Electrical Engineering - Transformers

In summary, the author provides information about how to calculate stacking factor and what it means.
  • #1
YoshiMoshi
228
8

Homework Statement



Please see the picture attached.

Homework Equations

The Attempt at a Solution



I was able to solve part A correctly, at least I believe I was able to do so. I'm struggling with part (b) however. I'm not sure were to start on this. My test that has this problem doesn't have anything on MLT. I pulled out my Power Electronics book from my undergraduate and found that

R = (rho * l_b)/A_w

R -> Resistance of the winding
rho -> resistivity of the conductor material
l_b is the length of the wire
A_w is the wire bare area

I believe I need to find l_b? I don't understand exactly how I can go about this. I believe that for A_w

A_w = (5 cm)(3 cm) = 15 cm^2
I used 3 cm because it's a 3 cm stack as specified in the problem

Am I just supposed to assume for rho that I'm using copper winding?

I don't understand the hint and how I'm supposed to solve the problem using Ohm's law. The wire has a resistance R, and I found the MMF in part A, but not the voltage. Hence I'm stuck because

V = IR

I don't know V or I. and I know that

F = IN

Where I solved for F in part (a) but don't know I or N

Any help would be greatly appreciated.
 

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  • #2
What is μ for the laminations? What does "S.F. = 0.90" mean?
You can get an approximate answer by neglecting reluctance everywhere except in the gap.
 
  • #3
rude man said:
What is μ for the laminations? What does "S.F. = 0.90" mean?
You can get an approximate answer by neglecting reluctance everywhere except in the gap.
I used to design xfmrs. "S.F. = 0.90" means that the "stacking factor" value is 0.90. "SF" is the percentage of the wound metal tape that consists of ferromagnetic material. The tape is coated with an insulation layer on both sides. When the tape is wound some of the core volume is insulation and this contributes little to flux path. At high frequencies thinner tape is needed to keep eddy current losses low. But insulation thickness remains about constant. So for a 12-mil tape thickness, and a 0.4-mil insulation thickness on each surface of the tape, stacking factor can be computed as follows. The total tape thickness = 12 + 0.4 + 0.4 mils = 12.8mils. Of the 12.8 mils, 12 mils is actual ferrous material. So SF = 12/12.8 = 0.938. If the tape thickness was only 4 mils, needed for higher frequency operation, with 0.4-mil insulation thickness on each side, the stacking factor is 4 / (4 + 0.4 + 0.4) = 0.833.

In general the thinner the tape, the lower the SF. Did I help? Regards.

Claude
 
  • #4
Thank you Claude for the information but the OP seems to have evanesced as usual. He/she did not respond with your info nor with a permeability number.
 

Related to Electrical Engineering - Transformers

1. What is a transformer and how does it work?

A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It consists of two or more coils of wire, known as the primary and secondary windings, that are wrapped around a ferromagnetic core. When an alternating current flows through the primary winding, it creates a changing magnetic field that induces a voltage in the secondary winding, thus transforming the voltage and current levels.

2. What are the different types of transformers?

There are several types of transformers, including step-up transformers, step-down transformers, isolation transformers, autotransformers, and distribution transformers. Step-up transformers increase the voltage from the primary to the secondary winding, while step-down transformers decrease the voltage. Isolation transformers are used to isolate the primary and secondary circuits, while autotransformers have a single winding that serves as both the primary and secondary. Distribution transformers are commonly used in power grids to step down high-voltage electricity to lower levels for consumer use.

3. What is the purpose of a transformer in an electrical system?

The main purpose of a transformer is to change the voltage and current levels in an electrical system. This is important because different devices and appliances require different voltage levels to operate safely and efficiently. Transformers also help to reduce energy losses in electrical transmission and distribution systems by stepping up the voltage for long-distance transmission and stepping it down again for local distribution.

4. How do I select the right transformer for my application?

To select the right transformer for your application, you need to consider factors such as the required voltage and current levels, the power rating, the type of load (resistive, inductive, or capacitive), and the frequency of the power supply. You should also take into account the efficiency, size, and cost of the transformer, as well as any special requirements for your specific application.

5. How do I maintain and troubleshoot a transformer?

To maintain a transformer, you should regularly check its insulation levels, perform oil tests, and inspect for any physical damage. If any issues are found, they should be addressed immediately to prevent further damage. When troubleshooting a transformer, you should first check the power supply and make sure it is within the rated voltage range. You should also check for any visible damage or signs of overheating. If the transformer is not functioning properly, it may need to be replaced or repaired by a trained professional.

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