What is Traction
Traction is the act of drawing or pulling, by an elastic or spring force. It refers to a maximum frictional force that can be produced by a surface without slipping
Traction is the result of specific friction coefficient for example in vehicles the traction is created between the rubber and ground
Why traction is needed
If we walk into a surface without good grip our legs and feet could not move us forward and it is same for the vehicles if the ground does not provide enough resistance or traction, the generated force from the engine won’t be able to move the car If there is more traction then more torque can be generated to move more weight
Types of a Traction system
• Non-electric traction system– this system does not use electricity at any stage example steam engine drive, internal combustion drive
• Electric traction system – if electric supply is used to drive a locomotive that system is called as electric traction
Examples are battery electric drive, diesel electric drive
Types of Electric traction
Electric traction is subdivided into
• A system which operates with DC such as trolley, buses, tramways, and railways
• A system which operates with AC such as railways
This system has self-contained locomotives they could generate their own power
Diesel-electric traction
A diesel-electric locomotive uses a diesel engine to drive the electric generator which will then supplies current to traction motors, which will then be geared to the locomotive wheels
What are the requirements for a traction system
• The starting tractive force should be high to have rapid acceleration
• The track wear should be minimum
• This equipment must be capable to withstand large temporary loads
• It must be pollution-free
• Speed control should be easy
• Maintenance and initial cost must be low
• The system should be self-contain
Advantages of Electric traction
• High starting torque
• Less maintenance cost
• It is the cheapest method of traction
• Quick acceleration and braking
• Less vibration
• It is free from smoke and flue gases
Disadvantages of electric traction
• High capital cost
• Supply failure problem
• The vehicle which is operated electrically have to move on guided tracks only
• To achieve electric braking and control additional equipment are needed
What is a traction motor
The traction motor is an electric motor which provides the primary rotational torque of a machine, mostly for conversion into linear motion, it is mostly used in electrically powered rail vehicles such as electric multiple units and electric locomotives
What is a SEPEX
It is expanded as separate excitement of traction motors, in which the armature and field coils of an electric motor are fed with the independently controlled current. It also controls a degree of automatic wheel slip control during acceleration