| Electronics > Beginners |
| Isolation transformer and electrons |
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| nForce:
I have a basic question: When we use isolation transformer we have a physical electric isolation between two systems. If we connect a wire between a system on the other side of an isolation transformer and ground then the current would not flow. But how do electrons know on the other side of an isolation transformer that we don't have a current loop? They just feel a potential difference, so they should flow because they don't know nothing about isolation. Thank you. |
| bson:
An electric potential causes charge to shift around, it's the force acting on electrons. A transformer is coupled through a magnetic field, so there is no potential between the two sides. (Capacitors are coupled through an electric field, hence they do have a potential.) The potential is between the individual taps on each side, not between the sides. Since there is no potential between the sides you can connect one of the taps on the secondary to ground or any other primary-side reference. The electrons simply have no force acting on them, hence no current. |
| Zero999:
As far as the secondary coil is concerned, the electrons are being moved around by the changing magnetic flux. The primary coil could be replaced with a spinning magnet, and it would behave in the same manner. |
| IanB:
Actually the electrons do flow, however the size of the current is too small to be of significance. The electrical potential on the secondary side of the transformer is fluctuating at the AC frequency and the ground potential is not. So a small AC current can flow due to the capacitance between the ground and the secondary. For normal low voltages the current is too small to matter, but for large electrical transmission transformers where the secondary voltage is (say) 500 kV this capacitance effect is very significant and considerable precautions have to be taken to prevent arc over. |
| nForce:
--- Quote from: bson on December 02, 2018, 06:08:49 pm ---An electric potential causes charge to shift around, it's the force acting on electrons. A transformer is coupled through a magnetic field, so there is no potential between the two sides. (Capacitors are coupled through an electric field, hence they do have a potential.) The potential is between the individual taps on each side, not between the sides. Since there is no potential between the sides you can connect one of the taps on the secondary to ground or any other primary-side reference. The electrons simply have no force acting on them, hence no current. --- End quote --- Ok, but the magnetic field also moves charges (qv x B), the Lorentz force? And there is also a magnetic potential not only electrical one. |
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