Transformers and alternators Flashcards
Explain how a transformer works.
The primary coil has a alternating voltage which induces a magnetic field in the iron core. The magnetic field in the iron core then fluctuates. The secondary coil will cut the magnetic flux and hence a current will be induced within the secondary coil. If the number of turns in the second coil is larger than the primary then the voltage will stepped up.
What is the equation for an ideal transformer?
Vp/Vs = Np/Ns
What is a step up transformer and a step down transformer?
- Step-up transformers increase the voltage by having more turns on the secondary coil than the primary.- Step-down transformers reduce the voltage by having fewer turns on the secondary coil.
What is the permeance of a material?
The permeance of a material is the amount of flux induced in it for a given number of current turns that surround it. The higher the permeance of the material, the greater amount of flux induced.
What is the equation to calculate the permeance of a material?
Permeance = uA/Lu = The permeability of a materialA = Cross-sectional areaL = length
How would you design an efficient transformer
When designing a transformer, you want to make the permeance of the core as high as possible to get the maximum flux induced in it. Ideally you want the core to be short(L) and fat(high A) and made from a high permeability material like iron.You want the wire to be of high conductivity to limit energy loss, so you want the wire wrapped around the core to be as short as possible.
Why is the iron core required in a transformer?
A magnetic circuit will still work if there’s an air gap in it. Air has very low permeability compared to ion, so the amount of flux in the circuit would be much lower if air was used rather than iron.
Explain why transformers are not a 100% efficient.
Energy in the transformer is lost in the form of heat.Heat can be produced by eddy currents in the transformer’s iron core. Currents induced by the changing magnetic flux in the core. The effect is reduced by laminating the core with layers of insulation.Heat is also generated by resistance in the coils - to minimise this thick copper wire is used, which has a low resistance.
Why is electricity from power stations sent around the national grid at the lowest current possible?
- The losses of energy due to the resistance in the cables in proportional to I^2.- A high voltage is used so that the current transmitted is low.
