Motors 101

Summary

This video delves into the workings of electric motors, which consume half of global electricity and power 70% of industry. Focusing on three-phase asynchronous AC induction motors, it explains their layout, components, and how they generate mechanical torque. It covers the stator and rotor interaction, the concept of slip, and the importance of motor design for different applications. The video also discusses motor efficiency, speed control, and the significance of the nameplate for technical specifications, emphasizing the need for careful management to maximize motor performance and efficiency.

Takeaways

• 🔌 Electric motors are responsible for approximately half of global electricity consumption and about 70% of industrial power use.
• 🚗 DC brushless motors are favored in electric vehicles due to their high torque and efficiency.
• 🔄 AC motors, which use alternating current, are more common and account for a significant portion of motor load in industrial power consumption.
• 🌀 The focus of the video is on three-phase asynchronous AC induction motors, which are prevalent in everyday applications like refrigeration and air conditioning units.
• 🏗️ The key components of an induction motor include the stator coils, rotor, and termination box for power input.
• 🔧 The rotor, also known as the armature, provides mechanical power output and is magnetically coupled to the stationary stator.
• 🔑 The motor shaft often has a key to prevent slippage within the load sleeve, ensuring proper mechanical connection.
• 📜 The nameplate on a motor provides crucial electrical and mechanical information necessary for operation and maintenance.
• 🌀 The operation of an induction motor relies on the generation of a rotating magnetic field by the stator, which induces a current in the rotor, creating torque.
• 🔌 The speed of the rotor is slightly less than the electrical frequency due to the slip, a measure of the difference in speed between the rotating magnetic field and the rotor.
• ⚙️ Induction motors are valued for their simple and robust design, which allows them to maintain a constant speed across a range of loads.
• 🔄 The design of the rotor, such as the squirrel cage rotor, influences the motor's mechanical performance, including starting torque and speed-torque characteristics.
• 🏢 Standard frame sizes and nameplate information, as set by organizations like NEMA, facilitate easy motor replacement and customization for specific applications.
• 📊 The nameplate also includes specifications like efficiency, power factor, voltage rating, and service factor, which are critical for understanding the motor's capabilities and limitations.

Q & A

What percentage of global electricity is consumed by electric motors?

Electric motors consume around half of global electricity.

What percentage of industrial power consumption is attributed to electric motors?

Electric motors are responsible for about 70% of industrial power consumption.

Why are DC brushless motors popular in electric vehicles?

DC brushless motors are popular in electric vehicles because of their high torque and efficiency.

What type of motors are more common and make up most of the motor load in industrial power consumption?

AC Motors are much more common and make up most of the motor load, being responsible for about 70% of industrial power consumption.

What specific type of AC Motors does the video focus on?

The video focuses on three phase asynchronous AC induction motors.

What is the function of the termination box in a motor?

The termination box is where the wires come in to provide three phase electric power to the motor.

How is the stator related to the rotor in an induction motor?

The stator is magnetically coupled to the rotor but does not physically touch it. The stator remains stationary while the rotor rotates.

What is the role of the rotor in an induction motor?

The rotor, sometimes called the armature, is the moving or rotating piece of the motor that provides the mechanical power output to the load through the shaft.

What is the purpose of the key and keyway on the motor shaft?

The key and keyway ensure that the shaft doesn't slip inside the load sleeve, linking it with the load such as a fan or pump.

What is the phenomenon called when the rotor speed is slightly less than the electrical speed due to losses in the induction process?

The difference in speed is called the slip.

Why is a variable frequency drive needed to change the speed of an AC motor?

A variable frequency drive is needed to change the speed of a motor because AC Motors run at a fixed speed when directly connected to the electrical system.

What is the typical motor inrush current when started across the line?

A typical motor inrush current when started across the line is six to eight times the rate at full load current.

What is the significance of the service factor in motor operation?

The service factor is an overload rating at nameplate voltage and frequency, indicating the allowable overload for a motor. It is used for short periods and helps to compensate for low or unbalanced voltage supply.

What does the nameplate of a motor typically include, and why is it important?

The nameplate includes necessary electrical and mechanical information such as frame designation, manufacturer's type, power rating, duty rating, max ambient temperature, insulation designation, service factor, speed, electrical frequency, phase, efficiency, power factor, and voltage rating. It is important for installation, operation, and maintenance of the motor.

Why might a motor run in the reverse direction if the power connection phases are swapped?

You can reverse the direction of a motor by swapping two of the three phases of the incoming power connection. If the phasing is incorrect, it will cause the motor to spin in the opposite direction during startup.

How does the design of the rotor affect the motor's mechanical operation?

The design of the rotor is very important as it influences how the motor will operate mechanically. Most induction machines have a squirrel cage rotor, and modifications to the shape and size of the conductors can minimize starting currents or vary the speed and torque relationship.

What is the difference between a squirrel cage rotor and a wound rotor?

A squirrel cage rotor is made up of axial conduction bars and radial shorting rings, and it is the most common type due to its simplicity. A wound rotor, on the other hand, can be used for high starting torque but requires brushes and commutators.

Outlines

00:00

🔋 Understanding Electric Motors and Their Applications

This paragraph introduces the significance of electric motors in global energy consumption and industrial power use, highlighting the prevalence of AC motors and focusing on three-phase asynchronous AC induction motors. It explains the physical components of an induction motor, including the stator, rotor, and shaft, and how these parts interact to generate mechanical power. The paragraph also touches on the concept of slip and the use of variable frequency drives and soft starters to manage motor speed and startup.

05:00

🏭 Motor Design and Industrial Motor Standards

This section delves into the design of induction motors, emphasizing the importance of the rotor's design and the different types of rotors, such as squirrel cage and wound rotor. It discusses the factors that affect motor performance, including torque and horsepower, and how these are determined by the stator windings and rotor design. The paragraph also explains the standardization of motor frame sizes by IEC or NEMA, the significance of motor nameplates, and the various parameters listed on them, such as horsepower rating, duty rating, insulation designation, service factor, speed, electrical frequency, and efficiency.

10:02

🔌 Motor Electrical Specifications and Efficiency

The final paragraph provides detailed insights into the electrical specifications of motors, including voltage ratings, the impact of system voltage drops, and the importance of correct wiring according to the motor's nameplate. It also discusses the ability to reverse motor direction by swapping power phase connections and the importance of motor management for energy efficiency. The paragraph concludes with an invitation to learn more about electric motors through visits to Eaton's Power Systems Experience Centers or online resources.

Keywords

💡Electric Motors

Electric motors are devices that convert electrical energy into mechanical energy, causing rotation or linear motion. In the context of the video, they are highlighted as significant consumers of global electricity, accounting for about half of the total consumption and 70% of industrial power use. The script emphasizes the importance of understanding how these motors work due to their prevalence and impact on energy usage.

💡DC Brushless Motors

DC brushless motors are a type of electric motor that operates on direct current and does not require brushes for commutation. They are noted for their high torque and efficiency, making them popular in electric vehicles. The script mentions this type of motor as an example of the different kinds of motors used in various power systems.

💡AC Motors

AC Motors, which stands for Alternating Current Motors, are motors that use alternating current to operate. They are more common than DC motors and are the focus of the video script. AC motors are responsible for a large portion of industrial power consumption, as mentioned in the script, and include three-phase asynchronous induction motors as a key example.

💡Three-Phase Asynchronous AC Induction Motors

This type of motor is a specific kind of AC motor that the video script focuses on. It operates on three alternating current phases and is asynchronous, meaning the rotor rotates at a speed slightly less than the rotating magnetic field produced by the stator. The script explains how these motors work, their components, and their importance in industrial applications.

💡Stator

The stator is the stationary part of an electric motor that houses the stator coils. In the script, it is described as being magnetically coupled to the rotor and is responsible for creating a rotating magnetic field when energized by three-phase electric power. The stator's function is crucial for the motor's operation.

💡Rotor

The rotor, sometimes referred to as the armature, is the moving part of the motor that converts the magnetic field interaction into mechanical power output. The script explains that in induction motors, the rotor is made of a conductive 'squirrel cage' that induces a current creating a magnetic field opposing the stator's field, leading to rotation.

💡Squirrel Cage Rotor

A squirrel cage rotor is a type of rotor construction in induction motors, made up of conductive bars and shorting rings, resembling the appearance of a hamster's exercise wheel. The script mentions this design as a common feature in induction motors, which allows for the induction of current and the generation of a magnetic field that opposes the stator's field.

💡Slip

Slip in the context of motors refers to the difference in speed between the rotating magnetic field and the rotor's actual speed. The script explains that due to losses in the induction process, the rotor's mechanical speed is slightly less than the speed of the stator's oscillating magnetic field, which is an important concept in understanding motor efficiency.

💡Variable Frequency Drive (VFD)

A variable frequency drive is a device used to control the speed of AC motors by altering the frequency of the electric power supplied to them. The script mentions VFDs as a method to change the speed of motors, which otherwise run at a fixed speed when connected directly to the electrical system.

💡Soft Starters

Soft starters are devices that allow motors to be brought up to their rated speed gradually, rather than starting abruptly. The script discusses soft starters as a way to reduce the large inrush current that can occur when a motor is started without a drive or soft starter, which can cause issues on the power system.

💡Nameplate

The nameplate on a motor is a metal plate that provides essential electrical and mechanical information about the motor, such as ratings, specifications, and manufacturer details. The script describes the nameplate as an important source of information for technicians and engineers, and it includes a breakdown of the various data typically found on a motor's nameplate.

Highlights

Electric motors consume around half of global electricity and are responsible for about 70% of industrial power consumption.

DC brushless motors are popular in electric vehicles due to their high torque and efficiency.

AC Motors are more common and make up most of the motor load in industrial power consumption.

Three phase asynchronous AC induction motors are the focus of the video for their widespread use.

Motors are integral to everyday life, used in various appliances like refrigeration, condensers, and hair dryers.

The stator and rotor are key components of an induction motor, with the stator remaining stationary and the rotor rotating.

The rotor, or armature, provides mechanical power output to the load through the shaft.

A motor's shaft has a key to ensure it doesn't slip inside the load sleeve, linking with the load side.

For large motors, a coupling may attach the shaft to the load, such as a fan or pump.

Motors often have lifting eyes for hoisting, especially important for very heavy industrial motors.

The nameplate on a motor provides necessary electrical and mechanical information.

The rotor spins due to the interaction of the stator's magnetic field with the induced current in the rotor.

The difference in speed between the electrical oscillation and the mechanical speed of the rotor is called slip.

AC Motors run at a fixed speed and require a variable frequency drive to change speed.

Soft starters can be used to reduce inrush current and slowly bring the motor up to rated speed.

The inrush current is large when starting a motor without a drive or soft starter, causing issues on the power system.

The design of the rotor is crucial for the motor's mechanical operation, with variations in stator windings and rotor design.

Induction machines are common due to their simple and rugged design, maintaining constant speed across their load range.

Motors come in various sizes for different applications, with specific torque and horsepower ratings required by the load.

Torque is the force a motor can apply, while horsepower is the speed at which the force can be applied.

Motors have standard frame sizes set by IEC or NEMA for easy replacement regardless of manufacturer.

The nameplate on a motor includes frame designation, manufacturer's type, power rating, and other essential specifications.

Service factor is an overload rating at nameplate voltage and frequency, affecting efficiency, power factor, and temperature rise.

The speed of a motor is given at rated load or horsepower, slightly below the electrical speed due to slip.

Electrical frequency and phase are listed on the nameplate, with considerations for use with variable frequency drives.

Efficiency and power factor ratings are provided on the nameplate, important for system design and operation.

Voltage rating is crucial, with motors able to operate + or -10% of the listed value.

Motor direction can be reversed by swapping two of the three phases of the incoming power connection.

Motor management is critical due to the significant electricity consumption by motors worldwide.

Transcripts

In this video, I'm going to explain how motors work.

Electric motors consume around half of global electricity.

They're responsible for about 70% of industrial power consumption.

There are different types of motors used in AC and DC power systems.

DC brushless motors are very popular for use in

electric vehicles because of their high torque and efficiency.

AC Motors use alternating current and are much more common.

They make up most of the motor load I mentioned earlier being responsible

for about 70% of industrial power consumption.

In this video, we will focus on AC Motors and even more specifically,

three phase asynchronous AC induction motors.

Motors are part of our everyday lives.

We use them in refrigeration, condensers, AC units, hair dryers,

and the list goes on.

Have you ever wondered

what makes a motor spin?

We know it's electricity,

but what really goes on inside

but what really goes on inside

the metal case that contains the motor?

First, let's do a physical breakdown of a motors layout.

Key components of induction

motors are the metal case that contains all of the parts of the motor.

On the outside of the case is the termination box where the wires

come in to provide three phase electric power to the motor.

The wires go inside the motor case and are attached to the stator coils.

The stator does not physically touch, but is magnetically coupled

to the next component the rotor,

the stator remains stationary and the rotor rotates.

The rotor, sometimes called the armature, is the moving

or rotating piece of the motor

that provides the mechanical power output to the load through the shaft.

Notice the shaft has a key set to ensure it doesn't slip inside the load sleeve.

A key sits in here, which then links up with the key way on the load side.

Whether that's a fan or a pump.

For large motors, there may be a coupling that attaches this shaft to the load.

Motors usually have one or more lifting eyes for hoisting.

This is particularly important for very heavy industrial motors.

And finally, we have the nameplate.

This provides all of the necessary electrical and mechanical information

about the motor.

We'll do a breakdown of the nameplate later on in this video.

But first, what makes the rotor spin?

For a three phase motor

The electric power energizes the three stator coils.

One for each phase.

These coils are evenly spaced

around the stator or 60 degrees apart for a four pole machine.

Three phases alternating 120 degrees apart

electrically results in a rotating magnetic field.

This magnetic field induces a current on the conductive squirrel cage or rotor

This is where the induction motor gets its name.

The current that flows through the squirrel cage produces

a magnetic field that opposes the magnetic field produced by the stator windings.

These magnetic fields will oppose each other,

just like the north poles of these magnets will oppose each other.

But because the fields are spinning, we get a rotation in the rotor.

We have a demo

here at the PSEC to help you visualize the magnetic field interaction.

The stator field is rotating and you can see that it pushes a magnet

and makes it spin

This mechanical torque is connected through the motor shaft to fans

and pumps and industrial systems for air conditioning, water treatment,

and a whole bunch of other industrial processes.

The electricity is oscillating at a speed of 60 hertz

or 60 cycles per second when it energizes the stator.

The resulting mechanical

speed of the rotor is a little less due to losses in the induction process,

and the difference in speed is called the slip. For a four pole machine

this equates to just under 1800 revolutions per minute

AC Motors run at a fixed speed when directly

connected, to the electrical system to change the speed of a motor

a variable frequency drive is needed.

Soft starters can be used to slowly bring the motor up to rated speed.

When you start a motor without a drive or a soft starter,

there is a large inrush current

that can cause voltage drop and other issues on the nearby power system.

This inrush of power is needed to overcome

the inertia of the motor and the physical load attached to it.

This is like spinning someone on a merry go round.

It's hard to get them spinning.

You might even run around in a circle a few times while pulling on the bar.

But once they're up to speed, it's easy to keep them moving

by pushing on one of the bars as it goes by.

A typical motor inrush current when started across the line,

meaning directly connected to the 60 Hertz power system,

is six to eight times the rate at full load current.

Another thing to note is that some motors run at 3600 RPM

and that is actually a two pole machine which has a different state

or winding structure.

The design of the rotor is very important

to how the motor will operate mechanically.

Most induction machines have what is called a squirrel cage rotor

made up of axial conduction bars and radial shorting rings

This is where the name squirrel cage rotor comes from.

The stator will magnetically induce current on these bars and rings

which will produce the rotors magnetic field.

The shape and size of the conductors are modified to minimize

starting currents or vary the speed and torque relationship.

A wound rotor can be used instead of a squirrel cage

for high starting torque, but requires brushes and commentators.

Induction machines are the most common industrial motors because of their simple

and rugged design that can maintain constant speed across their load range.

Motors come in all different shapes and sizes for various applications

for certain torque and horsepower ratings are required by the load.

Torque is the force the motor can apply and horsepower

is the speed at which the force can be applied.

For example,

an elevator needs a high torque in order to lift itself and the people inside,

but it doesn't need a very high horsepower rating

because it doesn't move very fast.

A high horsepower elevator would be more like an amusement park ride.

Compare this to a large

industrial pump that spins very fast, pumping a thousand gallons per minute.

This is an application of high torque and high horsepower

The design of the stator windings and squirrel cage

rotor is varied to allow for more current flow and induction

to create more or less mechanical torque and horsepower output of the motor.

Motors common industry standard frame sizes set by IEC or NEMA.

This allows motors to be easily replaced regardless of manufacturer.

Because of this, you will only have to replace the motor

and not a fan or pump when there is just a motor failure.

Motors have a nameplate like this to display the necessary electrical

and mechanical information for a technician or engineer.

Let's take a closer look at the nameplate.

This steel or aluminum plate is engraved

to make the information readable for the life of the motor.

Here in the US, nameplate information standards are set by NEMA,

the National Electrical Manufacturers Association,

but manufacturers

may include other information to help with installation, operation

and maintenance of Custom Motors or those manufactured for specific purposes.

The nameplate will list the frame designation for the mounting dimensions.

The manufacturer's type, which tells the function of the motor,

the power or horsepower rating is also listed.

A good rule of thumb is that one horsepower is about equal to one KVA

Here is a list of commonly used equations for motor calculations

There is a time or duty rating, which is how long the motor can run at rated load.

Usually you'll see CONT meaning that it can do so continuously.

Also, you'll see the max ambient temperature

for the surrounding environment that the motor can be in.

There is an insulation designation given by a letter A, B, F, or H.

The higher the letter is in the alphabet indicates

the windings can withstand a higher temperature for longer periods of time.

Another important spec is the service factor,

which is an overload rating at nameplate voltage and frequency,

the allowable overload for a motor equals

the rated load multiplied

by that service factor.

Such operation,

however, will adversely affect efficiency, power factor and temperature rise.

This is only allowed for a short period of time,

which is not specific, even in the NEMA code.

The best plan for an application needing temporary overload is to have temperature

monitoring to ensure the motor does not exceed installation temperature ratings.

Operating over a service factor

of 1.0 for extended periods will shorten

the life of the motor.

Service factors over 1.0 can be used to compensate

for low or unbalanced voltage supply.

The service factor is a complicated specification

and I recommend consulting NEMA MG 1.

The service factor is only required

on a nameplate if it is higher than 1.0.

So it's safe to assume 1.0 if you don't

see the service factor listed.

Also on the nameplate is the speed which is given at rated load or horsepower.

Remember, this is slightly below the electrical speed

because of the magnetic slip interaction between the stator and rotor.

As you can see here, this motor is rated at 1755 RPM instead of 1800 RPM.

The electrical frequency is listed typically 50 or 60 hertz.

Because motors are being paired with VFDs more and more

this is sometimes listed as a range.

Consult the motor manufacturer if you need to find out the range for use with a VFD.

Notice that this motor actually lists

the max safe mechanical RPM of 3600,

which means that it could be fed

a 120 hertz voltage by a VFD.

The motor might also say inverter duty rated,

indicating a higher installation level, making it appropriate for VFD application.

The phase is listed either three phase or single phase.

A nominal efficiency is given and is defined by the mechanical

output power divided by the electrical input power.

This rating is given with a range of + or - 20% because motor

efficiency can vary greatly if the power system is unbalanced.

The power factor rating is listed typically .8 to .88.

This is a ratio of real kilowatt to total

power consumption or KVA at full load.

This is useful for power factor correction design of a large system.

Note that the magnetic field is required for the motor to spin,

whether it is loaded or not.

So when the motor is unloaded, the power

factor is very low, about 0.1.

And last but not least, is the voltage rating, standard

NEMA ratings include 200, 230 and 460 volts.

Motors can operate + or -10% of this value.

You might be wondering why the values are at 240

and 480 volts like our power systems are rated.

Well, this is because the voltage rating of the motor accounts for a voltage

drop in the system and stator windings.

So you would in fact use a 460 volt motor on a 480 volt system.

Typically multiple voltages are listed like on this nameplate

and you'll see a wiring diagram that you need to follow carefully

to connect the stator windings for the high or low voltage rating.

Another very important thing to know is that you can reverse the direction

of a motor by swapping two of the three phases of the incoming power connection.

If you get the phasing wrong,

you will have a fan or pump spinning backwards during startup.

This is why electricians will bump start a motor

for the first energized option to check its rotation again.

Motors consume around half of the entire world's electricity.

This is why we here at Eaton take motor management very seriously.

Whether it be our variable frequency motor drives

or intelligent control and protection use to manage motor systems,

we do our best to maximize efficiency and safety.

To learn more about electric motors and their application in power systems,

schedule a visit to one of Eaton's Power Systems Experience Centers,

and check us out online at Eaton.com/experience.