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Direct current (dc) systems have an increasingly important role in electrical systems, especially photovoltaic (PV) solar power plants and battery storage systems as they are essential for the development of more sustainable, efficient, and reliable electrical systems. PV panels and batteries are generally composed of multiple series-parallel cells. This fact makes their fault diagnosis challenging, especially against ground faults as these systems are generally ungrounded. In this article, a ground fault location method for dc sources with multiple series-parallel cells is proposed. It estimates the faulty branch, the faulty cell location inside this branch and its fault resistance. The method is based on the output current measurement of each branch and on the voltage measurement on a grounding resistor, which is switched between three positions: the positive, the midpoint and the negative terminals of the protected dc system. To validate it, several computer simulations and experimental tests on a battery pack have been carried out. The results obtained proves an excellent performance for faulty cell location and fault resistance estimation, although further investigations are required to better discern the faulty branch. [ABSTRACT FROM AUTHOR]

Ground fault diagnosis is difficult to carry out in dc–ac systems due to the presence of power electronics. Additionally, it is common that neither relays could protect efficiently these systems as ac devices are not prepared to actuate under dc currents and vice versa. Previous studies were able to detect if the fault was in ac or dc but the faulty point still being incognita. This article presents a ground fault location method for the ac side of dc–ac systems that complements previous detection methods. It is based on a grounding resistor connected between the midpoint of the dc bus and ground. Then, an instantaneous voltage window record is analyzed into a histogram, obtaining two representative voltage peaks that are correlated. These values are the one with most repetitions and the one with most amplitude. Attending to a coefficient defined by these two parameters, the fault location can be estimated. The effectiveness of this method has been corroborated with simulations and experimental tests in a 140 kW dc–ac converter, achieving promising results. [ABSTRACT FROM AUTHOR]

Frequency response analysis (FRA) is an extended technique for transformer condition assessment. In recent times, its proven sensitivity for detecting different type of faults have generated interest for rotating machine applications. However, at present, the interpretation of FRA results is mostly made by visual inspection of curves and is a hard task for nonexpert maintenance personnel. This article presents a mathematical model to simplify diagnostic tasks from FRA results. The developed model is called “Fault Diagram” and it is conceptualized to be applied to any coil, so it could be extensive to any type of machine. The fault diagram is based on a paradigm which states that a healthy machine is a machine with infinite impedance fault. The model uses a first-order frequency response for the purpose of fitting a linear function ∊ R3. The input of the model is the FRA curve of the machine, and the output is a point in a three-dimensional space. This approach can give an accurate diagnosis without ambiguous interpretations about if the machine is healthy or not and can provide an estimation of the fault location in case of damage. For validating the method, it was applied in a pole of a 40 MVA synchronous generator. [ABSTRACT FROM AUTHOR]

The use of variable speed drives made essential the presence of power electronic in electrical systems. The ac to dc and dc to ac conversions, thanks to rectifiers and inverters cause difficulties in the ground fault detection. In this article, a new method to detect ground faults in variable speed drives is presented. It is based on the analysis of the terminal voltage signal of a grounding resistor connected between the neutral at the secondary of the main power transformer and ground. Attending to the waveform, the ground fault can be detected on the ac grid side, dc positive or negative terminals, or ac inverter side. To verify the method, numerous simulations and experimental tests in a 140-kW power converter were carried out achieving satisfactory results. [ABSTRACT FROM AUTHOR]

The growing adoption of electric vehicles has recently attracted increasing attention of scientists and brought about pioneering research studies from various fields. Safety concerns particularly those regarding ground faults detection and protection, have extensively been addressed. Ground faults occur quite frequently in electric vehicles and they may be due to severe operation conditions, such as vibrations, twists or even crashes. Generally, the first ground fault is not dangerous, since the powertrain systems, namely, the dc bus where the batteries are connected, the power inverter and one or more ac machines, are generally ungrounded. The second ground fault, however, can produce malfunction in some systems, power loss or even serious damages. Locating the fault has often proved hard and time consuming. For this reason, the present study focuses on developing a ground-fault detection method for electric vehicles capable of determining on which side, the dc or the ac, the ground fault is located. The method is based on the analysis of the voltage in a grounding resistor connected between the midpoint of the battery pack and ground. Based on the polarity and harmonics, it is possible to locate the ground fault. This method has been verified excellent results have been achieved using computer simulations and experimental tests in a 140-kW electronic power inverter fed by a 480 Vdc battery. [ABSTRACT FROM AUTHOR]

The analysis of the stray flux for electrical machine condition monitoring is a very modern and active research topic. Thanks to this technique, it is possible to detect several types of failures, including stator and rotor inter-turn faults, broken rotor bars and mechanical faults, among others. The main advantages are that it involves a non-invasive technique and low-cost monitoring equipment. The standard practice is to use coreless flux sensors, with which the stray flux of the machine is not perturbed and there are no problems due to saturation or nonlinear behavior of the iron. However, the induced voltage in the coreless coil sensor may be very low and even, in some cases, have a similar amplitude to the noise floor. This paper studies the use of iron core stray flux sensors for condition monitoring of electrical machines. The main advantage of iron core flux sensors is that the measured electromotive force is stronger. In the case of large machines in noisy environments, this can be crucial. Two different types of iron core stray flux sensors and a coreless flux sensor are tested. A comparison of the three sensors is presented. Extensive experimental testing with all sensors shows the superiority and greater sensitivity of sensors with core versus the coreless ones. [ABSTRACT FROM AUTHOR]