DC currents flow uni-directionally stays the same as it goes through a circuit. The armature is driven by a mechanical source of power for example, in commercial electric power production it would be a steam turbine.
As this wound rotor spins, its wire coil passes over the permanent magnets in the stator and an electric current is created in the wires of the armature. But because each individual loop in the coil passes first the north pole then the south pole of each magnet sequentially as it rotates on its axis, the induced current continually, and rapidly, changes direction.
Each change of direction is called a cycle, and it is measured in cycles-per-second or hertz Hz. In the United States, the cycle rate is 60 Hz 60 times per second , while in most other developed parts of the world it is 50 Hz. Individual slip rings are fitted to each of the two ends of the rotor's wire loop to provide a path for the current to leave the armature.
Brushes which are actually carbon contacts ride against the slip rings and complete the path for the current into the circuit to which the generator is attached.
Motor action supplying mechanical power is, in essence, the reverse of generator action. Instead of spinning the armature to make electricity, current is fed by a circuit, through the brushes and slip rings and into the armature.
This current flowing through the coil wound rotor armature turns it into an electromagnet. The permanent magnets in the stator repel this electromagnetic force causing the armature to spin. As long as electricity flows through the circuit, the motor will run. Actively scan device characteristics for identification.
Central to the universe as we know it, the electromagnetic force is thought to have existed in its current form since somewhere between 10 12 and 10 6 seconds after the Big Bang. In , physicist Michael Faraday discovered electromagnetic induction, revealing the intimate relationship between the observed phenomena of magnetism and electricity. Interestingly, in , another researcher, Joseph Henry, discovered it independently.
Faraday was the first to publish his findings, and to this day, he is credited with the discovery. EMFs convert other forms of energy, such as mechanical energy, into electrical energy.
This law of physics is what allows us to create both electric motors and electric generators. Although these two types of machinery perform opposite functions, they both rely on the same underlying laws of physics.
This generates electromotive force, which creates a flow of electrons in one direction. This phenomenon can be used to produce electricity in an electric generator. To create this magnetic flux, the magnets and the conductor are moved relative to one another.
The wires are wound into tight coils, increasing the number of wires and the resulting electromotive force. Continuously rotating either the coil or the magnet, while keeping the other in place, gives continual flux variation. The rotating component is referred to as a "rotor," while the stationary component is called a "stator. Electric generators fall into two broad categories: "dynamos," which generate direct current, and "alternators," which generate alternating current.
The dynamo was the first form of electric generator that was useful for industrial applications. During the Industrial Revolution, it was invented independently by several people. All motors are generators.
The emf in a generator increases its efficiency, but an emf in a motor contributes to energy waste and inefficiency in its performance. A back emf is a resistance to change in a magnetic field. A back emf appears in a motor after it has been turned on, though not immediately. It reduces the current in the loop, and gets larger as the speed of the motor increases.
This causes the power requirements of the motor to also increase, especially under loads that are very large. Kim Lewis is a professional programmer and web developer. She has been a technical writer for more than 10 years and has written articles for businesses and the federal government. Lewis holds a Bachelor of Science, and occasionally teaches classes on how to program for the Internet. How to Calculate the Henrys in a Coil. How to Calculate Induced Armature Voltage.
AC Vs. The Purpose of Coil Springs. To find the magnitude of the torque as the wire loop spins, consider Figure Notice that, as the loop spins, the current in the vertical loop segments is always perpendicular to the magnetic field. Because there are two vertical segments, the total torque is twice this, or. If we have a multiple loop with N turns, we get N times the torque of a single loop.
This is the torque on a current-carrying loop in a uniform magnetic field. This equation can be shown to be valid for a loop of any shape. Thus, the torque changes sign every half turn, so the wire loop will oscillate back and forth. Consider now what happens if we run the motor in reverse; that is, we attach a handle to the shaft and mechanically force the coil to rotate within the magnetic field, as shown in Figure However, charges in the vertical wires experience forces parallel to the wire, causing a current to flow through the wire and through an external circuit if one is connected.
A device such as this that converts mechanical energy into electrical energy is called a generator. Because current is induced only in the side wires, we can find the induced emf by only considering these wires.
The total emf around the loop is then. Although this expression is valid, it does not give the emf as a function of time. This can also be expressed as. In between, the emf goes through zero, which means that zero current flows through the light bulb at these times.
Thus, the light bulb actually flickers on and off at a frequency of 2 f , because there are two zero crossings per period.
Since alternating current such as this is used in homes around the world, why do we not notice the lights flickering on and off? In the United States, the frequency of alternating current is 60 Hz, so the lights flicker on and off at a frequency of Hz. Also, other factors prevent various different types of light bulbs from switching on and off so fast, so the light output is smoothed out a bit. Use this simulation to discover how an electrical generator works.
Control the water supply that makes a water wheel turn a magnet. This induces an emf in a nearby wire coil, which is used to light a light bulb. You can also replace the light bulb with a voltmeter, which allows you to see the polarity of the voltage, which changes from positive to negative. Set the number of wire loops to three, the bar-magnet strength to about 50 percent, and the loop area to percent. Note the maximum voltage on the voltmeter. Assuming that one major division on the voltmeter is 5V, what is the maximum voltage when using only a single wire loop instead of three wire loops?
In real life, electric generators look a lot different than the figures in this section, but the principles are the same. The source of mechanical energy that turns the coil can be falling water—hydropower—steam produced by the burning of fossil fuels, or the kinetic energy of wind. Another very useful and common device that exploits magnetic induction is called a transformer. Transformers do what their name implies—they transform voltages from one value to another; the term voltage is used rather than emf because transformers have internal resistance.
For example, many cell phones, laptops, video games, power tools, and small appliances have a transformer built into their plug-in unit that changes V or V AC into whatever voltage the device uses. Notice the wire coils that are visible in each device. The purpose of these coils is explained below.
0コメント