Section 2.3 Transportation Flashcards
Factor for the Cross-Sectional Area
The larger the cross-section of a material, the more current it can allow to pass through it
Factor for the Length of the conductor
A short conductor allows current to flow at a higher rate than a long conductor
Factor for the Temperature
With increasing temperature, resistivity increases.
Skin effect
- Tendency of current to concentrate uniformly throughout the cross-section area
- Presented in AC
- Higher the frequency, thinner the layer in which current flows
- The cause is because of the strands at the center of the conductor are surrounded by a greater magnetic flux
Most common Overhead line pole used in Germany
Donau pole type 110 - 380 kV
Types of Overhead Line Poles
- Single Platform 110 - 380 kV
- Donau Pole Type 110 - 380 kV
- Special Pole 110 - 1500kV
- LV Wood Pole 20 - 110kV
- Cement Pole 20 - 110kV
Special Pole
- Are designed for very high mechanical strain or strong icing
- Usually built in cold regions
Wood Pole and Cement Pole
Use for lighter constructions for medium and low voltages poles
Single Platform Poles
Ensure good transmission behavior and cost
Most common conductor metal for line
Aluminum
- Conductors usually consist of drilled strains
Maximum allowed operation temperature for conductor ropes
- 80C for simple ropes
- 210C for high-temperature ropes
Cables
- Usually laid below the frost line( 0.8m for LV / MV)
- Lower outage frequency
- Higher outage duration due to difficult accessibility
- Usually for LV/MV
Plastic Cables LV
- Insulated with synthetic materials
- Three conductor and the neutral wire together form one cable
Plastic Cables MV
- For larger voltages from 10kV onwards
- Single conductors cables are predominant
Lines vs Cables - Cost
- Line is cheaper
- Higher resistive losses for transmission for lines
- Lower repairing and outage cost for lines
- Cables are more expensive due to higher investment cost in combination with shorter lifetime
Line vs Cable - Reliability
Lines are a state of the art
- Availability > 99.8%
- Outage time: hours to few days
- Lifetime: 80 to 100 years
Cables are not yet state of the art
- Availability > 93%
- Outage time: weeks to months
- Lifetime: 20 to 40 years (expected)
HVDC Cables
- Beyond 30 km HVAC cables are not longer used
- Too high losses due to capacitive characteristic
- Overall cost of DC is lower at longer distances
HVDC Overhead Lines
At a critical distance, DC also becomes more economic than AC for overhead lines
HVDC vs HVAC - Advantages of DC
- No skin effect - Less losses
- No reactive power needed, less currents, less losses
- Feasible cable option for longer distances
- Can be used for actively controlling power flows in the grid
HVDC vs HVAC - Disadvantages of DC
- Less reliable due to extra conversion equipment
- Losses in the converter equipment
- Multi-terminal DC systems are difficult to construct
DC is interesting for
- Connecting unsynchronized networks
- Long distance connection between two locations
