Capacitor Switching Transients Research Articles

On-Line Cable Condition Monitoring Using Natural Power Disturbances

On-line cable insulation condition monitoring can significantly reduce the outages caused by insulation failure. This paper proposes a new method to achieve this by utilizing the natural power disturbances originating from outside of the cable, such as capacitor switching and fault transients. In this method, the relative permittivity of the cable insulation is used as the indicator to be monitored, which is closely associated with cable tanδ. The relative permittivity is extracted from the power disturbances and their responses, which are of sufficient strength and a wide range of frequencies. This method is beneficial to the on-line monitoring for it does not need the accurate remote synchronized phase angle information. Case studies and sensitivity studies demonstrate the good performance of the proposed method.

Cat Swarm Optimization to Shunt Capacitor Allocation in Algerian Radial Distribution Power System

This paper presents a Cat Swarm Optimization (CSO) Algorithm optimization method to shunt capacitor placement on distribution systems under capacitor switching constraints. The optimum capacitor allocation solution is found for the system of feeders fed through their transformer and not for any individual feeder. The main advantages due to capacitor installation, such as capacity release and reduction of overall power and energy losses are considered. The capacitor allocation constraints due to capacitor-switching transients are taken into account. These constraints are extremely important if pole-mounted capacitors are used together with station capacitor bank. Cat Swarm search algorithm is used as an optimization tool. An illustrative example for Algerian example is presented.

Power Factor Correction for ABO-TRABA Desalination Plant Case Study

Power factor is a way of measuring the percentage of reactive power in an electrical system. Reactive power represents the wasted energy electricity. Reactive power is used by inductive load (such as, motors, transformers, fluorescent light, arc welders and induction furnaces) to sustain their magnetic fields. Electric systems with many motors exhibit low power factors, increasedconductorandtransformerlosses,andlowervoltages.Utilities must supply both active and reactive power to compensate these losses. However, the influence of voltage and current harmonics on equipment connected to electrical system can cause serious problems in power factor correction; it can be improved by adding shunt capacitors. Capacitors act in opposition to inductive loads,therebyminimizingthereactivepowerrequiredtoservethem.Unfortunately,powerfactorcorrectioncapacitorsmayproduceharmonicresonance and magnify utility capacitor-switching transients. Therefore, it is often desirable to implement one or more capacitor banks in a facility as a harmonic filter [1].
 The main objective of this paper is to raise the power factor for ABO TRABA desalination plant to the economic and optimum value. The scope of the paper includes studying the phenomena's that can cause significant damage and distortion to a given power system such as harmonics and resonance.
 The study includes billing data monthly collected, which is a plant survey. From the study, some calculations have been done such as power factor penalty savings, Loss savings, payback period, losses reductions and increase system capacity.

Detection of high impedance faults using current transformers for sensing and identification based on features extracted using wavelet transform

High impedance fault (HIF) has long been a challenging problem in network protection due to its random behaviour and low magnitude. The conventional protection devices cannot be utilised since the HIF does not draw enough current to cause tripping. The feature of wavelet transform (WT) which decomposes a signal into different frequency bands and locations in time can be utilised to extract HIF features and detect its occurrence. In the study, HIF arcing currents associated with different types of contact surface are produced by experiments set up in the laboratory. Features of the fault currents are extracted and a new detection criterion is developed based on WT coefficients. Transformer magnetising inrush currents and capacitor switching transients are also produced by experiment and simulation, respectively, to represent transient disturbances commonly occurred in the distribution network. The detection criterion is used to discriminate the HIF from other normal non-fault transient events. Three different types of wavelet are tested and the Daubechies wavelet Db4 gives the best performance based on its detection and discrimination rates. The efficacy of utilising existing conventional current transformers for HIF application is also tested and verified by experiment.

Three‐phase resistive capacitor switching transient limiter for mitigating power capacitor switching transients

This study presents a new resistive capacitor switching transient limiter (RCSTL) for mitigating power capacitor switching transients. The RCSTL is composed of three limiting resistors, a three-phase full bridge diode rectifier, a thyristor and a three-phase coupling transformer. The limiting resistors are connected in series with the capacitor bank and the thyristor is installed at the DC side of the diode rectifier. During the capacitor bank energising, the thyristor remains off and hence, the secondary side of the coupling transformer acts as open circuit. Consequently, high impedance including the transformer's magnetic reactance in parallel with the limiting resistors is inserted in series with the capacitor bank. Under such circumstance, the limiting resistors restrain the capacitor switching transients. In the steady-state, the control system triggers the thyristor and the coupling transformer acts as short circuit. As a result, the limiting resistors are bypassed by the coupling transformer and thus, the RCSTL has no significant effect on the circuit. Analytical analysis is performed to describe different operation modes of the proposed RCSTL. A single stage of a three-phase wye-connected capacitor bank with 25 kVAR is energised and the performance of the proposed limiter is investigated. Both the simulation and experimental results confirm the effectiveness of the RCSTL.

Single-DC Reactor-Type Transient Limiter for Reducing Three-Phase Power Capacitor Switching Transients

This paper presents a new application of the single-dc reactor-type fault current limiter to suppress the three-phase low-voltage capacitor switching transients. The proposed limiter is composed of a three-phase coupling transformer, a three-phase bridge rectifier, a dc reactor, and a dc-bias voltage source. The dc reactor is connected in the three-phase coupling transformer's secondary winding and can automatically provide high impedance at the instant of energization, thus restraining the energizing transients of the three-phase capacitor. In the steady state, the bias voltage causes all rectifier diodes to conduct simultaneously, and the limiter freewheels. Therefore, the voltage across the coupling transformer's secondary side is nearly zero, and the transformer's primary side acts as a short circuit. The limiter will not result in a voltage rise at the capacitor's terminals or a distortion of the capacitor's current waveform in the steady state. Due to the freewheeling effect in the limiter, no transient overvoltage appears across the switching device at the instant of de-energization. Analytical equations to describe the performance of the system have been developed. Finally, a 2.7-kVAR three-phase capacitor is used for demonstration, and simulation and experimental results are carried out to verify the feasibility of the proposed limiter.

Initial Voltage Change on Capacitor Switching

This letter presents field measurements of capacitor switching transients with initial bus voltage changes different from widely used assumptions. Instead of being pulled toward zero in all three phases, initial voltage changes in both directions are seen in grounded capacitor switchings. Electromagnetic Transients Program simulation shows that the reason could be pole spread in breaker closing and mutual coupling between the three phases. The letter suggests that this transient pattern be considered in capacitor switching research.

Detection of Capacitor Switching Transients and L-G Fault Transients by Implementing Wavelet Transform

Abstact: In a electrical power system, whenever the voltage goes below the desired level,there is no need to improve the voltage profile. This increasing voltage can be obtained by using capacitor bank/s, as switching ON a capacitor bank/s causes increase in voltage while switching OFF a capacitor bank/s causes decrease in voltage. But these switching action, if not specifically controlled give rise to transients which are undesirable and hazardous for the power system. This introduces a voltage disturbance detection approach [1] identifies voltage disturbance, and[2] discriminate the type of event which has resulted in the voltage disturbance, e.g. either a fault or a capacitor switching incident. Feasibility of the proposed disturbance detection approach is demonstrated based on digital time domain simulation of a distribution power system using the PSCAD software package. Finally by using wavelet transform discriminate the type of event on the basic of energy levels. The demand for educational and awareness programs are recommended in order to contribute and increase the use of online transaction in the sultanate. Keyword: Capacitor switching,, distribution system, L-G,PSCAD wavelet transform, transient analysis.

Capacitor Banks Switching Transients in Power Systems

This study provides an introduction to capacitor bank switching transients, illustrates the effects of the capacitor banks switching in the utility primary distribution system at different places of the power system, but specially at the customer’s plant. Study covers different operational cases to find the suitable method or techniques can be used to limit the effect of capacitor switching transients. Transient disturbances in power systems may damage key equipment, potentially having a great impact on system reliability. These transients may be introduced during normal switching operations, lightning strikes, or because the equipment failure. Therefore, time-domain computer simulations are developed to study dangers cases due to transient occurrences. The simulations are performed using the simulation software Electromagnetic Transient Program (EMTP). In this study, the Alternative Transients Program (ATP) version 5.7p2 was applied on a simple industry network. Key words : Capacitor banks; Transient overvoltage and current; Energization inrush; Back-to-back switching; Preinsertion resistor and inductor

Symmetrical Structure Transient Limiter for Suppression of Capacitor Switching Transients

Capacitor switching transients are harmful to the capacitor and the switching device. For reducing these transient phenomena, this paper proposes a symmetrical structure transient limiter (SSTL). The proposed SSTL can automatically provide high impedance at the instant of capacitor energization, and, thus, the switching transients can be effectively suppressed. After the restriction, owing to the compensation of all power losses caused by the diodes and reactors, the SSTL acts as a short circuit during the steady state and, thus, has no effect in the circuit. As a result, the capacitor voltage and current waveforms will not be distorted. Moreover, due to the freewheeling effect in the SSTL, no transient overvoltage will appear across the switch contacts at the instant of capacitor de-energization even though the reactors are inserted into the circuit. Theoretical analyses of the proposed SSTL for the energization state, steady state, and de-energization state have been completely carried out. Also, the selections of the related components are depicted. Finally, the experimental results obtained using different methods of capacitor switching verify the feasibility and performance of the proposed SSTL.

Placement of power quality monitors using enhanced genetic algorithm and wavelet transform

Power quality (PQ) problems include harmonics, voltage flicker, three-phase imbalance, voltage swell/sag, interruption, switching transient and so on. Identification of accurate location and occurrence time of PQ problem is important for understanding the underlying cause and to prevent future occurrence. This study presents a new method for placement of power quality measurement facilities to identify PQ problems. The power harmonics and capacitor switching transients are used as disturbance sources for illustration. The proposed method first utilises harmonic voltages and wavelet coefficients as PQ features. An enhanced genetic algorithm is proposed for solving the modified K-means clustering to place PQ measurement monitors. Simulation results for an 18-bus system show that the proposed approach is effective in comparison with the existing approaches.

On Tracking the Source Location of Voltage Sags and Utility Shunt Capacitor Switching Transients

This paper presents a new procedure to track the disturbance source location of voltage sags and shunt capacitor switching transients in a power system based on branch current measurements. In the proposed method, the power-quality metering locations are first determined by the sensitivity of the system fault-current level to the fault voltage. Then, a current deviation index for representing the change of each measured branch current rms magnitudes before and after the disturbance is calculated to track the disturbance source location within an area confined by the directions of the top-priority branches. The IEEE 30-bus benchmark system and an actual transmission system with recorded power-quality disturbance events are used to illustrate the usefulness of the proposed method. Simulation results obtained by the proposed method are also compared with those obtained by a previously developed approach and by actual recorded data. By observing the results, it shows that the proposed method is efficient and accurate to track the source area of voltage sags or shunt capacitor switching transients.

Identification of Capacitor Switching Transients With Consideration of Uncertain System and Component Parameters

Capacitor switching transient is one of the most commonly encountered power quality disturbances. Measuring and identifying these transients remains a challenge as the characteristics depend on the system parameters, capacitor ratings and makeup of the connected loads. This paper describes a systematic approach to design an automated system for identifying such transients. It relies on the belief that some of the system and component parameters are either known or can be determined, and thus can be used to develop the necessary pattern for identification and discrimination. However, identification also needs to be robust against uncertainties in these parameters. The proposed method combines the techniques of wavelet transform, rank correlation and fuzzy logic to account for the uncertainties. Dynamic simulations were undertaken to verify the method and to illustrate its robustness when dealing with various uncertain transient characteristics. It is shown to be capable of identifying transients caused by switching of both isolated and back-to-back capacitors.

Wavelet Transform for Processing Power Quality Disturbances

The emergence of power quality as a topical issue in power systems in the 1990s largely coincides with the huge advancements achieved in the computing technology and information theory. This unsurprisingly has spurred the development of more sophisticated instruments for measuring power quality disturbances and the use of new methods in processing and analyzing the measurements. Fourier theory was the core of many traditional techniques and it is still widely used today. However, it is increasingly being replaced by newer approaches notably wavelet transformand especially in the post-event processing of the time-varying phenomena. This paper reviews the use of wavelet transform approach in processing power quality data. The strengths, limitations, and challenges in employing the methods are discussed with consideration of the needs and expectations when analyzing power quality disturbances. Several examples are given and discussions are made on the various design issues and considerations, which would be useful to those contemplating adopting wavelet transform in power quality applications. A new approach of combining wavelet transform and rank correlation is introduced as an alternative method for identifying capacitor-switching transients.

Sequential phase energisation technique for capacitor switching transient reduction

The application of a sequential switching scheme for the mitigation of capacitor switching transients is presented. The method utilises neutral grounding impedance connected at the neutral point of the switched capacitor bank together with sequential pole switching. The neutral impedance is sized to minimise the open-circuit contact voltage of the capacitor breaker phases. Theoretical analysis of the proposed scheme has been carried out together with computer simulation. In addition, neutral impedance sizing criteria are presented in order to achieve minimal transient over-voltage caused by capacitor switching. The proposed method was found capable of reducing the transient over-voltage at the utility switched capacitor location to 1.07 and 1.12 p.u. at the customer load bus.

Empirical Estimation of System Parallel Resonant Frequencies Using Capacitor Switching Transient Data

Simple yet accurate techniques for estimating system parallel resonant frequencies are presented. The proposed techniques make use of existing power quality data, specifically those of capacitor switching transients, to determine frequency estimates. A detailed representation of the system including the data required to develop device models (transmission lines, transformers, loads, etc.) is not required. The efficacy and pitfalls of the technique was demonstrated using power quality data collected at transmission and distribution systems where resonant frequencies were known so as to identify the best application environment of the technique. Frequency estimation results correspond closely to actual system resonant frequencies.

Capacitor Switching Transients: Analysis and Proposed Technique for Identifying Capacitor Size and Location

This paper deals with the analysis of transients initiated by the switching of shunt capacitors in power networks. These transients will propagate through the network along the transmission elements and will, accordingly, be felt at other locations far from the capacitors, such as load terminals. This can lead to adverse effects on the supply quality at those load buses. Based on a typical radial system, the distributed-parameter analysis will give analytical expressions for the expected transient voltages at the load terminals in terms of both the size and location of the switched capacitor. In its second part, this paper presents simple closed-form expressions for the accurate identification of the shunt capacitor's size and location, in terms of easily measurable parameters of the voltage signal at the load terminals.

A Power Quality Test Platform Based on a 120 kVA Programmable Source, Including Experimental Demonstrations

This paper describes the development of an invaluable power quality tool through the application of a 120 kVA three-phase programmable ac power source with an integrated arbitrary waveform generator. Implementation details and the programmable source characteristics are presented, including experimental results that demonstrate the flexibility of the source/arbitrary waveform generator to simulate common power quality disturbances such as voltage sags, swells, outages, harmonics, unbalance, and capacitor switching transients. Example test bed environments are developed and discussed allowing for the comprehensive power quality testing of loads such as adjustable speed drive systems, line-operated motors, and power supplies. Remote programming and control of the arbitrary waveform generator, including the development of an instrument driver library database, through LabVIEW are also discussed.

A new approach to mitigate nuisance tripping of PWM ASDs due to utility capacitor switching transients (CSTs)

Utility capacitor-switching transients (CSTs) are responsible for numerous nuisance trippings of PWM adjustable speed drives (ASDs) and result in costly down times. During a CST event, the DC link voltage of the ASD can momentarily rise to greater than 1.3 p.u. resulting in nuisance tripping. In this paper, a new approach to mitigate nuisance tripping of PWM ASDs is discussed. In this approach, the soft-charge resistor available in most ASDs, is momentarily introduced in the series path of the power flow to effectively damping the CST. Further, damping effect is electronically adjusted. The proposed approach demonstrates a method that can be incorporated within an ASD to electronically damp the oscillatory transient generated during a CST event. The advantages of the proposed approach are: (i) electronic damping for CST event is achieved by low cost modifications to ASD hardware; (ii) it adapts to several utility resonance conditions. The required additional hardware for ASDs to be immune to CSTs, can be viewed as an add-on option. This paper discusses the analysis, simulation and experimental performance on a 480 V, 16 kVA commercial ASD equipment.

System approach to shunt capacitor allocation in radial distribution systems

Abstract This paper presents a system approach to shunt capacitor placement on distribution systems under capacitor switching constraints. The optimum capacitor allocation solution is found for the system of feeders fed through their transformer and not for any individual feeder. The main benefits due to capacitor installation, such as system capacity release and reduction of overall power and energy losses are considered. The capacitor allocation constraints due to capacitor-switching transients are taken into account. These constraints are extremely important if pole-mounted capacitors are used together with a substation capacitor bank. A genetic algorithm is used as an optimization tool. An illustrative example is presented. The algorithm is currently in use in the Israel Electric Corporation (IECo).