Sergio Panetta

Of International Terminology and Wiring Methods Used in the Matter of Bonding and Earthing of Low-Voltage Power Systems

The worldwide global market requires electrical engineers to have a deep understanding of the bonding and earthing practices adopted in different countries around the world. This knowledge is essential to obtain effective designs and high safety standards and can promote the elimination of technical obstacles that can still create market barriers. The full comprehension of the “grounding” theory requires the command of key technical concepts regarding the earthing methods, which may cause confusion when used in the North American technical realm rather than in the International Electrotechnical Commission (IEC) world. This issue is further worsened by the lack of literature in this matter, as well as of harmonization documents between national codes and international standards. This paper, by analyzing the protection against indirect contact in ac (50/60-Hz) low-voltage power systems by automatic disconnection of supply, seeks to clarify both the terminologies and each type of grounding system adopted in IEC standards, with the intent to create a common reference for practicing engineers in the matter of bonding and earthing of power systems. Major differences encountered between sizing procedures adopted in IEC standards and the North American National Electrical Code are also examined.

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.

Neutral Grounding in MV Transformers Substations for Cranes Service

This paper analyzes crane power supply, typical distribution schemes in typical container terminals, the different system grounding techniques, and their impact on the service continuity of cranes. On the primary- and secondary-medium voltage (MV) distribution systems, provided by loop configuration, service continuity can be achieved also by TN-systems, with automatic disconnection of supply, due to the power source redundancy. The MV supplying system of a crane (lines of tertiary distribution, devices, machinery) constitutes an equipment under control EUC that has to be guaranteed to achieve or maintain a safe and integer state in case of fault events. On crane MV power supply lines with radial structure, the possibility to ensure service continuity consists in choosing an IT-system with high-resistance grounding (HRG). In fact, the faulted line can stay on service after a ground fault during the short time necessary to maintain the service of the faulted crane and contemporary to try in solving the fault or to remove the same crane.

Advanced concepts in high resistance grounding

Resistance grounding is relatively simple and easy to apply in radial distribution systems at Low Voltage. When high resistance grounding is applied, using one Neutral Grounding Resistor at the supply transformer, an alarm system to detect and indicate the ground fault is then required by the installation codes. This practice has been in use and is widely applied. This paper explores the application when the distribution systems involve multiple sources operating in parallel, such as multiple transformers, multiple generators or a combination. The sizing of NGR is explored and application of hybrid grounding is suggested for situations where Low resistance grounding needs to be used. In medium voltage systems 15 kV to 36 kV the practice has been to use very low resistance grounding. The paper suggests that the criteria for NGR sizing should be based on the net distributed charging current only. Application examples are presented showing the selective instantaneous feeder tripping and concept of hybrid grounding in Low and Medium voltage systems.

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.

Common problems in the commissioning of HRG systems

This document discusses some common mistakes that are made in the commissioning of High Resistance Grounding (HRG) systems. While high resistance grounding has been in use for some time, many commissioning teams are less familiar with HRG systems and various issues can arise in the commissioning process. Topics discussed include: compatibility of equipment with HRG systems; how system configuration affects testing and verification; and key points for training programs.

Hybrid Grounding of Electrical Systems

This paper will discuss the many different ways to ground medium voltage generators. Single source as well as multiple source units, either unit connected or bus connected, will be shown with preferred grounding schemes.

Neutral grounding in MV transformers substations for cranes service

This paper analyzes crane power supply, typical distribution schemes in typical container terminals, the different system grounding techniques, and their impact on the service continuity of cranes. On the primary- and secondary-medium voltage (MV) distribution systems, provided by loop configuration, service continuity can be achieved also by TN-systems, with automatic disconnection of supply, due to the power source redundancy. The MV supplying system of a crane (lines of tertiary distribution, devices, machinery) constitutes an equipment under control EUC that has to be guaranteed to achieve or maintain a safe and integer state in case of fault events. On crane MV power supply lines with radial structure, the possibility to ensure service continuity consists in choosing an IT-system with high-resistance grounding (HRG). In fact, the faulted line can stay on service after a ground fault during the short time necessary to maintain the service of the faulted crane and contemporary to try in solving the fault or to remove the same crane.

Mitigating electric shock and arc flash energy — A total system approach for personnel and equipment protection

This article provides a comprehensive discussion of the application and selection of various techniques and technologies available for the reduction and mitigation of arc-fault hazards to personnel and equipment. It also presents a broad approach that considers the total electrical system configuration and design. No technology can address all safety concerns. Current available technologies, such as optical light detection, pressure detection, temperature detection, and current signatures, for reducing arcflash hazard are discussed, and the advantages and disadvantages of each technique are outlined. An analysis is presented about how a total system approach can optimize the benefits of various technologies by using complementary technologies such as impedance grounding, equipment construction, and operational techniques. The importance of the fundamental power system configuration selection, equipment design aspects, and maintenance is also discussed.

Grounding of distributed low-voltage loads: The street lighting systems

Street lighting installations are publicly accessible electrical pieces of equipment out of the physical control of who operates/owns them. Street lighting systems are a typical case of low-voltage loads, distributed in a large area and collectively protected by the same protective device. In fault conditions, hazardous potentials may appear on the metal parts of such equipment, and expose persons to shock hazards. To reduce such risk, different solutions for the grounding are available. The Standard IEC 60364, and a current worldwide tendency, seem to encourage the use of Class II components, that is, equipment with double or reinforced insulation, for all the elements of the street light system (i.e. wiring systems, light fixtures, etc.). These authors examine possible technical alternatives in light of IEC standards, and propose to increase the safety of Class II metal poles by adopting a circuitry within lighting systems panelboards to monitor their double insulation-to-ground.