Rapid expansion of solar photovoltaic (PV) installations worldwide has increased the importance of electromagnetic compatibility (EMC) of PV components and systems. This has been highlighted by interference reported from PV installations (PVI) in the Netherlands, the United States, Sweden, etc. Significant research and development efforts are seen in the domain of enhancing efficiency and economic viability of PVI, whereas the EMC aspects have received less attention and are mainly focused on the PV system acting as a victim of lightning and a victim of changing grid impedance. This article presents a review of the important EMC aspects of PVI as a disturbance source. It has the following main parts: (a) reported cases of emissions and interference from PV installations; (b) modeling and analysis of PV subcomponents from an EMC perspective; and (c) the main standards related to the topic. Mitigation techniques for improving EMC aspects of PVI are also described, along with suggested directions for future research. The compilation brings together wide-ranging sources, both for EMC engineers who want to understand the EMC context of PV systems and for PV system designers seeking to improve EMC performance.

Grid-forming (GFM) inverters are anticipated to play an essential role in facilitating the integration of renewable energy in bulk power systems. The fault response of GFM inverters and its impact on traditional protection schemes are ongoing research topics. Distance protection is today one of the most commonly applied protection schemes and depends on multiple system preconditions for reliable operation—many of which may no longer hold in systems with a high penetration of inverters. This paper investigates the impacts of GFM inverters on distance protection, with the main objective of providing an improved understanding of the topic. Important interoperability issues are highlighted with simulation results and elaborated upon based on the theory behind the distance relay model and the behaviours of GFM inverters during faults. The simulations consider numerous fault types and two GFM inverters with different current-limiting control techniques in their fault-ride through strategies. Results indicate several challenges that state-of-the-art distance relays may face with GFM inverters.

One way forward in the development of protection schemes for power grids with a high penetration of renewable energy, is to assume very little about the sources and operate before the sources have had time to react to the fault. Instantaneous incremental quantities (IQs) are data signals that require very short time windows, while also being rich with information about the faulted system. Grid-forming (GFM) inverters are anticipated to take over the ancillary services currently provided by strong conventional sources to accommodate more renewable energy. They are controlled as voltage sources; hence the injected current changes near instantaneously upon a fault inception and activates the nonlinear current limiter. Consequently, the current limiter impacts not only the steady-state fault response of GFM inverters, but also their transient response, depending on the speed of the inner current control loop to realize the limited current reference. This paper investigates the performance of an instantaneous IQ-based relay with a GFM inverter, and explains from the fundamental theory of IQs, how GFM inverters may impact various IQ-based relay elements. A fault detection element, a phase-selection element, a directional element and a distance underreaching element are covered. Results indicate that, compared to traditional implementations of such relay elements, IQ-based relays can have improved dependability and security with GFM inverters. However, the current limiter still has a significant impact on the single-ended distance underreaching element.

This paper analyzes the interactions between conventional Line Distance Protection (LDP) relays and Grid-Forming (GFM) inverters. Various fault types, arc resistances and locations were investigated in a PSCAD model consisting of either a Synchronous Generator (SG) or a GFM inverter connected to the utility grid by a transformer and two transmission lines. A simple distance relay algorithm was coded in Matlab, tuned for the SG and then analyzed together with data obtained from the same system but using a GFM inverter instead. It is found that the inverter can make the relays able to trip correctly for many zone 1 faults, even if the impedance trajectory becomes unstable. However, the inverter causes several misoperations for zone 2 faults. The reasons are that the impedance trajectories either do not settle within zone 2 due to the inverter becoming unstable or they incorrectly enter zone 1. Moreover, the fault arc resistance and fault location can greatly impact the impedance trajectories obtained when the GFM inverter is connected. Additionally, operating the transmission line above its Surge Impedance Loading (SIL) also increases the risk of making the inverter unstable during faults, causing difficulties with zone 2 protection. When transferring power close to the SIL of the line, it can more reliably become stable but the fault current on the high voltage transmission line tends to be of capacitive nature and thereby making the impedance trajectories settle outside the trip zones.

Considering inverter as the source of electromagnetic emission signals in a photovoltaic (PV) plant, a comprehensive set of measurements of conducted emissions at the input and output of the inverter in a 10 kW PV plant are presented. These are particularly relevant on the backdrop of (a) ban of products in the EU market due to non-compliance and (b) the increased switching frequency in the inverters ( 100s of kHz) in near future. Specifically, the common mode (CM) and differential mode (DM) currents and voltages are measured, and their frequency domain behavior is studied. It is suggested that conducted emissions from PV can be classified into three zones: viz., extremely low frequency (ELF) zone, power frequency zone, and switching frequency zone. Important observations from this exercise are measurement of harmonic contents of current with total rated current distortion (TRD), imbalance in the output voltage and low frequency ripples in the DC voltage. Frequency domain behavior of the CM quantities is studied which throws light on important points like relation between input and output CM quantities, relation between CM voltage and CM current.

Detecting and locating local degradations at an incipient stage is very important for mission-critical high-voltage rotating machines. One particular challenge in the existing testing techniques is that the characteristic of a local incipient defect is not prominent due to various factors such as averaging with the healthy remainder, attenuation in signal propagation, interference, and varied operating conditions. This paper proposes and investigates the frequency domain reflectometry (FDR) technique based on the scattering parameter measurement. The FDR result presents the object length, wave impedance, and reflections due to impedance discontinuity along the measured windings. Experiments were performed on two commercial coils with artificially created defects. These defects include turn-to-turn short, surface creepage, loose coils, insufficient end-winding spacing, and local overheating, which are commonly seen in practice. Two practical water pumps in the field were also selected for investigation. The study outcome shows that FDR can identify and locate structural and insulation degradation in both shielded and unshielded objects with good sensitivity. This makes FDR a complementary technique for machine fault diagnosis and aging assessment.

Fault location methods are crucial for reducing fault restoration time, and thus improving a network's system average interruption duration index (SAIDI) and customer outage cost. Resonant-earthed systems pose problems for traditional fault location methods, leading to poor accuracy and a need for additional complexity. In this context, methods that detect fault direction (fault-passage indicators, FPI) at multiple points in the network may show advantages over a central distance-estimation method using fault locators (FL) of poor accuracy. This paper includes a comparative study of these two major fault location methods, comparing the reliability benefit from a varied number of FPIs or a central method. The optimal placement of the fault locating devices is found by formulating a mixed-integer linear programming (MILP) optimization approach that minimizes both outage and investment costs and assesses SAIDI. This approach has been tested on an example distribution system. However, to justify the universality of the algorithm, the RBTS reliability test system has also been analysed. The comparison of location methods and placement method of FPIs are useful for reliability centred planning of resonant-earthed distribution systems where fault location is to be used. Results show that a small number of FPIs that give accurate identification of direction may give more cost effective increase in reliability than a distance estimate by FL with typical levels of inaccuracy.

The nature of common mode (CM) parasitic impedance (ZPV) of photovoltaic (PV) panels is investigated by experimentation. Measurements are done by two methods: (a) time domain signal recording using a signal generator and an oscilloscope (b) frequency sweep using an LCR meter. It is shown that ZPV is not purely capacitive for the frequency range from 50 Hz to 1 MHz.  It is also shown that the total common mode impedance in a PV installation is affected by the nature of ZPV.  The frequency spectrum of CM current would be different if ZPV is not purely capacitive. This would affect the design of CM filters on the DC and AC side and also equipment like PV emulators, DC line impedance stabilization network, etc.

We propose a method for the fault passage indication of earth faults in resonant-earthed networks, based on phase current measurements alone. This is particularly relevant for electricity distribution systems at medium-voltage levels. The method is based on the relative magnitudes of the phasor changes in the phase currents due to the fault. It is tested for various network types and operation configurations by simulating the network in pscad and using the simulated currents as the input for an implementation of the method in matlab. In over-compensated networks, the method shows reliable detection of the fault passage, with good selectivity and sensitivity for both homogeneous and mixed (cable and overhead line) feeders. However, for the less common under-compensated systems, it has limitations that are described further in this study. The method has good potential for being cost effective since it requires only current measurements, from a single location, at a moderate sampling rate.

Present work deals with accelerated electrical and thermal stress on transformer oil and its characteristic variation on Fuller's earth (FE) reclamation. The influence of carbon particles in the fluid, its role on thermal ageing characteristics can be understood by electrical characterization. Reclamation of insulation fluid extends the lifetime and reliability of the transformer over the year of operation. The average particle size of carbon particles on electrical breakdown are in the range of 644 nm. Dielectric response spectroscopy (DRS) which identifies the conductivity and relative permittivity variation with the effect multi-stress ageing. Conduction mechanism with higher electric field is simulated by current-voltage (IV) characteristics using non-uniform field configuration to derive the ionic mobility of the liquid. Dissolved decayed products and turbidity showed drastic enhancement with multi-stress ageing than the thermally aged specimen. Reclamation with fuller earth treatment removes the carbon traces and ageing by-products in the fluid regaining its relative dielectric performances. Rheological aspects with viscosity indicates the ageing by-products build and also its characteristic variation on the reclamation process.