Transformers are used in various applications, from small electronic devices to large power stations. However, all transformers come with inherent losses regardless of their size or intended use. It can be due to several reasons like heating of the windings, hysteresis, and eddy current. This article will answer some of the most frequently asked questions about transformer losses and efficiency.
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How Many Types of Losses in Transformer?
Despite their size and power, transformers are like other devices—they're not entirely perfect. While the ideal transformer configuration is not to have any losses, the reality is that these devices also have power losses. A transformer's output power will always be less than its input power.
These power losses are then converted to heat that needs to be removed from the transformer to avoid damage. The electricity generated by the coils and the changing magnetic field in the interior generates heat. Load losses refer to the losses that occur with the coils. On the other hand, no-load losses are the ones that happen in the core.
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The four types of transformer losses are known as resistive, eddy, hysteresis, and flux losses.
Resistive Loss
The resistance of the transformer's windings causes resistive loss (12R), or copper loss, which is a type of electrical breakdown. The current flowing through the resistive material produces heat, which is then dissipated. As a result, the resistive loss is inversely proportional to the current flowing through the transformer.
Eddy Currents
Eddy current losses occur when a transformer's metallic core produces magnetic fields. These magnetic fields induce currents in the core that flow in the opposite direction of the primary current. These eddy currents produce heat that can damage the system if not removed.
Hysteresis
Hysteresis is caused by the magnetism that stays in the material even after removing the source of the magnetic field. In the case of transformers, this magnetism is induced by the alternating current flowing in the primary winding. Therefore, the hysteresis losses are proportional to the square of the magnetizing current.
Magnetic domains possess magnetic properties that move in iron when subjected to a magnetic field. When the magnetic field is removed, a small amount of magnetism remains in the iron. Hysteresis losses are the losses that happen as a result of this phenomenon.
Flux Loss
The last type of transformer loss is flux loss or flux leakage. This type of loss happens when a portion of the flux lines coming from the primary winding doesn't pass through the transformer core and to the secondary winding—resulting in a power loss. There are two reasons why the flux lines can potentially travel through the air instead of through the core:
Saturation in the iron core makes it unable to accept succeeding flux lines. As a result, the flux lines will travel through the air, not the core and secondary winding.
The reluctance ratio of the air and the core in the unsaturated region is 10,000:1. This ratio implies that for every 10,000 lines of flux that go through the core, one goes through the air.
Flux loss is generally minor, especially in a well-designed and well-constructed transformer.
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What are Iron Losses in Transformers?
Iron loss in a transformer is defined as the loss caused by the alternating flux in the transformer core. Due to this, iron loss is also referred to as core loss. Eddy and hysteresis current losses are examples of core losses.
To further understand how iron losses happen, let's look at iron's magnetic properties. When an alternating current flows in a conductor, it produces a magnetic field. This is the same case with transformer cores made of iron. The current in the primary winding is constantly changing, which in turn creates an alternating magnetic flux in the transformer core.
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Why Are Iron Losses in Transformers Called Constant Losses?
Iron losses in transformers are called constant losses because, as the name suggests, they remain constant, regardless of the load. They are irrespective of the load condition. No-load or core losses make up a large percentage of the constant losses. That's why iron losses are also called constant losses.
In addition, constant losses also include the losses caused by the resistance of the windings, as well as dielectric and stray losses. Dielectric losses are caused by the insulation heating, while the leakage flux causes stray losses.
What are Copper Losses in a Transformer?
Every material possesses some resistance level, even if it's a very good conductor. When an electric current flows through a material, some of the electrical energy is converted into heat due to the resistance of the material. Copper loss is a term used to describe the loss of conductivity in wire resulting from the use of low-quality copper for winding.
Copper loss is proportional to the square of the load current flowing through the transformer. That means that if we double the load current, the copper loss will increase by a factor of four. At the same time, the voltage will drop by half. Copper losses make up the remaining percentage of constant losses.
What are Stray Losses in a Transformer?
Stray losses refer to the heat losses that occur in all transformer components, except for the copper windings. Stray losses are caused by the leakage flux, which is the portion of the total magnetic flux that escapes from the transformer core. A part of the leakage flux will link with any nearby conductor, resulting in transformer losses.
Stray losses can be divided into two categories: proximity effect and skin effect.
The skin effectis the phenomenon that occurs when the current tends to flow on the surface of a conductor instead of flowing through the entire cross-section. The skin depth is the distance from the conductor's surface to the point where the current has diminished to 1/e (about 37%) of its original value.
The proximity effectis the tendency of an electric current in a conductor to produce an opposing magnetic field, which attracts the current in nearby conductors.
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How To Reduce Stray Losses in Transformers?
While losses in transformers are inevitable and frustrating, there are ways to mitigate their effects. In the case of stray losses, you can use two important methods: electromagnetic shielding and eddy current shielding.
Electromagnetic shielding is a conducting barrier that covers an entire device to protect it from environmental electromagnetic interference (EMI). An example of this would be the metal casing around your electrical transformer. It can also prevent emissions from the device itself from disrupting other devices that are in the same environment as the transformer.
On the other hand, Eddy current shielding is a flux rejection technique that is a suitable solution for unconventionally shaped tanks. However, the glaring disadvantage of this method is that eddy currents are transformer losses that occur within the shield, resulting in heating. This heating can potentially cause overheating in other structural parts of the transformer.
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How to Reduce Losses in Transformer?
As owners of a transformer, you would want to keep the losses to a minimum. Unfortunately, this hindrance is unavoidable, so you'll have to work with what you have. Thankfully, there are many ways to reduce the effects of transformer losses to a more manageable degree.
Keep in mind that the methods for reducing losses in a transformer depend on the type of transformer losses. For this discussion, let's focus on iron loss, copper loss, stray loss, and dielectric loss.
Iron Loss
To recap, iron loss (or core loss) results from the alternating influx in the core. The losses can be either hysteresis or eddy current.
The low coercive core material is the most common way to reduce iron losses. This means the core can be easily magnetized and demagnetized, reducing hysteresis losses. Another way to reduce iron losses is using a high resistivity core material.
With a high resistivity, the eddy current losses will be reduced because it would take longer for the electrons to flow through the material. This is due to the fact that the electrons will encounter more collisions with the atoms in the material.
Copper Loss
As for copper losses, the main way to reduce them is by using copper wires with a larger cross-sectional area. This is because a larger cross-sectional area results in a lower resistivity.
With a lower resistivity, the electrons will have an easier time flowing through the material, reducing the losses. Another way to reduce copper losses is by using a larger copper gauge.
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A larger copper gauge means that the wire is thicker, resulting in lower resistivity. However, keep in mind that there is a limit to how thin the wire can be before it becomes too fragile and breaks.
Stray Loss
Stray losses can be reduced in several ways, the most common of which is electromagnetic shielding. As mentioned earlier, this is a conductive barrier that covers the entire device and protects it from environmental electromagnetic interference.
Another way to reduce stray losses is by using eddy current shielding. This is a flux rejection technique that is suitable for unconventionally shaped tanks. However, the disadvantage of this method is that eddy currents are transformer losses that occur within the shield, resulting in heating.
Dielectric Loss
Dielectric losses, also known as insulation losses, are caused by the electrical current flowing through the insulation. The most common way to reduce dielectric losses is using a higher resistivity material.
This is because a material with a higher resistivity will have a lower electrical conductivity. This means that the electrons will have a harder time flowing through the material, which will control and reduce the effects of the losses. Another way to reduce dielectric losses is by using a material with a higher dielectric constant.
This is because a material with a higher dielectric constant can store more electrical energy, lowering the loss effects.
With over 20 years of experience in transformer design, the engineers at Daelim Transformer possess extensive expertise in their field. They are adept at minimizing various types of losses during the design process. If you require assistance with transformer design, our dedicated team is readily available to provide you with the optimal solution promptly. Get in touch with us, and we will swiftly deliver the best possible outcome to meet your specific requirements.
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How To Reduce Iron Losses in Transformer?
To reduce iron losses, you'll need to use a core material that has a low coercivity, which means that it can be easily magnetized and demagnetized and is referred to as "magnetically soft."
Since the hysteresis losses are directly proportional to the material's coercivity, using a magnetically soft material will reduce the hysteresis losses.
Some magnetically soft materials are powdered iron, nanocrystalline cores, and amorphous metal. Another way to reduce iron losses is using a high resistivity core material.
A high resistivity will reduce the amount of eddy current losses because it will take longer for the electrons to flow through the material. As a result, the electrons will experience more collisions within their atoms, ultimately mitigating the losses. Some examples of high resistivity materials are ceramic cores and air cores.
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How To Calculate Losses in Transformer?
Calculating transformer losses can be tricky, as many different factors can be considered. The loss in a transformer compares the input (primary power) to the output (secondary power). The input and output voltages, as well as the current rating of both ends, are data that are shown by most transformers.
For example, a step-up transformer raises the voltage but decreases the current. On the other hand, a step-down transformer will decrease voltage but increase current. Therefore, the power rating (in watts) will also differ for each type of transformer.
The Power (P) is the voltage (E) multiplied by the current in amperes (I). Therefore, P = IE.
When calculating the loss of a transformer, you must first calculate both the actual and current-voltage in both the primary and secondary coils. You'll also need to determine the resistance of both coils, as well as the length of the conductor (l).
Once you've obtained these figures, multiply the voltage in volts by the primary winding current in amperes. Next, take the voltage (V) and multiply it by the current (I) of the secondary transformer winding.
Subtract the secondary power from the primary. The resulting number is the power loss of your transformer.
For example, let's say you have a transformer with the following specs:
Primary voltage (V1) = 400 V
Secondary voltage (V2) = 120 V
Primary current (I1) = 10 A
Secondary current (I2) = 2.5 A
Length of conductor (l) = 1 m
Resistance of primary coil (R1) = 2 ohms
Resistance of secondary coil (R2) = 0.5 ohms
To calculate the power losses, you would need to multiply 400 V by 10 A to get the primary power (P1), which would equal 4000 W.
Next, you would like to multiply 120 V by 2.5 A to get the secondary power (P2), which would equal 300 W.
Then, you would subtract 300 W from 4000 W to get the power losses of 3700 W.
Power Losses = P1 - P2
= 4000 W - 300 W
= 3700 W
