How Electric Motors Work

Electric motors are everywhere.

Electric motors are everywhere! In your house, almost every mechanical movement that you see around you is caused by an AC (alternating current) or DC (direct current) electric motor.

1. A simple motor has six parts:
2. Armature or rotor
3. Commutator
4. Brushes
5. Axle
6. Field magnet
7. DC power supply of some sort

By understanding how a motor works you can learn a lot about magnets, electromagnets and electricity in general. In this article, you will learn what makes electric motors tick.

Inside an Electric Motor

An el­ectric motor is all about magnets and magnetism: A motor uses magnets to create motion. If you have ever played with magnets you know about the fundamental law of all magnets: Opposites attract and likes repel. So if you have two bar magnets with their ends marked "north" and "south," then the north end of one magnet will attract the south end of the other. On the other hand, the north end of one magnet will repel the north end of the other (and similarly, south will repel south). Inside an electric motor, these attracting and repelling forces create rotational motion. ­

In the above diagram, you can see two magnets in the motor: The armature (or rotor) is an electromagnet, while the field magnet is a permanent magnet (the field magnet could be an electromagnet as well, but in most small motors it isn't in order to save power).

Toy Motor

The motor being dissected here is a simple electric motor that you would typically find in a toy.

You can see that this is a small motor, about as big around as a dime. From the outside you can see the steel can that forms the body of the motor, an axle, a nylon end cap and two battery leads. If you hook the battery leads of the motor up to a flashlight battery, the axle will spin. If you reverse the leads, it will spin in the opposite direction. Here are two other views of the same motor. (Note the two slots in the side of the steel can in the second shot -- their purpose will become more evident in a moment.)

The nylon end cap is held in place by two tabs that are part of the steel can. By bendin­g the tabs back, you can free the end cap and remove it. Inside the end cap are the motor's brushes. These brushes transfer power from the battery to the commutator as the motor spins

More Motor Parts

The axle holds the armature and the commutator. The armature is a set of electromagnets, in this case three. The armature in this motor is a set of thin metal plates stacked together, with thin copper wire coiled around each of the three poles of the armature. The two ends of each wire (one wire for each pole) are soldered onto a terminal, and then each of the three terminals is wired to one plate of the commutator.

The final piece of any DC electric motor is the field magnet. The field magnet in this motor is formed by the can itself plus two curved permanent magnets.

One end of each magnet rests against a slot cut into the can, and then the retaining clip presses against the other ends of both magnets.

 

Electromagnet in a horseshoe magnet

Electromagnets and Motors

To understand how an electric motor works, the key is to understand how the electromagnet works. (See How Electromagnets Work for complete details.)

An electromagnet is the basis of an electric motor. You can understand how things work in the motor by imagining the following scenario. Say that you created a simple electromagnet by wrapping 100 loops of wire around a nail and connecting it to a battery. The nail would become a magnet and have a north and south pole while the battery is connected.

Now say that you take your nail electromagnet, run an axle through the middle of it and suspend it in the middle of a horseshoe magnet as shown in the figure below. If you were to attach a battery to the electromagnet so that the north end of the nail appeared as shown, the basic law of magnetism tells you what would happen: The north end of the electromagnet would be repelled from the north end of the horseshoe magnet and attracted to the south end of the horseshoe magnet. The south end of the electromagnet would be repelled in a similar way. The nail would move about half a turn and then stop in the position shown.

You can see that this half-turn of motion is simply due to the way magnets naturally attract and repel one another. The key to an electric motor is to then go one step further so that, at the moment that this half-turn of motion completes, the field of the electromagnet flips. The flip causes the electromagnet to complete another half-turn of motion. You flip the magnetic field just by changing the direction of the electrons flowing in the wire (you do that by flipping the battery over). If the field of the electromagnet were flipped at precisely the right moment at the end of each half-turn of motion, the electric motor would spin freely.

A:	Three-phase motors: A1 = Υ connection	A2 = Δ connection
B:	Single-phase motors: B1 = Rotation in one direction	B2 = Rotation in the opposite direction
C:	Three-phase brake motors: Standard braking: Fast braking: Separate brake supply:	C1 = Υ connection    C2 = Δ connection C3 = Υ connection    C4 = Δ connection C5

3 Phase Generation and 3 Phase Generators

3 Phase Power Generation There are several types of 3 phase power generators. These can vary from a utility power station, to a prime source power generator to portable diesel (and other fuels) 3 phase generator, to 3 phase generators which run on 1 phase power (some models of phase converters). At a utility power station, an electrical generator converts mechanical power into a set of alternating electric currents (AC), one from each electromagnetic coil or winding of the power generator. The currents are sinusoidal functions of time, all at the same frequency but with different phases. In a 3 phase system the phases are spaced equally, giving a phase separation of 120°. The frequency is typically 50 Hz in Europe and 60 Hz in the US (see List of countries with mains power plugs, voltages and frequencies). See Frequency Converters for changing 50 Hz to 60 Hz or the reverse of 60 Hz to 50 Hz frequency. Read more about 3 Phase Power Generation below.
Industrial Standby / Towable 3 Phase Power Generators Industrial and towable 3 phase generators are designed and engineered for optimum performance and superior reliability. From the ultra quiet sound attenuated enclosures (64-71 dba) to the state-of-the-art electronics and controls, these 3 phase generator units are engineered to meet the most rugged conditions. Place the unit at the job site, connect the 3 phase load and start it up. These full-featured standby 3 phase generator units are specially suited for all industrial, commercial and rental applications. Generators can also be used with an automatic transfer switch for standby 3 phase applications.
3 Phase Power Generators Power Output Generators voltage output ranges from hundreds of volts to 30,000 volts. This can be from small portable 3 phase generators, 3 phase generating rotary converters, or utility power stations. At the power station, transformers step-up this voltage to one more suitable for transmission. Popular Generators Fuel Includes Propane & Diesel Generators 3 phase power generators can be purchased to run on a variety of fuel types including two of the most popular: propane and diesel generators. Because of the common availability of propane, natural gas and diesel fuel, there are also a wide variety of generators built specifically to use these fuel types. 3 Phase Power Distribution and Transmission After numerous further conversions in the transmission and distribution network the 3 phase power is finally transformed to the standard mains voltage (the voltage of "house" or "household" current in American English). The power may already have been split into single phase at this point or it may still be 3 phase. Where the step-down is 3 phase, the output of this transformer is usually star connected with the standard mains voltage (120V in North America and 230V in Europe) being the phase-neutral voltage. Another system commonly seen in the USA is to have a delta connected secondary on the step down transformer with a center tap on one of the windings supplying the ground and neutral. This allows for 240V 3 phase as well as three different single phase voltages (120V between two of the phases and the neutral, 208V between the third phase (sometimes known as a wild leg) and neutral and 240V between any two phases) to be made available from the same supply. Click here to read more about 3 phase distribution. 3 Phase Loads The most common class of 3 phase load is the 3 phase electric motor. A 3 phase induction motor has a simple design, inherently high starting torque, and high efficiency. Such motors are applied in industry for 3 phase pumps, fans, blowers, compressors, conveyor drives, and many other types of motor-driven equipment. A 3 phase motor is more compact and less costly than a 1-phase motor of the same voltage class and rating; also 1-phase AC motors above 10 HP (7.5 kW) are not as efficient and thus not usually manufactured. Large air conditioning equipment (for example, most York air conditioning units above 2.5 tons (8.8 kW) cooling capacity) use 3 phase motors for reasons of economy and efficiency. Read more about 3 phase power loads here. 3 Phase Loads from 3 Phase Power Generated on 1 Phase Power There are many places and instances where 1 phase power is all that is available, or where the power company wants to charge tens, or even hundreds of thousands of dollars to install and supply 3 phase power. When this is the case a quality 3 phase generating phase converter can be run on 1 phase to power 3 phase equipment of any type. Click here to read more about powering 3 phase loads with 3 phase power generated from 1 phase power. Additional 3 Phase Generator Information Sources: Diesel Generators • Diesel Power Generators • Diesel Generator Sets • Power Generators • Onan Diesel Generators • Kipor Diesel Generator • Kubota Diesel Generator • Cummins Diesel Generator • Yanmar Diesel Generator Continue And Read About Additional 3 Phase Power Details: - 3 Phase Power Home - 3 Phase Wiring - 3 Phase Power Calculation - 3 Phase Electricity - 3 Phase Power Loads - 3 Phase Power Converter - 3 Phase Converters * Rotary Phase Converters * Static Phase Converters - 3 Phase Generators - 3 Phase Transformers * 3 Phase Isolation Transformers - 3 Phase Motors - 3 Phase Frequency * Frequency Converters - 3 Phase Distribution - 2 Phase Systems - 1 Phase Loads on 3 Phase Power - 3 Phase Loads on 1 Phase Power

Three-Phase Transformer Connections:

Three-phase transformers are connected in delta or wye configurations. A wye-delta transformer has its primary winding connected in a wye and its secondary winding connected in a delta (see figure 1-1). A delta-wye transformer has its primary winding connected in delta and its secondary winding connected in a wye (see figure 1-2).

Figure 1-1: Wye-Delta connection




Figure 1-2: Delta-Wye connection

"Three Phase Transformer Info"

This section will discuss three phase transformers and how to calculate transformer overcurrent protection..

Three Phase Transformers Introduction:

Three phase transformers are used throughout industry to change values of three phase voltage and current. Since three phase power is the most common way in which power is produced, transmitted, an used, an understanding of how three phase transformer connections are made is essential. In this section it will discuss different types of three phase transformers connections, and present examples of how values of voltage and current for these connections are computed.

Three Phase Transformer Construction:

A three phase transformer is constructed by winding three single phase transformers on a single core. These transformers are put into an enclosure which is then filled with dielectric oil. The dielectric oil performs several functions. Since it is a dielectric, a nonconductor of electricity, it provides electrical insulation between the windings and the case. It is also used to help provide cooling and to prevent the formation of moisture, which can deteriorate the winding insulation.

Three-Phase Transformer Connections:

There are only 4 possible transformer combinations:

Delta to Delta - use: industrial applications
Delta to Wye - use : most common; commercial and industrial
Wye to Delta - use : high voltage transmissions
Wye to Wye - use : rare, don't use causes harmonics and balancing problems.