Ravi

transformer mcq

Transformer MCQ

Electrical Machines / By
Previous
Next
1. A transformer having 1000 primary turns is connected to a 250-V A.C. supply. For a secondary voltage of 400 V, the number of secondary voltage of 400V, the number of secondary turns should be
  1. 1600
  2. 250
  3. 400
  4. 1250

Answer: 1

2. A step –up transformer increases
  1. Voltage
  2. Current
  3. Power
  4. frequency

Answer: 1

3. The primary and secondary windings of an ordinary2-winding transformer always have
  1. Different number of turns
  2. Same size of copper wire
  3. A common magnetic circuit
  4. Separate magnetic circuit

Answer: 3

4. In a transformer, the leakage flux of each winding is proportional to the current in that winding becauseer always have
  1. Ohm’s law applies to magnetic circuits
  2. Leakage paths do not saturate
  3. The two windings are electrically isolated
  4. Mutual flux is confined to the core

Answer: 2

5. In a two-winding transformer, e.m.f. per turn secondary winding is always the induced e.m.f. per turn in primary
  1. Equal to k times
  2. Equal to 1/k times
  3. Equal to
  4. Greater than

Answer: 3

Related Posts :-

Transformer MCQ

Why we need Transformer

6. In relation to a transformer, the ratio 20:1 indicates that
  1. There are 20 turns on primary one turn on secondary
  2. Secondary voltage is 1/20thof primary voltage
  3. Primary current is 20 times greater than the secondary current
  4. For every 20 turns on primary, there is one turn on secondary

Answer: 4

7. In performing the short circuit test of a transformer
  1. High voltage side is usually short circuited
  2. Low voltage side is usually short circuited
  3. Any side is short circuited with preference
  4. None of the above

Answer: 2

8. The equivalent resistance of the primary of a transformer having k=5 and R1=0.1 ohm when referred to secondary becomes __ohm.
  1. 0.5
  2. 0.02
  3. 0.004
  4. 2.5

Answer: 4

9. A transformer has negative voltage regulation when its load power factor is
  1. Zero
  2. Unity
  3. Leading
  4. Lagging

Answer: 3

10. The primary reason why open circuit test is performed on the low-voltage winding of the transformer is that it.
  1. Draw sufficiently large no-load current for convenient
  2. Requires least voltage to perform the test
  3. Needs minimum power input
  4. Involves less core less

Answer: 1

My Youtube Channel

Electricalstuff4u

power system mcq

Power System MCQ

Power System / By
Previous
1. ACSR conductor have
  1. all conductors made of aluminium
  2. outer conductors made of aluminium
  3. inner conductor made of aluminium
  4. core made of aluminium

Answer: 2

2. If the frequency of a transmission system is changed from 50 Hz to 100 Hz, the string efficiency, will
  1. increase
  2. decrease
  3. remain unchanged
  4. may increase or decrease

Answer: 3

3. If the length of a transmission line is increased its capacitance will
  1. increase
  2. decrease
  3. remain same
  4. increase or decrease

Answer: 1

4. The line parameters are (a) Shunt reactance (b) Series reactance (c) Conductance (d) Resistance
  1. a and b
  2. a and c
  3. b,c and d
  4. a,b,c and d

Answer: 4

5. The skin effect does not depends on,
  1. nature of material
  2. size of wire
  3. supply frequency
  4. temperature

Answer: 4

Also Read

MCQ on Electrical Machines

MCQ on Transformer

6. For OH transmission line, the self GMD method is used to find
  1. Capacitance
  2. Inductance
  3. Both
  4. None

Answer: 4

7. ACSR conductor have the central core made of
  1. Copper
  2. Steel
  3. Aluminium
  4. Cadmium

Answer: 2

8. Which of the following conductor spirality effect is ignored
  1. Magnetic
  2. Non-magnetic
  3. Both
  4. None

Answer: 2

9. Highest transmission voltage in India
  1. 400 KV
  2. 450 KV
  3. 500 KV
  4. 750 KV

Answer: 4

10. If the height of transmission tower is increased,
  1. line capacitance increases and line inductance decreases
  2. line capacitance decreases and line inductance increases
  3. line capacitance remain same and line inductance decreases
  4. line capacitance decreases and line inductance remain same

Answer: 4

My Youtube Channel

Electrical Stuff 4u

power system mcq

Power System MCQ

Power System / By
Next
1. If the conductor diameter decreases, inductance of the line,
  1. increases
  2. decreases
  3. remaining same
  4. cannot be determined

Answer: 1

2. A conductor carries more current on the surface as compared to core. This is called as
  1. Permeability
  2. Corona effect
  3. Skin effect
  4. Unsymmetrical fault

Answer: 3

3. The inductance of a line is minimum when,
  1. GMD is high
  2. GMR is high
  3. GMD and GMR are high
  4. GMD is low and GMR is high

Answer: 4

4. The economic size of a conductor is determined by,
  1. Kelvin’s law
  2. Kirchoff’s law
  3. Faraday’s law
  4. All of the above

Answer: 1

5. Skin effect depends upon,
  1. Supply frequency
  2. Size of conductor
  3. Nature of material
  4. All of the above

Answer: 4

Also Read

What is Electrical Resistance

Electrical Energy

6. The DC resistance of conductor is less than AC resistance due to,
  1. Skin effect
  2. Proximity effect
  3. Both
  4. None

Answer: 3

7. For increasing the capacity of a transmission line, to transmit power,which of the following must be decreased.
  1. Voltage
  2. Line inductance
  3. Capacitance
  4. All

Answer: 2

8. Use of bundled conductor increases,
  1. GMR
  2. GMD
  3. Potential gradient
  4. Radius of conductor

Answer: 1

9. Which of the following is not a standard transmission voltage.
  1. 400 KV
  2. 11 KV
  3. 190 KV
  4. 750 KV

Answer: 3

10. The overall diameter ‘D’of a standard conductor is given in terms of diameter of each strand ‘d’ and no. of layers ‘n’ as,
  1. D = 2(n-1)d
  2. D = 2n-1/d
  3. D = 2(2n-1)d
  4. D = 2(n-D)d

Answer: 3

My Youtube Channel

Electrical Stuff 4U

electrical machines mcq

Electrical Machines MCQ

Electrical Machines / By
Previous
1. The normal value of the armature resistance of a D.C motor is
  1. 0.005
  2. 0.5
  3. 10
  4. 100

Answer: 2

2. The Eb/V Ratio of a D.C motor is an indication of its
  1. Efficiency
  2. Speed regulation
  3. Starting torque
  4. Running torque

Answer: 1

3. The mechanical power developed by the armature of a D.C. motor is equal to
  1. Armature current multiplied by back e.m.f.
  2. Power input minus losses
  3. Power output multiplied by efficiency
  4. Power output plus iron losses

Answer: 1

Transformer Installation

4. The induced e.m.f .in the armature conductors of a D.C. motor is
  1. Sinusoidal
  2. Trapezoidal
  3. Rectangular
  4. alternating

Answer: 1

5. D.C motor can be looked upon as D.C. generator with the power flow
  1. Reduced
  2. Reversed
  3. Increased  
  4. Modified

Answer: 2

Also Read

Basic Electrical MCQ

Why we need Transformer

6. In a D.C. motor, the mechanical output power actually comes from.
  1. Field system
  2. Air- gap flux
  3. Back e.m.f.
  4. Electrical input power

Answer: 4

7. The maximum torque of D.C. motor is limited by
  1. Commutation
  2. Heating
  3. Speed
  4. Armature current

Answer: 1

8. which of the following quantity maintains the same direction whether D.C. machine runs as a generator or as a motor?
  1. Induced e.m.f
  2. Armature current
  3. Field current         
  4. supply current

Answer: 1

9. Under constant load conditions, the speed of a D.C. motor is affected by
  1. Field flux               
  2. Armature current
  3. Back e.m.f.                     
  4. Both (b) and(c)

Answer: 1

10. It is possible to increases the field flux and, at the same time, increase the speed of a D.C. Motor provided its- is held constant
  1. Applied voltage
  2. Torque
  3. Armature circuit resistance                  
  4. Armature current

Answer: 4

11. The current drawn by a 120-v D.C Motor of armature resistance 0.5 ohm and back e.m.f 110 V is ________ amperer
  1. 20
  2. 240
  3. 220                  
  4. 5

Answer: 1

12. The shaft torque of D.C. motor is less than its armature torque because of _________________ losses
  1. Copper 
  2. Mechanical
  3. Iron                
  4. rotational

Answer: 4

My Youtube Channel

Electrical Stuff 4u

electrical machines mcq

Electrical Machines MCQ

Electrical Machines / By
Previous
Next
1. The external characteristic of a shunt generator can be obtained directly from its _____________ characterstics.
  1. internal
  2. open-circuit
  3. load saturation
  4. performance

Answer: 2

2. The slight curvature at the lower end of the O.C.C. of a self-excited dc generator is due to
  1. V and Ia
  2. E and Ia
  3. Eo and If
  4. V and If

Answer: 3

3. The voltage build up process of a d.c. generator is
  1. difficult
  2. delayed
  3. cumulative
  4. infinite

Answer: 3

4. For the voltage built up of a self excited d.c. generator, which of the following is not an essential condition?
  1. there must be some residual flux
  2. field winding mmf must aid the residual flux
  3. total field circuit resistance must be less than the critical value
  4. armature speed must be very high

Answer: 4

Also Read

Electrical Energy

Transformer MCQ

5. Which of the following d.c. generator cannot build up on open-circuit?
  1. shunt
  2. series
  3. short shunt
  4. long shunt

Answer: 2

6. If a self excited d.c. generator after being installed, fails to build up on its first trial run, the first thing to do is to
  1. increase the field resistance
  2. check armature insulation
  3. reverse field connections
  4. increase the speed of prime mover

Answer: 3

7. If residual magnetism of a shunt generator is destroyed accidentally, it may be restored by connecting its shunt field
  1. to earth
  2. to an a.c. source
  3. in reverse
  4. to a d.c. source

Answer: 4

8. An ideal d.c. generator is one that has _____________ voltage regulation.
  1. low
  2. zero
  3. positive
  4. negative

Answer: 2

9. The ____________ generator has poorest voltage regulation
  1. series
  2. shunt
  3. compound
  4. over compound

Answer: 1

10.The voltage regulation of an over compound d.c. generator is always ________
  1. positive
  2. negative
  3. zero
  4. high

Answer: 2

My Youtube Channel

Electrical Stuff 4u

electrical machines mcq

DC Machines MCQ

Electrical Machines / By
Next
1. The armature of DC machine is laminated in order to reduce
  1. hysteresis losses
  2. copper losses
  3. frictional losses
  4. eddy current losses

Answer: 4

2. The yoke of a DC machine is generally made of
  1. silicon steel
  2. cast steel
  3. soft iron
  4. cast steel

Answer: 4

3. If field current is decreased in shunt dc motor, the speed of the motor
  1. increases
  2. decreases
  3. remain same
  4. none of the above

Answer: 1
As a shunt field current If decreases, φ also decreases and the speed rises as speed is inversely proportional to flux

4. In Ward-Leonard system, the lower limit of the speed imposed by
  1. armature resistance
  2. field resistance
  3. residual magnetism of the generator
  4. none of the above

Answer: 3
In Ward-Leonard method of speed control, the lower limit of speed is imposed by residual magnetism of the generator.

Also Read

Resistance in series/parallel connection

Why we need Transformer

5. Ward-Leonard control is basically a _________________________ control method.
  1. armature resistance control
  2. field control
  3. armature voltage control
  4. field diverter control

Answer: 3
Ward-Leonard speed control method consists a motor with a constant excitation and applying a variable voltage to its armature to provide the required speed. Hence it is armature voltage control method.

6. In a DC Machine, the current flow in a armature circuit is
  1. pulsating DC
  2. pure DC
  3. AC
  4. none of the above

Answer: 3

7. As the armature reaction effect increases, the main flux of DC machine is
  1. increases
  2. decreases
  3. remain same
  4. none of the above

Answer: 2

8. In DC machines, slot wedges are generally made of
  1. cotton
  2. fibre
  3. impregnated paper
  4. silicon steel

Answer: 2

9. Eddy current loss will depends on
  1. flux density
  2. frequency
  3. thickness
  4. all of the above

Answer: 4

10. Hysteresis loss will depends on
  1. f
  2. f²
  3. f³
  4. f1.6

Answer: 1

My Youtube Channel

Electrical Stuff 4u

Resistance in Series/Parallel Connection

Basic Electrical / By

Resistance in Series:-

More than one resistances can be connected either in series or in parallel connections. Now if we connect two resistances end on end then they are said to be connected in series.  Let’s take an example: Consider three resistances R1 and R2 be connected in series as shown below:

Series Connection

Now Equivalent resistance of this circuit equals to the sum of individual resistances,let’s prove it now:
In series circuit
(1) Same current flows through each resistance.
(2) Voltage drop across each resistance is different.
(3) Net voltage drop applied across circuit equals the sum of all voltage drops across each resistance

Therefore Vs= V1 + V2 = IR1 + IR2

Since Vs= IR 
(R is the equivalent resistance of circuit)

Then      IR = IR1 + IR2
              IR = I (R1+R2)
Cancelling out I from both sides we get

                  R = R1 + R2

My Youtube Channel

Series & Parallel connections of resistor

Electrical Stuff 4u

Resistances in Parallel:-

As shown In below figure Resistances are said to be connected in Parallel connection.

In parallel circuit 
(1) Potential difference across all resistances is same.
(2) Current flowing through each resistance is different.
(3) Net current flowing through circuit is sum of three currents.


             I = t1 + t2 + t3  = V/r1 + V/r2 + V/r3

             Also I = V/R
where V is the voltage applied and R is the equivalent resistance of circuit

              So V/R =  V/r1 + V/r2 + V/r3

                    1/R = 1/r1 + 1/r2 + 1/r3

Also read:

Transformer MCQ

Why we need Transformer

What is Electrical Resistance? Definition and Units.

Uncategorized / By

Resistance is the property of a substance due to which it opposes the flow of electrons (current) through it.

It varies from substance to substance, some substance have low resistance like class A Metals like Silver, Copper and Aluminium. These metals offers very less resistance to flow of electricity through them when we applied potential difference(voltage) across them, so these metals are called good conductors of Electricity.

                                    Those substances which offer relatively greater resistance or hindrance to the flow of electrons through them are called poor conductor or one can say Insulators of electricity like bakelite, Mica, glass, rubber P.V.C. (polyvinyl chloride) and wood etc. These substances are bad conductor of electricity and does allow electric charge to flow through them.

Resistance is donated by symbol R.

Units of Resistance   

SI Unit of Resistance is ohm.

A conductor contain one ohm resistance if it permits one ampere current to flow through it when one volt of potential difference is applied across it.

Bigger units of Resistance are Mega-ohm = 10⁶ ohm , Kilo-ohm = 10³ohm used for insulators having high resistance.

Smaller Units are Milli-ohm = 10ˉ³ohm and Micro-ohm=10ˉ⁶ ohm used for good conductors having low resistance.

Symbol used to donate ohm is Ω.

Also Read:

Electrical Energy

Resistance Laws:-

Resistance R offered by a conductor depends on:

  1. R is directly proportional to length L of conductor.
  2. R is inversely proportional to cross sectional area A of the conductor.
  3. R depends on the nature of material.
  4. R depends on the nature of material.
  5. R also depends on the temperature of conductor.

Neglecting last two factor we get:-

R = ρΙ/A

Where ρ is constant called specific resistance or resistivity.

l is length of conductor.

A is cross sectional area of conductor.

If length l =1metre and area A= 1 metre² then R =ρ

Units of Resistivity

Since R = ρΙ/A

Then from above equation

ρ=AR/l = A metre² * R ohm/ l metre

ρ = ohm-metre

Hence Unit of resistivity is ohm-metre (Ω-m)

Also Visit My Youtube Channel

Electrical Stuff 4u

Electrical Energy

Basic Electrical / By

What is Electric Energy? Definition & Example

Definition

Electric Energy is the product of Electric Power taken by the device and the time period.

Equation

Electric Energy = Electric Power(Watt) * Time(Hour)

Units

It is measured in Watt-Hour. As Electric Power is measured in Watt and Time is measured in Hour, So Product of Power(Watt) and Time(Hour) is Watt-Hour.

1 Watt-Hour equals to 1 Watt of Power released for 1 Hour. In terms of Joules 1 Watt-Hour equals to 3600 Joules (3.6*10³ Joules) of Energy. Mostly Joule is used as unit of Energy Except Electrical Energy.


Used to Measure Electricity Bill 

Since In Asia Electricity Bill is generated by computing No. of Units consumed by the consumer, then multiplying the same with the tariff or rate of one Unit. Unit is calculated with the help of Electric Energy Meter installed at the premises of Consumer.

Let’s take an Example

Consider A consumer consumes 100 Units of Energy. The tariff rate at their area is 5 rupees per unit. What is their Electricity Bill?

Solution : Here No. of Units = 100

                 Rate of one Unit   = 5

                 Electricity Bill = 100*5 = 500 rupees Answer

Now the Question rises How much one Unit Equals to?

So The answer is One Unit equals to 1 KWH  which is unit of Electric Energy, 

One KWH equals to 1 KW of Power drawn by the device during one hour.

Also Read:

Basic Electrical MCQ

Why we need Transformer?


Example

If A 100 W Bulb glows for 10 Hours then How much Units does it Consume?

Solution: Here Power = 100 W

                         Time  = 10 H

So Electrical Energy  = 100*10 = 1000 W-H

1000W-H = 1 KWH = 1 Unit

So If A 100 W Bulb glows or 10 Hours then it consumes 1 Unit, Similarly if it glows for 20 Hours then it consumes 2 Unit.

In a similar fashion we can Calculate Units consumed by different devices used at home and then calculate our Electricity Bill. 

Also Visit my Youtube Channel for electrical videos

Electrical Stuff 4u

power system mcq

Electric Power

Basic Electrical / By

Electric power is basically amount of Electric Energy used in a particular span of time. It is measured in watts.

Electric Power (watts) = Electrical Energy (Joule)/Time (Second)

Ø  If a device consume 1 Joule of energy in one second then power is 1 Watt.

As Power = 1 (joule)/1 (second) =1 Watt

So it’s clear Power is measure of energy per unit time like a second, it’s better to say Watt rather than joule/second.

Another definition:

Electric Power is product of Voltage (V) supplied to a device and Current(A) drawn by the device.

Electric Power (watts) = Voltage * Current

P = V*I

Let’s take an Example:-

·         Consider a Motor is feed with 220V supply and it draws 10A of load then what is Power of Motor?

Solution: Here Voltage (V) = 220V

                            Current (I) = 10A

                So Power = V*I

                                   = 220*10   = 2200 Watt

Since 1 KW = 1000W

Then 2200 Watt = 2200/1000 = 2.2KW

So Motor Power= 2.2KW Answer

Also Read

Why we need Transformer?

Transformer MCQ

Also Visit my Youtube Channel for electrical videos

Electrical Stuff 4U