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Dong, Liang (Safetech Research Institute (Beijing) Co. Ltd.) | Cui, Wei (Safetech Research Institute (Beijing) Co. Ltd.) | Yang, Yang (Safetech Research Institute (Beijing) Co. Ltd.) | Wang, Xiuyun (Safetech Research Institute (Beijing) Co. Ltd.) | Gu, Feng (China Petroleum Engineering Co., Ltd)
ABSTRACTRegional cathodic protection (CP) system is used to protect buried facilities in oil/gas stations from corrosion caused by soil and electrical grounding system with electropositive materials. However, the required current may increase tens to hundreds of times due to the existing electrical grounding materials, and extremely heterogeneous protected potential distribution on buried facilities may occur. To analyze and improve the compatibility of regional cathodic protection system and electrical grounding system in oil/gas stations, numerical simulation was used to calculate the potential and current distribution based on different cases with: (1) electrical isolation between grounding system and CP system; (2) different electrical grounding materials; (3) Optimization of anode beds with near/remote anode beds; (4) isolation of partial grounding electrodes. The results showed that the lower spacing including intersection between buried structures and grounding electrodes were the main cause of incompatibility. Isolation of the entire horizontal grounding electrodes and optical design of anode beds with numerical simulation technique could improve the CP effectiveness. Moreover, electrical isolation between grounding system and CP system or using electronegative materials like zinc anodes as electrical grounding materials are effective in some situations.INTRODUCTIONWith increased scale and automation level in oil & gas transmission system, the oil & gas station and its pipeline & grounding system become complex. Pipelines and the other structures are using the combined electrical grounding system as a kind of economic and effective protection that have been widely used at home and abroad , and it is mandatory in relevant standard . Corrosion occurs when pipelines are connected to electropositive grounding materials such as copper [3-8]. CP is therefore used to prevent buried metallic structures especially for pipelines from corrosion that are effective with the structure to soil potential in the range of -0.85~-1.2 V vs.CSE (copper / copper sulfate reference electrode). However, the effect of CP system is difficult to guarantee because of a large number of electrically connected grounding systems. Such influence could be different with different grounding materials (such as copper clad steel, zinc coated steel, zinc anode) due to the different electrochemical performance [9-11].
Personal Protective Grounding /Bonding (PPGB) is one of the most important yet often misunderstood topics in High Voltage (>600 volts) electrical work (author’s opinion). PPGB refers to techniques used to provide shock protection for electrical workers by connecting de-energized equipment on which work is to be performed to the earth. PPGB is a paradox in that, if it is done correctly, it is by far the most effective means of protecting electrical workers from electrical shock. However, if PPGB is done incorrectly, it can precipitate arc-flash events of unimaginable magnitude. This technical paper will explain the purpose of PPGB and proper methods for installing PPGB on typical industrial equipment. Although every effort has been made to put this topic into layman’s terms, PPGB is a very technical topic and it will be best understood by readers who possess a good understanding of basic electrical concepts such as Ohm’s law and Series and Parallel circuitry.
Why PPGB Is Necessary
The techniques of PPGB were developed because High Voltage (HV) workers were being killed on lines and equipment that either were mistakenly thought to be de-energized or accidentally became energized through some external means1.The “external means” could include the following:
Designing neutral grounding systems for Generators require careful consideration of various aspects, which are mainly related to the Generators themselves and, also with respect to other aspects of the overall system design. More importantly, when the Generators to be operated in parallel have dissimilar design, the neutral grounding design must address a whole array of issues and technical requirements. While there are solutions to mitigate these issues, some of them are not appropriate for offshore installations. Introduction This paper is intended to explore in detail the various factors that influence neutral grounding design, various options available for neutral grounding and the mitigation methods for various issues associated with Generator neutral grounding. The challenges for mitigating the issues assume greater proportion when the Generators that are to operate in parallel are dissimilar in design.
Jiang, Zitao (Safetech Research Institute (Beijing) Co., Ltd.) | Cao, Guofei (PetroChina West East Gas Pipeline Company) | Ge, Caigang (Beijing Safetech Pipeline Co., Ltd.) | Gu, Qinglin (PetroChina West East Gas Pipeline Company) | Wang, Xiuyun (Safetech Research Institute (Beijing) Co., Ltd.) | Du, Yanxia (University of Science and Technology Beijing)
ABSTRACTWhile HVDC transmission runs in monopolar mode, a large direct current will enter into the earth through its earth electrode. This current may cause serious interference on buried pipeline even though it is far away from the earth electrode. In this work, numerical simulation was used to study the mechanism and influencing factors of HVDC interference. The results indicated that while a large direct current entered into the earth through the earth electrode, it could create a strong electric field and induce serious interference on the pipeline. The better the pipeline's coating was, the higher interference the pipeline suffered. Mitigating grounding beds had interaction with each other. The mitigating effectiveness was decided by the location and ground resistance of each mitigation grounding bed. Then, a field experiment was carried out to verify numerical simulation results.INTRODUCTIONHigh voltage direct current (HVDC) transmission plays a more and more important role in China, due to the energy resource mainly existing in western China. However, the majority of energy consumption is in eastern China. HVDC transmission is usually performed using a bipolar wire-return system. This system has two running modes: bipolar mode or monopolar mode. In bipolar mode, which is the normal running condition, one wire is positive and the other wire is negative. Current through the earth is unbalanced current between the two wires, which is usually less than 1% of wire current (See Figure 1). In the case of a fault or equipment repair, bipolar mode generally turns to monopolar mode. The earth is used as a conductor, which results in large current entering into the earth and inducing serious interference to buried pipeline near HVDC earth electrode (See Figure 2).HVDC interference will cause serious hazards to buried pipeline such as electric shock risk, corrosion of pipeline, damage of equipment, hydrogen embrittlement, etc. There were several HVDC interference cases around the world.[2-5] Peter Nicholson reported the HVDC interference caused by Quebec-New England Intertie. Verhiel investigated the interference of B.C. Hydro's HVDC system on a 24-in crude oil pipeline. The results indicated that 1200A DC current entering into the earth from earth electrode might induce 0.214V shift of P/S (pipeline to soil) potential. There were several HVDC interference cases detected during our field test. For example, in Shanghai eastern China, a ±500kV HVDC earth electrode being about 20km far away from pipeline induced 2V shift of P/S on-potential, when the earth electrode ran in monopolar mode. In Guangdong southern China, a ±500kV HVDC earth electrode being about 7km far away from pipeline induced 304V shift of P/S on-potential. Moreover, field test results indicated that the mitigating grounding bed might increase the interference of other segments of the same pipeline.