Understanding RMF | The driving force behind every AC machine

Summary

This video script delves into the history and development of rotating magnetic fields (RMFs), a pivotal invention for AC motors that revolutionized the industrial era. From Walter Bailey's initial DC-based design to Nikola Tesla and Galileo Ferraris' advancements using two-phase AC currents, the script explores the evolution of RMFs. It highlights the superiority of Mikhail Dobrovolsky's three-phase RMF over its two-phase counterpart through modern finite element analysis. The video concludes by appreciating the ingenious winding designs of our ancestors that led to the creation of efficient, oscillation-free RMFs.

Takeaways

• 🔧 The concept of rotating magnetic fields (RMF) was instrumental in the industrial revolution and was first initiated by Walter Bailey using DC power and electromagnets.
• 🌀 Walter Bailey's design involved switching electromagnets to create a stepwise rotating magnetic field, but it resulted in a jerky movement due to the use of DC power.
• 💡 Nikola Tesla is credited with a significant advancement in RMF technology by introducing the use of two-phase alternating currents, which led to smoother RMF generation.
• 📜 Tesla's 1888 patent for induction motors marked a milestone in RMF development, coinciding with Galileo Ferraris' similar invention, which used an inductor for phase shifting.
• ⚙️ Tesla's design improved upon Bailey's by eliminating commutators and introducing a 90-degree phase difference between alternating currents to produce a continuous RMF.
• 🏗️ Mikhail Dobrovolsky expanded on Tesla's work by introducing three-phase RMF, which offered a more stable and efficient magnetic field rotation compared to two-phase systems.
• 📊 The three-phase RMF design is superior due to its reduced oscillations and smoother rotation, as demonstrated through finite element analysis in modern simulations.
• 🧲 The orientation of north and south poles in RMF is opposite to that in permanent magnets, defined to facilitate easier analysis and utilization of the internal magnetic field region.
• 🛠️ Modern winding techniques for three-phase RMFs produce fields with minimal oscillations, adhering to the ideal of a constant magnitude revolving magnetic field.
• 🛤️ The script provides a historical journey through the development of RMF, highlighting the contributions of inventors like Tesla, Ferraris, and Dobrovolsky to modern engineering.
• 🔮 The evolution of RMF winding designs showcases the ingenuity of inventors who, through imagination and precise calculations, created systems that form the backbone of today's electrical machinery.

Q & A

What is the significance of the rotating magnetic field (RMF) in AC motors?

The rotating magnetic field (RMF) is crucial in AC motors because it allows for the conversion of electrical energy into mechanical energy, which is essential for the operation of the motor. This invention significantly contributed to the industrial revolution.

Who is considered the pioneering father of modern engineering due to his contributions to RMF?

Nikola Tesla is considered the pioneering father of modern engineering due to his significant contributions to the development of the rotating magnetic field (RMF).

What was Walter Bailey's contribution to the development of RMF?

Walter Bailey's contribution to the development of RMF involved using a DC power supply with electromagnets and commutator rings to create the first RMF.

Why did Walter Bailey's RMF design have a 'jerky' movement?

Walter Bailey's RMF design had a 'jerky' movement because it used a DC power supply, which resulted in a step-wise rotation of the magnetic field instead of a smooth continuous rotation.

How did Nikola Tesla improve the RMF design?

Nikola Tesla improved the RMF design by using two-phase alternating currents, which created a smoother and more efficient rotating magnetic field. He eliminated the need for commutators and introduced a 90-degree phase shift between the two currents.

What alternative method did Galileo Ferraris propose for generating RMF?

Galileo Ferraris proposed an alternative method for generating RMF by using an inductor in one of the two coils, which was supplied by a single-phase AC dynamo.

Why is three-phase RMF considered superior to two-phase RMF?

Three-phase RMF is considered superior to two-phase RMF because it provides a more consistent and smooth rotating magnetic field with fewer oscillations, making it more efficient for motor operation.

What modern technique is used to demonstrate the superiority of three-phase RMF over two-phase RMF?

Finite Element Analysis (FEA) using EM Works 2D software is the modern technique used to demonstrate the superiority of three-phase RMF over two-phase RMF.

Why are the north and south poles of an RMF defined differently from those of a permanent magnet?

The north and south poles of an RMF are defined differently from those of a permanent magnet because, in an RMF, the internal area of the magnetic field is the most useful, whereas in a permanent magnet, the external area is useful. This helps in correct analysis and application of the RMF.

What is a significant feature of modern-day winding techniques for three-phase RMF?

A significant feature of modern-day winding techniques for three-phase RMF is their ability to produce RMFs with almost no oscillations, resulting in a magnetic field of constant magnitude and a smooth revolving nature.

Outlines

00:00

🔌 The Evolution of Rotating Magnetic Fields (RMFs)

This paragraph delves into the history and development of rotating magnetic fields (RMFs), a pivotal invention in the industrial revolution. It highlights Nikola Tesla's significant contributions to the field, alongside the foundational work of Walter Bailey. The script explains the step-by-step process of creating an RMF, starting from the initial DC-powered design with electromagnets and commutator rings to the more refined AC-powered versions. The limitations of the early design, such as the jerky movement due to DC power, are discussed, leading to Tesla's innovation of using two-phase alternating currents for smoother RMF generation. The paragraph also mentions Galileo Ferraris's concurrent work and the transition to more efficient AC polyphase generators.

05:02

🌀 Advancing to Three-Phase Rotating Magnetic Fields

The second paragraph introduces the progression to three-phase RMFs, pioneered by Russian engineer Mikhail Dobrovolsky. It provides a logical explanation of the three-phase RMF design, contrasting it with the two-phase RMF and explaining its superiority. The summary includes a simplified illustration of the winding design and the variation of magnetic fields over time, demonstrating the smooth rotation of the three-phase RMF. The use of finite element analysis in modern software, such as EM Works 2D, is highlighted to show the reduced oscillations in three-phase designs compared to two-phase ones. The paragraph also clarifies the unique notation of north and south poles in RMFs, which is opposite to that of permanent magnets, and concludes with a look at modern winding techniques that produce nearly oscillation-free RMFs, fulfilling the ideal definition of a rotating magnetic field.

Keywords

💡Rotating Magnetic Field (RMF)

A rotating magnetic field is a magnetic field that rotates in space, crucial for the operation of AC motors. The video discusses how RMF was developed, highlighting its significance in industrial applications and its evolution from early designs to modern winding techniques.

💡Nikola Tesla

Nikola Tesla was a pioneering inventor and electrical engineer who made significant contributions to the development of RMF. The video credits Tesla with improving RMF design by using two-phase alternating currents, which became a foundation for modern AC motor technology.

💡Walter Bailey

Walter Bailey was one of the early inventors who experimented with RMF using a DC power supply. His work laid the groundwork for future innovations, despite the initial design's limitations, such as the jerky movement of the magnetic field.

💡Two-phase Alternating Current

Two-phase alternating current involves two currents with a 90-degree phase difference. Nikola Tesla used this method to produce a smoother RMF, eliminating the need for commutators and enhancing the efficiency of electric motors.

💡Galileo Ferraris

Galileo Ferraris was an inventor contemporaneous with Tesla, who also contributed to RMF development. He used an inductor in one of the coils powered by a single-phase AC dynamo to create an RMF, similar to Tesla’s two-phase system.

💡Three-phase RMF

Three-phase RMF is an advancement over the two-phase system, introduced by Mikhail Dobrovolsky. It involves three alternating currents, which produce a smoother and more efficient RMF, making it superior for use in modern electric motors.

💡Eddy Currents

Eddy currents are loops of electric current induced within conductors by a changing magnetic field. Walter Bailey demonstrated the physical rotation of a copper disc using eddy currents, a concept predicted by Michael Faraday.

💡Commutators

Commutators are devices used in early DC motors to periodically reverse the direction of current flow. Nikola Tesla's innovation was to eliminate commutators in his RMF design, simplifying the operation and increasing the motor's reliability.

💡Finite Element Analysis

Finite element analysis is a modern computational technique used to simulate and analyze the behavior of systems. The video uses this method to compare the performance of two-phase and three-phase RMF designs, showing the superiority of the latter.

💡Modern Day Windings

Modern day windings refer to advanced techniques used in electric motor construction to produce an RMF with minimal oscillations. The video mentions that these designs are complex and highly optimized, requiring a detailed, dedicated discussion.

Highlights

The concept of a rotating magnetic field (RMF) was crucial to the industrial revolution.

Nikola Tesla is often considered the pioneering father of modern engineering for his contributions to RMF.

Walter Bailey initiated the idea of RMF using a DC power supply, electromagnets, and commutator rings.

Bailey's design showed that magnetic fields from oppositely wound electromagnets interact to produce a resultant magnetic field.

The interaction of magnetic fields in Bailey's design produces a rotating magnetic field in a step size of 45 degrees.

Bailey's RMF design had a flaw: the RMF movement was jerky due to the use of DC power.

Nikola Tesla improved RMF by using two-phase alternating currents, patented in 1888.

Galileo Ferraris independently developed a similar method for producing RMF with an inductor and single-phase AC dynamo.

Tesla's design removed commutators and used two-phase currents shifted by 90 degrees to produce a smooth RMF.

Tesla's AC polyphase generators were efficient and practical, making his designs popular.

Mikhail Dobrovolsky developed the three-phase RMF, improving upon Tesla's two-phase design.

Three-phase RMF provides a smoother and more efficient rotation compared to two-phase RMF.

Finite element analysis shows that three-phase RMF designs reduce oscillations compared to two-phase designs.

In RMFs, north and south poles are defined oppositely compared to permanent magnets for accurate magnetic field direction in the inner region.

Modern winding techniques produce RMFs with almost no oscillations, fulfilling the definition of a constant magnitude revolving magnetic field.

Transcripts

every ac motor uses a rotating magnetic

field

an invention that kicked off the

industrial revolution

can you guess how the rmf reached this

stage in this video

we'll travel through the minds of the

geniuses behind the development of

rmf the greatest contribution can

perhaps be attributed to nikola tesla

considered by many as the pioneering

father of modern engineering

to understand how the design theories

evolved over time

our trip will take us all the way

through to a glimpse of modern day

winding techniques

and rmf production let's go

the idea of rotating magnetic fields

first started with walter bailey

he used dc power supply and this

arrangement had electromagnets and

commutator rings

let's understand this rmf production in

a step-by-step manner

when a direct current passes through an

electromagnet

it creates a magnetic field with a

specific orientation

if you add a second electromagnet which

is oppositely wound

magnetic field lines get connected

between the opposite poles

let's represent these newly formed

magnetic field lines using an arrow

now add one more such pair diagonally

opposite to the first pair

the interaction between these two

magnetic field lines will produce a

resultant magnetic field line

now let's de-energize the first pair

keeping only the second pair energized

the resultant magnetic field in this

case will be as shown

if we energize both pairs again this

time reversing the polarity of current

in one of the coils

the resultant magnetic field changes

once again

in all four cases the resultant magnetic

fields have one thing in common

and one thing altered did you spot what

those were

in each case the field lines have the

same magnitude but different angles

in short the resultant magnetic field

rotates in a step size of 45 degrees

we have just seen the design of the

first ever rmf

further rotation can be induced by

repeatedly switching the operation

on and off in the same pattern

walter added a copper disc on top to

physically demonstrate the rotation

as the magnetic field changes it induces

eddy currents

just as michael faraday had once

predicted the disk starts to rotate

along with the rmf although a genius

invention

there was a flaw in the design can you

see what that might be

rather than being a smooth rotation the

rmf has a jerky movement

it's safe to say this was not a

particularly useful feature

for an electric motor to have this rocky

ride

is due to the use of dc power the genius

inventor of all time

nikola tesla came up with his own idea

of producing rmf

using two-phase alternating currents

this idea is elaborated

in his patent for induction motors in

1888

coincidentally the same year an

intelligent inventor named galileo

ferraris

also introduced a similar way of

producing rmf

tesla's design was a clever modification

of walters electromagnets

first on his list was to expel the

commutators which were notoriously

tedious to operate

next he supplied alternating currents

with an angular difference of 90 degrees

between them

this means that the field produced by

one coil is shifted in position

in reference to the other wondering how

that works

let's take a closer look first of all

let's consider the starting point the

current from coil a

is a small positive value whereas the

current from coil b

is a larger negative value the

individual magnetic fields produced by

both the coils

is as shown if we add both fields

together

we get this resultant field in the motor

now

hold that thought for future reference

let's see what happens as the currents

vary

in this instance coil a carries a

positive current of the highest

magnitude

and the current in coil b is zero

at this moment the magnetic field

produced by coil a

is the only field in operation

finally both the coil currents are

positive and are at equal magnitude

creating a resultant field as shown

if you observe these three instances you

will find that nikola tesla's two-phase

machine design

produces a rotating magnetic field while

tesla used his ac generator to make this

phase shift possible

galileo ferraris used an inductor in one

of the two coils

supplied by a single phase ac dynamo

later on nikola tesla's two phase was

increasingly popular due to the

practical viability of his designs

and the efficiency of the ac polyphase

generators

needed for these motors we'll leave

tesla and ferraris to battle this one

out

meanwhile the story of rmf development

is not over just yet

back then while the two-phase rmf was

just born

russian engineer mikhail dobrovolsky

gave the world

three-phase rmf we will understand the

three-phase rmf design

logically and by the end of this section

we will also understand why three-phase

rmfs are superior to nikola tesla's

two-phase rmf

let's use a simplified winding design to

understand the working of three-phase

rmf a three-phase current supply will

vary with the time as illustrated in

this arrangement

now we need to find out how the

resultant magnetic field

varies due to the current variation

let's freeze at this instant

the magnetic fields produced by all the

coils are illustrated here

this can be easily deduced using the

thumb rule

now let's combine all these six magnetic

field lines together to get the

resultant magnetic field

in short this is the shape of the rmf at

this instant

let's vary the currents for a small time

interval and freeze the scene

remember that the field density is

higher for conductors with larger

currents

let's trace the resultant path again

comparing both instances the resultant

field has clearly rotated

calculating for all other current

instances the magnetic field is seen to

rotate one revolution for one cycle of

current

and there we have it that's how a

three-phase rotating magnetic field

actually rotates so to round up today's

video

let's decide who is the ultimate winner

of rotating magnetic field systems

was it tesla or was it dobrovolsky

let's use the modern technique of finite

element analysis

to settle the vote the simulation

results from em works 2d software

make a clear case for why three-phase

rmf designs

are superior to two-phase designs as you

can see

the two-phase arrangement gives a dip or

oscillation in the rotating magnetic

field

in the three-phase design these

oscillations are effectively

reduced now for a word on north and

south pole notations of the rmf

did you notice something a little weird

about those

here is what we are talking about in a

permanent magnet north and south poles

are defined as shown

yet in the case of rmfs it is defined in

an opposite way

have you ever wondered why after all the

whole purpose of marking north and south

poles is to make the analysis

easier in a permanent magnet

its external area is the useful area

however for an rmf

the internal area or the magnetic field

in the inner region is the most useful

if you consider the case of an

alternator or an induction motor

this fact will be clear to you the

outside field of an rmf

is never used to get any useful work

when you focus on this useful internal

area of an rmf it is quite logical to

define the north and south poles as

shown

only if we mark the north and south

poles as shown while we get the magnetic

field direction correct in the inside

area

so hopefully that's cleared that up

let's move on to the last part of our

video modern day windings

the modern day winding for the

three-phase rmf is able to produce rmf

with almost

no oscillations this fulfills the actual

definition of an rmf

which is a magnetic field of constant

magnitude revolving in nature

one such modern winding which produces a

4-pole

rmf is shown here

a modern-day winding design is a broad

subject we need a separate dedicated

video to get into it

this concludes our journey through the

history of rotating magnetic fields

and the minds of their great inventors

it is amazing to know how our ancestors

developed winding designs

which produce perfect rmfs just by using

their imagination and precise

calculations

if you enjoyed this video why not hit

subscribe to stay tuned for our next one

thank you and see you next time