A novel voltage sag approach during unintentional islanding scenarios: A survey from real recorded events

In this paper, a new voltage sag approach is analytically modelled and validated using both simulation and field measurements. The main aspect of this approach is to propose a new voltage sag feature which appears during unintentional islanding operations (IOs). The unintentional IO occurs when an induction motor is removed from the main utility following a circuit breaker (CB) clearing, transiently, the induction motors (IMs) are acting as generators maintaining the affected distribution feeder with voltage until it is reconnected. The voltage sag modelled in the current article follows an exponential form, as a matter of fact, here it will be demonstrated that the proposed model reaches satisfactorily the field measurements and evidences the dependability of the model adopted. Furthermore, it is worthwhile to note that this novel power quality (PQ) event has not been investigated yet and enhances voltage sag studies. Lastly, it is crucial to point out that all recorded events and a large amount of data needed so as to validate this transient, has been measured in a distribution network (DN) located in Spain.Postprint (published version

A novel voltage sag approach during unintentional islanding scenarios: A survey from real recorded events

In this paper, a new voltage sag approach is analytically modelled and validated using both simulation and field measurements. The main aspect of this approach is to propose a new voltage sag feature which appears during unintentional islanding operations (IOs). The unintentional IO occurs when an induction motor is removed from the main utility following a circuit breaker (CB) clearing, transiently, the induction motors (IMs) are acting as generators maintaining the affected distribution feeder with voltage until it is reconnected. The voltage sag modelled in the current article follows an exponential form, as a matter of fact, here it will be demonstrated that the proposed model reaches satisfactorily the field measurements and evidences the dependability of the model adopted. Furthermore, it is worthwhile to note that this novel power quality (PQ) event has not been investigated yet and enhances voltage sag studies. Lastly, it is crucial to point out that all recorded events and a large amount of data needed so as to validate this transient, has been measured in a distribution network (DN) located in Spain.Postprint (published version

Power quality disturbances assessment during unintentional islanding scenarios. A contribution to voltage sag studies

This paper presents a novel voltage sag topology that occurs during an unintentional islanding operation (IO) within a distribution network (DN) due to large induction motors (IMs). When a fault occurs, following the circuit breaker (CB) fault clearing, transiently, the IMs act as generators due to their remanent kinetic energy until the CB reclosing takes place. This paper primarily contributes to voltage sag characterization. Therefore, this novel topology is presented, analytically modelled and further validated. It is worth mentioning that this voltage sag has been identified in a real DN in which events have been recorded for two years. The model validation of the proposed voltage sag is done via digital simulations with a model of the real DN implemented in Matlab considering a wide range of scenarios. Both simulations and field measurements confirm the voltage sag analytical expression presented in this paper as well as exhibiting the high accuracy achieved in the three-phase model adopted.Postprint (published version

Use of low smoke and halogen free cables for marine fire safety design

Safety of shipping is a growing concern. The causes of shipping casualties are various. A fire on a ship is one of the most hazardous incidents which can happen on board and a common cause of damages and accidents in ships. However, this knowledge decreases where electrical installations, whose effects are less well-understood, are involved. Because of these effects and risks, the regulations related to cables for a vessel’s electrical installations anticipate the use of special low fire propagation and fire-resistant cables made with low smoke emission and halogen-free materials. Despite these criteria, the regulations permit the use of materials such as PVC. The main purpose of this research is to identify the risks associated of the use of PVC versus Low Smoke Zero Halogen (LSOH) cables that could be present for equipment safety and people in case of fire. As a result of the implementation of the regulatory framework, test results from PVC and LSOH cables used in ships have beenobtained. Finally, the use of LSOH cables is implemented to assess the effect of fire risk reduction measure for the enhancement of safety of shipping in coastal waters, efficiency and protection of the environment.Postprint (published version

Theorical and descriptive analysis of the wave energy in the Barcelona World Race

The main objective of this paper is the presentation of a theoretical study of the wave energy in some zones of the Barcelona World Race (BWR) considering different theories, how much of this energy is transferred to the boat and if it is possible to use that energy, as propulsion energy. Nowadays, the absorption of wave energy (offshore, inshore or on board) is low utilized and has important costs. That makes this subject become more interesting. The first section of this paper is a study of the movement of the waves with different descriptions and of the energy potential depending on characteristic’s value. Secondly, a categorization of the wave’s characteristics is done of a part of BWR with the objective to be able to do an energy atlas of different areas. After that, a model of the vertical motion (simplified motion) is done in order to express the energy which is in the kinetic phase difference between the wave action and the boat reaction. Finally, all factors in the synchronism motion between wave and boat have been evaluated (in surf navigation) in order to analyze the results of equilibrium and the result force with different power propulsion.Postprint (published version

Reduced scale feasibility of temperature rise tests in substation connectors

Due to the important increase of the power of electrical transmission and distribution grids expected for the following years, especially in developing countries such as Kenya, Brazil, Philippines or Mexico among others, that have planes of generating energy from clean sources far away from the centres of consumption [1] it becomes a matter of special importance adapting and developing new substation connectors’ testing methods according to the power and temperature regimes at which they are expected to work. The international normative frame of substation connectors established both by the International Electrotechnical Committee (IEC) [2] and the National Electrical Manufacturers Association (NEMA) [3] sets standardized tests for the evaluation of high voltage connectors. These tests are routinely done within the quality plans of the manufacturers. At the moment, testing of substation connectors –and in general switchgear and fittings- is time demanding and costly due to the energy consumed by such tests. The expectations for the following years are that the power consumption of these tests will not do nothing but grow due to expected increase of power of worldwide overhead lines. For instance, today temperature rise tests in substation connectors involve power ranges up to 100 kVA, which are applied in cycles that can last several weeks. These tests are only feasible in few laboratories and at a very high cost: temporary, monetary, energetic and environmental. For this reason, following the line of other technologies such as aeronautics, naval engineering, or automotive as well as other studies done in the field of electrical engineering specially related to the corona effect [4], this study proposes to develop a reduced scale test system to perform temperature rise tests for substation connectors. Both, a theoretical framework based on analytical formulas, finite element method (FEM) simulations and experimental data has been developed to conduct reduced scale temperature rise tests and to set the conditions at which they provide comparable results to those attained in the original scale tests. Firstly, two circular loops (original and reduced scale loops) composed of a power conductor and two terminal connectors were analysed. The aim of this first study was to determine in an easy and trustful way the voltage and current values to be applied in experimental reduced scale tests to achieve the same steady-state temperature as in the original scale temperature rise test. The scale relationship between tests was set in 1:1.8, although the method proposed in this study can deal with any other scale factor. This study was useful in order to have a first sight of the final results of the procedure using substation connectors.Postprint (published version

Design of a simpler ampere-hourmeter

In any application in which working with batteries is a must, the knowledge of the batteries’ state-of-charge (SOC) is a fundamental parameter for anyone, so it determines the remaining capacity in the battery. There exist several methods for the estimation of this SOC in Lead-acid batteries; however, when the requisites of the measuring method must offer, besides precision and reliability, the possibility to integrate the results into an automatized system, the Coulomb’s counter is the method that prevails. This paper presents, then, the design of a simpler Ampere-hourmeter based lead-acid battery SOC estimating system. Supported by previous studies in the field of SOC estimation in Hybrid Electric Vehicles and by experimental tests carried out by the researchers, the modelling of the simpler measuring system has been parameterized by following Peukert’s Equation, and afterwards it has been integrated into a data acquisition and processing system designed through a CSNX25 current sensor and a low-cost and low-consume 16F877 microcontroller. The fundamental conclusion of this paper is that obtaining an accurate result while estimating the SOC of a lead-acid battery with an simpler Ampere-hourmeter developed through a microcontroller based system is achievable but only if the used microcontroller holds enough memory to include the whole data treatment algorithms.Peer ReviewedPostprint (published version

Simplification and cost reduction of visual corona tests

Peer ReviewedPostprint (author's final draft

Transient thermal modelling of substation connectors by means of dimensionality reduction

This paper proposes a simple, fast and accurate simulation approach based on one-dimensional reduction and the application of the finite difference method (FDM) to determine the temperatures rise in substation connectors. The method discretizes the studied three-dimensional geometry in a finite number of one-dimensional elements or regions in which the energy rate balance is calculated. Although a one-dimensional reduction is applied, to ensure the accuracy of the proposed transient method, it takes into account the three-dimensional geometry of the analyzed system to determine for all analyzed elements and at each time step different parameters such as the incremental resistance of each element or the convective coefficient. The proposed approach allows fulfilling both accuracy and low computational burden criteria, providing similar accuracy than the three-dimensional finite element method but with much lower computational requirements. Experimental results conducted in a high-current laboratory validate the accuracy and effectiveness of the proposed method and its usefulness to design substation connectors and other power devices and components with an optimal thermal behavior.Postprint (published version

The influence of the self-excited induction machine into the electrical grid under instability situation - Real case measurement

The three phase induction machine is used in the mainly part of the industry and it requires reactive power from the grid to start and function. The reactive power consumption is economically fined so the industries install capacitors in parallel with the motors and loads. The bank capacitor, gives this reactive power to the machine in order to improve the cos f factor in the installation. When a fault appears in the grid, this machine gives the active power to the fault, but when the overcurrent relay sets the fault, the induction machine is already with inertia with electromagnetic and mechanic specific parameters that originate a non-controlled islanding mode and it provides the power to the loads on this feeder. Even though several works are published within the islanding detection, the islanding operation about the induction machine as a generator in power wind energy applications, nevertheless in the following we show the motor perspective. The stability of the system in the time period between the relay opening and the fast reconnection is out of control, so a complete study a about the electric magnitudes, voltage and reactive power , active power and frequency and the angle stability is needed. In this paper we show a real case that appears in a distribution Medium Voltage (MV) radial network in Spain in a 25 kV feeder and we summarize the voltage /current wave form and the frequency oscillation.Postprint (published version