capacitor banks including a plurality of device capacitors are connected in parallel with each other. A method for protection of a parallel capacitor bank system connected in series with each other, the method comprising: measuring a first voltage across a first capacitor bank and a second voltage applied across a second capacitor bank; Obtaining a differential voltage of the first voltage and the second voltage; Determining whether there is no fault resistance or a low resistance fault inside the capacitor bank system by using the information about the magnitude of the differential voltage; Obtaining a harmonic component of the differential voltage; And using the information about the magnitude of the harmonic component, determining whether or not the high resistance failure is inside the capacitor bank system.

Capacitor Bank, Differential Voltage, Voltage Differential, Harmonics, Relay, Ground, Short, Arc

Description

METHOD AND APPARATUS FOR PROTECTING SHUNT CAPACITOR BANKS BASED ON VOLTAGE DIFFERENCE}

1 shows a configuration of a capacitor bank system of an unfused ground Y connection.

Fig. 2 shows the construction of one preferred embodiment of the parallel capacitor bank system protection device of the present invention.

Figure 3 illustrates one preferred embodiment of the method of protecting a parallel capacitor bank system of the present invention.

4 shows the configuration of a simulation system for verifying the effect of the present invention.

5 shows the waveform of the detected differential voltage in the case of a capacitor element short circuit by the simulation system.

6 shows the waveform of the differential voltage detected in the case of a capacitor element ground fault by the simulation system.

7 shows a model for simulating the case of arc current generation in a simulation system.

8 shows a waveform of arc current generated by the model of FIG. 7.

9 shows waveforms of differential voltages detected when an arc occurs.

10 shows the results of harmonic analysis of the differential voltage detected by the arc generator.

11 shows the results of differential voltage harmonic analysis under nonlinear load conditions.

<Explanation of symbols for the main parts of the drawings>

100: capacitor bank system 10: first capacitor bank

20: second capacitor bank 11, 21, 121: capacitor unit

22, 122: capacitor element 112: first voltage measuring unit

114: second voltage measurement unit 210: series reactor

300: ground terminal 110: overvoltage relay

120: low voltage relay 130: ground overvoltage relay

140: overcurrent relay section 150: differential voltage relay section

200: relay portion 102: transformer

105: breaker 108: current transformer

The present invention relates to a voltage differential protection method of a parallel capacitor bank, and more particularly, to a voltage differential method for accurately determining the internal failure of the parallel capacitor bank so as to prevent the spread of an accident and to perform a quick repair. To provide an improved protection method based on.

Parallel capacitors, one of the power capacitors, have been widely used as a reactive power supply source because of lower equipment cost, lower power loss, and easier operation and maintenance than the synchronous compensators. Power parallel capacitors are used in terms of reducing the voltage drop by improving the power factor of the distribution system, reducing the loss of distribution lines and transformers, increasing the capacity of the load facility, and reducing the electric charge. Parallel capacitors are usually installed at the faucet point, the secondary side of the transformer, or in parallel to the load.

The protection device for such a power capacitor is specified in the electrical equipment technical standards. According to the standard, the 22.9kV class capacitor, which is the subject of this study, must be protected against overcurrent and internal failure, and it is recommended to protect against overvoltage and undervoltage. Power capacitor bank fault protection can be broadly classified as follows. That is, it may be classified into a problem of protecting a bank facility in the event of an abnormality in an external system outside the bank, opening the bank facility against short circuits and ground faults occurring in the bank facility, and protecting the bank against element failures in the bank. have. The purpose of such bank failure protection is to prevent the failures occurring in the system from expanding, to prevent the failure in the bank equipment from spreading to the system and to cause secondary failures, and to minimize the effects of possible failures in the banks.

The system abnormality outside the bank mainly refers to overvoltage and undervoltage problems. To avoid this phenomenon, overvoltage, OVR (overvoltage relay), UVR (low voltage relay), etc. are used on the bus side together with PT (transformer). Low voltage is detected. In addition, short circuits and ground faults inside the facility are mainly detected by using an OCR (overcurrent relay) along with a CT (current flow section) outside the bank.

Protection against unbalance is important for bank internal device failures. The protection algorithm against internal failures depends on how the capacitors are connected and how the banks are configured. The present invention proposes an improved protection algorithm for the grounded wye connection and the unfused, unfused method of the capacitor device, which is one of the methods generally applied in the 22.9kV KEPCO system. do.

1 illustrates a configuration of a capacitor bank system 100 of an unfused ground Y connection. In the illustrated capacitor bank system 100, the A, B and C phases of the system are connected to the first capacitor bank 10 and the second capacitor bank 20, respectively. The first and second capacitor banks 10 and 20 have capacitor units 11 and 21 connected in parallel therewith. In addition, the individual capacitor units 11 and 21 include a plurality of capacitor elements 22 connected between the first terminal 25 and the second terminal 24, as shown, and the first terminal 25. And an internal discharge device 23 are usually provided between the second terminal 24 and the second terminal 24.

Unlike in the case of a fused method in which fuses are connected in series with each or several capacitor units 11 and 21 or fuses are connected in series with each capacitor element 22, the components shown in FIG. As described above, the unfused capacitor bank system 100 has an advantage of simple configuration and low installation cost. However, since the fuse is not used as a protection means, more accurate accident detection becomes important.

Conventional protection algorithms for such wiring and banking schemes include methods using current flowing from neutral to ground, methods using differential voltages in two regions divided by one bank, and bus voltages and bank phase currents. There is a method using the impedance of each bank through the method, and in the case of KEPCO system, the voltage difference method (Voltage Difference Method) is generally applied.

The method using the magnitude of the differential voltage is a differential between the first voltage V1, which is the voltage across the first capacitor bank 10, and the second voltage V2, which is the voltage across the second capacitor bank 20, shown in FIG. The method of determining an accident in the capacitor bank system 100 based on the magnitude of the voltage is obtained. The method using the magnitude of the differential voltage has an advantage that the sensitivity is doubled because twice the abnormal voltage is brought into the input voltage of the relay in case of failure.

Therefore, the voltage differential protection method using the magnitude of the differential voltage accurately detects a low resistance failure such as an internal capacitor element short circuit or ground fault, but in the case of an arc failure, which is a high resistance failure, the differential voltage is very small, making it difficult to determine the failure. There is a problem.

The present invention is to solve the above problems, and to provide a method and apparatus for protecting a parallel capacitor bank system capable of accurately determining an accident even in the case of a high resistance failure such as an arc.

In another aspect, the present invention is to provide a method and apparatus for protecting a parallel capacitor bank system that can accurately distinguish the case of high resistance failure such as arc and the occurrence of external harmonics such as nonlinear load.

In order to achieve the above object, a method of protecting a parallel capacitor bank system according to a first aspect of the present invention includes: a first capacitor bank and a second capacitor bank, in which one or more unit capacitor banks including a plurality of device capacitors are connected in parallel with each other. And a method for protecting a parallel capacitor bank system in which the first capacitor bank and the second capacitor bank are connected in series with each other, the first voltage being applied across the first capacitor bank and across the second capacitor bank. 2 measuring the voltage; Obtaining a differential voltage between the first voltage and the second voltage; Using the information about the magnitude of the differential voltage, determining whether a low resistance fault is inside the capacitor bank system; Obtaining a harmonic component of the differential voltage; And determining whether or not a high resistance failure occurs in the capacitor bank system by using the information about the magnitude of the harmonic component.

Here, the capacitor bank system is preferably a capacitor bank system of the grounding Y connection method.

In addition, the capacitor bank system is preferably an unfused capacitor bank system of a grounding Y connection method.

Here, the high resistance failure is often an arc generation inside the capacitor bank system, and it is preferable to use a third harmonic as the harmonic.

In the determining of whether the low resistance failure occurs, it is preferable that the effective value of the fundamental wave of the differential voltage is determined to be equal to or greater than a first predetermined reference value.

In the determining of whether the high resistance failure occurs, it is preferable that the ratio of the harmonic effective value to the effective value of the fundamental wave of the differential voltage is equal to or greater than a second predetermined reference value.

A recording medium according to a second aspect of the present invention is a recording medium which records a computer executable program for performing the above steps.

In addition, the protection device of a parallel capacitor bank system according to a third aspect of the present invention includes a first capacitor bank and a second capacitor bank in which one or more unit capacitor banks including a plurality of device capacitors are connected in parallel with each other. A system for protecting a parallel capacitor bank system in which a capacitor bank and a second capacitor bank are connected in series with each other, the measuring unit measuring a first voltage across the first capacitor bank and a second voltage applied across the second capacitor bank. ; Obtaining a differential voltage between the first voltage and the second voltage, and determining whether a low resistance failure occurs in the capacitor bank system by using information about the magnitude of the differential voltage, and a harmonic component of the differential voltage. A failure determination unit for determining a high resistance failure in the capacitor bank system by using information on the magnitude of the harmonic component; And a relay unit which receives a signal of the failure determination unit and disconnects the capacitor bank system from a system when the high resistance failure or the low resistance failure occurs.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 2 shows the construction of one preferred embodiment of the parallel capacitor bank system protection device of the present invention. The parallel capacitor bank system protection device of the illustrated embodiment is largely divided into a portion for protecting the bank itself and a portion for grid protection.

Bank self-protection refers to detecting faults in a bank and protecting them. In addition, the system protection is to protect the system from the abnormal phenomenon generated from the bank, and to protect the bank from the abnormal phenomenon generated from the system in reverse, and refers to protection for blocking the ripple effect of bank switching or external failure of the bank.

Bank self-protection elements include overvoltage, overcurrent, unbalance, and reversed phase elements. Grid protection elements include overvoltage, undervoltage, overcurrent, harmonics, and transmission blocking. In the case of grid protection elements, the same applies for other protection objects such as transformers. The embodiment of FIG. 2 shows a protective device in consideration of these protective relay elements.

The overvoltage and undervoltage phenomena generated in the system affect the capacitor bank system. In order not to enlarge the voltage, the overvoltage relay unit 110, the low voltage relay unit 120, and the ground fault are performed through the bus transformers PT and 102. An overvoltage relay 130 or the like is used to detect whether the phenomenon occurs.

The long-term voltage allowed in the capacitor is generally about 110% of the rated voltage, and the overvoltage relay 110 is used to protect the capacitor bank system 100 against such an abnormal voltage.

On the other hand, if the circuit is a low voltage or no voltage, if the capacitor is put into operation when the voltage recovery by the capacitor is a factor that damages other equipment due to the voltage rise by the capacitor. In order to prevent this phenomenon, a low voltage relay 120 is usually used. In addition, the ground fault overvoltage relay 130 is used for protection against ground fault overvoltage operation.

In order to discriminate between short circuit accidents and bus ground faults outside the bank, an overcurrent relay 140 for detecting an overcurrent through the bus side current transformer 108 is used.

As described above, the capacitor bank system 100 of the 22.9 kV class or the like is composed of a plurality of internal capacitor elements, and the internal accidents such as insulation breakdown of the elements, intermittent short circuits of the discharge coils, and wiring shorts are problematic. Therefore, the determination of the accident inside the bank system 100 divides the capacitor units inside the bank system 100 into the first capacitor bank 10 and the second capacitor bank 20 as shown in FIG. Voltage differential method (VRy) is used. Such a voltage differential method has an advantage that there is no influence on harmonics, system unbalance inrush current, etc., but it has a disadvantage in that it is difficult to discriminate when a high resistance failure occurs such as arcing at the inlet end.

The function of each relay unit and the operation of the protective relay device according to the failure situation are reviewed and summarized in the table as follows.

Relay Usage Correction standard Settling time Remarks VRy In-bank element fault detection 50% of voltage seen when shorting one device Minimum possible Fault detection OCR Line short and ground fault detection * Instant: 50% short circuit current * Time: 50% rated current Instantaneous minimum possible Fault detection UVR Low voltage operation prevention 70% of rated voltage 2 sec at 70% corrected value OVR Overvoltage Operation Prevention 130% of rated voltage 2 sec at 150% corrected value OVGR Ground fault overvoltage operation prevention 15 V Time lever 10 Ungrounded

In particular, in the case of a high resistance failure such as an arc frequently occurring at position ① (inlet end) in FIG. In fact, such high resistance accidents occur frequently, which makes bank operation difficult.

In order to solve this problem, the parallel capacitor bank system protection device according to the present invention includes a first voltage V1 across the first capacitor bank 10, which is obtained through the measuring units 112 and 114 including a transformer and the like. ) And the differential voltage of the first voltage V1 and the second voltage V2 in the failure determination unit 150 using the second voltage V2 applied across the second capacitor bank 20. Obtain

In addition, the failure determination unit 150 determines whether or not a low resistance failure inside the capacitor bank system 100 by using information about the magnitude of the differential voltage. At the same time, the failure determination unit 150 analyzes the harmonic components of the differential voltage and determines whether or not the high resistance failure is inside the capacitor bank system by using the information on the magnitude of the harmonic components.

If it is determined that the low resistance failure or high resistance failure, the blocking unit 105 receives the signal of the failure determination unit 150, and cuts the capacitor bank system 100 from the system.

Hereinafter, a preferred embodiment of the method of protecting a parallel capacitor system of the present invention will be described with reference to FIGS. 2 and 3. In the protection method of the embodiment, first, the first voltage V1 across the first capacitor bank 10 and the second voltage V2 applied across the second capacitor bank 20 at each time point are sampled (S10). . The differential voltage of the first voltage V1 and the second voltage V2 is obtained (S20), and information on the magnitude of the obtained differential voltage is used to determine whether or not a low resistance fault is inside the capacitor bank system. Determine (S30).

In addition, in order to determine whether or not a high resistance failure, the harmonic component of the differential voltage is extracted (S40). Next, using the extracted information on the magnitude of the harmonic component, it is determined whether or not a high resistance failure in the capacitor bank system (S50).

The information on the magnitude of the differential voltage used to determine whether or not the low resistance is faulty can be used as the effective value of the differential voltage. As a criterion for determining whether or not a low resistance failure occurs, for example, the effective value of the differential voltage which appears when one capacitor element in the capacitor unit 21 as shown in FIG. 1 is shorted may be used as a reference. In the case where the ratio of the measured differential voltage to the differential voltage rms in this case exceeds a predetermined level (for example, the rms value of the measured differential voltage exceeds 50% of the differential voltage rms at one short circuit), It can be judged as a low resistance failure.

In addition, in order to determine whether or not a high resistance failure is made using harmonic components of the differential voltage, a method of determining whether the effective value of the harmonic components exceeds a predetermined reference value can be used. A constant value may be used as the reference value.However, the magnitude of the effective value of the harmonic component is compared with the effective value of the fundamental component (e.g., when the ratio of the third harmonic to the fundamental is 5% or more). It is desirable for accurate failure detection.

Harmonics due to external accidents may be introduced into the capacitor bank system 100 instead of harmonics caused by failures such as arcs generated in the capacitor bank system 100. Such a situation may occur when a nonlinear load is present outside. Can be. However, since the method proposed in the present invention is to obtain harmonic components of the differential voltage, the harmonics drawn from the outside are the first voltage V1 of the first capacitor bank 10 and the second voltage of the second capacitor bank 20. It is canceled in the process of finding the difference of (V2), and it does not affect a detection result.

Hereinafter, application test results of the method and apparatus for protecting a capacitor bank system according to the present invention will be described with reference to FIGS. 4 to 11.

4 shows the configuration of a simulation system for verifying the effect of the present invention. The simulation system was constructed in a similar form to the 22.9kV distribution system. The capacitor bank system 100 connected to the grid is composed of the first capacitor bank 10 and the second capacitor bank 20, and a series resistor 310 is disposed in order to determine a ground fault near the ground terminal.

In order to determine an accident determination reference value (first reference value) at the time of a low resistance accident, the case of a short circuit of one capacitor element 112 in the capacitor unit 111 of FIG. 4 was simulated. 5 shows the waveform of the differential voltage generated in this case. The waveform shown is a pure waveform, the effective value is about 92 [V], and 46 [V], which is half of this voltage value, is set as the first reference value in accordance with the above-mentioned reference.

In FIG. 7, the instantaneous value of the differential voltage obtained by simulating the case where the capacitor element of a is grounded through a case in the same system as in FIG. 4 is shown. At this time, the failure resistance was 10 [ohm]. As shown in FIG. 7, the obtained differential voltage is 1.276 [kV], which is significantly larger than the first reference value of 46 [V], resulting in a low resistance failure including a complete ground failure without failure resistance as well as some failure resistance. Even in the case of, it is verified that the fault detection is performed correctly.

7 shows a model of an equivalent circuit used to simulate high resistance failures such as arcing. The arc current generated at this time is shown in FIG. 8. Arcs often occur at bushings near the inlet in the capacitor bank.

When such an arc failure occurs, the odd current is included in the load current, and the present invention uses the results of harmonic analysis for arc detection based on the observation of such a phenomenon. 9 shows waveforms of the differential voltages obtained when the arc generation is simulated. The differential voltage initially contains a small amount of DC components, but is smaller than the first reference value defined above with an effective value of 17.8 [V]. That is, the detection using the method of using only the magnitude of the differential voltage of the prior art becomes difficult.

Therefore, by applying the method of the present invention, harmonic analysis was performed, Figure 10 shows the results of harmonic analysis. In FIG. 10, fundamental waves, third harmonics, five harmonics, seventh harmonics, nineth harmonics, eleven harmonics, and the like are shown. The ratios of the effective values are obtained as shown in the following table.

frequency A fundamental wave 3 harmonics 5 harmonics 7th harmonic 9th harmonic 11th harmonic Content compared to fundamental wave 100% 6.22% 1.608% 0.469% 0.109% 0.09%

As shown in the table above, if the ratio of the third harmonic to the fundamental is 6.22%, the third harmonic is used for detection, and if the second reference value is set to 5% lower than the above ratio, the arc high resistance failure is also affected. Accurate determination is possible.

In addition, by applying the method of the present invention, when the harmonic content of the differential voltage is used as a failure detection element, it was verified whether the harmonics generated from the nonlinear load affect the differential voltage and malfunction. Nonlinear loads were simulated by adding a 6-pulse diode bridge circuit in parallel to the load model in FIG. As a result of the simulation, as shown in FIG. 11, harmonics generated by the load are introduced into the first voltage Va1 and the second voltage Va2, respectively, but the first voltage Va1 and the second voltage are respectively checked. Since Va2 is about the same voltage, the differential voltage does not contain harmonics as shown in FIG. Therefore, since the harmonics generated in the nonlinear load do not affect the harmonic detection element of the differential voltage, it can be seen that the protection method proposed by the present invention is effective even in the presence of the nonlinear load.

The method and apparatus for protecting a parallel capacitor bank system according to the present invention can be modified and applied in various forms within the scope of the technical idea of the present invention, and are not limited to the above preferred embodiment. In addition, the embodiments and drawings are only for the purpose of describing the contents of the invention in detail, and are not intended to limit the scope of the technical idea of the invention, the present invention described above is common in the technical field to which the present invention belongs From the perspective of the person skilled in the art, various substitutions, modifications and changes are possible within the scope without departing from the spirit of the present invention is not limited to the embodiment and the accompanying drawings, of course, not only the claims described below Judgment, including claims and equivalents, shall be determined.

According to the present invention, there is provided a method and apparatus for protecting a parallel capacitor bank system capable of accurately determining an accident even in a high resistance failure such as an arc inside a capacitor bank.

In addition, according to the present invention, it is possible to accurately distinguish between the case of high resistance failure such as an arc generated inside the capacitor bank and the occurrence of external harmonics such as nonlinear load, so that there is no risk of malfunction. Implementation is possible.

Claims (9)

At least one unit capacitor bank including a plurality of device capacitors includes a first capacitor bank and a second capacitor bank connected in parallel to each other, and the first capacitor bank and the second capacitor bank are connected to each other in series to protect the parallel capacitor bank system. In the method for Measuring a first voltage across the first capacitor bank and a second voltage applied across the second capacitor bank; Obtaining a differential voltage between the first voltage and the second voltage; Using the information about the magnitude of the differential voltage, determining whether a low resistance fault is inside the capacitor bank system; Obtaining a harmonic component of the differential voltage; And And determining whether a high resistance failure occurs in the capacitor bank system by using the information about the magnitude of the harmonic component. The method of claim 1, The capacitor bank system is a protection method of a parallel capacitor bank system, characterized in that the capacitor bank system of the grounding Y connection method. The method of claim 1, The capacitor bank system is a protection method of a parallel capacitor bank system, characterized in that the unfused (unfused) capacitor bank system of the ground Y connection method. The method of claim 1, And said harmonics are third harmonics. The method of claim 1, And wherein said high resistance fault is an arc generation inside said capacitor bank system. The method of claim 1, The determining of the low resistance failure may include determining whether the effective value of the fundamental wave of the differential voltage is equal to or greater than a first predetermined reference value. The method of claim 1, The determining of the high resistance failure may include determining whether the ratio of the harmonic effective value to the effective value of the fundamental wave of the differential voltage is equal to or greater than a second predetermined reference value. A recording medium having recorded thereon a computer executable program for performing the steps of any one of claims 1 to 7. At least one unit capacitor bank including a plurality of device capacitors includes a first capacitor bank and a second capacitor bank connected in parallel to each other, and the first capacitor bank and the second capacitor bank are connected to each other in series to protect the parallel capacitor bank system. In the system for A measuring unit measuring a first voltage across the first capacitor bank and a second voltage applied across the second capacitor bank; Obtaining a differential voltage between the first voltage and the second voltage, and determining whether a low resistance failure occurs in the capacitor bank system by using information about the magnitude of the differential voltage, and a harmonic component of the differential voltage. A failure determination unit for determining a high resistance failure in the capacitor bank system by using information on the magnitude of the harmonic component; And And a breaker configured to receive a signal of the failure determination unit and disconnect the capacitor bank system from a system in the event of the high resistance failure or the low resistance failure.

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