Introduction to Electric Distribution Grids

Question 1

The War of the Currents – AC vs. DC (5/5)

Answer 1

Question 2

Transmission and Distribution Grids

Answer 2

Question 3

Complexity of Power Systems

Answer 3

Question 4

Name advantages of higher frequencies for AC transmission

Answer 4

• Lighting flicker not perceivable (relevant for incandescent light bulbs)
• Arc lights did not work with lower frequencies (in 1880s)
• Higher power-to-weight ratio of transformers, motors and generators
• Greater range of speeds for induction motors

Question 5

Name advantages of lower frequencies for AC transmission

Answer 5

-Lower hysteresis and eddy current losses

• Lower capacitive susceptance of cables and transmission lines
• Lower inductive reactance and related voltage drop
• Synchronous generators driven by low speed engines in early years
• Rotating AC-DC converters could not be manufactured at high speeds in the past

Question 6

Name advantages of AC transmission

Answer 6

• Efficient voltage conversion (with transformers)
• Power can be generated at advantageous voltages
• Flexibility to connect loads and generation along the route

Question 7

Name advantages of DC transmission

Answer 7

• Low loss for long distance transmission
• Less insulation requirement (peak vs. rms voltage)
• Better operation & control

Question 8

Draw the schematic structure of today’s AC electricity systems. Include and label the
following parts: Extra High Voltage (EHV) level, High Voltage (HV) level, Medium
Voltage (MV) level, Low Voltage (LV) level, Transmission Grid, Distribution Grid,
Primary Substation, Secondary Substation

Answer 8