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

The circuit diagram of the buck and boost method of speed control of traction motors is shown in the figure.There are two traction motors viz. traction motor-I and traction motor-II. In this method of speed control, the armature of both the traction motors I and II and the motor-generator set are connected in series. This whole series combination is connected across the main supply.When the terminal voltage of the generator is equal to the supply voltage in magnitude but of opposite polarity and the main contactor (MC) is closed, the voltage across the traction motors will be zero and hence ... Read More

In addition to the main traction motors, the following additional equipment are required to be installed on an electric locomotive engine −Motor-Generator SetBatteryPantograph Operating EquipmentAir CompressorTraction Motor BlowersHeating EquipmentLet's check the functions of each of these equipment in detail.Motor–Generator SetThe motor-generator set used in the electric locomotives is of the two bearing type and it consists of a series motor and a shunt generator. The speed of the series motor at light load is limited by the ventilating fan and the voltage of the generator is controlled by an automatic voltage regulator (AVR).The generated voltage by the motor-generator set is ... Read More

An overhead wire of large cross-section made of copper or a copper alloy and provides the current required for the trolleys of electric vehicle is known as trolley wire.When a flexible wire is suspended horizontally between two pole supports, it would assume the form of catenary. But in case of tramways, the sag in the trolley wire rarely exceeds 1% to 1.5% of the span length and thus the trolley wire may be considered to hang in the form of a parabola as shown in the figure below.Let, $$\mathrm{Span\: length\: of\: trolley\: wire\: (in \: meters)\, \mathrm{\: =\: }\, 2\mathit{l} ... Read More

The method of electric braking of traction motor in which the motor remains connected to the supply line and return the braking energy to the supply system is known as regenerative braking.Figure-1 shows the connection diagram of Behn Eschenburg scheme of regenerative braking. In this scheme, an auxiliary transformer is used to excite the field winding of the traction motor. The armature of the traction motor is connected to the main transformer through a tap changer.A choke coil or iron cored reactor (Reactor-I) is inserted in between the armature of the traction motor and the tap changer as shown in ... Read More

An electrical device which converts light energy into electrical energy through the photovoltaic effect is known as photovoltaic cell or PV cell or solar cell. A photovoltaic cell is basically a specially designed p-n junction diode.Construction and Working of Photovoltaic CellThe construction of a photovoltaic cell is shown in the following figure.A photovoltaic cell consists of a base metal plate and it is made of either steel or aluminum over which a metallic selenium layer is situated which is light sensitive and acts as the positive terminal.An electrically conducting layer of cadmium oxide is applied by sputtering over the selenium ... Read More