Basic Transformers Essay, Research Paper
The Reason and Use of Transformers
A transformer is a device that raises or lowers voltage and is used mostly with alternating current, or ac. A transformer has no moving parts, is simple, rugged, durable, and can be up to ninety-nine percent efficient. Cities use a large amount of power, and power is based on the amount of current in electricity.
A transformer works by changing the amount of voltage and current of electricity. When voltage is increased current in electricity is decreased or if voltage is decreased current in electricity is increased. Sending a large amount of current through power lines would be very inefficient and large amounts of current would mean that larger conductors would have to be made or a larger amount of electricity would have to be produced to make up for the loss of power.
The reason that larger conductors would have to be used if transformers were not used is because the current in electricity causes heat and the larger the conductor used the more current can be sent through it without producing as much heat. The friction of atoms moving back and forth sending the electricity through the conductor produces the heat. When the heat is made though that means that the atoms are turning the electricity into heat instead of sending it to homes or business where the electricity is supposed to go. Most homes use 120 volts to 240 volts of electricity and some businesses use 480 volts or more of electricity. Using voltage this low though means that the current of electricity is high. When the voltage is increased that means that the electricity has less current. Most power plant generators produce electricity at 13,000 to 22,000 volts and if the electricity has a long way to travel then the voltage is usually raised 1,000 volts per mile. A transformer then steps down the electricity outside or sometimes inside a home or business to the rating that the specific appliance or appliances need to run.
Statement of Purpose
The reason behind this report is to answer the questions, Why do we use Transformers? and How do transformers work? .
The main audience for this report is Dr. Brucker. The secondary audience is for anyone that is interested in learning about transformers.
The operation of a transformer depends upon electromagnetic induction. Transformers consist of two sets of wire that are wrapped around a piece of metal with a hole in the middle of it. When the wire is wrapped around the metal then it forms coils and is known as the primary or secondary coil. The coil receiving the energy is called the primary, and the coil delivering the power to the load is called the secondary. When an alternating voltage is applied to the primary, an alternating current flows. This current sets up an alternating magnetic field, which moves across to the secondary coil, Figure 1. The only two types of coil that are used when dealing with low voltage are iron/steel cores and air core. The core decides on the efficiancy of the transformer. There are several different iron/steel cores but only one air core that is used. Table 1 shows the average efficiancy of these two cores. (Nadon 1999)
The moving magnetic lines of force induce voltage from the primary to the secondary. Induced voltage is hard to explain but it will be explained in its simpliest form in the rest of the paragraph. If you look at Figure 1 you notice that the metal core has a large hole in the middle of it. The wires that make up the primary and the secondary are insulated. The electricity flowing through the coiled wires put off a slight magnetic field but when the coils are wrapped around a metal core then the metal increases the magnetic field. This field then slightly magnetizes the secondary except when it reaches the secondary coil it changes back to electricity. This is known as induced voltage. The magnetic field that is created to produce induced voltage is known as a conducted electromagnetic field or CEMF. (Nadon 1999)
WAVES AND FRENQUENCIES
Electricity travels in waves like sound does and the waves are measured in degrees. In the transformer shown in Figure 1, there is no load connected to the secondary. So, no current is flowing in the secondary coil. Because the primary circuit has high inductance and low resistance, the current lags the voltage by nearly 90 degrees. The magnetic field produced by this current produces a CEMF that is nearly 180 degrees out of phase with the applied voltage.
The voltage induced into the secondary is a result of the current flowing in the primary and therefore is in phase with the CEMF in the primary. In another words at any instance the secondary voltage of a transformer is in the direction opposite to the voltage applied to the primary. (Schuler 1999)
Because the secondary voltage is a result of the primary current, their frequencies must be equal. Because the primary current is a result of the primary voltage, .the frequency of the secondary voltage is equal to that of the primary voltage. Also, the number of volts per turn on the primary coil is equal to the number ofvolts per turn on the secondary coil. In other words, a transformer with 100 turns of wire on the primary and 200 turns on the secondary produces a voltage across the secondary that is double the voltage of the primary. If 500 volts is applied to the primary, 1000 volts will appear across the secondary. (Nadon 1999)
Step-up and Step-down
If a transformer increases the voltage, it is called a step-up transformer. If it decreases the voltage, it is called a step-down transformer. The same transformer can be used for either stepping up or stepping down the voltage. For example, if the transformer described previously is supplied with 1000 volts to the 200-tum coil that coil becomes the primary coil. The 100-turn coil then becomes the secondary coil and will be rated at 500 volts. (Schuler 1999)
BUILDING A SIMPLE TRANSFORMER
If someone still does not understand how a transformer works then the best way to learn more is to build your own transformer. All someone needs is a piece of steel or iron that is square with a hole in the middle, this wil be used as the core, two strands of insulated wire, for the coils, a 9-volt or 12-volt battery, and a voltage meter, which all can be bought at a reasonably cheap price. Wrap the insulated wire around one side of the metal core until five to ten coils are formed then take the other strand of wire around the other side of the metal core until the coils have beened doubled, this is now a transformer. It should look similar to Figure 1. Next connect the voltage meter to one side of the transformer the side of the transformer that the meter is connected to is the secondary. Now the batter will be connected to the other side of the transformer, this side is the primary. If the secondary has more coils than the primary the voltage will be higher, but if the secondary has fewer coils than the primary then the voltage will be lower. Hopefully this hands-on experiment of building a transformer will let someone understand transformers even better.
Transformers are the simpliest and most effeciant way to get electricity to homes and businesses. If transformers are not used then the cost of electricity would be so large that the average person would never be able to afford it.
Types of Iron/Steel and Air Coreand Their Efficiancy
Iron/Steel Core Type Average Efficiancy AirCore type Average Efficiancy
Shell-type 80-90% Air core 0-50%
Wound core-type 90-100%
Schuler, Charles A., et al. Electronics Principles and Applications. New York:
Nadon, John M. Industrial Electricity. Albany: Delmar Publishers., 1999
Transformers. Electrical Shack. January 1999 http://www.geocities.com/siliconvalley/3424/