Faulty Power Research Articles

Delay Test for Diagnosis of Power Switches

Power switches are used as a part of the power-gating technique to reduce the leakage power of a design. To the best of our knowledge, this is the first report in open literature to show a systematic diagnosis method for accurately diagnosing power switches. The proposed diagnosis method utilizes the recently proposed design-for-test solution for efficient testing of power switches in the presence of process, voltage, and temperature variation. It divides power switches into segments such that any faulty power switch is detectable, thereby achieving high diagnosis accuracy. The proposed diagnosis method is validated through SPICE simulation using a number of ISCAS benchmarks synthesized with a 90-nm gate library. Simulation results show that, when considering the influence of process variation, the worst case loss of accuracy is less than 4.5%; it is less than 12% when considering VT variations.

Modified space vector modulation for fault‐tolerant operation of multilevel cascaded H‐bridge inverters

In this study, fault-tolerant operation of multilevel cascaded H-bridge (CHB) inverters is presented and a novel switching strategy based on space vector modulation is proposed. A faulty power switch in high power converters can lead to expensive downtime, loss of productivity and increased costs. Various power switch faults and their influence on space vector diagram of CHB inverters are investigated. In the event of a fault, the output voltage of inverter is reduced and redundant switching states are used to generate balanced line-to-line voltages. By adding some devices to the basic structure, CHB inverter will operate with maximum achievable output voltage. Simulation and experimental results are shown for a five-level CHB inverter to validate the proposed modulation technique.

New Neural Power System Stabilizer for Brushless Exciter

In this paper, a new brushless exciter generator power system stabilizer is proposed. The design is based on a recurrent neural network trained with a model-free approach and using the feed-forward error propagation learning algorithm. This is of great importance, as it will be outlined in the paper. The aim is to ensure a good damping of the power grid oscillations and to maintain constant voltage magnitude. This is done by providing an adequate control signal that delivers the reference input of the automatic voltage regulator. This stabilization signal is developed from the rotor speed. The results show the effectiveness of the proposed approach. The system response has less oscillations with a shorter transient time. The study was extended to faulty power plants.

Design and Control of a Modular Multilevel HVDC Converter With Redundant Power Modules for Noninterruptible Energy Transfer

This paper presents design and control methods for fault-tolerant operations with redundant converter modules, one of the most prominent features in modular multilevel converter (MMC) topology. In fully implementing MMC functionalities, a nearest level control is applied as a low-switching modulation method. A dual sorting algorithm is newly proposed for effectively reducing the switching commutations of each power module as well as for voltage balancing control. Built upon these primary MMC topological and control features, its redundant operation is comprehensively investigated for fail-safe energy transfer. In particular, a novel spare process is proposed to handle an emergency situation when the number of faulty power modules exceeds the module redundancy. Since topological redundancy may cause the switching commutations of power modules in an arm to be unevenly distributed, a practical and effective mitigation measure is incorporated to keep the energy balance while avoiding the undesired switching stresses. Rigorous simulation studies for MMC and its application for high-voltage direct current are performed to demonstrate the validity and effectiveness of the proposed spare process under normal and emergency conditions.

A DWT‐based approach for detection of interturn faults in power transformers

PurposeInterturn winding faults, one of the most important causes of power transformers failures, cannot be detected by existing detection methods until they develop into high‐level faults with more severe damage to the transformer. The purpose of this paper is to describe development of a new discrete wavelet transform (DWT) based approach for detection of winding interturn faults.Design/methodology/approachThe following approach was accomplished for development of the proposed fault detection method in this study. The DWT was first applied to decompose the terminal current signals of a transformer, which in turn were obtained from simulations using a finite elements method model of the transformer, into a series of wavelet components. Based on the characteristic features associated with interturn faults extracted from the decomposed waveforms of the terminal currents, a detection scheme was developed. An experimental setup was used to validate the proposed detection method.FindingsThe results of this study demonstrate the efficacy of DWT applied on terminal currents of the transformer to identify interturn faults on the windings well before such faults lead to a catastrophic failure. It is believed that, based on the present findings, there definitely exists scope for improving interturn fault diagnosis with wavelet transform.Research limitations/implicationsPerforming more detailed studies to find all relevant characteristics of the wavelet transform in this application, identifying the location of the faulted turns along winding, applying the method for indicating early stages of turn insulation deterioration and evaluating other type of wavelets for this application would be some future directions of this research.Practical implicationsWith the proposed method, it is becoming possible to detect early signs of the fault occurrence, so that the necessary corrective actions can be taken to prevent long‐lasting outages and reduce down times of the faulty power transformer. The method will be particularly useful as a complement for the classical protection devices of the power transformers.Originality/valueSome recent studies have been carried out regarding the application of DWT for discrimination between an internal fault and other disturbances such as magnetizing inrush and external faults. This paper extends those studies for the detection of interturn faults using more quantitative and qualitative characteristics features.

Two steps numerical method for calculating the AC interference from a faulty power line on nearby buried pipelines

The paper presents a numerical method for evaluating induced voltages and currents, at power frequency, on a buried pipeline due to inductive and conductive coupling with a power line in fault condition; both the systems can have generic layouts represented by broken lines. The algorithm consists of a two steps solution of a two wires transmission line model applied at first to the circuit shield wire(s) with earth return and then to the circuit pipeline with earth return. This calculation method is particularly tailored for industrial and real cases applications. Copyright © 2010 John Wiley & Sons, Ltd.

Alternative Visions of the Indigenous People’s Movement in Latin America

This article analyses the civilisational content of contemporary indigenous movement in Latin America. From a profound critique of Eurocentrism, this social movement builds on its rich historical roots and ancient civilisations to project themselves as a regional movement with a universal reach. The indigenous movement in Latin America has evolved from being a resistance movement to become a movement that challenges governments and political power in several countries of the region. Whilst developing a strategy for integration based on their acknowledgement of belonging to a historical, geographical and cultural unity, the Latin American indigenous movement has placed in the centre of the debate and political action, key issues that will redefine future political scenarios in the region. Key elements of this shift include: the construction of ‘pluri-national’ states based on the principle of ‘unity in diversity’ as the centrepiece of the new democracy in the region, the recognition of indigenous civilisations as a source of knowledge, skills and identities for the construction of a collective future; consideration of life as a main principle for social and political action; recognition of the motherland or Pachamama as the fundamental source and the space where life happens. These new processes are producing profound changes in the Americas, which certainly will create better conditions for the emergence of a globally oriented civilisation, more balanced, equitable, inclusive and able to overcome the colonial mentality and its faulty power structures.

A Fault-Tolerant Control Strategy for Cascaded H-Bridge Multilevel Rectifiers

Reliability is an important issue in cascaded H-bridge converters (CHB converters) because they use a high number of power semiconductors. A faulty power cell in a CHB converter can potentially lead to expensive downtime and great losses on the consumer side. With a fault-tolerant control strategy, operation can continue with the undamaged cells; thus increasing the reliability of the system. In this paper, the operating principles and the control method for a CHB multilevel rectifier are introduced. The influence of various faults on the CHB converter is investigated. The method of fault diagnosis and the bypassing of failed cells are explained. A fault-tolerant protection strategy is proposed to achieve redundancy in the CHB rectifier. The redundant H-bridge concept helps to deal with device failures and to increase system reliability. Simulation results verify the performance of the proposed strategy.

Application of classification methods in fault detection and diagnosis of inverter fed induction machine drive: a trend towards reliability

The aim of this paper is to present a method of detection and isolation of intermittent misfiring in power switches of a three phase inverter feeding an induction machine drive. The detection and diagnosis procedure is based solely on the output currents of the inverter flowing into the machine windings. The measured currents are transformed in the two dimensional frame obtained with the Concordia transform. The data are then treated by a time-average method. The results even promising lack of accuracy mainly in the fault isolation step. To enhance the fault detection and diagnosis by the use of the information enclosed in the data, a Principal Component Analysis classifier is applied. The detection of a fault occurrence is made by a two-class classifier. The isolation is a two-step approach which uses the Linear Discriminant Analysis; the first is to identify the faulty leg with a three-class classifier and the second one discriminates the faulty power switch. Both methods are evaluated with experimental data and pattern recognition method proves its effectiveness and accuracy in the faulty leg detection and isolation.

Treatment of L-Fuzzy contexts with absent values

This work shows how to extract the missing information from an interval-valued L-Fuzzy context with some unknown values. Absent values are replaced using implications between attributes with high levels of support and confidence. Three kinds of implications are defined and analyzed for this purpose. We apply these results to an electrical network simulation, where the estimated relations between faulty power lines and voltage measurements can be compared with their real values.

Application of classification methods in fault detection and diagnosis of inverter fed induction machine drive: a trend towards reliability

The aim of this paper is to present a method of detection and isolation of intermittent misfiring in power switches of a three phase inverter feeding an induction machine drive. The detection and diagnosis procedure is based solely on the output currents of the inverter flowing into the machine windings. The measured currents are transformed in the two dimensional frame obtained with the Concordia transform. The data are then treated by a time-average method. The results even promising lack of accuracy mainly in the fault isolation step. To enhance the fault detection and diagnosis by the use of the information enclosed in the data, a Principal Component Analysis classifier is applied. The detection of a fault occurrence is made by a two-class classifier. The isolation is a two-step approach which uses the Linear Discriminant Analysis; the first is to identify the faulty leg with a three-class classifier and the second one discriminates the faulty power switch. Both methods are evaluated with experimental data and pattern recognition method proves its effectiveness and accuracy in the faulty leg detection and isolation.

Efficient testing and diagnosis of faulty power switches in SOCs

The use of power switches in modern system chips (SOCs) is inevitable as they allow for efficient on-chip static power management. Leakage is one of the main hurdles in low-power applications. Power switches enable power gating functionality, that is one or more parts of the SOC can be powered-off during standby mode thus leading to savings in the SOC's overall power consumption. To this end, a circuit and a method to test power switch is presented. The proposed method allows for the testing of on/off functionality. In case of segmented power switches, individual failing segments can be identified by using the proposed test strategy. The method only requires a small number of test patterns that are easy to generate. Furthermore, the proposed method is very scalable with the number of power switches and has a very small area-overhead.

Fault-Tolerant Voltage-Fed PWM Inverter AC Motor Drive Systems

This paper shows how to integrate fault compensation strategies into two different types of configurations of induction motor drive systems. The proposed strategies provide compensation for open-circuit and short-circuit failures occurring in the converter power devices. The fault compensation is achieved by reconfiguring the power converter topology with the help of isolating and connecting devices. These devices are used to redefine the post-fault converter topology. This allows for continuous free operation of the drive after isolation of the faulty power switches in the converter. Experimental results demonstrate the validity of the proposed systems.

Adaptive harmonic estimation for power system protection

Many power system protection problems necessitate the measurement and track of the underlying current/voltage phasors. Adaptive LMS spectrum analyzers provide an ideal solution to such problems. This paper introduces a class of adaptive trigonometric spectrum analyzers. The underlying current/voltage is fed as a desired signal to an LMS adaptive algorithm. The reference input is a periodic regression derived from the basis set of the specified trigonometric discrete transform. The proposed algorithm is simple, computationally efficient, and exhibits a guaranteed stability and uniform convergence. A comparative study recommends the discrete Hartley transform. Simulations are provided to prove that the proposed spectrum analyzer is efficient in modeling faulty power system currents/voltages such as these arising from an over‐excitation of a power transformer.

Coordinated Intelligent Control for Normal and Faulty Power Plant Operation

Achieving a more autonomous power plant operation is an important part of power plant control. To be autonomous, a control system needs to provide adequate control actions in the presence of significant uncertainties and/or disturbances, such as actuator or component failures, with minimum or no human assistance. However, a reasonable degree of autonomy is difficult to obtain without incorporating intelligence in the control system. This paper presents a coordinated intelligent control scheme with a high degree of autonomy. In this scheme, a Fuzzy-Logic based supervisor monitors the overall plant operation and carries the tasks of coordination, fault diagnosis, fault isolation, and fault accommodation

A Large Power User's View of the Rural Electric System

Problems of operating unattended three-phase load systems on rural electric power systems are considered. Emphasis is placed on special fault patterns frequently not detected by simple sensing techniques. Improperly designed or inadequate sensing equipment will permit faulty commercial power to remain counected to the load equipment until catastrophic damage has occurred.

Operation of Weapon System Loads from Rural Power Systems

Problems of operating unattended equipment on rural power systems are considered. Criteria for switching to alternate power sources are developed and appropriate specifications are proposed for the power sensing devices. Emphasis is placed on special fault patterns frequently not detected by simple sensing techniques. Improperly designed or inadequate sensing equipment or circuits will permit faulty commercial power to remain connected to the load equipments, with resultant catastrophic damage. Sophisticated power sensing equipment is required to initiate a transfer from normal to standby and emergency power systems. Power sensing should detect low voltage, unbalanced voltages, reversed phase rotation or loss of neutral. The power transfer system must be designed to prevent contactor chatter or cycling from voltage differentials between drop out and pull-in levels.

Hydroelectric Generator Excitation Experience at Grand Coulee

1. Experience with the motor-driven exciter at the Grand Coulee Power Plant indicates that automatic transfer of power sources to the motor can be successfully done under full load by removing the motor from a faulty power source and reconnecting it to another power source. 2. However, experience also indicates that the best protection is to provide sufficient power sources so that the loss of one source will not cause the loss of excitation. 3. Additional pilot-exciter voltage-regulation equipment has reduced peak voltages on the generators approximately 1.5 kv on a 13.8-kv base with the possibility of reducing this still further by the addition of more resistance in the high-speed lowering relay circuit in the main exciter field.

Practical aspects of telephone interference arising from power systems

The paper summarizes investigations on telephone interference carried out in this country between 1934 and 1944. In many cases, experimental work could not be pursued to a logical conclusion owing to the war, and has therefore served only to indicate the need for future research. The paper is divided into six sections:Electromagnetic Induction at Fundamental Frequency.—A comparison of calculated and measured values of induced voltage at various sites shows that in most cases good agreement is possible with the available data on earth resistivity. Further work is required on the screening effect of various earthed conductors. The precautionary measures available for power and telephone systems to avoid damage to plant and injury to personnel from high induced voltages are discussed.Interference at Audio Frequencies.—Results of tests are given which show that noise interference is serious from faulty power lines which are maintained in operation through the use of arc-suppression coils. The propagation of harmonic currents on long power lines requires further study; the results so far obtained indicate that an analysis of neutral currents is insufficient to forecast the noise interference possible. Attention is drawn to the possibility of interference from a power line supplying a large rectifier.Multiple Earthing of High-Voltage Systems.—Tests which have enabled conditions to be laid down for authorizing the multiple earthing of h.v. systems are reviewed.Multiple Earthing of Low-Voltage Systems.—Tests show that the interconnection of l.v. systems, each earthed at one point, is unlikely to cause interference.Apparatus Developments.—Gas discharge tubes, noise-eliminating filters, and an improved psophometer are described.Rise of Earth Potential.—Records of damage sustained and the precautionary measures which can be taken are discussed.