Ground Fault Protection Research Articles

A Novel Ground Fault Non-Directional Selective Protection Method for Ungrounded Distribution Networks

This paper presents a new selective and non-directional protection method to detect ground faults in neutral isolated power systems. The new proposed method is based on the comparison of the rms value of the residual current of all the lines connected to a bus, and it is able to determine the line with ground defect. Additionally, this method can be used for the protection of secondary substation. This protection method avoids the unwanted trips produced by wrong settings or wiring errors, which sometimes occur in the existing directional ground fault protections. This new method has been validated through computer simulations and experimental laboratory tests.

Undercurrent Protection Power System: A Novel Ground-Fault Protection Relay Scheme

THE NATIONAL ELECTRICAL CODE (NEC) [1] requires that ground-fault protection of equipment be provided when the building service disconnecting rating becomes 1,000 A or higher. To meet such a requirement, generally, the main service breaker is specified with ground-fault protection capability. This type of breaker provides ground-fault protection for faults occurring on its load side but not for faults occurring on the line side. Such ground faults may be on the building transformer secondary windings, including the secondary feeder cable terminations at both ends. This article describes a ground-fault protection relay scheme that can provide low-level arcing, ground-fault current protection of the building transformer secondary, including secondary feeder cables. A discussion is included on meeting the design requirements of NEC 705.12 for the building's 480Y/277V main switchboard (MSB) bus rating when a photovoltaic (PV) ac inverter connection is implemented using a dedicated circuit breaker inside the switchboard.

High-Resistance Grounded Power-System Equivalent Circuit Damage at the Line–Ground Fault Location—Part I

This paper provides the electrical equivalent circuits of high-resistance grounded (HRG) power systems other than the delta-wye-connected utility power supply transformer included in Part I of this paper. This paper also provides the HRG of a medium-voltage generator for connection to an industrial power system and to a utility power system, and this paper discusses a line-ground fault with fault resistance. Three-line diagrams of ungrounded power systems are also included to illustrate the HRG application and its effect on the ground fault current during the line-ground fault. The damage at the fault location is based on the assumption that the fault remains a line-ground fault until it is cleared by appropriate ground fault protection relays. The fault resistance and the fault current that have an effect on the damage at the fault location are included. This paper provides guidance to update the current edition of the IEEE STD. 142, with respect to HRG systems.

High-Resistance Grounded Power-System Equivalent Circuit Damage at the Line–Ground Fault Location—Part II

This paper provides the electrical equivalent circuits of high-resistance grounded (HRG) power systems other than the delta-wye-connected utility power supply transformer included in Part I of this paper. This paper also provides the HRG of a medium-voltage generator for connection to an industrial power system and to a utility power system, and this paper discusses a line-ground fault with fault resistance. Three-line diagrams of ungrounded power systems are also included to illustrate the HRG application and its effect on the ground fault current during the line-ground fault. The damage at the fault location is based on the assumption that the fault remains a line-ground fault until it is cleared by appropriate ground fault protection relays. The fault resistance and the fault current that have an effect on the damage at the fault location are included. This paper provides guidance to update the current edition of the IEEE STD. 142, with respect to HRG systems.

Grounding Method and Protection of Low Voltage Multiple Generators

This paper focuses onproper grounding practicesandgrounding fault protectionfor low voltage generators in island mode. The paper presents the fundamentals of power system grounding and requirements of IEEE with respect to grounding, the need for low voltage ground fault protection and implement is execution. The paper outlines the solid grounding method is used and necessary grounding fault protection for multiple generators in low voltage system.

PARALLEL UNIT-CONNECTED GENERATOR MODEL FOR THIRD HARMONIC STATOR GROUND FAULT PROTECTION

Conventional ground fault protection schemes can be applied for any generator terminal connection but it covers at most 95% of generator stator length. 100% protection for synchronous generator stator winding can be achieved by a combination of zero sequence and third harmonic protection schemes. The implementation of the third harmonic scheme on any generator is determined by magnitude of third harmonic voltage produced in the generator. The methods of connecting the generator terminal also influence the range of third harmonic voltage at the stator terminal and neutral. An investigation into the compatibility of particular generator configuration with the third harmonic scheme is important to prevent protection mal-operation since the scheme is hampered in performance by certain factors which include grounding method employed and generator terminal connection among others. In this paper, the modelling of parallel unit-connected generators of the second order is presented to study the influence of parallel unit-connected generators on third harmonic stator ground fault protection. Application of mesh analysis method to the circuit models produced ordinary non-linear algebraic equations. The equations were solved using Cramer’s rule. Simulations of the circuit models were performed for no-load, light load and full load conditions using MATLAB/SIMULINK to study the character of third harmonic voltage at stator neutral and terminal when a ground fault occurs to validate the results of the models. Introduction of a ground fault at the neutral point of the single generator showed that the third harmonic voltage decreased towards zero at the neutral but increased towards maximum at the terminal.

Prevention of Electrical Failure in Photovoltaic Array-II (Ground-Fault Protection and Arc-Fault Protection)

太陽光発電システムの直流電気事故対策—Ⅱ (地絡保護およびアーク保護) 石井 隆文

Choosing the Correct Transfer Switch

Standby generation systems in low- and medium-voltage applications connect to the utility power system in a number of different ways. Typically, an automatic transfer switch is a part of most power system connections. Engineers can choose three- or four-pole transfer switches for the intertie point. The application's sensitivity to a power interruption during switching helps determine transfer-switch selection. The transfer switch can be contactor or circuit breaker based, or it can be a bypass design. At medium voltage, special requirements must be considered. Ultimately, the correct arrangement must be chosen depending upon grounding locations and neutral bonding. Incorrect power system bonding and grounding can cause unwanted transients or hazardous multiple grounds (improper ground-fault protection) depending upon the transfer-switch selection. Improper design can create unintentional current paths and defeat ground-fault protection. A transfer switch must be chosen for robust operation and maintenance at the beginning of the design process.

English

This paper presents a set of analysis tools for self learning for radial power system protection training (Bouhenna 2010). It automates a radial feeder for an overcurrent protection that would include fault calculations, fuse-fuse co-ordination, current transformer, relay-relay and fuse-relay co-ordination, directional overcurrent protection, ground fault protection, automatic recloser and sectionalizer. The software explains the function of all these protective elements and provides the students with the skills and knowledge necessary to understand and comprehend radial power system protection. Key words: Set of analysis tools, radial power system protection, fault calculations, co-ordination, protective elements.

Autonomous distributed temperature sensing for long-term heated applications in remote areas

Abstract. Distributed temperature sensing (DTS) is a fiber-optical method enabling simultaneous temperature measurements over long distances. Electrical resistance heating of the metallic components of the fiber-optic cable provides information on the thermal characteristics of the cable's environment, providing valuable insight into processes occurring in the surrounding medium, such as groundwater–surface water interactions, dam stability or soil moisture. Until now, heated applications required direct handling of the DTS instrument by a researcher, rendering long-term investigations in remote areas impractical due to the often difficult and time-consuming access to the field site. Remote control and automation of the DTS instrument and heating processes, however, resolve the issue with difficult access. The data can also be remotely accessed and stored on a central database. The power supply can be grid independent, although significant infrastructure investment is required here due to high power consumption during heated applications. Solar energy must be sufficient even in worst case scenarios, e.g. during long periods of intense cloud cover, to prevent system failure due to energy shortage. In combination with storage batteries and a low heating frequency, e.g. once per day or once per week (depending on the season and the solar radiation on site), issues of high power consumption may be resolved. Safety regulations dictate adequate shielding and ground-fault protection, to safeguard animals and humans from electricity and laser sources. In this paper the autonomous DTS system is presented to allow research with heated applications of DTS in remote areas for long-term investigations of temperature distributions in the environment.

Selection of Energizing Quantities for Sensitive Ground Fault Protection of MV Electric Power Networks

In the paper an approach to selection of energizing quantities applicable for the developed sensitive ground fault protection of MV networks is presented and results are discussed. The protection is operated basing on comparison of the argument difference value between selected harmonics of zero-sequence as voltage as well as current harmonics injected simultaneously. It was found that such correlations are particularly useful for successful detection of onerous high resistive ground faults. On the basis of simulation and investigated results the suitable conclusions if about application of proper quantities for practice were formulated. Ill. 11, bibl. 4 (in English; abstracts in English and Lithuanian).DOI: http://dx.doi.org/10.5755/j01.eee.123.7.2374

Safety Analysis of Trailing Cables Used on 2400-V Continuous Mining Machines

An analysis was performed to determine whether an increased shock hazard occurs with 2400-V continuous-miner trailing cables, as compared with those used with existing low and medium-voltage systems. (It should be noted that the Code of Federal Regulations defines low-voltage, medium-voltage, and high-voltage for mine power systems as 0 - 660 V, 661 - 1000 V, and greater than 1000 V, respectively). The study assumed that Mine Safety and Health Administration's Proposed Rule for High-Voltage Continuous Mining Machines was implemented with the exception of the special cable- handling requirements. Two major differences between the high-voltage proposed rule and existing low and medium-voltage regulations that are relevant to this study deal with ground-fault protection and include: (1) The maximum ground-fault current of the 2400-V system must be limited to 0.5 A, while the low and medium- voltage systems typically use a limit of 15 A, and (2) The maximum ground-fault pickup of the 2400-V system must be set at 0.125 A with a maximum time delay of 0.05 s; whereas, low and medium-voltage systems require an instantaneous pickup set at, or below, 40% of the maximum ground-fault current (6 A for 15-A systems). Results of the study show that the 2400-V trailing cable, in conjunction with the strict ground-fault protection requirements and enhanced cable construction, provide a higher level of safety compared with the trailing cables used on low and medium-voltage continuous miners.

Switching Transient Analysis and Specifications for Practical Hybrid High-Resistance Grounded Generator Applications—An IEEE/IAS Working Group Report #2

This paper reports on the continuing efforts of an IAS Working Group to investigate industry concerns with excessive stator fault-point burning damage in conjunction with various industrial generator grounding and ground fault protection practices. Previous working group efforts were reported in a series of papers discussing typical voltage bus connected industrial generator applications. These papers proposed a new method of grounding, called hybrid grounding, that offered the ability to limit damage while still providing the required level of ground fault current under all operating conditions. This new Working Group paper reports on the detailed design requirements for hybrid grounding. The paper reports the results of switching transient studies that formed the bases for recommended overvoltage protection. It also provides guidance in selection of equipment and fault protection required for hybrid grounding. The experience gained with several hybrid grounding applications is also reported.

Evaluación de la protección del estátor de un generador sincrónico ante fallas a tierra por medio del método de inyección subarmónica

En este artículo se hace una evaluación de la protección completa del estátor de generadores sincrónicos ante fallas a tierra utilizando el método de inyección subarmónica. Primeramente, se hace una descripción de dos enfoques para la protección completa del estátor: el método del tercer armónico y el método de inyección subarmónica. Después, se lleva a cabo un análisis del error en la determinación de la resistencia de falla a tierra para un generador sincrónico de 11.4 kV, considerando diversas condiciones de operación. Este error está relacionado con el tipo de transformadores de voltaje utilizados, la presencia de ruido en las señales, el proceso de digitalización y las variaciones en los valores numéricos de los parámetros requeridos. Finalmente, se demuestra que el método de inyección subarmónica es muy útil en la determinación de la resistencia de falla a tierra y que tiene un buen desempeño en la protección completa del estátor.

New On-Line Rotor Ground Fault Location Method for Synchronous Machines With Static Excitation

This paper presents a novel on-line rotor ground fault location method for synchronous machines, which, combined with rotor ground fault protection, can detect and locate faults in the rotor. This method is suitable for synchronous machines with static excitation systems, whose excitation field winding is fed by rectifiers through an excitation transformer. The main contribution of this new technique is that it can locate the position of a ground fault in the rotor winding online, reducing the repair time. The proposed technique is based on the analysis of the ac and dc components of the excitation voltage and the voltage measured in a grounding resistance located in the neutral terminal of the excitation transformer. This technique has been validated through computer simulations and experimental laboratory tests.

Grounding Faulted Feeder Detection Based on Fuzzy Clustering Algorithms

Many power distribution systems have been operated with neutral ineffectively earthed, and earth fault current is no more than a few tens of amperes. Traditional earth fault detection methods based on zero sequence current has poor precision and sensitivity in this case. For improvement, a novel principle for feeder grounding fault protection based on fuzzy clustering algorithms is presented in this paper. First, the historical data are divided into two groups by fuzzy clustering algorithms. The space relative distance among detected pattern and two cluster centers is then calculated to discriminate the faulted feeder. It can detect high impedance grounding faults (HIGF). The scheme has been verified by EMTP simulation, and results show that the proposed scheme always trips all kinds of grounding faults with high sensitivity and robustness in neutral ineffectively earthed power systems (NIEPS).

2 Step 이상 운용 고객의 구내배전계통 지락보호시스템 구성 현황 및 문제점 검토

Most accidents occurred in power receiving & transforming facility are ground fault. The quality of power supply is deteriorated since the ground fault is not detected promptly. This paper analyzes the problems about system-grounding type of 2 step power receiving & transforming facility, arrangement of protection relaying scheme and ground-fault protection system of ungrounded system. Then, this paper presents the arranging scheme of system-grounding type to improve power supply reliability.

On Human Life Risk-Assessment and Sensitive Ground Fault Protection in MV Distribution Networks

The minimum phase-to-ground fault current required to be sensed by protection systems in medium-voltage (MV) networks can be as low as 0.7 A in a few countries, leading to a lot of undesired relay trips and poor service quality to costumers. However, these settings raise the protection threshold above the minimum fault current that concerns network operators regarding human safety, although they cannot be practiced when grounding is distributed. The purpose of this paper is to present a risk assessment foundation to determine the required protection sensitivity to ensure human safety in MV distribution networks. The proposed approach is based on a biophysical model included in IEC standards, the consideration of current paths models for typical faults and Monte Carlo methods to deal with nonlinearity, and the many involved random variables. Downed conductors and line-to-concrete pole faults are investigated and sensitivity analysis performed to highlight some important determinants of the results.

The Dangers of Grounding Resistor Failure

A resistance-grounded power system has a critical element that is often ignored-the neutral-grounding resistor (NGR). During a single-phase-to-ground fault, current flows from the transformer or generator winding through the faulted-phase conductor to the fault and to ground, returning to the source winding through the ground-return path and the NGR. The information presented here has shown that an open NGR is an undesirable situation. A system with an open NGR is subject to transient overvoltages, and so current sensing ground-fault protection will not indicate the presence of a ground fault. A ground fault then remains on the system and might escalate to a phase-to-phase fault. NGRs are subject to failures related to thermal overload, lightning, storms, earthquakes, wildlife, extended service life, manufacturing defects, vibration, corrosion, and improper specification or installation. A well-designed NGR monitor provides continuous protection against failures that previously rendered ground-fault protection, coordination, and annunciation systems inoperative, as well as leaving the system exposed to damaging transient overvoltages. An NGR monitor provides confidence that current-sensing ground-fault protection will operate as designed on the next ground fault.

Protection from ground faults in the stator winding of generators at power plants in the Siberian networks

The experience of many years of experience in developing and utilization of ground fault protection in the stator winding of generators in the Siberian networks is generalized. The main method of protection is to apply a direct current or an alternating current with a frequency of 25 Hz to the primary circuits of the stator. A direct current is applied to turbo generators operating in a unit with a transformer without a resistive coupling to the external grid or to other generators. Applying a 25 Hz control current is appropriate for power generation systems with compensation of a capacitive short circuit current to ground. This method forms the basis for protection of generators operating on busbars, hydroelectric generators with a neutral grounded through an arc-suppression reactor, including in consolidated units with generators operating in parallel on a single low-voltage transformer winding.