Grounding medium-voltage mobile or portable equipment

Examples of medium-voltage mobile equipment in pulp and paper mills include rail-mounted portal cranes for log handling, chip and bark stackers, and chip-reclaim screws. No examples of portable medium-voltage equipment can be cited. National Electrical Code (NEC) section 250-188 describes the requirements for system and equipment grounding of portable or mobile equipment rated 1 kV and higher. One of the requirements of NEC section 250-188 is: the grounding electrode to which portable or mobile equipment is connected must be isolated from, and separated in the ground by at least 20 ft. from any other system or equipment grounding electrode. There must be no direct connection between the electrodes such as a buried pipe, fence, etc. This article demonstrates that even if two separate ground systems are installed in the vicinity of each other, with a spacing of 20 ft and no direct metallic bonds between these two systems, a high portion of the system ground potential rate (GPR) will be transferred to the safety ground. A spacing of 20 ft is grossly inadequate to isolate the two grid systems from most faults encountered in utility substations serving industrial distribution systems. We also demonstrate that in an industrial environment, achieving isolation between system and safety grounds may not be practical due to the physical size of the property, existing installations, or geological formations. In addition, it may not be possible to isolate medium-voltage mobile equipment frames from the plant's ground grid     

A Cathodically Protected Electrical Substation Ground Grid

A discussion is presented on the design of a cathodically protected electrical substation grounding system in which a steel ground grid and steel ground rods were used in place of the commonly used copper ground grid and copperweld ground rods. Several electrical constraints are presented which discuss common electrical utility requirements, safety considerations, and economic factors. The grounding system materials chosen are discussed along with the means of cathodic protection. Finally, the design, construction, and testing considerations are presented as an aid to others who wish to design a similar system.     

Avoiding Hazards from Earth Currents in Industrial Plants

Earth currents occurring during phase-to-ground faults can result in hazardous touch and step potentials within and around the perimeter of an industrial plant ground grid. For a plant with a common type of buried ground grid, it is shown how these earth currents occur and how the grid may be designed to ensure safety.     

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     

Development of transmission system reliability performancebenchmarks

The reliability of an electric utility transmission system is a measure of its ability to continuously meet the demands of all its customers (i.e., points of delivery). Enhancing the supply reliability is one of planning and design targets of any utility within the constraints of capital investments, intense free-market competition, variable and higher level of customer preferences, and safety and environmental considerations. The utilization of transmission system facilities is changing from its traditional role in this new deregulated era and raising significant concerns about the possible erosion of the reliability of utility transmission facilities. It has been recognized that, with the movement toward a deregulated and competitive electricity market, decisions to improve reliability will be heavily influenced by industrial and commercial customer preferences requiring service level benchmarks to be defined. This paper presents an approach to establish realistic transmission system reliability performance benchmarks that provide a measure against which the different planning and design procedures can be evaluated to assist in achieving the primary objective of providing reliable electricity with competitive rates to utility customers     

Power system grounding. Ill. Large portable machines

There are several methods available to ground the neutrals of industrial power systems. One of these methods, high-resistance grounding, was first applied in 1936 to solve a safety problem associated with operating large portable equipment used in open-pit mines. Today, grounding of most land-based power distribution circuits is mandated by codes and regulations. Here, the author presents an historical overview of the protection of open cast mining power system equipment     

Covering all the bases - industrial power system design in a utility environment

The scheme discussed here is unique: a large electrical network is spread over a very large geographic area. This creates an exceptional set of circumstances. Construction specifications and techniques are used that increase the reliability of the system above standard utility practices. This adds to the cost of the project, and necessitates modified approaches to overhead line construction. Transformer selection and design is greatly influenced by the size of the load, as well as overhead pole construction. PF correction is accomplished using both standard distribution level capacitors, and using medium-voltage capacitors at the voltage terminals. Lightning protection uses both standard surge arrestors on the line, as well as advanced grounding systems. In each of these cases, standard utility construction techniques are combined with industrial design to meet the requirements of the system. Without the use of computer-based system modeling, proper design and operation of such a complex system would be impossible. Computer models give an accurate picture of the loading on the system in a particular configuration. They also aid the engineer in selection and coordination of protective devices, as well as power-factor correction. Conclusively, with the aid of modern tools, a system can be constructed that serves the needs of an industrial user in a utility environment.     

The function and composition of the global industrial grounding system

This paper describes the basic functions of, and the parts that make up, the global grounding system. It discusses the destructive effects on equipment and the danger to human life presented by the existence of high-frequency lightning-surge currents in the earth or ground. Emphasis is on the important role of the global grounding system in minimizing the attendant hazardous voltage gradients that occur in the ground surface. The effect of 60-Hz-frequency ground-fault current in seeking a path in closest proximity to the outgoing power conductors within its ground-fault island is asserted. The operation of wye-delta-wye transformers to interconnect a resistance-grounded industrial system to a solidly grounded high-voltage utility system is explained without the customary utilization of symmetrical components.     

基于ARM嵌入式系统的挂接地线监测单元研制

挂接地线是接触网停电检修作业保障人员及设备安全的重要环节。针对接触网停电检修作业挂接地线时常产生误挂、漏拆等情况,设计了一种集实时监测接地线挂接及接地状态并自动上传等功能于一体的挂接地线监测单元。该单元以ARM微控制器为核心,设计了超声波测距模块、图像采集模块、GPRS通信模块等外围电路,同时在嵌入式操作系统平台上开发了各功能模块的应用程序。该单元实现了对接地线的实时远方监测,可有效防止挂接地线误送电等事故发生,为现场作业人员提供一道安全保障。     

Protection and commissioning of multifunction digital transformer relays at medium voltage industrial facilities

The application of multifunction digital relays to protect medium voltage power transformers has become a common industrial practice. Industrial transformers, unlike utility transformers, frequently use neutral grounding resistors to limit ground current during faults to the 200-400-A level on medium voltage systems. This paper will discuss why these types of transformers require sensitive ground differential protection. The paper will also discuss the basics of transformer protection including phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, current transformer (CT) requirements, and harmonic restraint, and communicating these properly to new digital relays. The rationale for providing transformer overexcitation protection on all major transformers within mill facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address increasingly more transformer winding configurations. This has resulted in digital transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einsteins or Edisons among us, the next generation of transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital transformer protective relays.     

基于金刚石氮-空位色心的裂纹无损检测

磁场测量在材料科学、电子工程、电力系统甚至工业领域中扮演着极其重要的作用,尤其是磁场测量为工业无损检测提供了安全又可靠的工具,而磁场测量的灵敏度决定了检测的最高水平。金刚石氮-空位(NV)色心是最近几年发展的一种新型的量子传感器,外界磁场存在会导致金刚石NV色心的基态能级发生塞曼劈裂,通过光学探测磁共振技术(ODMR),利用微波源和锁相放大器探测NV色心的共振频率,最后由共振频率的变化可以精准地计算出出外界磁场的大小和外界磁场变化的灵敏度。实验中将含有高浓度NV色心的金刚石与光纤进行耦合实现磁场扫描式探针的制备,之后对磁化后的铁板焊缝表面裂纹进行扫描,并将扫描的结果绘制成二维磁力分布图,根据磁力分布图的磁场梯度变化可以非常准确地判断出裂纹的位置和大小,为工业安全提供了非常有效的诊断工具。     

Reliability of various industrial substations

Many utility and industrial substation configurations have been designed to interconnect energy sources and individual industrial load points. The design, protection schemes, and operating procedures of a substation configuration directly affect the reliability of the power supply to these load points. When an existing or planned substation configuration is unreliable, the question is: which substation configuration will be more reliable? Another question is: what reliability methodology will account for the protection schemes in place, the operating procedures and the common cause failures of utility supplies? This paper will discuss and present a reliability analysis of eight basic industrial substation configurations that are typically used inside process plants. The zone branch reliability methodology is used to calculate load point reliability indexes of each substation configuration. The reliability analysis includes open and short-circuit failure modes of circuit protective devices, operating practices and common cause failures of utility supplies. The significant impact of common cause utility supply failures on load point reliability levels will be presented and discussed in detail.     

Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial power systems - Part 1: The problem defined Working Group Report

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.     

Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial systems-Part 2: Grounding Methods Working Group report

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.     

Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial power systems - Part 4: Conclusion and Bibliography Working Group Report

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.     

Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial power systems - Part 3: Protection Methods Working Group Report

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.     

联网型高耗能电解铝工业电网源荷协调平抑风电功率波动控制策略

对于含有大规模新能源接入的联网型高耗能工业电网,新能源功率波动势必产生联络线功率波动以及额外备用容量费用,不利于工业电网经济运行。通过对工业电网内部火电机组与电解铝负荷联合控制进行建模,提出源荷协调平抑风电功率控制策略。基于模型预测控制方法,将电解铝负荷和火电机组调节范围以及响应速率作为约束条件,以平抑风电功率波动为控制目标,优化电解铝负荷和火电机组的有功功率调节量,减少由风电功率波动引起的联络线备用容量。以云南文山地区某个工业电网为例进行仿真,结果表明所提的源荷协调控制策略可以有效实现对工业电网内部风电功率波动的平抑,限制与大电网联络线上的有功功率交换。     

Ground Fault Protection for Bus-Connected Generators in an Interconnected 13.8-kV System

This paper is based on modifications implemented in the protection and grounding systems of a large paper mill and describes selective ground fault protection for a 13.8-kV system with multiple bus-connected generators, synchronous bus ties, and utility interconnections. The ground fault current in the system is reduced from the existing 3400 A to 500 A, and a hybrid grounding system is implemented for each of the generators. As the ground fault currents are reduced to limit the fault damage, the sensitivity and selectivity of the ground fault protection become important. Directional ground fault relays with coordinating pickup settings are applied to achieve this objective. The new platform for directional elements (numerical relays) drives its performance from sequence impedance measurements     

分时电价下的高耗能企业发用电响应

高耗能企业通常是所在地区的用电大户,具备一定量可调度负荷,许多高耗能企业还建设有自备电厂。针对分时电价下高耗能企业发用电响应问题,讨论了各时段之间的价格关系对高耗能企业发用电响应行为的影响,进而建立了高耗能企业自发电调度和负荷转移一体化调度模型。针对案例企业情况,讨论了不同价格信号下企业的发用电决策,并讨论了能够促使企业将用电向谷时转移并在峰时多发电的电价信号。研究表明,电网在制定基于价格的需求响应机制时如果充分考虑企业的自发电成本、负荷转移成本等信息,电网可以通过价格手段引导高耗能企业的发用电决策,从而实现电网和企业的双赢。     

Load Flow? What Can It Tell You?

Load flows, more recently called power flows, have been a tool of the systems analyst for many years. Mostly load flow studies in the past have been made by large utilities to determine the system behavior under certain specified conditions. In the recent past some industrial plants have electrical systems as large and complex as some of the utility systems of yesteryear. This paper is an effort to set forth the benefits that the industrial plant operator may obtain from a load flow study of his electrical system.