Search Previous Year Questions

The correct answer is option 2):(increase)

Concept:

Ferranti Effect:

• The effect in that the receiving end voltage is higher than sending end voltage in the long transmission line.
• It mainly occurs because of a light load or open circuit at the receiving end
• . It is due to the charging current of the line. When an alternating voltage is applied, the current that flows into the capacitor is called the charging current.
• The charging current increases in the line when the receiving end voltage of the line is larger than the sending end.

Method to Minimize Ferrant Effect:

• This voltage can be controlled by placing the shunt reactors at the receiving end of the lines
• A shunt reactor is an inductive current element connected between line and neutral to compensate for the capacitive current from transmission lines.
• When this effect occurs in long transmission lines, shunt reactors compensate the capacitive VAr of the lines and therefore the voltage is regulated within the prescribed limits.

Ferranti on long overhead lines can't be experienced

• when The line heavily loaded.
• The power factor is unity.

The correct answer is option 1):(AND Gate)

Concept:

Logic gates: It is an electric circuit, which works on simple Boolean algebra to perform a logical operation for one or more binary inputs that produce a single binary output.

AND Gate:

If both the inputs are high, it produces a high output.

It  performs the multiplication operation

The Boolean algebra for AND gate is X = A. B

The correct answer is option 1): Air friction

Concept:

• A Dynamometer wattmeter is an instrument commonly used for the measurement of DC as well as AC electric power.
• It works on the principle of a dynamometer i.e. a mechanical force acts between two current-carrying conductors
• The electrodynamometer wattmeter has a fixed coil divided into two parts and is connected in series with the load and caries the load current (I₁).
• The moving coil is connected across the load through a series multiplier resistance (R) and carries a current (I₂) proportional to the load voltage.
• The fixed coil is called as Current Coil and the moving coil is called as Potential Coil.
• The controlling torque is provided by two spiral springs.
• Air friction damping is provided in an electrodynamometer wattmeter. A pointer is attached to the moving coil

Concept:

The DC value or the average value of a waveform f(t) is given by the Area under the curve for one complete time period; i.e.,

\({f_{DC}} = \frac{1}{T}\mathop \smallint \nolimits_o^T f\left( t \right)dt\)

RMS value 'or' the effective value of an alternating quantity is calculated as:

\({V_{rms}} = \sqrt{\frac{1}{T}\mathop \smallint \limits_0^T {v^2}\left( t \right)dt} \)

For a Square wave 

If V_PK is the peak value then

RMS value = Average value = V_PK

The correct answer is option 4):(Low starting current)

Concept:

Comparison between double squirrel cage motor and round bar cage motor:

• A double cage rotor has a low starting current and high starting torque, therefore, it is more suitable for direct online starting
• Since the effective rotor resistance of a double cage motor is higher, there is larger rotor heating at the time of starting as compared to that of a single cage rotor
• The high resistance of the outer cage increases the resistance of the double cage motor, so full-load copper losses are raised, and efficiency is decreased
• The pull-out torque of double cage motor is smaller than single cage motor
• The cost of a double cage motor is about 20-30% more than that of a single cage motor of the same rating

Additional Information

• The rotor of a double squirrel cage motor has two independent cages on the same rotor. Bars of high resistance and low reactance are placed in the outer cage, and bars of low resistance and high reactance are placed in the inner cage.

The correct answer is option 4):C - Rate

Concept:

• The C-rate is the unit battery experts use to measure the speed at which a battery is fully charged or discharged.
• For example, charging at a C-rate of 1C means that the battery is charged from 0-100% in one hour.
• A C-rate higher than 1C means a faster charge
• For example, a 3C rate is three times faster, so a full charge in 20 minutes. Likewise, a lower C-rate means a slower charge: C/5 (or 0.2C) would be five times slower than 1C, amounting to a five-hour charge.
• It depends on the current density
• The amount of electrical current that goes through the battery is divided by the area of its layers.
• For a given C-rate, the current density will be a function of the loading of the cathode, which is closely related to its thickness.
• Thus, when comparing C-rates, it’s important to ensure the cathode loading is at commercially relevant levels: for EVs, this is typically in the range of 2.5-5 mAh/cm².

The correct answer option 3):(Self-excited generator)

Concept:

• A shunt generator is a type of electric generator in which field winding and armature winding are connected in parallel, and in which the armature supplies both the load current and the field current for the excitation (the generator is therefore self-excited)
• The following conditions must be satisfied for voltage build-up in a self-excited DC generator.
• There must be sufficient residual flux in the field poles.
• The field terminals should be connected in such a way that the field current increases flux in the direction of residual flux.
• The field circuit resistance should be less than the critical field circuit resistance.

Additional Information

​

The correct answer option 1): (Series area tapping method)

Concept:

The speed control method is used in small motors like food mixers, and fans can be done by connecting resistors in series to adjust the input current

The speed is inversely proportional to the armature current.

By Adjusting the input taps the speed can be controlled.

The correct answer is option 3):  Unbalanced coil

Concept:

An unbalanced winding has a combination of a number of poles and the number of slots that do not allow the arrangement of the coil in such a way that they produce a symmetrical system of equally time-phase displaced emf of identical magnitude, frequency, and waveform.

A 6-pole 9-slot winding has 3 winding symmetries and is balanced

A 6-pole 12-slot winding has also 3 winding symmetries but is unbalanced.

The number of slots = Q_s

The number of poles = P

For unbalanced winding:

\(\frac{Q_s}{3\cdot GCD\left( Q_s, \frac{p}{2} \right)} \mbox{ is not integer} \)

balanced winding:

\(\frac{Q_s}{3\cdot GCD\left( Q_s, \frac{p}{2} \right)} \mbox{ is integer} \)

The greatest common divisor (GCD) between the number of slots and the number of pole pairs indicates the number of winding symmetries.

The correct answer is option 3): (Weight of personnel/persons working in that area)

Concept:

The key steps in the design process are:

1. Identify the requirements. Measurement of the area where the light is to be provided.Area Requirement Study of Artificial Lighting
2. Determine the method of lighting.
3. Select the lighting equipment.
4. Calculate the lighting parameters and adjust the design as required. Manufacturer Data Sheet of Lamp
5. Determine the control system.
6. Choice of the luminaire.
7. Inspect the installation upon completion.

So option 3 is wrong