{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture20_Kim

# Lecture20_Kim - Lecture 20-1 Transformers(1 When using or...

This preview shows pages 1–5. Sign up to view the full content.

Lecture 20-1 1 Transformers (1) When using or generating electrical power, high currents and low voltages are desirable for convenience and safety When transmitting electric power, high voltages and low currents are desirable The power loss in the transmission wires goes as P = I 2 R Assume we have 500 MW of power to transmit If we transmit at 750 kV , the current would be 667 A (U=IV) If the resistance of the power lines is 200 , the power dissipated in the power lines is 89 MW 18% loss Suppose we transmit at 375 kV instead 75% loss The ability to raise and lower alternating voltages would be very useful in everyday life

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Lecture 20-2 2 Transformers (2) We use a transformer to transform alternating currents and voltages from high to low or from low to high A transformer consists of two sets of coils wrapped around an iron core as illustrated Consider the primary windings with N P turns connected to a source of emf We can assume that the primary windings act as an inductor The current is out of phase with the voltage and no power is delivered to the transformer is delivered to the trans max sin emf V V t