Transformer

AC Source  Alternating current comes from generators, not batteries. Ideal sinusoidal sourceIdeal sinusoidal source  The symbol for an AC source uses a sine curve. R VV

Internal Flux  Faraday’s law links flux to voltage. Change in voltage to change in fluxChange in voltage to change in flux Change in flux to change in voltageChange in flux to change in voltage  The flux can link one conductor to another. Iron for better flux linkIron for better flux link Minimize lossesMinimize losses

Primary Coil  An AC voltage source produces a changing voltage.  The changing voltage creates an opposing magnetic flux in the iron.

Secondary Coil  Faraday’s law describes the induced voltage in the second coil. Assume all field lines from primary go through secondaryAssume all field lines from primary go through secondary  The induced voltage directly depends on the primary voltage.

Turns Ratio  The output voltage depends on the ratio of the turns in the coils. Symbol represents linked coils  If N B > N A then the voltage increases. Step-up transformer  If N B < N A then the voltage decreases. Step-down transformer

Transformers  Commercial transformers wind two coils around a linkng medium. Single cylinder of air or ironSingle cylinder of air or iron Connecting bar of ironConnecting bar of iron  The schematic symbol represents two coils.

AC Adapter  An AC adaptor is an example of a step-down transformer. Convert 120 V AC to 18 V DC  Power transmission uses step- up up and step-down transformers. Power plant: 10 kV to 345 kV Substation: 345 kV to 7200 V Power pole: 7200 V to 120 V

Power Law next  Transformers do not create power. Energy conservedEnergy conserved Losses small compared to resistorsLosses small compared to resistors  For no power loss, current and voltage must maintain same power. Current decrease for step-upCurrent decrease for step-up Current increase for step- downCurrent increase for step- down