Unbalanced Supply Voltage Research Articles

Analysis of direct power control AC-DC converter under unbalance voltage supply for steady-state and dynamic response

This paper presents an analysis of Direct Power Control (DPC) technique for the Three-Phase Pulse Width Modulation (PWM) AC-DC converter under unbalanced supply condition. Unbalance condition will cause the presence of unbalanced current and voltages thus produce the negative components on the grid voltage as well as severe performance degradation of a grid connected Voltage Source Inverter (VSI). The input structures for conventional DPC has been modified with a three simpler sequence networks instead of coupled by a detailed Three-Phase system method. The imbalance voltage can be resolved by separating from the individual elements of voltage and current into symmetrical components called Sequence Network. Consequently, the input power relatively improved during unbalanced condition almost 70% through the measurement of Total Harmonic Distortion (THD) from the conventional Direct Power Control (DPC) in individual elements which is higher compared to separate components. Hence, several analyses are performed in order to analyze the steady state and dynamic performance of the converter, particularly during the load and DC voltage output reference variations.

Experimental diagnosis of inter-turns stator fault and unbalanced voltage supply in induction motor using MCSA and DWER

This paper presents a comparative study between two techniques of signal processing to diagnose both faults the inter-turn short circuit (ITSC) in stator windings and the unbalanced voltage supply (UVS) in induction motors. The first is considered a classical technique called Motor Current Signature Analysis (MCSA) which is based on the processing of the stator current by the Fast Fourier Transform (FFT). The second is anadvanced technique based on a Discrete Wavelet Energy Ratio (DWER) of three stator currents. The aim objective of this paper is to compare the ability and effectiveness of both techniques to detect the ITSC fault and the UVS in induction motors, and distinguishing between them. An experimental implementation tests the two diagnosis techniques.The results obtained show that the MCAS technique by the FFT analysis has a difficult to discriminate between the current harmonics due to the provide voltage unbalance and those originated by ITSC faults. Unlike the DWERtechnique, which has high sensitivity and exceptional ability to detect and distinguish between the two faults that lead to the reliability of the diagnosis system. To demonstrate that the DWER is an accurate and robust diagnosis approach are used the neural network (NN) as a tool to classify the faults (ITSC and USV) where using DWER indicators as NN input. The results obtained of combination between the DWER and NN are effective and proved its ability to detect both faults under different load conditions and distinguish between them accurately with low error (10-5).

Derating of Induction Motors Due to Power Quality Issues Considering the Motor Efficiency Class

Heating and losses of induction motor (IM) grow with the supply voltage unbalance and harmonic distortion. To avoid thermal overload, the IEEE 141-1993, the IEEE 3004.8, NEMA MG1-2014, and the IEC 60034-26 standards establish derating factors for IMs operating under those conditions. In this article, we show that while the derating factors proposed by these standards adequately protect standard-efficiency IMs, they are only marginally adequate to protect modern higher-efficiency IMs. To this end, we compare the derating factors provided by the standards with the derating factors required to maintain the losses at rated values in a standard-efficiency IM, in a premium-efficiency IM, and in a super-premium-efficiency IM. To extrapolate the results from these IM, we compared the nameplate data of 548 IMs of different efficiency classes and found that higher efficiency classes correlate to higher IM starting currents and lower impedances to the negative sequence and harmonic voltages. These lower impedances in turn may lead to higher losses for unbalanced and harmonic voltages conditions.

A Novel Reference Current Extraction Technique with Multi-Functional Capability for Shunt Active Filter

The exponential growth of non-linear loads results the generation of harmonics in electrical distribution system. Major Harmonic generation effects due to non-linear loads are energy loss, nuisance tripping, equipment failure/mal-operation, and transformer saturation, overheating of neutral conductors and/or capacitors, interference with communication circuits, excess reactive power burden and lowering the true power factor. Improving the current quality is the prime responsibility of the consumers whereas utility is accountable for minimizing the supply voltage distortions. Shunt active filters (SAFs) were being used for many years to mitigate the current harmonics typically up to 25th order. Mainly, time and frequency domain reference current extraction control techniques were being used for SAF. Time-domain reference current extraction techniques were proved efficient than frequency-domain techniques due to their faster response. Time-domain reference current extraction techniques such as real and reactive (p-q) and synchronous reference frame (SRF) are having their own merits and demerits. The p-q control does not perform well under distorted and unbalanced supply voltage conditions whereas SRF control is limited to balanced loads. In this paper a novel reference current extraction control strategy is proposed i.e. inverse matrix averaging pq-SRF (IMApq-SRF) control. IMApq-SRF control extract the features of both conventional p-q and SRF control, based on inverse matrix average. The mathematical modeling of the proposed IMApq-SRF control is tested with MATLAB Simulink environment and it validates that the proposed IMApq-SRF control gives the superior performance as compared with conventional p-q and SRF techniques under balanced, unbalanced and distorted supply voltage and dynamic loading conditions.

Internet of Things-Based Steam Pump Motor Protection Due to Voltage Unbalance

PLTGU is a gas and steam power plant, producing electrical energy of 3x526 MW. The PLTGU generation process has several supporting components, one of which is a three-phase induction motor. It requires a balanced three-phase supply voltage in its operation. The problem that frequently occurs is unbalanced voltage supply, causing an imbalance of current going to the motor stator, if not directly corrected. It causes a high temperature on the motor, possible to cause a fire. Based on the problems, a system for monitoring the protection of steam pump motorcycles due to voltage unbalance based on the Internet of Things is designed. It used a 1-phase AC Adapter voltage sensor, a current sensor SCT-013, an Arduino Uno as the processor, and a web to display the system. The test results showed that the sensor could work well. It could read voltage with an error percentage not exceeding 1%. The percentage error of the current sensor SCT-013 was 5.15%, but the value difference between the sensor and the Avo meter was 0.01. The system was displayed on the web to make to monitor the motor condition more easily

Impact of Supply Voltage Unbalance and Harmonics on dc Bus Electrolytic Capacitor of Adjustable Speed Drives

Among the various supply voltage abnormalities, unbalance and distortion are some of the major threats to the dc bus capacitor of adjustable speed drives. The effect of supply voltage unbalance on the dc bus capacitor changes in the presence of supply voltage harmonics. Further, the value of grid impedance and the load on the drive influences the response of these supply voltage abnormalities on the dc bus capacitor. This article analyzes the impact of unbalance, distortion, and simultaneous presence of unbalance and distortion in the supply voltage, on the dc bus capacitor, along with the effect of grid impedance and the load on the drive. As a result of the analysis, the article proposes the derating of load required to keep the capacitor current within the safe value irrespective of the level of abnormalities and grid impedance. The effects are analyzed by simulations and validated by the hardware test setup.

Investigation of The impact of Unbalanced and Non-sinusoidal Supply Voltages on Converters.

In this paper two input current modulation strategies for matrix converters are experimentally analyzed under two different supply conditions: sinusoidal unbalanced voltages and non-sinusoidal balanced voltages. Both strategies use the Space Vector Modulation (SVM) technique in order to control the matrix converter accordingly to the input and output constraints. Strategy A modulates the input currents keeping the corresponding space vector in phase with the input voltage vector. Strategy B operates in order to keep the input current vector in phase with the positive sequence fundamental component of the input voltage vector. A comparison between the two strategies is made in terms of the reduction of the input current disturbances due to the unbalanced and non sinusoidal voltage on the grid. It is found that a dynamic current modulation strategy, independent of the voltage disturbances such as Strategy B, is more effective for the reduction of the RMS value of input current disturbances. The validity of the theoretical investigation i.e. the effectiveness of the current modulation strategy conforms to experimental tests result carried out on a matrix converter prototype.

Predictive Maintenance Applied to Three phase Induction Motors

Induction machines are widely used in industry. The operating conditions may sometimes lead the machine into different fault situations. The machine should be shut down when a fault is experienced to avoid complete process failure and for the safety of the workers. The predictive maintenance consists of scheduling maintenance activities only when a functional failure is detected. The advantages of predictive maintenance are accepted in many industries because of its efficiency in fault detection during early stages and thus reducing unscheduled down time. It increases productivity, improves quality and provides the feeling of safety and reliability to staff. The main types of external faults experienced by these motors are over loading; single phasing, unbalanced supply voltage, phase reversal, ground fault, under voltage and over voltage. MATLAB/SIMULINK simulation is used in this work for the detection and analysis of the faults on induction motor.

Theoretical and Experimental Investigation of the Supply Voltage Unbalance Effects on Squirrel Cage Induction Motors

Voltage unbalance is one of the power quality problems causing a lot of ill effects on induction motors. These are namely: Overheating, line-current unbalance, derating, torque pulsation, and inefficiency. The objective of the present work is to assess and quantify the effects of voltage unbalance on induction motors using both theory and experimentation. The analytical study is performed using the complex voltage unbalance factor model of this problem. The work deals specifically with the influence of the variations in the complex angle of the voltage unbalance factor on the stator and rotor currents, stator and rotor copper losses and total losses. The experimental investigation is carried out using an apparatus that measures currents, torque and power losses.

A Simplified Equivalent Circuit Method for Induction Machine Nonintrusive Field Efficiency Estimation

Energy efficiency estimation for in-service induction motors has become a crucial area of research due to the increasing need for energy savings and demand-side management. As a result, several in-service efficiency estimation methods for induction motors have been proposed. This article presents a nonintrusive method for estimating the efficiency of induction motors operating on-site using limited terminal measurements and motor nameplate data. The method uses a modified inverse Г-model equivalent circuit with series core loss arrangement to mitigate the inherent problems of higher computational burden and parameter redundancy in the conventional T-model. Furthermore, a new method is presented for estimating the friction and windage loss using the airgap torque and motor nameplate data. The proposed nonintrusive field efficiency estimation technique was validated experimentally on standard and premium efficiency induction motors for both balanced and unbalanced voltage supply. The results demonstrate the accuracy of the proposed method and confirm its advantage over the conventional method for in-service efficiency determination.

Inter-Turn Fault Detection of Dry-Type Transformers Using Core-Leakage Fluxes

In this paper, a new technique for low-severity inter-turn fault detection under online operating conditions of dry-type transformers is proposed. The proposed methodology requires just two inexpensive flux sensors and is based on the fundamental component of the core-leakage fluxes at the transformer's outer limbs. Theoretical analysis using the proposed analytical models and experimental validation on a 10-kVA experimental prototype transformer are carried out to evaluate the performance of the proposed methodology under various fault severities. The real-time fault-detection capability of the proposed technique is also evaluated using a fabricated prototype health monitoring device, which reveals that as low as 2-turns bolted fault out of 150 turns can be detected within 3 fundamental cycles. The methodology is immune to loading and supply voltage unbalance conditions and on par with the classical differential negative sequence current based technique with an additional advantage of 78% reduction in the total number of sensors required for a three-phase three-winding transformer.

The Influence of Power Quality Indices on Active Power Losses in a Local Distribution Grid

This paper deals with the topic of power quality in a local distribution grid. It is aimed to analyze the individual influences, which aggravate the power quality of the distribution grid. Based on the analysis, the most adverse effects were determined, and they were the voltage drops and supply voltage interruptions, supply voltage unbalance, load power factor, and also higher harmonics. These influences cause the technical losses in a distribution grid, which subsequently have a financial impact not only on the distribution, but also on the transmission of electricity. Only the load voltage unbalance, the load power factor, and the higher harmonics, which mainly cause the technical losses, were analyzed in this paper. The measurement of the influences of the adverse effects was performed on the model of a 22-kV distribution grid. The measurement was performed on the basis of three types of power line conductors and their different lengths, three types of active power consumption, and the different values of these adverse effects. According to this measurement, a simulation in program Matlab-Simulink was created. This simulation represented part of a 22-kV distribution grid, which was influenced by the abovementioned adverse effects. The results of the measurements were compared with the results of the simulation. Based on the evaluation of the technical losses from the measurement and the simulation, the financial losses during a certain period were calculated for the distribution system operators.

Thermal analysis of power transformers under unbalanced supply voltage

High temperatures may damage power transformers. These problems leading to the high temperature are more revealed under non-rating operating conditions such as unbalanced supply voltage. The aim of the present study is thermal analysis of such supply and obtaining its temperature distribution. Existing thermal analysis methods through thermal equivalent circuit (TEC) have some drawbacks; in these models, thermal parameters of different regions of transformer such as core, tank, metallic parts and winding are not defined. On the other hand, those models are not applicable for thermal analysis of transformer with unbalanced supply voltage. Here, a novel TEC model is proposed which is able to define temperatures of different components of oil-immersed power transformers individually under unbalanced supply voltage. The merit of the introduced model is that losses of different parts of transformer are considered as heat generating sources which are used as the inputs of thermal model. At this end, a three-dimensional finite-element method is suggested which is able to estimate the losses of different parts of power transformer. Finally, the results of applying the TEC to the transformer are compared with the temperature distribution of finite-element modelling and high accuracy of the TEC model in estimation of the temperatures of different regions are emphasised.

A Novel Approach for Sensitive Inter-turn Fault Detection in Induction Motor Under Various Operating Conditions

Induction motors are subjected to thermal, electrical and mechanical stresses during continuous operation. If any of these stresses become excess than normal condition, it is a symptom of commencement of fault in the induction motor. If these faults are not detected at an incipient stage, it may result in the failure of the motor. Turn-to-turn short-circuit faults are the major causes for the stator winding insulation failure. In the proposed work, a novel approach is suggested to detect these faults in the induction motor. In this approach, the discrete wavelet transform (DWT) is performed on the Park’s vector modulus of current signals. The accuracy of DWT can be enhanced by selecting the proper wavelet type and its order along with levels of decomposition. With this context, an attempt is made to investigate the best-suited mother wavelet by testing various orthogonal wavelet functions on simulated signal and justified that the db44 is to be the best suitable wavelet for the detection of an inter-turn fault in the induction motor. The current signals are obtained experimentally under operating conditions with balanced supply voltages, unbalanced supply voltages, load slip variation and gradual variation in load condition and analyzed. The obtained results show the sensitivity and robustness of the proposed approach. The fault severity factor is also suggested for evaluating the severity of fault in the induction motor.

Determining the operational status of a three phase induction motor using a predictive data mining model

<span lang="EN-GB">The operational performance of a three phase induction motor is impaired by unbalanced voltage supply due to the generation of negative sequence currents, and negative sequence torque which increase motor losses and also trigger torque pulsations. In this study, data mining approach was applied in developing a predictive model using the historical, simulated operational data of a motor for classifying sample motor data under the appropriate type of voltage supply i.e. balanced (BV) and unbalance voltage supply (UB = 1% to 5%). A dataset containing the values of a three phase induction motor’s performance parameter values was analysed using KNIME (Konstanz Information Miner) analytics platform. Three predictive models; the Naïve Bayes, Decision Tree and the Probabilistic Neural Network (PNN) Predictors were deployed for comparative analysis. The dataset was divided into two; 70% for model training and learning, and 30% for performance evaluation. The three predictors had accuracies of 98.649%, 100% and 98.649% respectively, and this confirms the suitability of data mining methods for predictive evaluation of a three phase induction motor’s performance using machine learning</span>

Renewable Energy–Supported Hybrid Active Power Filter for Grid-Connected Application

Abstract This research article presents a Photovoltaic (PV) and battery-supported Series Hybrid Active Power Filter (SHAPF), which includes a series APF (SAPF), parallel-connected passive filter, and PV system with a battery energy storage unit. The PV-supported SHAPF provides compensation against the voltage harmonics, current harmonics, and voltage interruption for a whole day. The SHAPF systems need certainty in order to provide active power to the power system to maintain the load voltage level during voltage sag. Conventionally, the SAPF has the capacity to compensate for a limited amount of active power in the system. Thus, additional energy sources need to be added into the dc link of the SAPF. The proposed SHAPF circuitry utilizes the renewable energy source with an energy storage unit to meet the dc-link voltage requirement of the SAPF. Additionally, it exports the power that is generated in the PV system to the load. The series inverter is used to supply part of or the entire reactive power required by the load along with compensating the sag and swell, supply voltage unbalance, and distortions. This is achieved by controlling the phase angle and the magnitude of series-injected voltage, which is called the power angle control method. The fuzzy logic controller-based power angle control method is employed to compensate the voltage-based disturbances in the distribution system. The performance of the PV and battery-supported SHAPF is evaluated by conducting MATLAB/Simulink simulation and experimental studies.

A recursive discrete Kalman filter for the generation of reference signal to UPQC with unbalanced and distorted supply conditions

This paper describes the development of a robust control technology adapting Kalman filter in order to attend to the problems that arise in power quality. This methodology makes use of a three-phase three-wire unified power quality conditioner (UPQC) under unbalanced and distorted supply conditions. In spite of harmonics and frequency oscillation, the Kalman filter determines the amplitude, phase angle and frequency of load currents and source voltages. The main ideas are to use Kalman filtering algorithm to acquire fundamental component of load current and source voltage and to use the least squares method which is relatively simple and faster. The proposed robust Kalman filter-based UPQC system mitigated the issues such as voltage sag, voltage swell, harmonics distortions (voltage and current), and unbalanced supply voltage and power factor. The results are justified using the MATLAB/Simulink software to support the Kalman filter-based control algorithm under steady state and dynamic operating conditions.

The Propagation Mechanism of Fault Signatures in Squirrel Cage Induction Motor Drives

This work presents a new approach for analyzing the propagation mechanism of fault signatures in squirrel cage induction motor drives. The used method is based on the analysis of different currents of solid states converters and the fault signatures are investigated when motor is supplied by the volt-per-hertz control mode. Analytical expressions of currents at different location for broken bar, mixed air-gap eccentricity, unbalanced voltage supply are developed using switching functions of both inverter and diode rectifier. Experimental results are provided throughout the paper, to underpin the theoretical analysis. The results show that capacitor current spectrum can give useful information about the state of squirrel cage induction motor. However, due to the low-pass filter composed by capacitor only the fault signatures at low frequency range can be detected from the rectifier supply line current spectrum.

Current Reference Control for Shunt Active Power Filters Under Unbalanced and Distorted Supply Voltage Conditions

This paper proposes a current reference control method for shunt active power filter under unbalanced and distorted supply voltage conditions. The method uses the Kalman filter and the symmetrical component method to obtain the fundamental sequence component of the supply voltage. The Fryze-Buchholz-Dpenbrock method is used to decompose the load current under the reference of the fundamental positive-sequence voltage to obtain the reference value of the compensation current. The method is characterized without need of coordinate transformation, simple calculation, and clear physical meaning. The harmonic current, reactive current and negative sequence current can be compensated at the same time even under the condition of unbalanced supply voltage. The proposed method is compared with the traditional method under various experimental conditions to prove the validity and accuracy of the proposed method. The results show that the proposed method has wider applicability.

Research on the Unbalanced Compensation of Delta-Connected Cascaded H-Bridge Multilevel SVG

The paper presents the application of delta-connected cascaded H-bridge multilevel static var generator (SVG) under unbalanced compensation currents or unbalanced supply voltages. Clustered balancing control for delta-connected SVG can be realized by injecting a zero-sequence current to the delta loop. But zero-sequence current injection may cause the high peak phase current which may break converter switches. The aim of this paper is to analyze the key factors that affect the maximum output current of the SVG with injecting zero-sequence current and acquire the quantitative relationship among unbalance compensation capability, the unbalance degree of the supply voltage, the initial phase of negative-sequence voltage, the unbalance degree of the compensation current, and the initial phase of negative-sequence current. On this foundation, the valid compensation range of delta-connected SVG under unbalanced conditions is obtained. Furthermore, the compensation characteristic of the negative-sequence current is deduced with the certain supply voltage, and the influence of supply voltage variation on the maximum output current for SVG is also considered with the certain compensation current. Finally, the correctness of the relevant theoretical analysis is verified by simulation and experiment.