14,422 research outputs found
Laboratory Manual for AC Electrical Circuits
No full textThis 90-page laboratory manual was written by James M. Fiore and is intended for use in an AC electrical circuits course and two and four year electrical engineering curriculums. The manual contains an introduction, a table of contents, and fifteen exercises. Each exercise includes an objective, a theory overview, equipment needed, schematics, step-by-step procedures, and questions. "The topics range from introductory RL and RC circuits and oscilloscope orientation through series-parallel circuits, superposition, Thevenin's Theorem, Maximum Power Transfer Theorem, and concludes with series and parallel resonance.&quot
Influence of ac ageing on space charge dynamics in LDPE
No full textPolymeric materials have been widely used as insulation in power industry due to their excellent electrical properties. However, these properties deteriorate in time irreversibly when the material is subjected to electric stress. Although space charge is believed to play an important role in ac ageing, exact mechanisms are poorly understood due to very limited experimental data. In the present work efforts have been made to investigate the influence of ac ageing on space charge dynamics in low-density polyethylene (LDPE). LDPE films with 200mm were aged at 50 kV/mm at 50 Hz for various times at ambient temperature. Space charge dynamics in the samples prior to and after ageing were monitored using the pulsed electroacoustic (PEA) technique under dc electric stress. The results indicate that there is a significant amount of homocharge accumulation in the unaged sample due to charge injection. These injected charges are the captured by the deep traps originated from the interface between crystalline and amorphous regions in LDPE. Ageing under ac condition does not necessarily lead to an increase in amount of charge in the bulk but leads to an increase in mobility of charge carriers. Chemical analysis by infrared spectroscope (FTIR) reveals there are chemical changes taken place in the bulk of the material after ac ageing. It is believed that the chemical changes introduce shallow traps which promote the movement of charge carriers in the bulk. Consequently, the injected charges spread across the sample
A power sharing series power BJT array with isolated low voltage control for AC power control applications
No full textA technique for a continuously variable AC resistance using a series BJT array is presented. This array provides high power dissipation capability and uniform voltage and power distribution across the individual transistors. The array, controlled using a set of optoisolators to maintain the electrical isolation between the control circuits and the power stage, could be used as the basis to develop several useful techniques including a solid state AC regulator with comparable performance to the commonly used ferro-resonant systems; a linear AC electronic load suitable for testing UPS and other power conditioners; and, in other AC power control applications such as switching capacitors in AC resonant circuits
A group of men in a circle viewing turf on the inside track at Santa Anita Park racetrack, California, 1953, with the dirt track and the grandstand in the background, during a field day event
No full textView from the middle endzone seats of an empty Rose Bowl stadium, with field markings for American football. Field well worn.Photographer uncertain"Exp. Field day at Santa Anita Race track. Seed[?ed] Last wk. July Ber 100, Alta 300, Mer. 10[?0]0 #/ac. Ber Predom. some alta, V. L. HL [?Merion] 12 1/2 ac Santa Anita Racetrack 10-1[3?]-53"Image taken on Kodachrome.Race tracksCool semiarid Pacifi
'Y Beibl Cymraeg, ei hanes a’i ddylanwad’
No full textRhagarweiniad gan Christine James ac E. Wyn James yn olrhain hanes a dylanwad y Beibl Cymraeg yng nghyfrol Dewi Arwel Hughes, 'Gair Duw ar Lafar Gwlad'
Feasibility of high-frequency alternating current power for motor auxiliary loads in vehicles
No full textThis paper presents a feasibility study into the application of a 100-V, 50-kHz high-frequency ac (HFAC) network for powering automotive electrical auxiliaries. The study is focused on motor-actuated loads and is divided into two sections. First, the investigation indicates the benefits of replacing low-torque dc motors with lighter and more efficient 400-Hz ac machines for applications such as electric fans, fuel pumps, or blower motors. A comparative examination of commercially available machines indicates space and weight reduction of more than 60%, and efficiency savings between 25% and 100% are possible. Second, the inquiry evaluates the viability of replacing existing dc/ac inverters with HFAC/ ac converters for high-torque ac machines as employed, for example, in electric- power-assisted steering (EPAS) or heating, ventilation, and air conditioning systems. Based on experimental and simulation results for a column-assist EPAS application employing a three-phase permanent-magnet synchronous motor, this paper shows that an HFAC drive is expected to reduce the voltage harmonic content below 50 kHz by at least 10% compared with the dc/ac inverter. However, the disadvantages of the former drive make it less attractive than the existing dc/ac circuit. Specifically, the EPAS motor torque ripple is expected to be approximately 2% higher compared with the dc counterpart drive. Further drawbacks of the HFAC/ac drive include high metal-oxide-semiconductor field-effect transistor (MOSFET) conduction losses, higher voltage harmonics above 50 kHz, and complex control requirements of the inverter. Conclusively, significant HFAC advantages for motor loads can only be attributed to machines with a nominal torque capability that is limited to 2 N ·m. However, given the number of such devices within a typical vehicle, this translates into a possible vehicle mass saving of 30 kg and a potential reduction in fuel consumption by 0.8 L/100 kmIEEE Transactions on Vehicular Technolog
Experimental High-Frequency Parameter Identification of AC Electrical Motors
No full textIn order to predict conducted electromagnetic interference in inverter-motor drive systems, high-frequency (HF) motor models are requested and the involved parameters have to be available. In previous studies, the authors have presented an accurate HF model for induction motors and they have defined the procedures to identify the model parameters. In this paper, these results are extended to several types and sizes of industrial ac motors such as induction, synchronous reluctance (without interior permanent magnets), and brushless motors. The model parameter-identification procedure has been improved, and it is based on a least-squares data fitting applied to the measured magnitude and phase-frequency-response curves of the phase-to-ground and the phase-to-neutral impedances. The aim of this paper is to provide quick indications to select the suitable values of the HF model parameters, with reference to the size and type of the ac motor, to evaluate the HF voltage and current components in inverted-fed ac motor system
Using the AC Drive Motor as a Transducer for Detecting Electrical and Electromechanical Faults
No full textCondition monitoring of AC motors is a subject area that has received extensive research. Whether this monitoring is carried out on a scheduled basis by engineer intervention, or continuously using an on-line unit, the results of this testing enable preventative maintenance work to be a carried out earlier, before any major failure occurs. Monitoring using vibration analysis is the most common and depending on the plant, can be done once or twice a year. This is usually limited to the condition of motor bearings and is not commonly used to detect failures in the motor electromagnetic systems. Monitoring units that use motor current measurements are also available, but these are less widely-used and usually on major plant motors (>250kW for example) that have a large capital outlay to replace.
The industry drivers – as always – are maximum plant and machinery uptime, with the minimal amount of scheduled maintenance. If maintenance is carried out too regularly, costs rise significantly not only due to the maintenance activity itself, but disruption to production schedules. Maintenance schedules that are too infrequent can result in an unacceptable rise in total failures of plant that are unexpected and may cause a significant amount of production disruption and downtime, especially if this occurs during out-of-hours working time. However, industry now faces another big challenge and one that has had a good share of exposure over the last few years. It is of course, the drive to reduce carbon emissions and with it the amount of energy that a plant itself consumes. What has brought this more to the fore recently is the significant rise in energy costs. Whilst product margins have to remain the same, many companies energy costs have seen a two to three-fold increase in energy budgets in the last few years alone. For industry processes that have a significant amount of fan and pump applications, the manufacturers of low-cost AC inverters have saturated the lower-performance market of inverter drives such that any drive can control these type of fan and pump applications, where accurate speed control is not a major driver.
Unfortunately, this can be a step backwards for end-users of plant that use equipment to monitor motor condition via motor current signals. Additionally, vibration analysis that relies upon ‘base-lining’ motor data when the AC motor is running at base speed may not give accurate readings when the motor is under inverter control and running at a different speed.
For manufacturers of AC inverter drives in this low-end market, it can be difficult to sell a product from one manufacturer over another without the unit having a “USP”, or Unique Selling Proposition. Most decisions taken on inverter equipment purchase at this level are usually in favour of the equipment that costs the least to purchase. Credibility of manufacturers based on product history and perceived reliability cuts little ground with an ever cost-conscious industry.
This is where the research into diagnosis of faults on inverter driven motor systems can provide just this USP for manufacturers. If the incorporation of on-line diagnosis for simple inverter applications can be brought to a typical inverter unit at a reasonable cost, the manufacturer who can offer this gains a unique foothold in the marketplace – a drive that can monitor and signal that the motor it is driving is showing signs of early failure.
It will be sensible to limit this research to simple inverter applications as high-end inverter drives that operate equipment such as high-speed printing presses, rotary shears will be more difficult to model and simulate than a fan or pump application.
It is hoped that a typical inverter drive can relay enough detailed information about the load which it is driving to allow this to be used for abnormal motor load conditions as this will provide a platform on which to extend the research beyond this MSc and into the realms of incorporating such technology into a drive manufacturers equipment. If this can be done without major modification to an inverter, then it may be easier to implement in equipment offered by different manufacturers.
It is quite possible that this technology could be licensed under a name that guarantees the performance of the condition monitoring algorithms and reliability from one drive manufacturer to another
Judge James Crawford AC SC FBA (1948 2021)
No full textScholars and practitioners of international law mourned a true great in 2021 with the passing of James Richard Crawford AC SC FBA, Judge of the International Court of Justice. Crawford’s encyclopedic command of international law and his enduring influence on its development inspire awe in generations of international lawyers. He served as judge, academic, advocate, expert (for both international and domestic law reform bodies), teacher and mentor. Crawford’s intellectual legacy continues in many fields, including state responsibility, statehood and the law of the sea. He was made Companion of the Order of Australia in 2013 for ‘eminent service to the law through significant contributions to international and constitutional legal practice, reform and arbitration, and as a leading jurist, academic and author’
Women and independence in the nineteenth century novel : a study of Austen, Trollope and James
No full text'Women
and
independence in the nineteenth century novel : a
study
of
Austen, Trollope
and
James', begins
with the
concept of
independence
and works through the three
most common usages of
the
word.
The first, financial independence (not
needing to
earn one's
livelihood)
appears to be
a necessary prerequisite
for the
second
and third forms
of
independence,
although it is by
no means an
unequivocal good
in
any of
the
novels.
The
second,
intellectual
independence (not
depending
on others
for
one's opinion or conduct;
unwilling
to be
under obligation
to
others),
is
a matter of asserting independence
while employing
terms
which society recognizes.
The third,
of
being independent, is
exemplified
by
an
inward
struggle
for
a
knowledge
of self.
In
order
to trace the development
of
the idea
of self
during the
nineteenth century,
I have
chosen a group of novels which seem
to be
representative of
the beginning, the
middle, and the
end of
the period.
Particular
attention
is
given
to the
characterizations of
Emma
Woodhouse, Glencora Palliser, Isabel Archer, Milly Theale and
Maggie
Verver. Whereas in Jane Austen's
novels
the self
has a
definite shape
which the heroine
must
discover, and
in Anthony Trollope's
novels
the
self
(reflecting
the idea
of socially-determined man) must
learn to
accommodate social and political changes,
in Henry James's
novels
the
self
determined by
external manifestations
(hollow
man)
is
posed
against
the exercise of
the free
spirit or soul.
Jane Austen's
novels
look backward,
as she reacts against
late
eighteenth century romanticism, and
forward,
with
the development
of
the heroine
who exemplifies
intellectual independence. Anthony
Trollope's
women characters are creatures of social and political
adaptation; although
they do
not
derive their
reason
for being
from
men,
they
must accommodate
themselves to
men's wishes.
And
Henry James looks backward,
wistfully, at
Austen's
solid, comforting,
innocent
self and
forward, despairingly, to the dark,
unknowable self
of
the twentieth
century
- …
