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Motors are designed with certain speed-torque characteristics to match speed-torque requirements of various loads. A motor must be able to develop enough torque to start, accelerate, and operate a load at rated speed. The National Electrical Manufacturers Association (NEMA) has established class designations for motors on the basis of motors' starting-torque and accelerating loads. The four standard NEMA designs are NEMA A, NEMA B, NEMA C, and NEMA D. NEMA A motors usually are used for applications that require extremely high efficiency and extremely high full-load speed. NEMA A-design motors are special and are not used very often.
Understanding why incidents re-occur from similar causes despite the previous experiences, lessons and available tools to ensure that they do not happen again has been a cause of concern for company management for years and different reasons have been attributed to this issue. In recent past, below are few examples of incidents from similar causes.
On 25 January 2012, during the pre-mob inspection of a pile load tester pump by a DIL pile rig operator (Mechanical-24yrs old) with his Supervisor, the unit was put under pressure three times successfully but there was no movement of the pump piston. The pump was put under pressure the fourth time with a declared pressure of 500 bars, the pile load tester flange suddenly gave way and caused several severe injuries to the operator. He was confirmed dead at around 18h30. The unit was brand new with test certificate; IP was trained for it and note that the design pressure of the pile load tester was 690bars. In addition, when the unit failed, the 25 out of 26 bolts of the flange cut off while the last one had its nut pulled out.
On 15 May 2017, a fatal accident occurred when an analyzer engineer removed the cover on an explosion-proof enclosure as part of the routine task for the day. The ~5.5kg weighing threaded cover and with a 14 inches in diameter was propelled forcefully from the enclosure as the Engineer unscrewed it inflicting a fatal head injury. The pressure inside the enclosure from leaking sample gas or instrument air components caused the forceful propulsion of the enclosure cover. There was no gauge or indicator on the enclosure to monitor the internal pressure inside the enclosure and there was no means to relieve internal pressure (
Electrical grounding can be classified in either system grounding and equipment grounding. Requirements for system grounding are covered in detail in the Natl. System grounding includes grounding of the power supply neutral so that the circuit protective devices will remove a faulty circuit from the system quickly and effectively. To protect personnel from electric shock, all enclosures that house electrical devices that might become energized because of unintentional contact with energized electrical conductors should be effectively grounded. If the enclosures are not grounded properly, unsafe voltages could exist, which could be fatal to the operating personnel.
An enclosure protects a motor from contaminants in the environment in which it is operating. In addition, the type of enclosure affects the cooling of the motor. Enclosures are categorized as either open or totally enclosed, and there are different types of enclosures within each category. Open enclosures permit cooling air to flow through the motor. One type of open enclosure is the ODP enclosure.
ABSTRACT: Hydraulic fracturing arises as a method to enhance oil and gas production, and also as a way to recover geothermal energy. It is, therefore, essential to understand how injecting a fluid inside a rock reservoir will affect its surroundings. Hydraulic fracturing processes can be strongly affected by the interaction between two mechanisms: the elastic effects caused by the hydraulic pressure applied inside fractures and the poro-mechanical effects caused by the fluid infiltration inside the porous media (i.e. fluid diffusivity); this, in turn, is affected by the injection rate used. The interaction between poro-elastic mechanisms, particularly the effect of the fluid diffusivity, in the hydraulic fracturing processes is not well-understood and is investigated in this paper. This study aims to experimentally and theoretically comprehend the effects of the injection rate on crack propagation and on pore pressures, when flaws pre-fabricated in prismatic gypsum specimens are hydraulically pressurized. In order to accomplish this, laboratory experiments were performed using two injection rates (2 and 20 ml/min), applied by an apparatus consisting of a pressure enclosure with an impermeable membrane in both faces of the specimen, which allowed one to observe the growth of a fluid front from the pre-fabricated flaws to the unsaturated porous media (i.e. rock), before fracturing took place. It was observed that the fracturing pressures and patterns are injection-rate-dependent. This was interpreted to be caused by the different pore pressures that developed in the rock matrix, which resulted from the significantly distinct fluid fronts observed for the two injection rates tested.
Hydraulic fracturing arises as a process to enhance oil and gas production or to recover geothermal energy, by injecting pressurized fluid into a wellbore until the target rock fractures, which causes an increase in its permeability. Hydraulic fracturing experienced major technical developments in 1957 (Strain, 1962), but has been more widely used over the world in the last decade and, consequently, its environmental impacts and efficiency.
Janarthanan, C. (National Institute of Ocean Technology) | Chandran, V. (National Institute of Ocean Technology) | Sundaramoorthi, V. (National Institute of Ocean Technology) | Vishwanath, B. O. (National Institute of Ocean Technology) | Rajesh, S. (National Institute of Ocean Technology) | Muthuvel, P. (National Institute of Ocean Technology) | Gopkumar, K. (National Institute of Ocean Technology) | Ramesh, N. R. (National Institute of Ocean Technology) | Ramadass, G. A. (National Institute of Ocean Technology) | Atmanand, M. A. (National Institute of Ocean Technology)
India has been developing technology for deep sea mining to harvest polymetallic nodules from the Central Indian Ocean Basin (CIOB). The seabed mining system is a crawler type mining machine. The mining machine collects the nodules from the seabed, crushes them into smaller sizes and pumps it as seawater slurry to an intermediate pumping station. The mining machine in static and dynamic state is to be supported on the very soft sea bed of shear strength, in some places being less than 2 kPa. The maneuverability of the mining machine is thus a challenge while operating on the soft seabed. Predicting the traction of the mining machine and other associated parameters are very important for developing the locomotion system of the mining machine. An Experimental Undercarriage (EUC) system was equipped with a latching system in order to estimate the riser loads on the machine during locomotion. The EUC system will also measure the static and dynamic sinkage, vehicle slip, power required and drive motor pressure. This paper presents the design, analysis, configurations and functional testing of an Experimental under-carriage (EUC) system. The stability analysis was carried out using numerical and analytical methods to arrive at an optimum configuration of EUC system. After the configuration is finalized the whole main frame and super structure system has been analyzed using a finite element analysis software by considering the launching and retrieval loading conditions. The weakest positions were identified and reinforced adequately such that the stress and deformations are within the permissible limits. The load test experiments were also carried out with various loading conditions to qualify the design and FEA analysis. This paper also discusses the qualifications of various underwater sensors, design and development of sensor’s enclosures at hyperbaric conditions for 6000 m depth for measuring the traction parameters of an Experimental Under-Carriage system.
Use of GIS to handle bulk power distribution has now become popular in offshore facilities due to the inherent advantage of a compact design. This paper highlights the challenges faced during GIS (and associated items) design based on experience on recent offshore projects and recommendations are proposed for methodical approach.
Handling of bulk power at Extra High Voltages poses numerous risks to both personnel as well as assets. This paper discusses the key design parameters, industry standards, interface requirements with transformers/subsea cables/platform structure and installation challenges.
Design engineer must be familiar with industry codes so that all design requirements, including proper selection of GIS configuration, are considered from early stages of the project. Omissions or oversight in this regard can impact the whole project.
Duration for design, procurement, installation and commissioning phases must be adequately accounted for. Specialist studies such as insulation coordination, very fast transient and touch potentials shall be carried out in addition to usual power system and arc flash studies.
Special consideration must be given in case of ring configuration with regard to logic diagrams and differential protection based on multiple CT locations and interconnections. Requirement of voltage selection scheme requires extensive wiring for synchronization function. Relay & CT selection shall be made considering required protection functions, interface with remote location and communication interface with Electrical Control & Monitoring System.
Interfaces with transformers and subsea cables shall be in strict compliance with industry standards such as IEC 62271-209 & 211. Requirement of additional surge arrestors shall be verified.
GIS exerts large static and dynamic forces on platform steel structure. These are also sensitive to forces during platform lifting and transportation. Support structure suitably shall be designed to mitigate the same.
This paper addresses concerns and interface requirements to be considered during design of GIS which will benefit the design engineers, Client personnel and Structural designers along with Project Management Team for safe and smooth execution.
This paper will share the experience in the development of an online mercury measurement system for high pressure liquid hydrocarbon streams. It focuses on challenges in handling high pressure volatile hydrocarbon, impurities associated with the matrix, particulates, water and mercury concentration. Challenges associated with assurance in sample representativeness, and validation complete with automation are also discussed. The project was initiated to reduce cost of current offline mercury analysis, the need to minimize analytical error, expedite acquisition of analytical results, and minimize personnel exposure to mercury during manual sampling and analysis.
In addition, the determination of mercury in natural gas and condensate is made difficult by the very low concentrations involved, the highly volatile nature of mercury and the complexity of the sample matrix. This dictates that either a highly sensitive detector or a large sample volume or both are needed to perform adequate analysis. A variety of techniques with different sensitivities are presently available for the determination of mercury. The system developed consists of 4 main modules; sample pretreatment, sample capture, sample conditioning and mercury measurement (i.e. detection system). The detection system utilizes a spectroscopic technique for mercury analysis hyphenated with in-house developed liquid hydrocarbon conversion system and sampling system. Results gained from performance testing demonstrate good reliability and opens new prospects to further develop the system for other facilities where mercury monitoring is required, especially for remote facilities.
The entire industry of PPE against the thermal hazard of an electric arc has existed for 20 years. However, gaps still exist in electric arc knowledge and standardization. This three-article series provides a broad overview of today’s state of the art for electrical workers’ protection against electric arc thermal hazard.
Part 1 of the series identifies key factors for future progress, and discusses electric arc classification, properties, behavior and methods of thermal energy dissipation.
Statistical trends in general electric and electric-arc- related fatalities and trauma are essential for future improvements. However, information on electric arc incidents is hard to find in government statistical reviews. Part 2 of the series is dedicated to reviewing statistical data and identifying gaps in reporting electric-arc-related incidents and corresponding skin burn trauma. The authors also review previously published electric arc incidents.
Part 3 of the series discusses multiple elements for reliable protection against electric arc. These include arc hazard assessment, standardization for PPE test method requirements, results of the latest research, challenges and suggestions.
Factors for PPE Progress
Fire Retardant Materials
During the past 15 years, revolutionary changes occurred in the availability of different fabrics and materials for PPE used by electrical workers to protect against the thermal effect of an electric arc during live electrical work. Removing flammable and melting materials and fabrics from the face, body and hands was a major factor in reducing burn incidents.
The purpose of this project was to evaluate the effectiveness of a hybrid inert gas/water mist fire suppression system on aero-derivative style gas turbines. A utility company and its fire protection engineer provided the opportunity to test the system on an operating unit under load, enabling the research team to assess system efficacy in real-world scenarios. The utility company established the test criteria; testing would be deemed successful if the system could cool the turbine skin to less than 380°F within 10 minutes. 380°F represents the auto ignition temperature of lube oil and turbine fuel plus a safety factor, as determined by the company. The 10-minute timeframe was established to match the performance of the existing CO2 extinguishing system.
A series of tests were devised to demonstrate the suppression system's effectiveness for cooling. The tests involved operating a Pratt and Whitney FT4 aero-derivative turbine generator off and on the power grid at full speed/base load and allowing the unit to cool naturally, as well as on the grid and allowing the system to discharge. Systematic changes in water flow and installation parameters were used to find optimal results. Temperatures were recorded at the compressor section, combustion section front, combustion section rear, hot turbine section, exhaust diffuser and in the enclosure.
Testing demonstrated that the hybrid fire suppression system is capable of quickly cooling the turbine skin to below 380°F—within 33 seconds, in fact—without damaging the turbine. The test results show successful cooling with the emitters installed overhead and aimed toward the hot section of the turbine. Results indicate that the hybrid fire suppression system adequately protects aero-derivative turbines under normal operating conditions. The testing offers a proof point that the system is not damaging to equipment, overcoming historic objections to the use of water mist style systems.
Testing was conducted at a site in Holtsville, New York, housing 10 twin pack FT4 aeroderivative turbines. Each pack consists of a generator and two FT4 aircraft turbines at each end. The thrust of each turbine engine is directed through a “free turbine” that is on the same shaft as the generator. The turbine generators are used to generate electricity during peak demands. Each twin pack is capable of producing electricity on the grid in just over 2 minutes, and can provide full capacity—approximately 50 MW—within 8 minutes of startup. Upon shutdown, the turbine is no longer producing thrust, however the independent “free turbine” and generator shaft continues to rotate for 20 minutes until it coasts to a stop.