WHAT IS A GENERATOR?

Generator is a latin word that means originator or maker. In power industry, this term refers to a device that produces electrical energy. Note that although electricity does occur naturally, it does not exist in the forms that currently can be practically used. For practical use it is produced from other forms of energy. Since energy cannot be created but can only be transferred from one form to another, any form of electricity generation obviously needs a source of fuel. Technically speaking, in electric generators electricity is generated from mechanical energy. The mechanical energy in turn is produced from so-called primary sources, such as chemical, nuclear or thermal energy contained in various types of fuel. It can also be obtained from renewable resources such as sunlight, wind or falling water. The machine that converts primary energy into mechanical energy is called prime mover. Steam turbines, internal-combustion engines, gas combustion turbines, water and wind turbines are the common types of prime movers.

If you've ever moved paper clips around with a magnet or killed time arranging metal shavings into a beard on a "Wooly Willy" toy, then you've dabbled in the basic principles behind even the most complicated electric generators. The magnetic field responsible for lining up all those little bits of metal into a proper Mohawk haircut is due to the movement of electrons. Move a magnet toward a paper clip and you'll force the electrons in the clip to move. Similarly, if you allow electrons to move through a metal wire, a magnetic field will form around the wire.

Thanks to Wooly Willy, we can see that there's a definite link between the phenomena of electricity and magnetism. A generator is simply a device that moves a magnet near a wire to create a steady flow of electrons. The action that forces this movement varies greatly, ranging from hand cranks and steam engines to nuclear fission, but the principle remains the same.

One simple way to think about a generator is to imagine it acting like a pump pushing water through a pipe. Only instead of pushing water, a generator uses a magnet to push electrons along. This is a slight oversimplification, but it paints a helpful picture of the properties at work in a generator. A water pump moves a certain number of water molecules and applies a certain amount of pressure to them. In the same way, the magnet in a generator pushes a certain number of electrons along and applies a certain amount of "pressure" to the electrons.

In an electrical circuit, the number of electrons in motion is called the amperage or current, and it's measured in amps. The "pressure" pushing the electrons along is called the voltage and is measured in volts. For instance, a generator spinning at 1,000 rotations per minute might produce 1 amp at 6 volts. The 1 amp is the number of electrons moving (1 amp physically means that 6.24 x 1018 electrons move through a wire every second), and the voltage is the amount of pressure behind those electrons.

Generators form the heart of a modern power station. In the next section, we'll take a look at how one of these stations works.

HOW IT WORKS

The operation of electric generators is based on the phenomenon of electromagnetic induction: whenever a conductor moves relative to a magnetic field, voltage is induced in this conductor. Particularly, if a magnet is spinning inside a coil, AC voltage is induced in the coil. For more information see our tutorial on how generators work with an animation that illustrates their basic operation.

The induced voltage (called electromotive force or emf) will create a current through an external circuit connected to the coil terminals resulting in energy being delivered to the load. Thus, the kinetic energy that spins the source of the magnetic field is converted into electricity. Note that the current flowing through an external load in turn creates a magnetic field that opposes the change in the flux of the coil, so the coil opposes the motion. The higher the current, the larger the force that must be applied to the magnet to keep it from slowing down.

How An Electric Generator Works
An electric generator is a device used to convert mechanical energy into electrical energy.

The generator is based on the principle of "electromagnetic induction" discovered in 1831 by Michael Faraday, a British scientist. Faraday discovered that if an electric conductor, like a copper wire, is moved through a magnetic field, electric current will flow (be induced) in the conductor. So the mechanical energy of the moving wire is converted into the electric energy of the current that flows in the wire.

In practice, the magnetic field is most often induced by an electromagnet rather then a permanent magnet. In AC systems, usually the electromagnet is spinning, and the power-producing armature is stationary. The armature normally comprises of a set of coils that form a cylinder. The electromagnet consists of so called field coils mounted on an iron core. A current flow in the field coils is required to produce magnetic field. This current may be obtained from an external source or from the system's own armature. Most modern AC sources with field coils are self-excited. In such devices the current for field coils is supplied by an additional exciting winding in the armature. The initial magnetic field is produced by residual magnetism in the electromagnet's cores. When the prime mover starts turning the armature, at first the armature rotates in a very weak magnetic field and produces small emf. This emf creates a current in field coils, which increases magnetic flux, which in turn increases emf in the armature. This process continues until the rated output voltage is reached.

The negative diode applies the negative alternation (- peak) into negative voltage to force electrons into the negative post of the battery. When the associated sine wave is in its negative swing, the negative diode is forward biased and sends electrons into the battery negative post. Electrons flow against the arrow in the negative diode. This establishes a DC current through the battery to charge it. DC current means the electrons always flow in one direction, from negative to positive, through the battery and vehicle circuits.

Any electrical circuit on the vehicle is connected in parallel to the battery between B+ and B-. Generator current flows through each circuit as it does through the battery. At no time does any diode network stop contributing its share of electrical energy to charge the battery or provide electron flow to vehicle circuits. Each phase of the generator simply "peaks" in numerical order as long as the rotor is energized and turning. The end result is a constant DC voltage and current source at the generator terminals.

All DC current that runs the vehicle passes through the diode bridge. The diode bridge generates a lot of heat from all the hard work it must perform. If the heat is not dissipated adequately, the diode bridge will burn up and the generator fails - resulting in no charging voltage and no charging current.

EMERGENCY BACKUP GENERATORS FOR HOME USE

In power plants the electricity generating devices are most often driven by steam or hydraulic turbines or by diesel engines. The same concept of converting mechanical energy into electricity is widely used in small consumer-grade units. In commercially available models suitable for home use, an alternator is integrated with an internal-combustion engine into a single appliance. The resulting device is referred to as an engine-generator set or a genset. It is the most common type of a backup power source for the home. A genset is often casually called just a generator even though it also includes an engine. There are two main types of such devices that differ by their connection and activation methods: standby and portable. Standby generators for home use are permanently connected to the house wiring system and are also hooked up to a fuel source, such as a natural gas line or a large propane or diesel tank. They cost more than portables and require professional installation of a transfer switch and the fuel line. Their main advantage is they can provide practically continuous power for as long as the fuel is available. Portable devices are intended primarily for a temporary connection to several appliances via extension cords rather than to the whole house. They are normally fueled from an on-board tank and therefore need frequent refueling. Some more expensive models can also be connected to an external source for extended run time. A portable unit is generally cheaper than a standby, often sold at a discount and does not require a professional installation. Of course you want to connect it to the house wiring you need to install a transfer switch. Choosing the best device for your application involves selecting the right type and a proper sizing based on the amount of power you may need during an emergency