Continuous Monitoring of Neutral Grounding Resistors and Reactors

Electrical power system components are designed three-phase balanced and symmetric with the internal connection of wye or delta. The common point of the wye-connected equipment, which is called neutral, is impedance grounded for many reasons such as fault ride through by controlling transient overvoltages, and limiting the ground overcurrents. Depending on the application, different neutral impedance grounding methods exist that employ resistors or reactors with/without neutral grounding transformers. These apparatuses are known as Neutral Grounding Devices (NGD). The most well-known sort of NGDsarethe Neutral Grounding Resistor (NGR) and Neutral Grounding Reactor (NGL) which are the main focus of this research work. As said, NGDs provide many benefits; however, they fail due to many reasons such as corrosion, lightning, and extended service life. Upon this failure, the advantages of impedance grounding are replaced by disadvantages of the ungrounded or solidly grounded traditional systems. Consequences of such a failure are the false sense of security, ungrounded system, transient overvoltages, overcurrents, line-to-ground voltage test non-safety, and so on. In order to prevent these issues, the intactness and integrity of the neutral-to-ground circuit shall be ensured. However, this cannot be done easily since the neutral-to-ground circuit is dead or de-energized during the steady-state condition. However, there has to be a continuous and online monitor, which without it there is no guarantee or indication that these apparatuses have failed. That is why the Canadian Electric Code (CEC) mandates monitoring of the neutral-to-ground circuit in industrial and commercial networks. Accordingly, this research work first reviews the existing monitoring methods to understand the fundamentals, and performance of these techniques. The performed literature survey results in a conceptual classification of the existing methods into three categories called passive, active, and passive-active. This part of the carried-out research highlights the advantages and disadvantages of the methods on one hand, and the evolution trend of the methods on the other. It also reveals that all of the existing methods suffer from one shared issue which is the hard-to-achieve continuous monitoring. In fact, they cannot provide continuous or uninterrupted operation in all system conditions, i.e., normal, faulted, and de-energized. It is this major shortcoming of the literature which motivates towards making a difference. Therefore, the mission is to resolve this issue relying on the existing measurement instruments and protection installations. As the results, three new or enhanced methods are achieved. The first technique is a cost-effective combination of two existing techniques resulted in a better performance. The performance of this proposed method is comprehensively studied using software analysis, and a fabricated prototype of the invented mechanism for full-range neutral voltage measurement. The resulted method provides reliable monitoring during both faulted and unfaulted conditions of the power system which is the most prominent advantage of the proposed technique since none of the existing methods, with the same measurements, provide the such a performance. The second proposed technique is an economical solution that employs the third harmonic of neutral and residual voltages for monitoring the NGR installed at the neutral of the unit-connected generators. The proposed technique is comprehensively studied including further hardware validations using an available industrial generator protective relay. The required measurement instruments and protection infrastructures are readily available which means that the proposed method could be implemented with no additional cost. In fact, the proposed method could be easily incorporated into the core of the existing digital protective relays. Lastly, the third technique employs an existing sub-harmonic injection based generator stator ground protection for monitoring the neutral-to-ground circuit of the same generator, which is equipped with either the neutral grounding resistor or neutral grounding reactor. This alternative is also a money-saving solution since it only demands a current sensor to measure the injected current. It is also easily retrofitted to installed digital protective relays. The other advantage of this proposed method is its functionality in de-energized condition of the power system besides its reliable performance in both faulted and unfaulted operation conditions. It is this one last accomplishment that brings the mission to completion

Improving the Performance of Low Voltage Networks by an Optimized Unbalance Operation of Three-Phase Distributed Generators

This work focuses on using the full potential of PV inverters in order to improve the efficiency of low voltage networks. More specifically, the independent per-phase control capability of PV three-phase four-wire inverters, which are able to inject different active and reactive powers in each phase, in order to reduce the system phase unbalance is considered. This new operational procedure is analyzed by raising an optimization problem which uses a very accurate modelling of European low voltage networks. The paper includes a comprehensive quantitative comparison of the proposed strategy with two state-of-the-art methodologies to highlight the obtained benefits. The achieved results evidence that the proposed independent per-phase control of three-phase PV inverters improves considerably the network performance contributing to increase the penetration of renewable energy sources.Ministerio de Economía y Competitividad ENE2017-84813-R, ENE2014-54115-

Contactless Rotor Ground Fault Detection Method for Brushless Synchronous Machines Based on an AC/DC Rotating Current Sensor

Brushless synchronous machines (BSMs) are replacing conventional synchronous machines with static excitation in generation facilities due to the absence of sparking and lower maintenance. However, this excitation system makes measuring electric parameters in the rotor challenging. It is highly difficult to detect ground faults, which are the most common type of electrical fault in electric machines. In this paper, a ground fault detection method for BSMs is proposed. It is based on an inductive AC/DC rotating current sensor installed in the shaft. In the case of a ground fault in the rotating parts of the BSM, a fault current will flow through the rotor’s sensor, inducing voltage in its stator. By analyzing the frequency components of the induced voltage, the detection of a ground fault in the rotating elements is possible. The ground faults detection method proposed covers the whole rotor and discerns between DC and AC sides. This method does not need any additional power source, slip ring, or brush, which is an important advantage in comparison with the existing methods. To corroborate the detection method, experimental tests have been performed using a prototype of this sensor connected to laboratory synchronous machines, achieving satisfactory results.This research was funded by Universidad Politécnica de Madrid under grant number RP2304330031

Comparative analysis of cold ironing rules

Postprint (published version

Effect of Induction on Control/Signal Cables on Shunt Capacitor Bank Protective Schemes

Power factor correction is the main application for shunt capacitor units in the power system. The advantage of improved power factor is reduced line and transformer losses, improved voltage profile, reduced maximum demand, and improved power quality. The capacitors are installed in a distribution system on pole-mounted racks, substation banks, and high voltage (HV) or extra-high voltage (EHV) units for bulk power applications. Capacitors have many applications in power systems: they can be used in series to compensate the inductance of transmission lines to transmit more power. They can also be used as surge capacitors, starting motors, and static VAR compensators. Capacitor banks installed in power substations are vital in the sense that they provide the reactive power needed for the power system, which in turn improves the voltage profile in the system. There is always the option of grounding the banks or leaving them ungrounded. Each of the above configurations has its own advantages and disadvantages; to name a few, ungrounded banks are slightly more expensive compared to grounded banks as the neutral point needs to be insulated up to system basic insulation level; whilst grounded banks are prone to inject high-frequency transients (e.g., switching, ground faults) into the ground mat. This study is intended to address the recent incident in a high-voltage substation which led to the explosion of a capacitor bank. The study goes on to suggest grounding as a method to prevent such incidents. Furthermore, the effects of grounding and induction on control/signal cables as well as protecting relays are investigated

Modeling Of Generator Neutral Ground System Using Labview 2017 Application IEEE std C62.92.2TM

The generator is a device for an important source of electrical energy, so the continuity of the generator operation must be maintained and well controlled, in controlling the grounding on the generator can use in control with software such as MATLAB and Modeling the design of the grid grounding system using LabView 2017, Determination of the grounding system for the neutral value of the generator through the distribution transformer, can be done through manual calculation. The use of many parameters considered in the calculation to obtain appropriate and measurable results there is a possibility of repeated calculations. This is very difficult and causes a large difference in calculation results. Therefore, a computer-based computing system is needed to overcome problems like this. Several papers have developed calculations of the amount of generator neutral grounding required that consider the voltage level, short circuit fault current and ground fault protection system. This paper discusses modeling and simulation in designing generator neutral grounding using LabView 2017 application. The goal is to be easier, faster and more accurate. As an implementation of modeling, data from std C62.92.2TM-2017 is used

Grounding and Charging Strategy for Ships during Cold Ironing Operation

In order to minimize the pollution that ships generate at ports, ships can be connected to the utility grid during charging, also known as shore-to-ship connection or cold ironing operation. The pollution can also be remarkably reduced if the ships are full-electric or hybrid. With the utilization of a common DC bus, several ships can be charged simultaneously. However, due to the common DC bus, the ships are not galvanic isolated from each other such that leakage current can occur among the ships and the quay when the current leaks to the ground during a fault. Hence, this paper proposes a complete charging and grounding strategy, which will provide galvanic isolation between the ships and the quay. The charging and grounding strategy are verified through simulations in the Matlab/Simulink environment. An isolated and ideal PSFB DC-DC converter with a rated power of 400 kW was proposed to obtain galvanic isolation. The proposed converter obtained a stable output during nominal and half load from the simulation results. In addition, two grounding systems on the shore-side and the ship-side were proposed. On the shore-side, a double grounding TN-C grounding system with a NGR resistor was designed such that the leakage current can easily be detected when a ground fault occurs. On the ship-side, an IT system with HRMG resistors was designed to reduce the leakage current such that the risk of corrosion was reduced and provided safety for personnel. As a result, a fault on the shore-side did not affect the ship-side grounding system and opposite. Faults that can appear on the charging system were found through research and simulated with the complete charging and grounding system to verify that the grounding system was optimally designed. The results during a fault on the system showed that the shore-side grounding system was not optimally designed because the NGR did not reduce the fault current to a lower value than 25 A. The common DC bus was created from an uncontrolled rectifier that suffered a substantial power dissipation. As a result, the output of the PSFB DC-DC converter was unstable. Therefore, a resistor was added to the TN-C grounding configuration during simulations of the charging system to achieve a stable output of the DC-DC converter. The IT grounding configuration on the ship-side reduced the fault current to 6 mA during a LG fault, and personnel safety was kept at a safe level when a person touched one of the DC lines. However, it was shown that the personnel safety was not obtained when a person touched the energized chassis due to a dangerous voltage potential

ACTIVE CURRENT INJECTION METHOD FOR LIMITING GROUND FAULT CURRENT HARMONICS IN UNDERGROUND COAL MINES

Current practice in U.S. underground coal mine high-voltage distribution systems is to attempt to limit ground fault current to 25 Amperes and de-energize the circuit at 10 Amperes. However, the significant amount of system capacitance due to the use of shielded cables can cause ground fault current to be two or three times the intended ground fault limit. Consequently, this practice can cause several issues such as ground fault currents significantly exceeding the neutral grounding resistor current limit, loss of relay selectivity in the distribution system, and transient overvoltages in certain ground fault situations. These issues are solved to some extent by using a resonance grounded system, currently used in some other countries. However, a shortcoming of traditional resonance grounded systems is the inability to deal with the harmonic components existing in ground fault current. With the increasing use of nonlinear sources such as variable frequency drives, the proportion of harmonic components in ground fault current can be significant. Consequently, although the fundamental component can be almost fully compensated in a traditional resonance grounded system, the harmonic components can still be large enough to maintain arcing and cause personal injury and equipment damage. In this dissertation, a novel method is developed to perform real-time prediction of the harmonics in ground fault currents. Methods for neutralizing the ground fault current harmonics and identifying ground fault location are also developed. Results indicate that the combination of traditional high-resistance grounding and active current injection to neutralize harmonics in the ground fault has the potential to significantly reduce the total ground fault current and reduce arc and flash hazards during ground faults in high voltage distribution systems

Retention and application of Skylab experiment experiences to future programs

Problems encountered on Skylab Experiments are listed in order that these experiences and associated recommendations might help to prevent similar problems on future programs. The criteria for selection of the data to be utilized was to identify the problem areas within the Skylab Program which would be of major significance with respect to future programs. Also, the problem had to be unique in that it would help identify to a designer/manufacturer an unforeseen or unanticipated occurrence which could cause failures, delays, or additional cost. Only those unexpected problems that may occur due to the nature of aerospace experiment environmental and operational requirements are included

Simulation and Analysis of High Voltage Engineering in Power Systems

This book address important issues regarding the modelling and simulation tools and techniques that are applied in high-voltage engineering in modern power systems. The presented conceptual, constructive, empirical, experimental, and theoretical results are obtained in the area of high-voltage engineering. Special attention is given to protection methods against direct lightning strikes, partial discharge tests, discharges’ influence on different structures, cable screening, and induced voltages, among others