Transformer efficiency at low (and high) frequencies

In summary, the efficiency of a transformer decreases at very low frequencies due to the phenomenon of mutual induction and hysteresis effects. This is why equipment is designed to work efficiently at 60 Hz. Higher frequencies can be used for special motors, but they require different materials such as ferrite.
  • #1
v0id
45
0
Hello,

I've been thinking about why (elementary) transformer efficiency drops drastically at very low frequencies. I know hysteresis effects play a major role in reducing efficiency at high frequencies, but why low? I realize that as we reduce the frequency of the emf, we're making the circuit "more and more DC", but a freqency still exists, no? The transformer that I'm talking about is a simple two-solenoids-magnetically-linked-by-a-ferromagnetic-core single phase one (home-made). Any help would be greatly appreciated.
 
Engineering news on Phys.org
  • #2
>I realize that as we reduce the frequency of the emf, we're making the circuit "more and more DC"...

You've basically answered your own question.
The phenomenon of mutual induction (a.k.a. back EMF) between conductors in a transformer (or motor) winding is what limits the current. A very large utility distribution transformer will have 735 Kv on a primary winding of only a few ohms resistance. (0 ohms if they could make it). The equipment is designed to work efficiently on 60 Hz.
Another example is an adjustable frequency motor drive. As the frequency is reduced, so is the voltage. Otherwise the current would be excessive and burn the motor out.
 
  • #3
What are the pros/cons of 60Hz and (what was it) 440Hz?
 
  • #4
The phenomenon of mutual induction (a.k.a. back EMF) between conductors in a transformer (or motor) winding is what limits the current. A very large utility distribution transformer will have 735 Kv on a primary winding of only a few ohms resistance. (0 ohms if they could make it). The equipment is designed to work efficiently on 60 Hz.
Another example is an adjustable frequency motor drive. As the frequency is reduced, so is the voltage. Otherwise the current would be excessive and burn the motor out.

Wow, that seems logical. Thank you so much. :biggrin:
 
  • #5
Arctic Fox said:
What are the pros/cons of 60Hz and (what was it) 440Hz?

Almost all motors and power transformers use a core of laminated steel to conduct magnetism. The iron molecules line up according to the direction of the magnetic lines, which is decided by the electrical polarity. There's a slight hesitation of the molecules to follow the (constantly reversing) magnetism called hysteresis, which is energy loss. At 60 Hz the loss is small but increases with frequency.
A 2 pole induction motor will spin at 3500 rpm at 60 Hz so 400 Hz is used to run special motors at higher speeds. For even higher frequencies into the MHz range, ferrite is used in place of iron.
 

1. What is transformer efficiency and why is it important?

Transformer efficiency refers to the ratio of output power to input power in a transformer. It is an important factor to consider in the design and operation of transformers, as a higher efficiency means less power loss and better performance.

2. How does frequency affect transformer efficiency?

At low frequencies, transformer efficiency can decrease due to the presence of eddy currents and hysteresis losses in the transformer core. At high frequencies, skin and proximity effects can also contribute to efficiency loss.

3. Can a transformer be designed to have high efficiency at both low and high frequencies?

Yes, it is possible to design a transformer that has high efficiency at both low and high frequencies. This can be achieved through careful selection of materials and design considerations, such as using laminated cores and minimizing winding resistance.

4. What is the typical efficiency range for transformers at different frequencies?

The efficiency of a transformer can vary greatly depending on the design and operating conditions. Generally, transformer efficiency can range from 85-99% at low frequencies and 70-95% at high frequencies.

5. How can I improve the efficiency of a transformer at low and high frequencies?

Improving transformer efficiency at low and high frequencies can be achieved through various methods, such as using high-quality materials, reducing the number of winding layers, and optimizing the core design. Proper maintenance and regular testing can also help to identify and address any efficiency issues.

Similar threads

Replies
2
Views
1K
Replies
19
Views
2K
  • Electrical Engineering
Replies
5
Views
2K
  • Electrical Engineering
Replies
6
Views
3K
Replies
12
Views
1K
Replies
70
Views
8K
Replies
62
Views
3K
  • Electrical Engineering
Replies
21
Views
4K
Replies
3
Views
2K
Replies
9
Views
1K
Back
Top