Use Of Variable Frequency Research Articles

Floating, Production, Storage, and Offloading Unit: A Case Study Using Variable Frequency Drives

The use of variable frequency drives (VFD) in floating, production, storage, and offloading (FPSO) units provides well-known benefits to the power system, such as: soft-starting of motors, increase of energy-efficiency, reduction of short-circuit currents, and enhancement of the load shedding capability. The VFDs with passive front-end rectifiers are the most commonly used for these applications due to their wider commercial availability and lower cost compared to VFDs with active front-end rectifiers. However, the latter can control the exchange of reactive power with the grid, which may contribute to voltage support and power factor regulation at the electrical system. This paper presents a case study considering the Production operating mode of an FPSO unit with two VFDs connected to the largest motors (i.e., water injection pumps). Simulations of the FPSO power system are evaluated using both active and passive VFDs, considering scenarios with analysis of steady-state, start of largest motors and symmetrical three-phase short-circuit.

Torsional vibration feature extraction method from lateral vibrations based on decomposed forward and backward whirl motions

The high-speed turbomachinery rotor-bearing system faces potential torsional vibration problems due to its large span, flexible structure, and the wildly use of variable frequency drive systems. In this paper, a method based on the Hilbert technique to extract weak torsional vibration signals from measured lateral vibration signals is proposed, and the forward whirl signal is constructed to make full use of the information contained in lateral vibration signals. Furthermore, it was found that the forward whirl signal has better stability and stronger anti-noise ability after comparing the utilization of horizontal, vertical, forward, and backward vibration signals applied to the proposed method to extract the torsional vibration signal from simulated vibration responses of a rotor system. Numerical simulation and experimental results indicate that the method can detect torsional vibration signals accurately, with a high resolution in frequency estimation. This method enables additional monitoring of torsional vibrations for machines without dedicated torsional vibration testers and provides a convenient way to measure torsional vibrations in engineering applications.

PERFORMANCE OF OVERSIZED PUMPS CONTROLLED BY VARIABLE FREQUENCY DRIVES IN WATER SUPPLY SYSTEMS

Reducing water and energy consumption is an essential condition for reducing the operational costs of water supply systems (WSS). The use of pumping systems driven by variable frequency drives (VFD) is one of the most suitable alternatives to optimize the pressurization of the distribution networks and, consequently, reduce the consumption of electricity and water losses. This article aims to analyze the performance of oversized pumps, driven with variable frequency drives, from WSS. The work was carried out in two experimental setups that have oversized pumps. The methodology consisted of evaluating data collected in experimental tests using hydraulic and electric meters. Tests were realized for different operating conditions of the systems, with the variation of the rotation of the pumps, in order to obtain the pump efficiency curve according to the VFD output frequency. The results demonstrated that the use of variable frequency drives proved to be an alternative to increase the energy efficiency of the evaluated systems. It was observed that the highest efficiencies were recorded in the lowest frequency bands (30 Hz and 35 Hz), while in the values close to the nominal frequency (45 Hz to 60 Hz) there is little variation in the efficiency values.

Choosing variable-frequency drive systems for the mining process units

Mining enterprises are energy intensive facilities. The capacity of single technological units can reach 5 MW. Variable-frequency drive systems are often used to set them in motion. The paper analyzes the features of choosing and using variable-frequency drives under diamond mining conditions. The study objective is to formulate and formalize the problems of introducing and operating variable-frequency drives at diamond-mining enterprises to further develop and implement guidelines for improving the performance of this drive type. To achieve this objective, the use of variable frequency drives in various process units of diamond mining should be studied and analyzed. The units are considered, for which in recent years, electric drive systems have been groundlessly (according to the authors) chosen by the engineering staff of enterprises. A technical and economic comparison of low-voltage frequency converters with the same power but different control modes is performed. The economic indicators of introducing high-voltage and low-voltage frequency converters into an existing electric drive system are calculated and represented as a comparative table. Conclusions are made on the need to proceed with the research and develop guidelines for implementing frequency converters at diamond-mining enterprises.

Tissue Characterization by Low-Frequency Acoustic Waves Generated by a Single High-Frequency Focused Ultrasound Beam

The mechanical properties of biological tissues are fingerprints of certain pathologic processes. Ultrasound systems have been used as a non-invasive technique to both induce kilohertz-frequency mechanical vibrations and detect waves resulting from interactions with biological structures. However, existing methodologies to produce kilohertz-frequency mechanical vibrations using ultrasound require the use of variable-frequency, dual-frequency and high-power systems. Here, we propose and demonstrate the use of bursts of megahertz- frequency acoustic radiation to observe kilohertz-frequency mechanical responses in biological tissues. Femoral bones were obtained from 10 healthy mice and 10 mice in which osteoporosis had been induced. The bones’ porosity, trabecular number, trabecular spacing, connectivity and connectivity density were determined using micro-computed tomography (μCT). The samples were irradiated with short, focused acoustic radiation pulses (f = 3.1 MHz, t = 15 μs), and the low-frequency acoustic response (1–100 kHz) was acquired using a dedicated hydrophone. A strong correlation between the spectral maps of the acquired signals and the μCT data was found. In a subsequent evaluation, soft tissue stiffness measurements were performed with a gel wax-based tissue-mimicking phantom containing three spherical inclusions of the same type of gel but different densities and Young's moduli, yet with approximately the same echogenicity. Conventional B-mode ultrasound was unable to image the inclusions, while the novel technique proposed here showed good image contrast.

The use of variable frequency drive for the operation of the NBT mud pump

The article discusses the process of optimizing the operation of the NBT-600 mud pump by adjusting the frequency of the current supplied to the pump drive. As a result of a technical measure, efficient operation of the pump is ensured, the energy consumption of the pump unit is reduced, and the main parameters of the pump are increased.

The Use of Variable Frequency Drives of Centrifugal Pumps atthe Pumping Station

The article presents the experience of operating real pumping stations in urban water supply. The basic principles of practical modeling of the operation of a group of pumps for a common load are considered. The main errors in the modernization of pumping equipment of water supply units are analyzed.

Targeted, Precision Irrigation for Moving Platforms: Selected Papers from a Center Pivot Technology Transfer Effort

Abstract. This article is an introduction to an ASABE Special Collection of ten articles concerning center pivot (CP) technology transfer that appears in this issue of and in . The year 2018 marked the 40th anniversary of research and development of low-energy precision application (LEPA) for use with CP sprinkler irrigation systems. Since 1978, researchers, extension specialists, and industry have continued development of multiple technologies that are suitable for mobile lateral irrigation platforms. A two-year technology transfer effort with funding from the USDA-ARS Ogallala Aquifer Program (OAP) was initiated in January 2017 to promote adoption of advanced and efficient irrigation technologies and to highlight recommended practices for mobile irrigation platforms, including both CP and lateral-move (LM) systems. The articles in this Special Collection address five major topic areas: in-canopy and near-canopy irrigation application from moving platforms, site-specific variable-rate irrigation (VRI) and associated sensor technologies for moving platforms, the use of variable-frequency drives (VFDs) with CP systems, and uniformity evaluations for CP systems. While these ten articles are not inclusive of all the important advances in irrigation from moving platforms since 1978, they illustrate that continued improvement in irrigation management occurs by combining engineering and agronomic sciences. Pressurized irrigation from moving platforms is increasing in the U.S. and will be an important tool for meeting global food and water challenges. In addition to introducing and summarizing the Special Collection, this article provides additional rationale for the CP technology transfer effort. Keywords: Center pivot, Irrigation uniformity, Lateral-move sprinkler, LEPA, Linear-move sprinkler, Low-energy precision application, Site-specific irrigation, Sprinkler irrigation, Variable-frequency drives, Variable-rate irrigation, VFD, VRI.

Analysis of a High-Power, Resonant DC–DC Converter for DC Wind Turbines

This paper is introducing a new method of operation for a series resonant converter, with intended application in megawatt high-voltage dc wind turbines. Compared to a frequency controlled series resonant converter operated in subresonant mode, the method (entitled pulse removal technique) allows the design of the medium frequency transformer for highest switching frequency, while being operated at lower frequency without saturation. The main focus of this paper is to identify and analyze the operating modes of the converter with pulse removal technique. With the use of variable frequency and variable phase displacement in subresonant mode, the new method of operation promises transformer size reduction and facilitates soft-switching transition of the insulated gate bipolar transistors (IGBTs) and line frequency diodes on rectifier side. Four modes of operation are identified, while equations for output power, voltage, and current stress are identified. Experimental results are concluded on a 1 kW, 250 V/500 V prototype.

Implementation of Energy Efficiency Strategies in Cooling Towers—A Techno-Economic Analysis

This paper depicts the results of a detailed energy audit, analysis, and implementation of energy efficient operations and maintenance strategies in a large commercial mall in Kuwait. Initially, the cooling towers (CTs) operated only at high speed, and on a typical summer day, nearly one-fourth of the make-up water was used for self-cooling of air. The study based on measured data and analysis, for a period of one year, revealed that the use of variable frequency drive (VFD) could reduce the water wastage for self-cooling of air by as much as 75% and overall water consumption by 18.6% while keeping the cooling system performance at the design level. An optimization model was developed, suitable exclusively for arid climatic conditions. Implementation of various energy efficient operation and maintenance strategies (EEO&MS) with ventilation and air-conditioning (VAC), and lighting systems obtained an overall reduction of 9879 MWh/y, equivalent to a percentage reduction of 11.7% in the annual energy consumption and a 345 kW in peak power demand. The study estimated an economical benefit of 19,958 KD/y for the owners and to the Ministry of Electricity and Water, in addition to a considerable environmental benefit of deduction in CO2 emissions by 6990 t/y.

A Systematic Power-Quality Assessment and Harmonic Filter Design Methodology for Variable-Frequency Drive Application in Marine Vessels

In maritime industry, high fuel costs encourage use of variable-frequency drives (VFDs) for energy-saving applications. However, introduction of such nonlinear loads in the vessel's power distribution network induces harmonics, which can lead to potential risks if are not predicted and controlled. In this paper, a systematic power-quality assessment and monitoring methodology is proposed to calculate VFD contribution to voltage distortion at the point of common coupling (PCC), considering the source short-circuit capacity and the existing vessel's power system harmonics. According to voltage harmonic distortion limits set by marine classification societies, design and sizing of appropriate harmonic attenuation filters is made, including ac and dc chokes and frequency-tuned passive filter options. The effectiveness of the proposed power-quality analyzing procedure is evaluated through a real practical example, which includes harmonic filter design for VFD retrofit application to fan and pump motors that operate constantly during sea-going operation in a typical tanker vessel. Power-quality field measurements obtained through a harmonic monitoring platform implemented on board verify that total voltage harmonic distortion and individual voltage harmonics at PCC are maintained below 5% and 3%, respectively, showing that design complies with relevant marine harmonic standards even in the worst operating case.

The Influence of Main Pump with High-Voltage Variable Frequency Drives on Electric Motors Periodic Repair

The main objective of the work - to investigate the effect on the wear of high voltage electric motors of main pump units periodic switching on and off in cyclical pumping. Frequent starts motors in a cyclic pumping lead to accelerated wear of the mechanical parts of the motor due to the impact of dynamic loads at start-up, as well as winding insulation due to high inrush currents flow. As a result of accelerated depreciation may decrease residual life, overhaul period and service life of electric motors. The main factor affecting the service life of insulation motors are winding temperature, and as a consequence, the thermal aging of the insulation. The use of variable frequency drive can significantly reduce the cyclic transfer modes, or even eliminate them. The authors obtained analytical expressions for the evaluation of insulation deterioration at the start of the motor, which allow us to study the impact of the following factors: insulation class, the start time, break time at work, initial and nominal temperature, the temperature rise of the windings over the ambient temperature. The effect on the deterioration of the insulation cold start and hot conditions, as well as the percentage of the hottest start-ups in the total number of starts. Obtained expressions for the depreciation of isolation to determine the change timing of overhauls of high voltage electric main pump units. The developed method was approved by the example of the use of a variable frequency drive on the oil pumping stations construction section Leninsk-Nurlino trunk pipeline Nizhnevartovsk - Kurgan - Kuibyshev. The analysis showed that the installation of a variable frequency drive motors on three main pump units technological area of the number of starts to decline by 14%. The results can be used for pipeline transport of oil companies when planning the timing and costs of the current and capital repairs of high voltage electric motors main pump units.

Quality evaluation of energy consumed in flow regulation method by speed variation in centrifugal pumps

Nowadays, energy efficiency and the Electric Power Quality are two inseparable issues in the evaluation of three-phase induction motors, framed within the program of Rational and Efficient Use of Energy (RUE).The use of efficient energy saving devices has been increasing significantly in RUE programs, for example the use of variable frequency drives (VFD) in pumping systems.The overall objective of the project was to evaluate the impact on power quality and energy efficiency in a centrifugal pump driven by an induction three-phase motor, using the flow control method of speed variation by VFD. The fundamental purpose was to test the opinions continuously heard about the use of flow control methods in centrifugal pumps, analyzing the advantages and disadvantages that have been formulated deliberately in order to offer support to the industry in taking correct decisions. The VFD changes the speed of the motor-pump system increasing efficiency compared to the classical methods of regulation. However, the VFD originates conditions that degrade the quality of the electric power supplied to the system and therefore its efficiency, due to the nonlinearity and presence of harmonic currents. It was possible to analyze the power quality, ensuring that the information that comes to the industry is generally biased.

Recovery of airflow resistivity of poroelastic beams submitted to transient mechanical stress

The airflow resistivities of air-saturated poroelastic slender beams submitted to transient mechanical stress are recovered using fluid and solid borne compressional mode phase velocity expressions drawn from a modified Biot theory. A point where the two dilatational modes intersect and their phase velocities equal is first sought. This point also corresponds to the Biot transitional frequency indicating the frequency at which the solid and the pore fluid start disassociating due to the weakening of the viscous forces by the thinning of the viscous boundary layer in the pores. A bilinear time–frequency (TF) distribution is used to represent on the time–frequency plane, the captured transient mechanical stress waves from which the point of intersection/separation of the two modes is located. The projection of the Eigenfrequencies obtained from a simple 3D finite element modeling of the thin poroelastic beam, on a (TF) diagram, facilitates the identification of the modes. The transition frequencies for the poroelastic beams thus retrieved are verified through the use of variable frequency, single cycle sine wave bursts. The anisotropy of the foams are also revealed by analyzing the transient responses of the poroelastic beam specimens cut from the same panel but in two perpendicular directions in orientation to each other.

Automation and Surveillance Improve Progressing Cavity Pump Performance

This article is based on paper SPE 136690 by the same author, which was presented at the 2010 SPE Progressing Cavity Pumps Conference, Edmonton, Canada, 12-14 September. To extend the run life of the pump while producing all available fluid is the goal of all progressing cavity pump (PCP) operators. The primary challenge is to do so without starving the pump and causing damage to the stator. The petroleum industry has been searching for years for a reliable way to control PCPs for pump-off. Several methods have been used, from monitoring torque to manual fluid levels. To date, none have been commercially successful. A method for controlling these wells has been developed combining wedge meter flow technology and microprocessor control of both electric motors through the use of variable frequency drives (VFDs) and hydraulic motors using proportional control valves. This method has proved accurate and reliable, extending run life while producing all available fluids. Combining this automated technology at the well with a web-based system that feeds back real-time data to a dedicated supervisory control and data acquisition (SCADA) host allows PCP technical experts to diagnose problems, and operators to respond quickly to changing well conditions. This article discusses the advances in automation and optimization of PCPs. The acceptance of PCPs in the oil and gas industry has grown worldwide. A major concern is potential damage to the stator if the well is pumped off. The most common prevention is to ensure that there is a substantial amount of fluid level above the pump. Operators taking manual fluid level shots and adjusting pump speed has been the most widely used method to maintain a safe fluid level. With advancements in fluid flow measurement and proven algorithms, the PCP controller has eliminated this concern, while producing all the available fluid from the wellbore without damaging the pump. With this automated technology and a web-based SCADA system, it became possible to monitor several data trends and discover additional control algorithms. Further development of these algorithms is ongoing. Pump-Off Control for PCPs Two main objectives were defined when the theory of the PCP controller was introduced. The first objective was to reduce premature pump failure. The most common failure is stator damage due to pump-off. Pump-off is defined as a lack of fluid entry into the pump. This causes a lack of lubrication to the stator, resulting in extremely high temperatures being generated. The high temperature ultimately burns the elastomer in the pump. The stator’s rubber surface becomes hard, brittle, and cracked. In severe circumstances, the stator contour is torn up, producing rubber at surface. This may be caused by one or a combination of the following problems: plugged pump intake, poor inflow, or production rates exceeding inflow.

Methodology for grouping intakes of pressurised irrigation networks into sectors to minimise energy consumption

Grouping intakes into sectors so they operate in scheduled periods allows irrigation networks to be operated more efficiently from an energy point of view. In the case of systems where water is supplied by pumps, the criteria used to date to create irrigation sectors does not guarantee that pumping sets work in the most efficient manner, despite the use of variable frequency drives. A new methodology, using a genetic algorithm and a hydraulic network model, has been developed to group intakes into sectors to minimise energy consumption. The methodology was applied to a case study and several scenarios compared using energy performance indicators. Predictions on a case study in Spain showed that energy savings of 36.4% could be possible and operational network conditions can be improved by ensuring minimum pressures are guaranteed.

Conventional and High-Speed Roller Ginning of Upland Cotton in Commercial Gins

A conventional rotary-knife roller gin stand in a commercial ginning plant was converted to operate at high speed during the 2005 ginning season. Ginning rate on the high-speed stand was more than three times higher than a conventional roller gin stand. The ginning roller on the high-speed stand operated at normal temperature. A field test was conducted at the commercial ginning plant to compare roller ginning and saw ginning using one cultivar of upland cotton. The field test included the high-speed roller gin stand along with 11 conventional roller gin stands, and two saw gin stands. Fiber properties from the field test showed that HVI color grade, staple length, length uniformity, and fiber value were improved when using roller gin stands. Results from the 2006 California crop showed similar improvements in staple length and length uniformity when comparing roller-ginned upland cotton and saw-ginned upland cotton. Textile mills that value the significance of improved fiber properties were willing to pay a premium for roller-ginned upland cotton. Between 2005 and 2009, there were 48 roller gin stands converted to high speed, and 25 new high-speed roller gins sold. Life of the ginning roller on high-speed roller gin stands during 2006 was slightly less than conventional roller gin stands, but roller life improved in 2007-08 with use of variable frequency drives that may optimize ginning roller wear. Evaluation of high-speed roller ginning in commercial ginning plants will continue.

Effects of electric field on characteristics of nano-confined lubricant films with ZDDP additive

The consequence of bearings exposed to shaft voltage is a very important tribological problem, especially with the increasing use of variable-frequency drives (VFDs) to control alternate current (AC) motors. The emerging behavior of gas micro-bubbles and the film forming characteristics between base oil (liquid paraffin) films with and without ZDDP additive under an external electric field (EEF) in a nanogap have been compared. Experimental results indicated that the micro-bubble emerging intensity increases slightly when the additive is involved in the base oil. The magnitude of the electric current flowing through the lubricant film closely related to the intensity of the micro-bubble emerging. No obvious difference in the film thickness can be found between the liquid paraffin films with and without ZDDP additive. The influence of the EEF on the film thickness of the liquid paraffin with the additive is more significant.

Use of variable-frequency drives in the heat network of Tver’ TÉTs-3

Engineering solutions developed and implemented within the project of updating the makeup module of the heat network at the Tver’ TETs-4 cogeneration plant with the use of variable-frequency drives for scheduled startups and control of the makeup pumps delivery are considered.

Industrial Applications of Variable Frequency Microwave Energy in Materials Processing

AbstractA review of some market-driven research, process applications and systems development is provided. The variable frequency microwave processing concepts are briefly described. Industrial processing using variable frequency microwave energy in the areas of polymerization, composite processing, bonding and plasma is discussed. Analytical applications inherent in the use of variable frequency and its control are demonstrated in the areas of materials signature analysis for volumetric cure monitoring.