Armature reaction in a DC machine is the effect of armature flux on the main field flux. It has two undesirable effects - it demagnetizes the main flux and distorts the main flux. This reduces generated voltage and torque and influences commutation limits. Methods to reduce armature reaction include compensating windings and interpoles, which produce fields opposing the armature flux effects.
O.C & S.C Test, Sumpner or back to back Test, Condition for maximum efficienc...Abhishek Choksi
Sub: DC Machines and Transformer (2130904)
Active Learning Assignment
Topic: O.C & S.C Test, Sumpner or back to back Test, Condition for maximum efficiency, All day Efficiency
O.C & S.C Test, Sumpner or back to back Test, Condition for maximum efficienc...Abhishek Choksi
Sub: DC Machines and Transformer (2130904)
Active Learning Assignment
Topic: O.C & S.C Test, Sumpner or back to back Test, Condition for maximum efficiency, All day Efficiency
A synchronous motor is electrically identical with an alternator or AC generator.
A given alternator ( or synchronous machine) can be used as a motor, when driven electrically.
Some characteristic features of a synchronous motor are as follows:
1. It runs either at synchronous speed or not at all i.e. while running it maintains a constant speed. The only way to change its speed is to vary the supply frequency (because NS=120f/P).
2. It is not inherently self-starting. It has to be run up to synchronous (or near synchronous) speed by some means, before it can be synchronized to the supply.
3. It is capable of being operated under a wide range of power factors, both lagging and leading. Hence, it can be used for power correction purposes, in addition to supplying torque to drive loads.
This presentation contains basics of Magnetic circuits such as, magnetic flux, flux density, MMF, Reluctance, Magnetization Curve(B-H Curve), Difference between Electric & Magnetic Circuit, Series & Parallel magnetic Circuits etc.
This ppt is more useful for Civil Engineering students.
I have prepared this ppt during my college days as a part of semester evaluation . Hope this will help to current civil students for their ppt presentations and in many more activities as a part of their semester assessments.
I have prepared this ppt as per the syllabus concerned in the particular topic of the subject, so one can directly use it just by editing their names.
A synchronous motor is electrically identical with an alternator or AC generator.
A given alternator ( or synchronous machine) can be used as a motor, when driven electrically.
Some characteristic features of a synchronous motor are as follows:
1. It runs either at synchronous speed or not at all i.e. while running it maintains a constant speed. The only way to change its speed is to vary the supply frequency (because NS=120f/P).
2. It is not inherently self-starting. It has to be run up to synchronous (or near synchronous) speed by some means, before it can be synchronized to the supply.
3. It is capable of being operated under a wide range of power factors, both lagging and leading. Hence, it can be used for power correction purposes, in addition to supplying torque to drive loads.
This presentation contains basics of Magnetic circuits such as, magnetic flux, flux density, MMF, Reluctance, Magnetization Curve(B-H Curve), Difference between Electric & Magnetic Circuit, Series & Parallel magnetic Circuits etc.
This ppt is more useful for Civil Engineering students.
I have prepared this ppt during my college days as a part of semester evaluation . Hope this will help to current civil students for their ppt presentations and in many more activities as a part of their semester assessments.
I have prepared this ppt as per the syllabus concerned in the particular topic of the subject, so one can directly use it just by editing their names.
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Analysis of Transformer Loadings and Failure Rate in Onitsha Electricity Dist...Dr. Hachimenum Amadi
This study investigated transformer loadings and failure rate in the Onitsha Electricity Distribution Network by using the Electrical Transient Analysis Program (ETAP) software 12.6 and the Statistical Package for the Social Sciences (SPSS) software 16.0. Data collected over the period 2011-2015 on the distribution network were simulated on ETAP software using the Newton-Raphson (N-R) technique to determine the transformer loadings while responses to 350 copies of questionnaire distributed among the technical staff were statistically analysed on the SPSS software to ascertain the failure rate among transformers in the network. The findings of the study show that during the 5 years period covered by the study, the sampled substations recorded transformer average failure rate of 11.7 %. It was further revealed that besides insulation issues which accounted for 24.2% of all the failures, overload (22.5%) was the next major cause of transformer breakdowns in the distribution network. The study recommends installation of more transformer units, use of high quality transformers, balanced loading of the transformers and proactive inspection and maintenance program of transformers units within the network. The outcome of this work would help electricity utilities provide more reliable and cost effective services to customers.
This paper explains losses associated with conventional generators due to armature reaction and self-induced emf and introduces a new design, dual generators, to scale down these losses. In the following paper, it will be shown how dual generators can offer better conversion of energy from mechanical to electrical and also reduce the above mentioned losses.
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A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
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Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
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Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
2. What is Armature Reaction ?
Armature Reaction in a d.c. machine is
basically the effect of armature produced
flux on the main flux or field flux .
3. Effects…
• The armature reaction produces the following
two undesirable effects:
1. It demagnetizes or weakens the main flux.
2. It cross-magnetizes or distorts the main flux.
4. Reduction in main flux per voltage reduces
the generated voltage and torque whereas
distortion of the main-field flux influences
the limits of successful commutation in d.c.
machines.
5. Explanation…
• To understand this process let us first assume a 2-
pole d.c. machine at no load . At that instant there is
no armature current . So the flux due to mmf
produced by field current in the machine at north
pole of the magnet will flow towards the south pole
of the magnet.
6. • The net / resultant flux of the system can be taken as
a straight horizontal line OA and can be shown in
phasor as :-
• Also at that instant the Magnetic Neutral Axis
(M.N.A) of the machine will concide with the
Geometrical Neutral Axis (G.N.A) of the machine as
the M.N.A is always perpendicular to the net flux.
7. • Now when the dc machine is loaded , current flows
in armature windings . This armature current set up
armature flux . With field windings unexcited , the
flux can be shown as vertical lines across armature
conductors .
• The conductors on the left side of the M.N.A will
have current flowing in inside direction whereas on
right side of MNA , the current will flow in outside
direction. The direction of the flux thus produced can
be determined by using Maxwell‘s Right hand Screw
rule.
8. • The resultant flux of the system is a straight vertical
line OB and can be shown in phasor as :-
• Note that the magnitude of OB will always be less
than OA since the cause of armature flux is field flux
and it is known to us that effect is always less than
cause. Here armature flux is the effect and field flux
is its cause.
9. • An examination to the above two phasors reveals
that the path of armature flux is perpendicular to the
main field flux.
• In other words, the path of the armature flux crosses
the path of the main field flux. This can be shown in
phasor as :-
• Thus the effect of armature flux on the main field
flux is entirely ‘cross-magnetizing’ and it is for this
reason that the flux produced by armature mmf is
also called as cross-flux.
10. • When the current flows in both the armature and
field windings, the resultant flux distribution is
obtained by superimposing theses two fluxes. i.e.
11. • It is observed that the armature flux aids the main
field flux at the lower end of the N-pole and at the
upper end of the S-pole, therefore at these two
poles, the armature flux strengthens the main field
flux.
• Likewise, the armature flux weakens the main field
flux at Upper end of the N-pole and at lower end of
the S-pole.
12.
13. • Now, if there is no magnetic saturation, then the
amount of strengthening and weakening of the main
field flux are equal and the resultant flux per pole
remains unaltered from its no load value.
• Actually, the magnetic saturation does occurs and as
a consequence, the strengthening effect is less as
compared to the weakening effect and the resultant
flux is decreased from its no-load value. This is called
‘Demagnetizing effect of armature reaction’
14. • So when the machine is run loaded , M.N.A will shift
from G.N.A of the machine .
• The resultant shift is completely dependent on the
magnitude of armature current.
• Thus, greater the value of armature current , greater
is the shift of MNA from GNA .
15. • It may therefore be stated from the above that
net effect of armature flux on the main field flux
is:-
1. To distort the main field flux thereby causing
non-uniform distribution of flux under the main
poles.
2. To shift the MNA in the direction of the rotation
for a generator and against the direction of
rotation for a motor.
3. To reduce the main field flux from its no-load
value due to magnetic saturation.
16. Methods to reduce Armature Reaction
• There are various methods of reducing the armature
reaction, some of them are:-
1. Compensate Windings
2. Interpoles or copoles
17. Compensating Windings
• The compensating windings consist of a series
of coils embedded in slots in the pole faces.
• These coils are connected in series with the
armature in such a way that the current in
them flows in opposite direction to that
flowing in armature conductors directly below
the pole shoes.
18. • The series-connected compensating windings
produce a magnetic field, which varies directly
with armature current.
• As the compensating windings are wound to
produce a field that opposes the magnetic
field of the armature, they tend to cancel the
effects of the armature magnetic field.
19.
20. Interpoles
• Another way to reduce the effects of armature
reaction is to place small auxiliary poles
called "interpoles" between the main field
poles.
• Interpoles have a few turns of large wire and
are connected in series with the armature.
21. • Interpoles are wound and placed so that each
interpole has the same magnetic polarity as the
main pole ahead of it, in the direction of rotation.
• The field generated by the interpoles produces
the same effect as the compensating winding.
This field, in effect, cancels the armature reaction
for all values of load current.