Transformers
Vprimary/Vsecondary = Nprimary/Nsecondary Where Vprimary = voltage in primary coil Vsecondary = voltage in secondary coil Nprimary = turns in primary coil Nsecondary = turns in secondary coil |
|
Transmission of Electric Power: Plant to Home | Transformer: Theory of Operation |
From Faraday's law
Vsecondary = NsecondaryDFB/Dt Vprimary = NprimaryDFB/Dt
Dividing the two, we arrive at the transformer equation
Vsecondary /Vprimary = NsecondaryDFB/Dt/NprimaryDFB/Dt
Vsecondary /Vprimary = Nsecondary/Nprimary or Vsecondary = Vprimary (Nsecondary/Nprimary )
To create a Step-up transformer: Nsecondary > Nprimary
To create a Step-down transformer: Nsecondary < Nprimary |
|
Power Transmission: Plant to Home |
Transformer Drum | Transmission Substation | Transmission Lines |
Some of the many uses for transformers
ð Computer network interface cards
ð Modems
ð Power amlifiers
ð Microwave ovens
ð Car ignition systems
ð etc.
Why AC Used in Transmission of Power
The transformer equation does not work with DC - there is no changing magnetic field
Why Power Transmitted at High Voltages
Assume that 240 kW of electric power is consumed by a certain location that receives this power from 10 miles away over transmission lines.
The transmission lines have a total resistance of 0.40 ohms.
I = current in the lines = P/V
If the power is transmitted at 240 volts
I = 240,000 W/240 V = 1,000 A
Ploss = I2R = (1x103 A)2(0.40 W) = 400,000 W loss if transmitted at 240 volts
If the power is transmitted at 24,000 volts
I = 240,000 W/24,000 V = 10 A
Ploss = I2R = (10 A)(0.40 W) = 4 W loss if transmitted at 24,000 volts