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Co-efficient of adhesion is
High in case of D.C. traction than in the case of AC. Traction
Low in case of D.C. traction than in the case of AC. Traction
Equal in both AC. and D.C. traction
Any of the above
Low in case of D.C. traction than in the case of AC. Traction
The coefficient of adhesion (╬╝) is lower in DC traction compared to AC traction due to the nature of the torque produced by the traction motors. In DC series motors, the torque is pulsating and non-uniform, which increases the likelihood of wheel slipping compared to the smoother torque characteristics often managed in modern AC drive systems.
The coefficient of adhesion (╬╝) is lower in DC traction compared to AC traction due to the nature of the torque produced by the traction motors. In DC series motors, the torque is pulsating and non-uniform, which increases the likelihood of wheel slipping compared to the smoother torque characteristics often managed in modern AC drive systems.
╬╝=WaтАЛFtтАЛтАЛ тАФ where ╬╝ is the coefficient of adhesion, FtтАЛ is the tractive effort, and WaтАЛ is the adhesive weight.
Adhesion depends on the tangential effort exerted by the wheels on the rails and the normal weight on the driving wheels. DC motors produce high starting torque with significant ripples; because the tractive effort fluctuates, it reaches the limit of adhesion more frequently during acceleration. AC systems, particularly those using variable frequency drives and induction motors, provide more precise control over torque, allowing for higher utilization of the adhesive weight.
Adhesion is essentially the frictional force between the wheel and the rail.
DC series motors exhibit higher torque pulsations which can lead to wheel slip.
AC traction with vector control allows for better slip management and higher adhesion coefficients.
Weather conditions, track lubrication, and track gradient significantly influence the practical coefficient of adhesion.
AC traction allows for higher power-to-weight ratios.
AC traction provides better control of slip due to advanced power electronics.
DC traction is limited by the physical mechanical torque ripples of the motor.
Higher adhesion in AC systems reduces the required number of driving axles.
Electric Locomotives
High-speed trains (AC traction)
Metros and Suburban EMU trains
| Feature | DC Traction | AC Traction |
|---|---|---|
Coefficient of Adhesion | Lower (High Pulsation) | Higher (Controlled) |
The coefficient of adhesion typically ranges from 0.25 to 0.33 for clean, dry rails.
Option B is correct because the inherent pulsating torque of DC motors results in a lower effective coefficient of adhesion compared to electronically controlled AC traction drives.
B is correct тАФ The coefficient of adhesion is lower in DC traction than in AC traction because AC systems utilize more precise control electronics to minimize wheel slip.
Always remember that in electrical traction, the control method (Chopper for DC, VFD for AC) directly dictates the performance limits of the adhesion coefficient.