What is a Speed-Time Curve?Speed-time curves are the most convenient means of studying the movement of trains and their energy consumption. A speed-time curve is defined as the graph plotted between the speed and time, by taking speed (in km/hour) on the Y-axis and time (in seconds or minutes) on X-axis. The speed-time curve provides complete information of the motion of the train.The speed-time curve gives the speed of the train at various time instants after the start of the run directly. The slope of the curve at any point gives the acceleration at the corresponding instant or speed.The area ... Read More

Power Output from the Driving AxlesLet, 𝐹𝑡 = Tractive effort in Newton𝑉 = Speed of the train in kmphSince, the power output is defined as the work done per unit time, i.e., $$\mathrm{Power\: output, \mathit{P}\mathrm{\: =\: }Rate\: of \: work\: done\mathrm{\: =\: }\frac{Work \: done}{time}}$$$$\mathrm{\Rightarrow \mathit{P}\mathrm{\: =\: }\frac{Tractive\: effort\times Distance}{Time}\mathrm{\: =\: }Tractive\: effort\times Speed}$$$$\mathrm{\therefore \mathit{P\mathrm{\: =\: }F_{t}\times V}\: Nm/s}$$$$\mathrm{\Rightarrow \mathit{P\mathrm{\: =\: }F_{t}\times V}\times \frac{1000}{3600}\, Watts}$$$$\mathrm{\therefore \mathit{P\mathrm{\: =\: }\frac{F_{t}\times V}{\mathrm{3600}}}\: kW\: \cdot \cdot \cdot \left ( 1 \right )}$$Now, if 𝜼 is the efficiency of gear transmission, then the power output of motor (or power input to driving axles) is given ... Read More

In the plain rheostatic starting method, the voltage across the traction motor is gradually increased from zero to full line voltage and the current is kept constant at normal rated value by reducing the external resistance gradually.Let, 𝑇 = Starting period in seconds𝑉 = Line voltage in volts𝐼 = Constant current in amperesThen, at the instant of switching ON the supply, the back EMF produced by the motor is zero and it starts building up immediately as the motor starts rotating.At any instant, the supply voltage to the motor is equal to the back EMF developed by the motor plus ... Read More

In this article, we will take a look at the various methods used for starting and controlling the speed of DC series motors.Rheostatic ControlThe basic traction motor circuit with rheostatic starting is shown in the figure below.A DC series motor can be started by connecting an external resistance in series with the main circuit of the motor. At the starting instant, the back EMF developed by the motor is zero, thus the resistance connected in series with the motor is maximum and is of such a value that the voltage-drop across it with the full load rated current is equal ... Read More

In electric traction, the control equipment is required for −Connecting the motors to the supply mains without taking excessive current at start and provide smooth acceleration without causing sudden shock so as to avoid damage to the coupling.Adjusting the speed as per requirement.Providing rheostatic or regenerative braking.The master controller system is used in the electric traction work, where the currents to be dealt are too high for the equipment. In the master controller system, the contact instead of being made or broken by hand are closed or opened by the switches known as contactors.For closing and opening of these contactors, ... Read More

Mechanical BrakingFor stopping the electric train and holding it stationary, in addition to the electric brakes, the mechanical brakes are also required. The mechanical braking is required because the electric braking is unable to hold the train at standstill.In modern electric locomotives, the regenerative braking is employed down to a speed of 16 kmph, then rheostatic braking down to about 6.5 kmph and finally mechanical braking to a standstill.The mechanical braking is usually applied by brake block shoes pressed with force against the tread of the wheels and the required braking force is caused by the movement of the piston ... Read More

This article explains the phenomenon of interference with the communication systems caused by the electric power lines employed for traction purposes. The phenomenon which modifies a signal in a disruptive manner, when the signal travels along a communication channel between its transmitter and receiver is known as interference in the communication system.As the electric traction system uses high-voltage power lines, the electromagnetic and electrostatic fields produced by these traction power lines disturb the neighbouring communication lines, i.e., the traction power lines cause interference with the communication lines.In electric traction systems, the track is used as the return path for the ... Read More

Linear Induction MotorA linear induction motor is a special type of induction motor that gives linear motion instead of rotational motion, as in the case of a conventional motion. In case of linear induction motor, the movement of field and movement of the conductors are linear.Construction and Working of Linear Induction MotorA linear induction motor consists of a three-phase distributed field winding placed in the slots and the secondary winding is nothing but a conducting plate made up of either copper or aluminium as shown in Figure-1.The field system of the linear induction motor may be either of following two ... Read More

Many single phase AC motors have been developed for traction purposes but only compensated series type commutator motor is found to be best suited for traction services. Practically, the AC series motor is best suited for traction purpose because of high-starting torque.When DC series motor is fed from AC supply, it works but not satisfactorily due to the following reasons −If a DC series motor is fed from AC supply both the field and the armature currents reverse for every half cycle. Thus, unidirectional torque is developed in the motor at double frequency.When AC supply is given to the DC ... Read More

A DC series motor has the following characteristics that make it suitable for traction work −DC series motors develop high starting torque which is required for traction purpose.DC series motors produce high starting torque at low speeds and low torque at high speeds.The speed of a DC series motor can be controlled easily and effectively.The torque developed by a DC series motor is unaffected by variations in supply voltage.DC series motors are ideally suitable for parallel running. Because, the DC series motors when operated in parallel to drive a vehicle by means of different driving axles, share load almost equally ... Read More