UPPCL JE 2016 Electrical question paper with Solution (Evening Shift)

Mechanical braking (i.e. non-electrical braking) is the oldest form of the braking mechanism. This braking system can be subdivided into

1. Pneumatic braking
2. Vacuum braking
3. Air braking
4. Hydraulic braking
5. Electro-pneumatic braking.

Energy may also be dissipated as heat directly in a mechanical brake. This may be much more economical than by transmitting it through a generator. Furthermore, a mechanical brake may be less subject to dangerous failures than a dynamic or regenerative generator.

For locking stored potential energy, such as for holding elevators in position, mechanical brakes that need not dissipate are used. Mechanical braking is also employed in a motorbike, Bicycle, Battery operated a scooter, Lift etc. Mechanical brakes such as pneumatic brakes, air brakes, vacuum brakes, etc, are used in transport vehicles.

An Ideal capacitor or Inductor do not dissipate power. When power is transferred to a capacitor, all of it is stored as energy in the capacitor’s electric field. When the capacitor is discharged, this stored energy is returned to the circuit. In fact, the word capacitor is derived from the element’s capacity to store energy in the electric field.

Three types of operating forces are needed for the satisfactory operation of any Electromechanical indicating instrument. These are—

1. Deflecting force
2. Controlling force
3. Damping force.

• Deflecting force — The deflecting or operating force is required for moving the pointer from its zero position. The system producing the deflecting force is called the ‘Deflecting System or Moving System’. The deflecting system of an instrument converts the electric current or potential into a mechanical force called deflecting force.
• Controlling force — This force is required in an indicating instrument in order that the current produces deflection of the pointer proportional to its magnitude. The system producing a controlling force is called a ‘Controlling system’. Controlling force is used to bring the moving system back to zero when the force causing the instrument moving system to deflect is removed. Controlling force is usually provided by springs.
• Damping force — in the absence of damping force, the pointer of indicating instrument oscillates about its final value. To bring it immediately to the final, damping force is Provided.

Rotor current in the running condition is given as

${I_2} = \frac{{s{E_2}}}{{\sqrt {{R^2}_2 + {{(S{X_2})}^2}} }}$

Where E = Induced EMF in the rotor circuit

R₂ = Rotor Resistor

X₂ = Rotor Reactance

Hence if the Rotor resistance will be small then the rotor current will be large.

Resistivity ρ of a conductor is given by

ρ = (0.025 × 5)/2.2

ρ = 0.57 Ω-m

The voltage regulators in cellular phones are used to accomplish different goals.

1. To step down the voltage between the battery and the different sub-circuits that require lower supply voltage, or to step up the voltage for sub-circuits that need a higher voltage than the battery (like SIM card, backlight LED, etc.).
2. To isolate the different subsystems from each other. This is important in the RF section, and also between digital and analog/mixed-signal circuits.
3. To isolate sensitive circuitry from the transient voltage changes of the battery.
4. Switching regulators are used in mobile phones to boost the supply
   voltages to higher values, and subsequently, low dropout voltage (LDO) regulators are cascaded in series in order to suppress the inherent noise associated with the switching devices.

The instruments which add up the electrical quantity, i.e electrical energy, and measure the total energy (in kilowatt-hours) or the total Amper hours (in ampere-hours) supplied to a circuit in a given period are called integrating instruments.

In such instruments, there are sets of dials or gears which register the total quantity of electricity or the total amount of electrical energy supplied to a circuit in a given period. A Household energy meter is an integrating instrument. The Watt-hour meter is another example of integrating instruments.

The primary function of the breather is to absorb air moisture during breathing. A breather consists of a small vessel that contains a drying agent like silica gel or calcium chloride.

The permanent magnet moving coil (PMMC) instruments work on the d’Arsonval galvanometers principle. A small coil of fine wire is supported but can move in the magnetic field of a permanent magnet.

A deflecting torque is necessary for the deflection of the pointer. The deflecting torque is produced in a moving coil wound on a former placed inside the magnetic field when current passes through it. The expression for deflecting torque is given by

T = NIAB

Where

N = number of turns in the moving coil.
I = Current flowing in the moving coil.
A = Cross-sectional area of the coil
B = Flux density in the gap due to the permanent magnet.

Hence torque is directly proportional to the current flowing through the coil.

The material which we choose for making magnets should have high coercivity. The high coercivity ensures that magnetism in the material stays for a longer time.

As steel and alnico have high coercivity, therefore, they are used for making permanent magnets. The metals in Alnico magnets are indicated by the pairs of letters making up the name, Aluminum, Nickel, and Cobalt.