What is the frequency of a single phase traction system?

Types of track electrification:

1. DC System

2. Single Phase AC System

3. Three Phase AC System

4. Composite Systems

DC System:

• In this system, the electric motors employed for getting the necessary motive power are usually dc series motors
• Although the compound motors are coming into favor where regenerative braking is desired.
• The operating voltage is from 600 volts to 750 volts for tramways and for many suburban railways and from 1,500 volts to 3,000 volts for mainline railways.

Single Phase AC System:

• In single-phase, ac system ac series motors are used for getting the necessary motive power.
• The voltage employed for distribution network is 15,000 to 25,000 volts at \(16 {2 \over 3}\) or 25 Hz, which is stepped down on the locomotive to a low voltage (300 to 400 V) suitable for supplying to single-phase ac series motors by means of a step-down transformer carried on the locomotive.

Three Phase AC System:

• In this system, 3-phase induction motors operating at 3,000 to 3,600 volts and a normal frequency of \(16 {2 \over 3}\) Hz are employed for getting the required motive power.
• The three-phase induction motors are simple and robust in construction and have high operating efficiency and property of automatic regenerative braking without requiring any additional equipment.
• However, the induction motors have few drawbacks such as low starting torque, high starting current, and absence of speed control.

Composite Systems:

• The composite system combines the advantages of the dc/ac and 3-phase/single-phase systems
• The single-phase ac system is preferable from the viewpoint of the distribution and contact wire system.
• It can be converted into either three-phase ac or dc at low voltage in the locomotive.

At present, there are two composite systems.

1. Single phase-to-three phase system.
2. Single-phase ac-to-dc system.