Copper losses in transformer

Litz wire conductors are well known and massively used in The increasing market of electrical and plug-in hybrid vehicles requires powerful embedded switch-mode power supplies (figure 1), including large inductive devices as well as AC/DC high voltage battery chargers of some 7-11-22kW (figure 2a) and DC/DC 400-800V/14V converters of a few kW (figure 2b) to supply in energy conventional low voltage equipment (lighting and air-conditioning systems, ECUs, radio-set, GPS, etc.). The magnetic components used in such power electronic assemblies generally count for 1/4th to 1/3rd in volume, weight, and cost within such devices. Therefore, their optimization in terms of power density is fully mandatory till the limit of an acceptable efficiency and temperature rise depends also on the cooling strategy [1]. For transformers and inductors used in such parts, low-loss ferrite cores and Litz wire windings are mostly selected. The best Figure 1.7-11kW OBC + 2.4kW/14V DCDC presented by BOSCH Mobility Solutions [2].Image used courtesy of This article will first summarize the well-known properties of Litz wire by highlighting special care and tips in its selection (part 1). The modelization approach of such conductors will be then discussed and the models available in FEA simulation tools will be compared. Eventually, a few words and references about the equivalent thermal conductivitythat can be assigned to a given Litz wire will be introduced to help in thermal simulation (part 2). Lit...

Amorphous and nanocrystalline alloys are now widely used for the cores of high-frequency transformers, and Litz-wire is commonly used as the windings, while it is difficult to calculate the resistance accurately. In order to design a high-frequency transformer, it is important to accurately calculate the core loss and copper loss. To calculate the core loss accurately, the additional core loss by the effect of end stripe should be considered. It is difficult to simulate the whole stripes in the core due to the limit of computation, so a scale down model with 5 stripes of amorphous alloy is simulated by the 2D finite element method (FEM). An analytical model is presented to calculate the copper loss in the Litz-wire, and the results are compared with the calculations by FEM. With the demand of high power electrical power conversion, the high-frequency transformers coupled with switching power converters have attracted significant attention in the recent years. 1,2 Thanks to the low loss property, amorphous and nanocrystalline alloys have been widely used for the core of high-frequency transformers. For the core of transformer design, the amorphous and nanocrystalline alloy strips are wound layer by layer. It is a smart choice to use Litz-wire as the high-frequency transformer winding. Litz-wires are weaved by several solid wires in a pattern, which can reduce the eddy current effect. Eddy-current effects, including skin effect and proximity effect, cause the non-uniform dis...

Transformer Losses Since distribution transformers has no rotating parts, it has no mechanical losses. This contributes to its high operating efficiency of over 90%. However, like any electrical device, a transformer does have load losses due to several factors. These losses appear in the form of heat and produce an increase in temperature and a drop in efficiency. Losses can be classified into two categories: copper losses and core losses. Copper Loss: This loss is caused by the resistance of the copper wire in the primary and secondary windings. A transformer winding can consist of hundreds of turns of fine copper wire, resulting in a relatively-high resistance value. As current flows through this resistance, some power is dissipated in the form of heat. Copper losses are minimized by employing large diameter conductors to reduce the resistance per unit length of the wires. Copper losses are generally about twice as great as core losses in most transformers. Eddy Current Losses: Eddy currents are caused by the alternating current inducing a current in the core of the transformer. The eddy current losses are kept to a minimum though the use of laminated cores. Eddy currents increase with frequency; they are directly proportional to the square of the AC frequency. Hysteresis Loss A rather esoteric form of loss, called hysteresis loss, occurs in all ferromagnetic transformer cores, but especially in laminated iron. Hysteresis is the tendency for a core material to act "slug...

I know what transformer impedance is and how it is calculated. It is, of course, a somewhat unique use of the word "impedance" How does %Z relate to load and no load losses? I suspect there are other factors at play where we could have transformer A that has a lower %Z yet higher no load losses than transformer B with a higher %Z. In fact I know this is true from measurements I have made. I dont quite understand this. Anyone want to take a stab at this? It’s about %Z, X/R ratio and MVA base (which essentially boil down to resistive elements in a Steinmetz approximate model). The %Z is just a percentage of base impedance, so you cannot compare transformer A and transformer B unless they are compared at the same base power. Transformer losses are a function of core loss (hysteresis/excitation) and copper loss. When determining no load and full load losses, the Steinmetz model is reduced to a simple series circuit with an equivalent %Z. Sent from my iPhone using Tapatalk The %Z given on a transformer nameplate does take into account the all the losses however as Xptpcrewx points out you must convert the %Z values to the actual impedance. For any transformer the nameplate %Z is given assuming the base kVA or MVA is the rating of the transformer. So if you have a 100 kVA transformer, the base kVA is 100. The base voltage is the nameplate voltage. If you want to know the actual impedance referenced to the primary side, you would use the primary nameplate voltage. IF you want the...

We don't see iron losses equal to copper losses in a transformer. Iron losses are due to the input voltage, so are the same (roughly) at no load and full load. In fact, they're slightly lower at full load as the primary voltage drop requires less flux swing. Copper losses are due to the current flowing, so are small at no load and large at full load. As the load varies, then so does the proportion of iron and copper losses. When we design a transformer, we pick an operating level, and change the transformer dimensions to optimise losses at that operating point. Choosing to make iron and copper losses equal at that power level is a good starting point for optimising the transformer, but may not be the end of the optimisation. For instance, when we make a transformer that spends most of its time at low load, like an audio power amplifier, we may choose a low flux to minimise iron hysteresis loss, maximising its inductance which minimises magnetising current, which minimises copper losses. The cost of this is that the many turns required means copper losses are high during its brief full load operation. In contrast, when designing a microwave oven transformer which only operates at full load and has forced air cooling, flux is pushed up to the limit, and beyond, resulting in a magnetising current more or less equal in magnitude to the load current. However, these currents are in quadrature, so do not add up as badly as it first seems. This minimises the number of turns needed...

6 Types of Losses in a Transformer Since a perfect transformer is extremely efficient and doesn’t lose power, the power applied to its input side should be equal to the power applied to its output side. As a result, a perfect transformer has no friction, no static losses, and equal input and output power. However, in reality, the transformer’s electrical input and output power won’t be equal because of internal electrical losses. Because it is an electrical static device without any moving parts, we cannot see mechanical losses, but there will be electrical losses like those from copper and iron. This article describes the different types of significant losses that can happen in transformers. Types of Losses in a Transformer 1-Iron loss, 2—copper loss, 3—hysteresis loss, 4—eddy loss, 5—stray loss, and 6—dielectric loss, among other types of power and distribution transformer losses, will all occur in the transformer. While copper loss is primarily brought on by resistance in the transformer’s two windings, hysteresis losses are based on a change in magnetization within the transformer core. Loss of iron in a power and distribution transformer The alternating flux inside the transformer’s core is the primary cause of iron losses. Core loss refers to this loss when it occurs inside the core. The core loss is mostly caused by the electromagnetic properties of the material in the power and distribution transformer cores. These losses are known as “iron losses” because iron may...