In trains there are many compartments full of passengers & luggage, so during the starting, it requires high starting torque. The DC series motor is used for the locomotive because it has very high starting torque and variable speed.

DC series motors will have a starting torque as high as 500% compared to normal operating torque

The balance condition of wheatstone bridge is given as

$\frac{{{R_1}}}{{{R_2}}} = \frac{{{R_3}}}{{{R_4}}}$

R₁ = 10Ω

R₂ = 5Ω

R₃ = D

R₄ = 3Ω

$\begin{array}{l}\frac{{10}}{5} = \frac{D}{2}\\\\D = 6\Omega \end{array}$

A body that absorbs all the radiation incident on it would then appear ‘perfectly black’ to us. This is because we observe a body due to the ‘reflection’ of radiation incident on it; and if a body absorbs all the radiation incident on it, then it would reflect no radiation. So, a body would be invisible to us or appear black to us. Such a body was called by Kirchhoff a black body.

A body whose absorptive power is unity at all the wavelengths or that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence is termed the black body

In squirrel cage induction motor, the rotor bars are permanently short-circuited by end rings and there are no slip rings and brush gears hence it is not possible to connect an external resistance in the circuit in series with the rotor conductors.

A four-wire system allows you to have phase voltages or line to ground voltages. In 3 phase 4 wire system, neutral wire carries return current in case of any fault occurs in the line there is more flexibility to keep the system running since it may only affect one of the phases.

• Cross arms are either made up of wood or steel angle sections.
• Cross arms are installed at the top of the pole for holding the insulator on which the conductors are fastened.
• If the cross arms are fixed in the center of the pole then it is simply called cross arms.
• If the cross arms are fixed on the side of the pole then it is termed as side cross arms.
• For the three-phase line, U-shaped Cross arms are used.

Beading (Inner Sheath)

This portion of the cable is also known as an inner sheath. Mostly it is used in Multicore cables. It works as the binder for insulating conductors together in multi-core power cables and provides bedding to armor. This portion of the cable is mainly made of PVC, RUBBER etc.

Armouring

Armoring is the process that is done mainly for providing the earthing shield to the current-carrying conductors as well as it is also used for earthing purposes of the cable for safety. When there is any insulation failure in the conductor, the fault current gets enough paths to flow through the armor if it is properly earthed. Providing extra mechanical protection and strength to cable is an important added advantage of armoring. In MINING CABLES it is done for conductance.

Voltage transformer ratio of the transformer is given as

$\frac{{{V_2}}}{{{V_1}}} = \frac{{{N_2}}}{{{N_1}}}$

N₂ = 4N₁ i.e

N₂/N₁ = 4/1

V₁ = 200V

V₂ = ?

$\begin{array}{l}\frac{{{V_2}}}{{200}} = \frac{4}{1}\\\\{V_2} = 800V\end{array}$

Shunt generators are used to charge batteries. In this application, the voltage should drop off slightly as the load increases, because the voltage of a lead battery is lower when the battery is discharged than when the battery is charged. Because of its drooping characteristic, the shunt generator is admirably suited for battery charging service. In a general way, the voltage curve of the generator has the same shape as the voltage curve of the battery itself. In both cases, as the load falls the voltage rises.