WBSETCL Junior Engineer Electrical Grade II 14th March 2022 First Shift Solution

WBSETCL Junior Engineer Electrical Grade II

WBSETCL Junior Engineer Electrical Grade II 14th March 2022 First Shift Solution PDF

Question : 1

A room of 12 m length and 10 m breadth is lighted by 15 lamps to a fairly uniform illumination of 100 Im/m². Calculate the utilisation coefficient of the room given that the output of each lamp is 1600 lumens.

A. 80%

B. 60%

C. 90%

D. 50%

Answer-D

Solution

Given A = 12 m × 10 m

Total lamps = 15 lamps

Each lamp output = 1600 lumens

Illumination E = 100 lm/m²

Total lumens reaching the working plane = 100 × 12 × 10 =12000 lumen

Total lumen emitting from source = 1600 × 15 = 24000 lumen
Utilization Coefficient=total lumens reaching the working plane/total lumens emitting from source

Utilization Coefficient=12000/24000 = 0.5 or 50%

WBSETCL Junior Engineer Electrical Grade II

Question : 8

How many elements are joined to a principal node?

A. None

B. Three or more

C. One

D. Two

Answer-B

Solution:

There are two types of nodes

Simple node-A simple node connect 2 elements.

Principal node-It connect more than 2 elements.

WBSETCL Junior Engineer Electrical Grade II

Question : 10

Find the force (F in Newton) between two point-source charges (Q₁ and Q₂) in Coulomb) in air when the distance between the charges is d in metre.

Answer-A

Solution:

Coulomb’s law-It states that the magnitude of the electrostatic force F between two point charges D₁ and D₂ is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance d between them.

Question : 11

Which of the following instruments is used to measure the air gap between the rotor and stator of the starter motor?

A. Dial caliper

B. Tapper gauge

C. Vernier caliper

D. Feeler gauge

Answer-D

Solution:

A feeler gauge is a tool used to measure gap widths.

They consist of a number of small lengths of steel of different thicknesses with measurements marked on each piece.

Feeler gauge is used to measure the air gap between the rotor and stator of the starter motor.

WBSETCL Junior Engineer Electrical Grade II

Question : 12

What happens to the diversity factor in the case of an interconnected Grid System?

A. No effect on diversity factor

B. Diversity factor decreases

C. Diversity factor tends to infinity

D. Diversity factor increases

Answer-D

Solution:

Interconnected grid system-The connection of several generating stations in parallel is known as interconnected grid system.

Interconnected grid Advantages

1.Exchange of peak loads.
2.Ensures economical operation.
3.Increases diversity factor.
4.Reduces plant reserve capacity.
The grid system can improve the diversity factor of each generating station connected to the grid. The diversity factor gets improved because the maximum demand of the grid shared by the generating station is much lesser than the maximum demand imposed on the generating station if it runs individually.

Question : 13

A. Schottky Diode

B. Zener Diode

C. Tunnel Diode

D. Varactor Diode

Answer-B

Solution:

A heavily doped semiconductor diode which is designed to operate in reverse direction is known as the Zener diode.

The diode which is specially designed for optimising the breakdown region is known as the Zener diode.

The symbolic representation of Zener diode is shown in the figure below.

WBSETCL Junior Engineer Electrical Grade II

Question : 57

Which of the following is a non-conventional source of energy?

A. Biogas

B. Uranium

C. Natural gas

D. Petroleum

Answer-A

Solution:

Non-conventional sources of energy are the energy sources which are continuously replenished by natural processes. These cannot be exhausted easily, can be generated constantly so can be used again and again, e.g. solar energy, wind energy, tidal energy, biomass energy and geothermal energy etc.

Conventional sources of energy	Non-conventional sources of energy
These sources of energy are not abundant, present in limited quantity, e.g. coal, petroleum, natural gas.	These sources of energy are abundant in nature, e.g. solar energy, wind energy, tidal energy, biogas from biomass etc.
They have been in use for a long time.	They are yet in development phase over the past few years.
They are not replenished continuously. They are formed over a million years.	They are replenished continuously by natural processes.
They are called non-renewable sources of energy.	They are called renewable sources of energy.
They can be exhausted completely due to over-consumption except for hydel power.	They cannot be exhausted completely.
WBSETCL Junior Engineer Electrical Grade II
They pollute the environment by emitting harmful gases and also contribute to global warming.	They are environment-friendly, do not pollute the environment.
They are commonly used for industrial and commercial purposes.	They are used commonly used for household purposes.
Heavy expenditure is involved in using and maintaining these sources of energy.	Using these sources is less expensive.
They are used extensively, at a higher rate than the non-conventional sources.	They are not used as extensively as conventional sources.

WBSETCL Junior Engineer Electrical Grade II

Question : 58

Which of the following is NOT true for the Core type transformer?

A. It has a single magnetic circuit.

B. Coils used are multilayer disc type or sandwich type.

C. Coils are wound in helical layers with different layers, insulated from each other on two limbs.

D. A core is rectangular in the shape of a uniform cross-section. It consists of two vertical limbs and the horizontal yokes connecting two limbs.

Answer-B

Solution:

In core type transformer coils used are Concentric Winding or Cylindrical Winding.

WBSETCL Junior Engineer Electrical Grade II

Basis for Comparison	Core Type Transformer	Shell Type Transformer
Definition	The winding surround the core.	The core surround the winding.
Lamination Shape	The lamination is cut in the form of the L strips.	Lamination are cut in the form of the long strips of E and L.
Cross Section	Cross-section may be square, cruciform and three stepped	The cross section is rectangular in shape.
Copper Require	More	Less
WBSETCL Junior Engineer Electrical Grade II
Coils	Concentric Winding or Cylindrical Winding.	Sandwich or Disc Winding
Limb	Two	Three
Insulation	More	Less
Flux	The flux is equally distributed on the side limbs of the core.	Central limb carry the whole flux and side limbs carries the half of the flux.
Winding	The primary and secondary winding are placed on the side limbs.	Primary and secondary windings are placed on the central limb
Magnetic Circuit	Two	One
Losses	More	Less
Maintenance	Easy	Difficult
Mechanical Strength	Low	High
Output	Less	High
Natural Cooling	Does not Exist	Exist

Salient pole rotor	Cylindrical rotor
Large diameter and short axial length	Small diameter and long axial length
used for low-speed alternators	Used for high-speed turbo alternators
Has no projecting poles	Has no projecting poles
Needs damper windings	Do not need damper windings
Windage loss is more	Windage loss is less

Slip ring induction motor	Squirrel cage induction motor
It has a slip ring type rotor	It has a squirrel cage type rotor
Cylindrical laminated core with parallel slots and each slot consist one bar	The slots of the rotor are not parallel but are skewed
Construction is complicated	Construction is simple
We can add external resistance to the rotor	The rotor bar is permanently shorted at the end of the ring; thus, it is not possible to add any external resistance
The rotor resistance starter can be used	Rotor resistance starter cannot be used
Starting torque is high	Starting torque is low
Brushes are present	Brushes are absent
The air gap between the stator and rotor is non-uniform.	The air gap between the stator and rotor is uniform.
Frequent maintenance is required	Less maintenance required
The power factor is low	Power factor is high
Speed control is possible	Speed control is not possible

	Class of task	Recommended foot candles
1	Precision work to a high degree of accuracy, tasks requiring rapid discrimination and response	100
2	Severe and prolonged visual tasks, such as fine engraving, and discrimination and inspection of fine details of low contrast.	50
3	Prolonged critical tasks, such as proof reading, type-setting, drawing, fine machine work, fine assembling, sewing on dark goods.	25
	WBSETCL Junior Engineer Electrical Grade II
4	Visual tasks, such as detailed office work, reading, skilled bench work, sewing on light goods, and retail shops.	15
5	Less exacting visual tasks such as in general offices, on large assembly work and in class rooms.	10
6	Work of simple character not involving attention to details	6
7	Casual observation where no specific task is performed	4

WBSETCL Junior Engineer Electrical Grade II 14th March 2022 First Shift Solution