Single-point Grounding Research Articles

DC ground fault monitoring method of electrical equipment in 110 kV smart substation based on improved rough set

Abstract In order to improve the effect and timeliness of ground fault monitoring and improve the effect of fault early warning, a DC ground fault monitoring method for electrical equipment in 110 kV smart substations based on improved rough sets is proposed. The characteristics of the DC ground fault current are analyzed, and the equivalent model of the DC system is constructed according to the analysis results. The low-frequency signal is enhanced according to the fuzzy rough set, and the low-frequency sampled transient zero-sequence current signal is enhanced preprocessing and wavelet packet decomposition according to the signal enhancement proportional coefficient, and the fault line is selected according to the principle of maximum energy. The wavelet packet transform method is used to decompose and analyze the waveform of the leakage current generated when a single-point grounding fault occurs in a branch of the DC system, and the grounding fault location of the DC system of the substation is realized by relative entropy operation. With the help of the cloud platform, a DC ground fault monitoring platform is built, and the ground fault monitoring is completed by using this platform. The experimental results show that the method can obtain the characteristic harmonics of the ground fault, accurately monitor whether the mutation occurs, and can realize the early warning of the ground fault of the electrical equipment in a faster time, indicating that it can realize the accurate and timely monitoring of the ground fault.

Temporary Protective Ground Cable Impedance K-Factors for Predicting Worker Touch Voltage–Basic Single-Point Grounding (1 of 2)

The IEEE Standard 1246-2011 Guide provides a method to predict worker touch voltage at grounded worksites in high-voltage alternating current (ac) substations using impedance correction K-factors for temporary protective grounds (TPGs). This is the first of two papers that provide supportive information for the grounding models and derivations of TPG impedance equations presented in that Guide. This paper introduces the reactive voltage drop principle that occurs on a TPG and develops the ground loop induction formulas for basic single- and three-phase TPG grounding scenarios.

Series-Connected Grounding of Common-Mode EMI Filter

Due to the effects of parasitic inductance, the common groundline (CGL) of capacitors in common-mode (CM) electromagnetic interference (EMI) filter is influential to filtration performance of the filter. In this paper, the effect of a single-point grounding method of CM EMI filter is first analyzed, and then, in order to eliminate the negative effect of CGL, a series-connected grounding method is introduced and analyzed. The effectiveness of the series-connected grounding method on improving the performance of CM EMI filter with CGL is verified through experiment.

On Safety Measures in Working with Induced-Voltage Overhead Lines

The authors of [1] confirm our standpoint presented in [2] concerning the hazard of induced voltage arising from the ground fault in inducing overhead lines (OL). They agree that it is necessary to determine the maximum ground-fault voltage in a network of inducing OL and reduce the induced voltage to a permissible level using terminal and intermediate OL groundings; they also suggest methods of protection from induced voltage at the repair site. They also question the correctness of the OL inducedvoltage grounding technique recommended in [3] (item 4.3.11), which has been included in the new edition of Safety Regulations [4] (items 4.15.52 – 4.15.54) with the only exception that the maximum induced-voltage potential is taken to be 25 V rather than 42 V. The criticism in [3] seems to be valid to the extent that the Safety Regulations (SR) for electric plants fail to specify requirements to the grounding device at the repair site (for an OL grounded at a single point only). On the other hand, it has been argued repeatedly [2, 5] that the single-point grounding should be installed with allowance for the voltage drop associated with the capacitive component of the ground current. It was further argued that the OL single-point grounding using a ground rod with a length of 0.5 m (the technique accepted by SR, item 3.6.8 [4]) develops a voltage that may be hazardous to human health. We believe that the reasons in [1] are quite interesting and should be taken into account when dealing with 330 kV OLs or higher; however, expanding them on all OLs and OL networks under induced voltage will be problematic. In view of the aforementioned, we reiterate that the OL induced-voltage grounding at a single point (at the repair site) is a simple and sufficiently effective means of protection from the electromagnetic component (including ground-fault situations). Protection of the personnel of electric power plants from the electrostatic component of induced voltage is effected by grounding devices of low resistance (grounding wire for 110 kV OL supports, rods for 220 kV (and higher) steel and concrete OL supports, grounding circuits, and special grounding devices for 6 – 10 kV OLs). The capacitive ground current can roughly be estimated using formulas given in [1] or in [4]; based on these data it is possible to determine the safe ground resistance at the repair site. In compliance with the new SR requirements for which the permissible grounding voltage is 25 V (formerly, 42 V), re-evaluated data in [5] for 110 and 220 V twin OLs can be used for practical purposes: safety conditions are reached using a single grounding with R < 30 U per 60 km for a 110 kV OL and per 30 km for a 220 kV OL. To check for safety, the grounding voltage should necessarily be measured at the repair site; this voltage should not exceed the rated value of 25 V. The technique for measuring the grounding voltage is rather simple, and the necessary measurements can readily be accomplished by the repair team at the working site [6]. The single-point grounding technique for induced-voltage OLs can in principle be applied to overhead lines. The use of this technique prevents the discharge of potential from the substation circuit to the de-energized line (intended for repair) through the grounding in emergency short-circuit situations at the substation or in a connected network (110 or 220 kV). Such situations are not uncommon (at the relatively high failure rate of support porcelain insulators for 110 and 220 kV disconnecting switches or actuation of short circuiters). As required by the SR, to prevent the OL under repair from being accidentally energized (or from the discharge of potential from the substation circuit), the grounding at the substation should be installed before the line-disconnecting switch as viewed from the substation. The single-point grounding (rather than the terminal grounding or on-site grounding) is less effective in the case of a “galvanic effect” produced by the accidental contact with a traversing OL. Such accidental effects are disastrous for any OL grounding scheme; however, accidents of this kind are highly unlikely if the appropriate construction-and-use regulations for electric power plants and electric power lines are strictly observed. It should be noted that in certain situations where the induced voltage is difficult to reduce using conventional grounding schemes (terminal grounding and on-site ground-

Analysis of lightning-related damages to instrumentation and control systems for water and wastewater plants

A water and wastewater treatment plant, each at a different geographical location, experienced serious damage to instrumentation and control (I&C) equipment in 1994 because of lightning-induced surges. The damage may have been caused by the following problems in installation: • • Incorrect surge suppressor installation and grounding. • • Improper grounding of shields. • • Lack of programmable logic controller (PLC) data highway protection. • • Lack of conduit bonding. • •Lack of protection on control valves. • •Violation of principle of single point grounding within control panels. Changes in installation were recommended to eliminate these problems. Following implementation of the recommendations, neither plant has experienced any lightning-related damage.

Use of Single-Point Grounding for Instrumentation and Control Systems Installed in Existing Generating Stations

General guidelines for the design of single-point grounding systems for instrumentation and control (I&C) systems are presented, along with an example illustrating the practical difficulties often involved in trying to implement an ideal theoretical solution. The single-point grounding methods presented should be recognized as an ideal approach that often has practical limitations in implementation. When properly designed and installed, however, a single-point grounding system plays a vital role in the proper operation of modern I&C equipment. >

Electromagnetic compatibility, essential for fusion experiments

Electromagnetic compatibility has been of crucial importance to fusion experiments, long before ot was known by its present name, EMC. The huge amounts of pulsed power required to create and heat a plasma, and the stray fields produced in large volumes made it difficult, in earlier and in present experiments, to reach the ideal EMC-state where interference does not hinder (or impede) operation, measurements and data acquisition. The pressure to obtain results from the experiments has led to many ingenious solutions, but left usually little time for a more fundamental study. A basic problem is that the complex three-dimensional (and often toroidal) circuitry of a fusion experiment cannot be correctly represented by network theory models. In particular extended leads no longer “transport” potentials or voltages, but of course continue to transport currents. We therefore concentrate on currents and on all closed current loops rather than on worrisome (but meaningless) “jumping potentials”. With concepts developed along these lines we can design grounding systems which protect large interconnected electrical systems against interference. Such a grounding system may use wide strips, conduits or tubes to carry all interconnecting cables from subsystem to subsystem. Alternative descriptions of this grounding system may help to clarify its operation: a screen room reduced to its essential current-carrying elements, a minimization of transfer impedances or a structure to keep the common mode circuits closely under control. In this context ground loops can be quite useful, and we abandon the concept of single-point grounding. Next to the protection by grounding and shielding, additional measures can be taken to carry signals safely into subsystems. Larger amplitude or differentiated signals are advantageous, provided the first attenuator or integrator section in the “receiver” uses only passive, linear components. EMC is essential for fusion experiments, as stated in the title. Techniques borrowed from fusion can however also be quite useful in other fields. Examples in power engineering measurements and in lightning studies are briefly mentioned.

Impact of fiberoptics on grounding of distributed electronics

How fiber optics is being used for proper single-point grounding of distributed electronic systems in industrial facilities with varying existing grounding approaches is outlined. Grounding schemes such as the conventional approach, single-point ground, total single-point ground, and signal reference grid are discussed. A fiber optics solution for a single-point ground system is presented. The author stresses that in all situations, grounding must be recognised first and foremost as a safety method and must adhere to the National Electrical Code. >

Use of single-point grounding for instrumentation and control systems installed in existing generating stations

Use of single-point grounding for instrumentation and control systems installed in existing generating stations

Test results of personal protective grounding on distribution line wood pole construction

The results are presented of a series of tests to determine the most effective method of protecting distribution line workers from accidental line energization. The project scope was limited to three-phase, grounded-wye, distributed wood-pole construction. Voltages and currents across the work area were recorded with various configurations of temporary grounds. Several configurations provided currents which are considered lethal. The results indicate that the personal protective grounding method, also called single-point grounding, provides the most effective means of protecting distribution line workers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Computer Study and Model Demonstration of Safety Ground Locations During High Voltage Line Maintenance

A digital computer study was performed to help determine whether safety grounds should be placed at the work site or at adjacent towers. Literature reviews and approximate formulas were used in addition to detailed computer simulation. During an accidental line energization, single-phase, single-point grounding reduces phase-to-tower voltages, and on that basis is the prefered method, but measures must be taken to counteract the ground level step and touch potentials. After the study, a working three-phase transmission line model was constructed to help demonstrate the study results to linemen.

Application of simple hardening techniques in system design and verification of survival by EMP and &amp;#x003B3; tests

The design and test verification of this system intended for use on the ground have demonstrated the success of the often quoted EMP and γ hardening techniques such as radio frequency shielded enclosures, single point grounding, shielded cables, surge arrestors, series resistance limiting, and circumvention. All of these simple techniques were applied in the design of the system described in this paper. This paper discusses in some detail the design and the problems associated with four of these techniques, namely series resistance limiting, circumvention, surge arrestors, and hard memory. The system survived exposure to EMP fields of 53 kV/m and dose rates of ≈ 1010 rads(Si)/s. These results also showed that the failure dose rate for a memory subsystem will be less than the dose rate for the discrete devices if the design does not take circuit interactions with the memory devices into account. Test data predicts that the memory failure level of midrange 1010 to 1011 rads(Si)/s can be achieved with careful circuit design.

A Theoretical Analysis of Grounding

This study considers three cases, ideal, single point, and ground bus grounding networks. Theoretical analysis is developed by reduction to a composite network suitable in each case. Single point and ground bus grounding networks are evaluated in terms of ideal ground plane. Derivations of these possible networks are provided, with evaluations of these networks with respect to ideal. Derivation of a realizable equipotential plane when fed by two conductors spaced a finite distance apart is developed. Various simplification reducible to closed form are used to analyze the relative merits of a common ground bus versus a steel floor ground plane. Evaluation of the derived relations and their application to the real case including recommendations for improving current grounding practice is provided.

Grounding of instrument transformer secondary circuits

The inadequacies of certain methods of grounding of instrument transformer secondary circuits have been studied by the AIEE relay subcommittee. Multi- and singlepoint grounding have been considered both pro and con. Preferred practices for grounding these circuits are recommended by this subcommittee, which is composed of engineers who have had vast experience with the subject matter.