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Electrical Engineering Articles
Page 9 of 12
Mechanics of Train Movement and Derivation for Tractive Effort
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 MoreSystems of Track Electrification: AC Electrification System
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 MoreElectric Traction: Trapezoidal Speed Time Curve
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 MoreElectric Traction: Quadrilateral Speed Time Curve
For urban and suburban services, the simplified quadrilateral speed-time curve of electric traction is shown in the figure.Let, $\alpha$ = Acceleration in kmphps$\beta$ = Braking retardation in kmphps$\beta_{c}$ = Coasting retardation in kmphpsV1 = Maximum speed at the end of acceleration in kmphV2 = Speed at the end of coasting in kmphT = Total time of run in secondst1 = Acceleration time in secondst2 = Coasting time in secondst3 = Braking time in secondsD = Total distance travell in kmTherefore, the time of acceleration is given by, $$\mathrm{\mathit{t_{\mathrm{1}}}\:=\:\frac{\mathit{V_{\mathrm{1}}}}{\alpha } }$$The time of coasting is given by, $$\mathrm{\mathit{t_{\mathrm{2}}}\:=\:\frac{\mathit{V_{\mathrm{1}}}-\mathit{V_{\mathrm{2}}}}{\beta_{c} } \:\:\:\cdot \cdot ...
Read MoreCrest Speed, Average Speed & Schedule Speed of an Electric Train
Crest Speed of Electric TrainThe maximum speed attained by an electric train during running is termed as its "crest speed". It is denoted by Vm.Average Speed of Electric TrainAverage speed is defined as the mean of the speeds attained by the electric train from start to stop. In other words, average speed is defined as the ratio of the distance covered by the train between two stops to the actual time of run. The average speed of train is denoted by Va and is given by, $$\mathrm{\mathrm{Average\: speed, }V_{a}\:=\:\frac{\mathrm{Distance\: between \:two\: stops\: (\mathit{D})}}{\mathrm{Actual\: time\: of\: run (\mathit{T_{\mathrm{run}}})}}\:\mathrm{kmph}}$$Schedule Speed of Electric ...
Read MoreWhat is a Photometer? – Principle, working and Types
Photometry and PhotometerThe measurement of light's brightness or luminous intensity is known as photometry. Photometry focuses on the perceived brightness to the human eyes. The photometry takes into account the eye's sensitivity to varying degrees of light and focuses primarily on the visible light spectrum.Thus, the photometry involves the measurement of candle power. The candle power of a given source of light in any given direction is measured by comparison with a standard source. In order to eliminate the errors in the measurement of the candle power, the measurement is performed in a dark room with dead black walls."The device ...
Read MoreWhat is Seam Welding? – Working and Applications
Seam WeldingThe welding process in which two similar or dissimilar materials are joined at the seam by the application of heat generated from electrical resistance is known as seam welding. The seam welding is a types of resistance welding, in which weld is produced by roller electrodes instead of tipped electrodes.Most seam welding processes produce a continuous or intermittent seam weld near the edge of two overlapped metals by using two machine driven roller electrodes. As in the seam welding process, the roller electrodes move over the metal workpieces, the workpieces are under pressure and the current passing through them ...
Read MoreWhat is Polar Curve in Illumination?
Polar CurvesThe plots drawn between the candle power and angular position are known as polar curves. Due to unsymmetrical shape of the lamps, the luminous intensity is not uniform in all directions. The luminous intensity in all directions can be represented with the help of polar curves.The polar curves are drawn by taking the luminous intensities in various directions at an equal angular displacement in the sphere. A radial ordinate pointing in any particular direction on a polar curve represents the luminous intensity of the source when it is viewed from the direction.Therefore, the polar curves are classified into two ...
Read MoreWhat is Laser Beam Welding? – Process, Advantages, Disadvantages and Applications
Laser Beam Welding (LBW) is a fusion welding process in which multiple pieces of metal are joined together through the use of laser. In LBW, the laser beam acts as a concentrated source of heat, which allows narrow, deep welds and high welding rates. The laser beam welding process is frequently used in high volume applications, such as in the automotive industry.Laser Beam Welding ProcessThe figure shows the schematic diagram of the laser beam welding (LBW).The main parts of the set up used for the laser beam welding are as follows −Laser Machine – It is the machine that is ...
Read MoreWhat is Lambert's Cosine Law? (Laws of Illumination)
The light received by any surface depends upon the angle made by the normal to the surface, to the light flux. The Lambert's cosine law of illumination explains the relation between the illumination of the surface and the cosine of the angle.StatementThe Lambert's cosine law of illumination states that"The illumination of a surface is directly proportional to the cosine of the angle between the normal to the surface and the direction of incident light".That is, $$\mathrm{\mathit{E}\propto cos\, \theta \: \: \: \cdot \cdot \cdot \left ( 1 \right )}$$ExplanationCase I – Consider a surface that is normal to the luminous ...
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