Now that you know the main parts of a transformer, let's look at how a basic transformer works.
Induced Voltage .When an input voltage is applied to the primary winding, alternating current starts to flow in the primary winding. As the current flows, a changing magnetic field is set up in the transformer core. As this magnetic field cuts across the secondary winding, alternating voltage is produced in the secondary winding. In short, a voltage is being induced on the secondary winding.
Eddy Currents
As a magnetic field expands and collapses about the windings of the iron-core transformer, its flux lines cut across both of the Turns of the winding and the core. As a result, voltages are induced in the core itself. These voltages in the core create Eddy Currents. These currents move through the core in circular paths. Because eddy currents create heat in the core and do not aid the induction process, they are a waste of energy, referred to as Eddy-Current Losses. Core designs have been created in an attempt to minimize these losses. For example, basic transformers use a laminated core made up of insulated layers, rather than a solid core.
Because the sheets are insulated from one another, the resistance across the core is high. Eddy currents are thereby reduced.
Transformers are often subjected to abnormally high voltage stresses caused by abnormal operating conditions, such as lightning and switching. This is especially true of high-voltage transformers, like the one pictured here, in use at a power relay station.
The end turns are the ones subjected to abnormal voltages, often high enough to break down the insulation. If this were to happen, current could arc between the turns. As a protective measure, the turns on the top and bottom of this coil are more widely spaced. They are also more heavily insulated.
Turns Ratio
The ratio between the number of actual turns of wire in each coil is the key in determining the type of transformer and what the output voltage will be. The ratio between output voltage and input voltage is the same as the ratio of the number of turns between the two windings.
The ratio between the number of actual turns of wire in each coil is the key in determining the type of transformer and what the output voltage will be. The ratio between output voltage and input voltage is the same as the ratio of the number of turns between the two windings.
The relationship between the number of turns in the secondary and the number of turns in the primary is commonly called the Turns Ratio or Voltage Ratio. It is common practice to write the turns ratio with the primary (input) number first, followed by the secondary (output) number. The two numbers are often separated by a colon.
Transformer Primary Voltage: 480 volts
Transformer Secondary Voltage: 120 volts
This transformer has four primary turns for every one secondary turn. Turns ratio is written as 4 to 1, or 4:1.
A transformer's output voltage is greater than the input voltage if the secondary winding has more turns of wire than the primary winding. The output voltage is stepped up, and we have a Step-Up Transformer. If the secondary winding has fewer turns than the primary winding, the output voltage is lower. This is a Step-Down Transformer.
Step-Up vs. Step-DownStep-Up Transformer: The primary winding of a step-up transformer has fewer turns than the secondary winding, with the resultant secondary voltage being higher than the primary.
Step-Down Transformer: The primary winding of a step-down transformer has more turns than the secondary winding, so the secondary voltage is lower than the primary.
Is There Something for Nothing?
In Figure 10, the step-up transformer has a 1 to 2 ratio. As a result, the output voltage is doubled. At first, this might seem like we are gaining or multiplying voltage without sacrificing anything. Of course, this is not the case. Ignoring small losses, the amount of power transferred in the transformer is equal on both the primary and secondary sides.
Power is equal to Voltage multiplied by Current. This is expressed by the formula:In Figure 10, the step-up transformer has a 1 to 2 ratio. As a result, the output voltage is doubled. At first, this might seem like we are gaining or multiplying voltage without sacrificing anything. Of course, this is not the case. Ignoring small losses, the amount of power transferred in the transformer is equal on both the primary and secondary sides.
P = V x I
Power is also always equal on both sides of the transformer, meaning both sides of the equation must have the same value. This means we cannot change the voltage without changing the current also.
In Figure we can see that when voltage is stepped down from 240 V to 120 V in a 2 to 1 ratio, the current is increased from 1 to 2 amps, keeping the power equal on each side of the transformer. In contrast, in Figure 11, when the voltage is stepped up from 120 V to 240 V in a 1 to 2 ratio, the current is reduced from 2 to 1 amp to maintain the power balance. In other words, voltage and current may be changed for particular reasons, but power is merely transferred from one point to another.
Voltage Taps
As you know, the turns ratio determines the voltage transformation that takes place. There are times when the actual incoming voltage is different than the expected normal incoming voltage. When this happens, it could be advantageous to be able to change the turns ratio in order to get the desired (rated) output voltage. You might view this as fine tuning the input voltage to get the desired output. Voltage Taps, designed into the transformer's primary winding, deliver this desired flexibility.
Suppose a transformer has a 4 to 1 turns ratio. Remember, that means the primary has 4 times as many turns as the secondary, which tells you the transformer is a step-down transformer. If the input voltage is 480 volts, the output would be 120 volts.What if the input delivered to the transformer primary is less than the expected normal of 480 volts, say 456 volts for this example? This could be significant if getting 120 volts from the secondary is critical. Tapping the primary in a number of different spots helps to eliminate the problem by providing a means to adjust the turns ratio, and fine-tune the secondary output voltage.
This transformer has taps at 2 1/2% and 5% below the normal voltage of 480 volts. In the industry, this would be referred to as having two 2 1/2% Full Capacity Below Normal Taps (FCBN). These two taps provide a 5% voltage range below the normal 480 volts. When taps are provided above the normal as illustrated, they are called Full Capacity Above Normal Taps (FCAN).
For standardization purposes, taps are in 2 1/2% or 5% steps. The tap arrangement used on many transformers is two@2 1/2% FCAN and four@2 1/2% FCBN, which provides a 15% total range of tap voltage adjustments.
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Transformer
10 comments:
Transformers helps a lot in increasing or decreasing the voltage output that depends on the requirement. They can be used for any environment may be it is industrial,residential or commercial.
Power transformers in India | | Inductor Coil Manufacturer in India
Thanks for sharing, Transformers are helps a lot to increase or maybe decrease the voltage output.
SMPS Transformer, Power Transformer
Yeah! we use a regular bench power supply to inject the DC bias to the choke, capacitance of the power supply can act as a capacitor connected in parallel to the test inductor.
Yeah! we use a regular bench power supply to inject the DC bias to the choke, capacitance of the power supply can act as a capacitor connected in parallel to the test inductor.
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Good Post! And valuable information you shared about how transformers works in electric devices. It is so helpful for Engineers. Thanks for sharing.
Power Transformers in India | Transformer Manufacturer in India
Nice blog! Thanks for Sharing such a valuable information. Keep on posting.
Inductor Coil Manufacturer in India | Medical Isolation Transformer in India
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Power Transformers in India | Transformer Manufacturer in India
Great post about transformer working,thanks for sharing such a valuable information.
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Great Post. Good information. Thank you foe sharing.
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Thank you for sharing such a useful information. keep sharing.
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