Difference Between Dielectric Constant and Permittivity

Updated on 18-Apr-2023 16:33:16
The study of dielectrics and their behavior in electric fields continue to fascinate physicists and electrical engineers alike. Despite the fact that dielectrics are poor conductors of electricity, they play a fundamental role in electronic circuits, which need a dielectric medium to build the circuit. A basic understanding of dielectrics and their properties is thus required. A dielectric material is nothing but an insulator with a poor conductor of electricity meaning they do not allow current to flow. They are the exact opposite of conductors. Like any other material, a dielectric is an assembly of ions with positive and negative ... Read More

Mechanics of Train Movement and Derivation for Tractive Effort

Updated on 03-May-2022 08:27:28
Mechanism of Train MovementThe essential mechanism of an electric locomotive is shown in the figure below.Here, the armature of the driving motor has a pinion of the diameter d1 attached to it. The tractive effort at the edge of the pinion is transferred to the driving wheel by means of a gearwheel.Let, T = Torque exterted by the motor in NmF1 = Tractive effort at the pinionFt = Tractive effort at the wheel$\gamma$ = Gear ratiod1 = Diameter of piniond2 = Diameter of gear wheelD = Diameter of driving wheel$\eta$ = Efficiency of power transmission from motor to ... Read More

Systems of Track Electrification: AC Electrification System

Updated on 03-May-2022 08:24:50
There are two types of AC system of track electrification −Single-Phase Low-Frequency AC System (15 kV to 25 kV at 16$\frac{2}{3}$ Hz, 25 Hz and 50 Hz)Three-Phase AC System (3.3 kV to 3.6 kV at 16$\frac{2}{3}$ Hz)Single-Phase Low-Frequency AC SystemIn a single-phase low-frequency system of track electrification, an AC voltage of 15 kV at a frequency of 16$\frac{2}{3}$ to 25 Hz is used.The use of high voltage AC in the system reduces the current flowing through the overhead transmission line resulting in the reduced voltage drops and it helps in installing the substations at larger distances, about 50 to 80 ... Read More

Electric Traction: Trapezoidal Speed Time Curve

Updated on 03-May-2022 08:19:33
The speed-time curve of a main line service is best and most easily replaced by trapezoid. The figure shows the simplified trapezoidal speed-time curve for the main line service.Let, $\mathit{V_{m}}$ = Crest speed in kmph$\alpha$ = Acceleration in kmphps$\beta$ = Retardation in kmphpsT = Total time of run in seconds$\mathit{t_{\mathrm{1}}}$ = Acceleration time in seconds$\mathit{t_{\mathrm{2}}}$ = Free running time in seconds$\mathit{t_{\mathrm{3}}}$ = Retardation time in secondsD = Total distance of run in kmTherefore, the time of acceleration in seconds is given by, $$\mathrm{\mathit{t_{\mathrm{1}}}\:=\:\frac{\mathit{V_{m}}}{\alpha }}$$And the time for retardation in seconds is, $$\mathrm{\mathit{t_{\mathrm{3}}}\:=\:\frac{\mathit{V_{m}}}{\beta }}$$Hence, the time for free running in seconds is, ... Read More

Electric Traction: Quadrilateral Speed Time Curve

Updated on 03-May-2022 08:16:12

General Features of Traction Motors: Mechanical Features & Electrical Features

Updated on 28-Apr-2022 08:43:11
An electric motor which is used to provide the primary rotational torque to a machine such as electric locomotives, elevators, conveyors, trolley buses and other electric vehicles etc. is described as a traction motor.General Features of Traction MotorsThe general features of the electric motors used for traction purpose are classified into two classes as −Mechanical FeaturesElectrical FeaturesMechanical Features of Traction MotorsThe mechanical features of electric motors used for traction applications are listed below −Robustness - A traction motor must be mechanically strong and robust so that it can be capable of withstanding severe mechanical vibrations.Small Size - The overall dimensions ... Read More

Updated on 28-Apr-2022 08:41:08
An electric traction system is the type of traction system that uses electrical energy for the movement of vehicle at any stage.The electric traction system is classified into two groups as −Self-contained vehicles or locomotives (Ex. – battery-electric drive and diesel-electric drive)Vehicles or locomotives which receive electric power from a distribution network or suitably placed substations (Ex. - railway electric locomotives, tramways and trolleybuses, etc.)Here, we described different types of electric traction systems along with their advantages and disadvantages −Straight Electric Traction SystemIn the straight electric traction system, either DC series motor or single phase AC series motor or three-phase ... Read More

Systems of Track Electrification: Composite System of Track Electrification

Updated on 28-Apr-2022 08:37:31
There is no system of track electrification which is good in all aspects, i.e. it suffers from some disadvantage.The composite system (as the name implies) combines together any two of the systems of track electrification so as to incorporate good points of both the systems. The composite systems presently being used are as −Single-Phase AC to Three-Phase AC SystemSingle-Phase AC to DC SystemSingle-Phase AC to Three-Phase AC SystemThe single-phase to three-phase system of track electrification is also known as Kando System. As the three phase AC traction system has some disadvantages such as tapping of power supply through two overhead conductors ... Read More