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. In this article we'll look at both types. By understanding how a motor works you can learn a lot about magnets, electromagnets and electricity in general.
An electric 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 south will repel south. Inside an electric motor, these attracting and repelling forces create rotational motion. 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. Say that you created a simple electromagnet by wrapping 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 illustration.
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 half a turn and then stop in the position shown. The key to an electric motor is to go one step further so that, at the moment that this half turn of motion completes, the field of the electromagnet flips.
You flip the magnetic field by changing the direction of the electrons flowing in the wire, which means flipping the battery over. The flip causes the electromagnet to complete another half turn of motion. 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.
As we mentioned, you'll encounter two types of electric motors: direct current and alternating current. The latter, direct current, or DC, motors were first developed in the mids, and they're still in use today. The outside of a DC motor is the stator: a permanent magnet that does not move. The inside part is the rotor, which does move. The rotor here is like the nail in our previous example, and the stator is like the horseshoe magnet. When DC power is sent through the rotor, it creates a temporary electromagnetic field that interacts with the permanent magnetic field of the stator.
The commutator's job is to keep the polarity of the field flipping, which keeps the rotor rotating. This creates the torque needed to produce mechanical power. The toy DC motor pictured is small, about as big around as a dime, with two battery leads.
If you hook the battery leads of the motor up to a battery, the axle will spin. If you reverse the leads, it will spin in the opposite direction. Starting from the position shown in the diagram of the dc motor :. When the coil is vertical, it moves parallel to the magnetic field, producing no force.
This would tend to make the motor come to a stop, but two features allow the coil to continue rotating:. Climate Change. Climate Feedback.
Ocean Acidification. Rising Sea Level. Electric motor. The bars of the rotor are often skewed. This helps distribute the magnetic field across multiple bars and stops the motor being able to align and jam.
The stator contains all the coils or windings used to create the rotating electromagnetic field when electricity is passed through the wires. To power the coils, we find an electrical terminal box on the top, or sometimes on the side. Inside this box we have 6 electrical terminals. We have our phase one coil connected to the two U terminals, then the phase 2 coils connected to the two V terminals and lastly the phase 3 coil connected to the two W terminals.
Notice that the electrical terminals are arranged in a different configuration on one side to the other. We now bring in our three-phase power supply and connect these to their respective terminals. For the motor to run we need to complete the circuit and there are two ways to do this. The first way is the delta configuration. This will give us our delta configuration. Now, when we provide AC current through the phases, we see that electricity flows from one phase to another as the direction of ac power reverses in each phase at a different time.
The other way we can connect the terminals is to use the star, or wye, configuration. In this method we connect between W2, U2 and V2 on only one side. This will give us our star or wye equivalent connection. Now, when we pass electricity through the phases, we see the electrons are shared between the terminals of the phases. Due to their design differences, the amount of current flowing in the star and delta configuration is different, and we will see some calculations for these towards the end of the article.
That means when we use a multimeter to measure the voltage between any two phases, we will get a reading of Volts, we call this a line to line voltage. Now if we measure across the two ends of a coil, we again see the line to line voltage of Volts. Lets say each coil has a resistance or, impedance as this is alternating current, of 20 Ohms.
That means we will get a current reading on the coil of 20 amps. We can calculate that from Volts divided by 20 Ohms which is 20 Amps. But, the current in the line will be different, it will be We get that from 20Amps multiplied by the square root of 3 which is Now if we look at the star or wye configuration, we again have a line to line voltage of V.
We see that, if we measure between any two phases. But, with the star configuration, all our coils are connected together and meet at the star point or the neutral point. The voltage is less as one phase is always in reverse. We can calculate this by Volts divided by square root of 3 which is Volts. As the voltage is less, the current will be too. The line current will also therefore be the same at So we can see from the delta configuration, the coil is exposed to the full V between two phases, but the start configuration is only exposed to V between the phase and neutral point.
So the star uses less voltage and less current compared to the delta version. Save my name, email, and website in this browser for the next time I comment.
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