SSC JE electrical question paper 2019 with solution SET-2

Answer.3. Regenerative

Explanation:-

Regenerative Braking

Regenerative braking occurs whenever the speed of the motor is more than that of the synchronous speed. In this method, the motor runs as a generator, and the load is used to provide the required power to the supply. The main criterion for regenerative braking is that the speed of the motor becomes greater than the synchronous speed. This condition will lead to the motor acting as a generator and the direction of both the current and torque reversing. This method can be utilized where the load on the motor has very high inertia.

When the applied voltage to the motor is less than the back electromotive force (EMF), then both the armature current as well as armature torque reverses and the speed reduces. As generated EMF exceeds the applied voltage, the power transport takes place from the load to the supply.

Answer.1. Maximum Value/Average Value

Explanation:-

Form factor: The ratio of r.m.s (or effective) value to average value is the form factor (K_f) of the Waveform. It has used in voltage generation and instrument correction factors.

Peak factor: The ratio of maximum value to the r.m.s value is the peak factor (K_p) of the waveform.

Form Factor × Peak Factor =

$\begin{array}{l}\dfrac{{{\text{RMS Value}}}}{{{\text{Average Value}}}} \times \dfrac{{{\text{Maximum Value}}}}{{{\text{RMS Value}}}}\\\\\dfrac{{{\text{Maximum Value}}}}{{{\text{Average Value}}}}\end{array}$

Answer.3. AC transmission

Explanation:-

Skin Effect

The steady direct current distributes itself uniformly over the whole section of a conductor but the alternating current does not distribute uniformly rather than it tends to concentrate near the surface of a conductor. In fact in the AC system, no current flows through the core and the entire current is concentric at the surface regions. This phenomenon is called skin effect.

The skin effect causes the effective resistance of the conductor to increase with the frequency of the current. The skin effect is due to eddy currents set up by the AC current. The skin effect has practical consequences in the design of radiofrequency and microwave circuits and to some extent in AC electrical power transmission and distribution systems.

Answer.4. 1.8A, 1.2A

Explanation:-

Applying current divider rule for the given circuit in 20 ohm resistor

$\begin{array}{l}{I_1} = I\dfrac{{{{\rm{R}}_{\rm{2}}}}}{{{R_1} + {R_2}}}\;\\\\ = 3\dfrac{{30}}{{20 + 30}} = 1.8A\end{array}$

Now applying current divider rule in 30 ohm resistor

$\begin{array}{l}{I_2} = I\dfrac{{{{\rm{R}}_{\rm{1}}}}}{{{R_1} + {R_2}}}\;\\\\ = 3\dfrac{{20}}{{20 + 30}} = 1.2A\end{array}$

∴ I₁ = 1.8 A & I₂ = 1.2 A

Answer.3. Has zero internal resistance

Explanation:-

An ideal voltage source is the one in which all the three elements R, L, and C, are assumed to be negligible. Thus. the terminal voltage of an ideal voltage source is always equal to its internal e.m.f. Thus a voltage source having internal resistance (or impedance) zero is an ideal voltage source.

An ideal voltage source has the following characteristics:

1. It is a voltage generator whose output voltage remains absolutely constant whatever be the value of the output current.
2. It has zero internal resistance so that the voltage drop in the source is zero.
3. The power drawn by the source is zero.

Answer.2. 240

Explanation:-

No of disc required for 11 kV transmission line = 1 disc

Since the transmission line is 3-phase, therefore, the number of discs required for a single-pole will be 3.

Total no. of poles = 80

No of disc = 3 × 80 = 240

Answer.1. Universal motor

Explanation:-

The commutator is a feature of d.c motors. But a.c. motors having wound rotor with brushes and commutator arrangements, are called commutator motors that work on single-phase a.c. supply. The commutator arrangement present in these motors is similar to the armature of a d.c. motor.E.g. of single-phase commutator type induction motor is

1. Repulsion Motor
2. Repulsion-Induction Motor
3. AC Series Motor
4. Universal Motor

Universal motors with brushes and commutators have been designed to operate on either AC or DC power. For this type of motor, the stator’s windings are connected in series with the rotor windings through a commutator. The advantages of universal motors are high starting torque, compact size, and ability to run at high operating speed. The negative aspects include the short lifetime caused by the commutator and brushes and high noise and vibration. This type of motor is often used in applications where the motor only operates intermittently.

Universal motors generally run at high speeds, making them suitable in home appliances (e.g., vacuum cleaners and food mixers) and home power tools (e.g., electric drills) where single-phase wall plug-in power is abundant.

Answer.3. I_L = I_se = I_a

Explanation:-

When the field winding is connected in series with the armature winding while supplying the load then the generator is called a  series generator.

Current Relations

As all armature, field, and load are in series they carry the same current.

I_L = I_se = I_a

Answer.4. Saturation region, cut-off region

Explanation:-

The transistor is a three-terminal device. If it were to be used as an amplifier or a switch, it is supposed to be a two-port device. For a two-port device, four terminals are required. One port is referred to as an input port where the signals are fed into the network and the other port is the output port, where the response of the network is available. So, when a transistor is supposed to be used as a two-port network, one of the terminals of the transistor is made common between input and output.

• When both the junctions are forward biased, the transistor is said to be in the saturation region.
• When both the junctions are reverse biased, the transistor is in cut off region.
• When the emitter junction is forward biased and the collector junction is reverse biased, the transistor operates in active region.

If the circuit uses the Bipolar Transistor as a Switch, then the biasing of the transistor, either NPN or PNP is arranged to operate the transistor at both sides of the I-V characteristics curves. The areas of operation for a transistor switch are known as the Saturation Region and the Cut-off Region.

Answer.2. PMMC type

Explanation:-

PMMC instruments are used only to measure DC quantities and not AC quantities. This is because permanent magnets are used for creating magnetic fields. During the positive half, the pointer experiences a force in one direction, and in the negative half the pointer experiences the force in the opposite direction. Due to the inertia of the pointer, it retains it’s zero position.

In the PMMC type instrument, the deflection is directly proportional to the current flowing through the instrument, we get a uniform scale for the instrument. It gives a uniform scale of upto 270° or more.

T_d ∝ I