Electric Traction System

Study Notes

Electric traction is a locomotion method where the driving force is obtained from electric motors.
Electric traction is a practical application of electricity in everyday life, used in transportation, such as electric trains, trolley buses, tramcars, and diesel-electric and gas turbine electric vehicles.

An ideal traction system should have the following characteristics:
High starting tractive effort for rapid acceleration
Self-contained and compact locomotive or train units
Equipment capable of withstanding large temporary overloads
Minimum wear on the track
Braking system that causes minimum wear on the brake shoes and regenerates energy back to the supply during braking
Minimum equipment required with high efficiency and low initial and maintenance cost
No interference with communication lines
Easy speed control

There are two main groups of electric traction systems:
Units that receive electric power from a distributing network at suitable points (e.g. trolley buses, tramways, and railways)
Self-contained locomotives that generate their own power (e.g. diesel-electric traction, ships, and petrol-electric trucks)

Electric traction has several advantages over steam traction, including:
Cleanliness: no smoke and flue gases
Lower maintenance cost (50% of steam traction)
Shorter starting time (no need to wait for hours like steam locomotives)
Regenerative braking, which feeds back 80% of the energy required during ascent
Lower maintenance cost of brake shoes, wheel treys, and rails
Lower center of gravity, making it more stable and able to take curves at higher speeds
Saving in high-grade coal, which is deficient in many countries
Absence of unbalanced forces, resulting in a higher coefficient of adhesion
Less noise
Regenerative braking can be applied, returning power back to the supply

Despite its advantages, electric traction has some disadvantages, including:
High capital cost of the overall electric traction system
Failure of power can cause disruption of traffic for several hours
Interference with communication lines, which can be solved by removing them to a far-off place or using underground cables, making the system more expensive