Transformers Flashcards
1
Q
What are transformers?
A
- devices that use EM induction to change the size of the voltage for an alternating current
2
Q
How does a transformer work?
A
- AC current flowing in the primary (or input) coil produces magnetic flux
- the changing magnetic field is passed through the iron core to the secondary (output) coil
- where it induces an alternating voltage of the same freq as the input voltage
3
Q
Using Faraday’s law, how can the induced emf in both the primary and secondary coils be calculated?
A
- Vp = Np ΔΦ / Δt
- Vs = Ns ΔΦ / Δt
- therefore
- Ns / Np = Vs / Vp
4
Q
WHat are step-up and step-down transformers?
A
- step-up
- increase voltage
- by having more turns in secondary coil than the primary
- step-down transfers
- reduce voltage
- have fewer turns on the secondary coil
5
Q
Why does IpVp = IsVs not happen?
A
- not 100% efficient
- power in does not equal power out
- that is forn an ideal transformer
6
Q
What causes the loss in power from the transformer
A
- eddy currents in the transform’s iron core
- eddy currents are looping currents induced by the changing magnetic flux in the core
- they crease a magnetic field that acts against the field that induced them , reducing the field strength
- they also disspate energy by general heat
7
Q
How are eddy currents reduced>?
A
- laminating the core with layer of insulation
8
Q
How is heat also generated? How is it reduced?
A
- caused by resistance in the coils
- thick copper wire used , which has a low resistance
9
Q
How are transformers used in the national grid?
A
- electricity from power station sent round the country in the national grid at the lowest possible currrent
- because the power losses due to the resistance of the cables is equal to P = I2R
- so if you double the transmitted current, you quadruple the power lost
- since power = IV, low current means a high voltage
- transformers allow us to step up to voltage to aroudn 400,000V for transmission through national grid
- and reduce in to 230V for domestic use
