# Superconductors and storage

1. Jul 23, 2009

### Mr 4738

Hi all! It's my first post.

How is electrical energy sent into a superconducting loop for storage and taken out for use? Is there power loss during these actions?

Peace!

2. Jul 23, 2009

### MATLABdude

Welcome to PhysicsForums!

I believe it's usually done via Lenz's Law, and inducing a current via a changing magnetic field. This process wouldn't be 100% efficient, nor would doing the opposite to extract energy. Also, you've got to cool a big superconducting magnet such that it remains superconducting!

Also: Electric Energy Storage at Superconducting Temperatures?:

3. Jul 23, 2009

### Bob S

See the following site for superconducting magnetic energy storage (SMES):
http://en.wikipedia.org/wiki/Superconducting_magnetic_energy_storage
People have been discussing storage of megawatt-hours in very large superconducting coils, either solenoid or toroid. The energy is stored as very high magnetic fields. The total energy stored is (1/2) L I2, where L is the inductance and I is the current. To put more current in, apply a voltage to the coil, and more current flows in. Specifically V = L dI/dt. where dI/dt is the rate of current increase. If you short the two superconducting coil ends together, the current will persist in the coil, like in MRI machines. If ou attach a load, like a resistor to the coil terminals, the equation becomes I/R = -L dI/dt, so current flows out. It requires a lot of cooling to keep the superconducting coil cold, and heat leaks are a big problem. Also mechanical stresses to keep the coils from moving are very high.

4. Jul 24, 2009

### Mr 4738

Awesome! So, I don't know much about electrical engineering but it's super duper fun.

Hey, Bob S are there any good books or online recources where I can learn about the terms and equations you put down a little better? I'm a visual person too so anything with pics will be good. Thanks!

AND..

Let's say there are two SMES in a room. Each has its own energy stored at the moment. The two SMES are connected together so each can send their energy to the other in an infinite loop.

Now, at the sections that connect these two SMES's are EM's. Everytime the SMES's exchange energy they turn on the EM's for a time.

If you stick a permanent magnet (rotor) in between the two EM's (stator) could this produce an efficient motor? This goes back to my origional question of SMES storage and transfer efficiency.

5. Jul 24, 2009

### MATLABdude

There are at least proof-of-concept superconducting motors in existence. The windings are superconducting, reducing ohmic losses, and I believe that superconductors also have lowered sliding friction (for things like bearings and collars).
http://www.physorg.com/news99220532.html

A company that, at least, does research into them:
http://www.amsc.com/products/motorsgenerators/faq.html [Broken]

Last edited by a moderator: May 4, 2017
6. Jul 24, 2009

### Mr 4738

That's right.. I read about the bearings (frictionless because they float I think) and I've checked out the AMSC site once or twice. I should look into how AMSC's motors/generators work some more.

7. Jul 24, 2009