Makarand Sudhakar Ballal

Soft-Switching DC–DC Converter for Distributed Energy Sources With High Step-Up Voltage Capability

This paper presents high step-up dc-to-dc converter for low voltage sources such as solar photovoltaics, fuel cells, and battery banks. To achieve high voltage gain without large duty cycle operation, combination of coupled inductor and switched capacitor voltage doubler cells are used. By incorporating active clamp circuit, voltage spike due to the leakage inductance of the coupled inductor is alleviated and zero-voltage switching turn on of the main and auxiliary switch is obtained. Due to the use of MOSFETs of low voltage rating and soft turn on of the switches, conduction loss and switching losses are reduced. This improves the efficiency and power density of the converter. The proposed converter can achieve high voltage gain with reduced voltage stress on MOSFET switches and output diodes. Design and analysis of the proposed converter is carried out, and finally, a 500-W experimental prototype is built to verify theoretical analysis.

Stator Winding Inter-turn Insulation Fault Detection in Induction Motors by Symmetrical Components Method

Abstract The theory of instantaneous symmetrical components is used for the detection of insulation faults in a three-phase induction motor. Based on the experimental data of motor intake currents and the system voltages, the loci of positive- and negative-sequence components of currents are plotted. These loci overlap with each other under healthy winding conditions as their major and minor axes coincides. When an inter-turn short circuit occurs, these axes do not coincide with each other and displacement angle ϕ appears between two major axes. Thereby, the non-overlapping area comes into existence. The proposed system considers the effects due to unbalance in voltages, asymmetry in stator winding design, and measurement errors. Experimental results are reported to demonstrate the effectiveness of the proposed technique at different load conditions.

Interturn Faults Detection of Transformers by Diagnosis of Neutral Current

Interturn short-circuit faults are the leading cause of power transformers failure. If not detected at the incipient stage, these faults usually develop into more severe faults that would result in irreversible damage to the transformer, unexpected outages, and consequential losses. This paper presents a transformer interturn fault detection system (TIFDS) for the detection of an interturn fault at the inception stage in power transformers. TIFDS is immune to supply voltage imbalance, constructional asymmetries, and instrumental errors. It also takes care of unequal load distribution. The TIFDS algorithm makes the transformer symmetrical in its entire three phases and sets primary-side neutral current to zero value. This is achieved by computing and applying various correction coefficients. However, under the interturn fault condition, TIFDS characterizes the behavior of neutral current. Simulation and experimentation studies are carried out on the 400/110-V, 3 × 2.5 kVA power transformer. Presented test results demonstrate the effectiveness of the proposed system.

ZVS–ZCS High Voltage Gain Integrated Boost Converter for DC Microgrid

A nonisolated soft-switched-integrated boost converter having high voltage gain is proposed for the module-integrated PV systems, fuel cells, and other low voltage energy sources. Here, a bidirectional boost converter is integrated with a resonant voltage quadrupler cell to obtain higher voltage gain. The auxiliary switch of the converter, which is connected to the output port acts as an active clamp circuit. Hence, zero voltage switching turn-on of the MOSFET switches are achieved. Coupled inductors leakage energy is recycled to the output port through this auxiliary switch. In the proposed converter, all the diodes of the quadrupler cell are turned off with zero-current switching (ZCS). This considerably reduces the high-frequency turn-off losses and reverse recovery losses of the diodes. ZCS turn-off of the diodes also remove the diode voltage ringing caused due to the interaction of the parasitic capacitance of the diodes and the leakage inductance of the coupled inductor. Hence, to protect the diodes from the voltage spikes, snubbers are not required. The voltage stress on all the MOSFETs and diodes are lower. This helps to choose switches of low voltage rating (low RDS(ON)) and, thus improve the efficiency. Design and mathematical analysis of the proposed converter are made. A 250-W prototype of the converter is built to verify the performance.

A Novel Offline to Online Approach to Detect Transformer Interturn Fault

This paper presents an approach based on the use of transformer no-load and light load current harmonic analysis to detect the presence of an interturn fault at the incipient stage. The presence of fault is detected by performing a trend analysis of specific harmonic components and primary current magnitude. Transformer testing methods suffer from a common drawback of offline nature and require an expert opinion for accurate condition assessment. This paper presents a method that transforms no-load current harmonic analysis, which is a special test for transformer testing, into an online method at light load conditions. Thus, the necessity of complete shutdown and dependency on expert opinion is eliminated since it only requires one reference signature per phase. The proposed approach is verified for different vector groups of the three-phase core-type transformer and three independent units connected in star-star and for a fault on the low-voltage or high-voltage winding of the transformer. The presented experimentation shows that the proposed approach can detect the presence of a fault at an incipient stage involving less than 2% of turns and fault current up to 1 p.u. A case study is presented that validates the method for the transformer of a higher power rating.

Remote condition monitoring system for distribution transformer

Distribution transformer is an important asset in distribution network. Its operation and control are important aspects which determine the reliability and quality of power supply. A remote condition monitoring system for distribution transformer is discussed here. Different parameters are acquired and processed in remote terminal unit. This communicates the data to the operator end using internet. According to parameter values, health index of a transformer is found out at the operator end interface. Analysis is based on health index. This system is different from power transformer condition monitoring systems in condition monitoring techniques used and communication. A cheaper system is designed which precisely evaluates the health status of a transformer. The test results are taken from a specially designed transformer. This article explains the system architecture and method of analysis used in the first sections. Then test results on a distribution transformer is discussed.

Search coil based transformer inter-turn fault detection

Detection of transformer inter-turn fault at early stage is essential for increasing life of transformer and avoiding economical impacts. This paper presents a novel approach to detect transformer inter-turn fault by search coil induced voltage analysis. A healthy winding is associated with symmetrical leakage flux pattern. With initiation of inter-turn fault it does not remain symmetrical and creates distorted leakage flux pattern. This distorted leakage flux linking with search coil induces voltage based on degree of symmetry of leakage flux. Analysis of this induced voltage can detect presence of fault and also predict its severity.

Grid Interfaced Distributed Generation System With Modified Current Control Loop Using Adaptive Synchronization Technique

This paper presents real-time implementation of a grid interfaced distributed generation (DG) system with modified current control loop using three phase amplitude adaptive notch filter (AANF) based synchronization tool. A grid current feedback based modified

A Simplified Frequency-Domain Detection of Stator Turn Fault in Squirrel-Cage Induction Motors Using an Observer Coil Technique

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Computational intelligence algorithm based condition monitoring system for power transformer

-current control technique for interfacing inverter is developed in order to achieve constant loading on the grid, transient-free operation, and power factor improvement close to unity power factor (UPF) of the utility grid during sudden load variations. This technique does not require separate calculation of reference reactive component and harmonics component of currents hence reduces control circuit complexity. In addition, it requires only three voltage and three current sensors. Three phase AANF is developed and is used for online extraction of utility voltage phase angle to generate synchronized reference current signals for interfacing inverter. AANF is used because of its adjustable accuracy and amplitude adaptability even under unbalanced voltage sag and swell, frequency variation, and distorted grid conditions. Fast and accurate behavior of three phase AANF improves the dynamic response of entire DG system control performance for sudden load variations. The dynamic behavior of the proposed grid interfaced DG system is experimentally evaluated in maintaining constant loading on grid, transient-free operation, and power factor improvement close to UPF operation of the utility grid, by compensating total reactive power and harmonic current demanded by variable linear as well as nonlinear load.