Design Of Electrical Machines MCQs – Design of Current Transformers (CT) MCQs ( Design Of Electrical Machines ) MCQs
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Design Of Electrical Machines MCQs – Design of Current Transformers (CT) MCQs ( Design Of Electrical Machines ) MCQs
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Errors
1. What is the definition of current transformer?
a) it is used for measuring high voltage
b) it is used for measuring low voltage
c) it is used for measuring high current
d) it is used for measuring low current
Answer: c
Explanation: For the measuring of high currents, the current transformer is made use of. The measured current is scaled down to lower values equivalently.
2. How many classifications are present for the current transformers?
a) 1
b) 2
c) 3
d) 4
Answer: b
Explanation: The current transformers is divided into 2 types. They are I) measuring current transformer and II) protective current transformer.
3. What is the definition of the ideal current transformer?
a) the primary and secondary windings are in exact ratio and same phase relationship
b) the primary winding and secondary winding ratio is greater than 1 and same phase relationship
c) the primary and secondary winding ratio is lesser than 1 are in exact ratio and different phase relationship
d) the primary and secondary windings ratio is greater than 1 and different phase relationship
Answer: a
Explanation: The primary and secondary winding ratio are same. The phase relationship of the windings are also same.
4. How many types of errors are present in the current transformers?
a) 1
b) 2
c) 3
d) 4
Answer: b
Explanation: There are 2 types of errors present in the current transformers. They are ratio error and phase angle error.
5. What is the formula of the angle between secondary induced voltage and secondary current?
a) phase angle = tan-1 *[(reactance of the secondary winding – reactance of the external burden) / (resistance of the secondary winding + resistance of the external burden)]
b) phase angle = tan-1 *[(reactance of the secondary winding – reactance of the external burden) / (resistance of the secondary winding – resistance of the external burden)]
c) phase angle = tan-1 *[(reactance of the secondary winding * reactance of the external burden) / (resistance of the secondary winding + resistance of the external burden)]
d) phase angle = tan-1 *[(reactance of the secondary winding + reactance of the external burden) / (resistance of the secondary winding + resistance of the external burden)]
Answer: d
Explanation: The reactance of the secondary windings and the external burden is first calculated. Next, the resistance of the secondary windings and external burden is calculated and on substitution gives the value of the phase angle.
6. What is the formula of the phase angle of the secondary load circuit?
a) phase angle of secondary load circuit = tan-1 * (reactance of the external burden/resistance of the external burden)
b) phase angle of secondary load circuit = tan-1 * (reactance of the external burden + resistance of the external burden)
c) phase angle of secondary load circuit = tan-1 * (reactance of the external burden – resistance of the external burden)
d) phase angle of secondary load circuit = tan-1 * (reactance of the external burden * resistance of the external burden)
Answer: a
Explanation: The reactance and resistance of the external burden is first calculated. Next, the value is taken tan inverse to obtain the phase angle of secondary load circuit.
7. What is the formula of the ratio error in the current transformers?
a) ratio error = turns ratio – regulation / regulation
b) ratio error = turns ratio + regulation / regulation
c) ratio error = turns ratio * regulation / regulation
d) ratio error = 1 / turns ratio * regulation
Answer: a
Explanation: First the turns ratio is calculated. Next the regulation of the current transformer is obtained and on substitution gives the ratio error.
8. The ratio of active conductor section to total conductor section is called space factor.
a) true
b) false
Answer: a
Explanation: The space factor is a term that is used in the d
Current Transformers Construction
1. How many types are the current transformers classified into?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: The current transformers are classified into 2 types. They are wound type and bar type.
2. What is the wound type current transformer?
a) primary winding having one full turn wound on core
b) primary winding having more than one full turn wound on core
c) secondary winding having one full turn wound on core
d) secondary winding having more than one full turn wound on core
Answer: b
Explanation: The wound type current transformer is one of the classifications of the current transformers. The primary winding has more than one full turn wound on core.
3. What is the bar type current transformer?
a) primary winding consists of a rod of suitable size and material
b) primary winding consists of a bar of suitable size and material
c) secondary winding consists of a rod of suitable size and material
d) secondary winding consists of a bar of suitable size and material
Answer: b
Explanation: The bar type current transformer is one of the classifications of the current transformers. In bar type winding, primary winding consists of a bar of suitable size and material.
4. How many commonly used shapes of current transformer are present?
a) 1
b) 2
c) 3
d) 4
Answer: c
Explanation: The current transformers consist of 3 commonly used shapes. They are stadium, circular, rectangular orifices.
5. What material is made use of for the lamination in the current transformer?
a) cold rolled steels
b) hot rolled steels
c) copper
d) hot iron
Answer: b
Explanation: The current transformer consists of stacks of laminations. The lamination used in the current transformer is hot rolled steel.
6. What is the insulation material used in the current transformer?
a) elephantide
b) presspahn
c) elephantide and presspahn
d) elephantide or presspahn
Answer: d
Explanation: The insulation in current transformer is by means of end collars and circumferential wraps. The insulation material used in elephantide or presspahn.
7. What is the additional usage of the presspahn material used as insulation material?
a) lamination
b) to reduce the losses
c) to protect secondary winding conductor from mechanical damage
d) to protect secondary winding conductor from electrical damage
Answer: c
Explanation: The presspahn is used as insulating material in the current transformer. In addition to that the presspahn is also used to protect the secondary winding conductor from mechanical damage.
8. What is the other name of the ring type current transformer?
a) brush transformer
b) cloud transformer
c) circular transformer
d) bushing transformer
Answer: d
Explanation: The ring type current transformer is one type of current transformer. It is also known as the bushing transformer.
9. How many faces are present in the split core current transformer?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: The split core transformer consists of a split core. The split half consists of 2 finely grounded or lapped gap faces.
10. The current transformers are assembled on to the secondary conductors “on site” for either permanent or temporary duty.
a) true
b) false
Answer: b
Explanation: The current transformers are assembled on to the primary conductors. They are assembled “on site” for the permanent or temporary duty.
11. What is the insulation material on the primary conductor?
a) bakelized paper tube
b) resin
c) bakelized paper tube and resin
d) bakelized paper tube or resin
Answer: d
Explanation: The insulation material on the primary conductors is generally made up of the bakelized paper tube. It can also be made use of resin directly moulded on the bar.
12. How is the reluctance of the interleaved corner related with the magnetizing current?
a) reluctance of the interleaved corner is directly proportional to the magnetizing current
b) reluctance of the interleaved corner is indirectly proportional to the magnetizing current
c) reluctance of the interleaved corner is directly proportional to the square of the magnetizing current
d) reluctance of the interleaved corner is indirectly proportional to the square of the magnetizing current
Answer: a
Explanation: The reluctance of the interleaved corner is directly proportional to the magnetizing current. As the reluctance is being reduced it in turn reduces the magnetizing current.
13. To reduce the peak voltage between layers, the secondary winding is being sectionalized.
a) true
b) false
Answer: a
Explanation: The large number of secondary turns requiring more than 1 winding layer, the secondary winding is sectionalized. This is because to reduce the peak voltage between layers.
Design Principles
1. How many design principles are present in the current transformers?
a) 2
b) 3
c) 4
d) 5
Answer: d
Explanation: There are 5 design principles present in the current transformers. They are core design, secondary current rating, primary current rating, windings and behavior of the transformer under short circuit current.
Aspects Of Designs Of Mechanical Parts MCQs
2. What should be done in order to reduce the errors in the core?
a) armature mmf is to kept low
b) field mmf to be kept high
c) the exciting mmf is to be kept low
d) the field mmf is to be kept high
Answer: c
Explanation: The errors in the core are reduced by keeping the exciting mmf low. This can take place with the core having a low reluctance and low iron loss.
3. How many classifications are the magnetic alloys used in the current transformers classified into?
a) 3
b) 2
c) 4
d) 5
Answer: a
Explanation: The magnetic alloys used in the current transformers are divided into 3 types. They are hot rolled silicon steel, cold rolled grain oriented silicon steel and nickel iron alloys.
4. What is the material used in the transformer when the transformer errors should be small?
a) mumetal cores
b) steel cores
c) permender cores
d) presshamn cores
Answer: a
Explanation: The mumetal cores are commonly used when it is essential that transformer errors shall be small. Mumetal has the properties of high permeability, low loss and small retentivity.
5. What is the relation of the secondary winding leakage reactance and secondary circuit impedance?
a) secondary winding leakage reactance is directly proportional to the secondary circuit impedance
b) secondary winding leakage reactance is indirectly proportional to the secondary circuit impedance
c) secondary winding leakage reactance is directly proportional to the square of the secondary circuit impedance
d) secondary winding leakage reactance is indirectly proportional to the square of the secondary circuit impedance
Answer: a
Explanation: The secondary winding leakage reactance is directly proportional to the secondary circuit impedance. In secondary winding the leakage reactance is reduced and in turn the secondary circuit impedance is reduced.
6. The ring shaped cores are made use of in the reduction of the secondary winding leakage reactance and secondary impedance.
a) true
b) false
Answer: a
Explanation: The secondary winding leakage reactance is directly proportional to the secondary impedance. The ring shaped cores around which the toroidal secondary windings of one or more layers are uniformly distributed.
7. What type of core is employed when the performance standard required is not so high?
a) rectangular strips
b) c-shaped sections
c) rectangular strips or c-shaped sections
d) rectangular strips and c-shaped sections
Answer: c
Explanation: Ring core type is used only for the high performance operation. The rectangular strips or c-shaped sections are used when the standard of performance required is not so high.
8. What should the magnetic path be in order to reduce the core reluctance?
a) length of the magnetic path in core should be low
b) length of the magnetic path in core should be medium
c) length of the magnetic path in core should be high
d) length of the magnetic path in core should be very high
Answer: a
Explanation: The length of the magnetic path in core should be as small as possible. This reduces the core reluctance of the current transformer.
9. What is the value of the rated secondary current?
a) 1 A
b) 2 A
c) 3 A
d) 5 A
Answer: d
Explanation: The rating of the secondary current is the maximum current that can be passed through the secondary windings. It is 5 A for the current transformer.
10. What are the disadvantages of the low rated secondary current transformer?
a) high cost
b) high voltages
c) high voltages or high cost
d) high voltages and high cost
Answer: d
Explanation: When there is a low secondary current rating in the current transformers they produces high voltages if the secondary is left open. It is also costly to produce the windings because of the extra time involved in the making.
11. What is the ideal condition with respect to the primary current rating?
a) ratio of secondary mmf to primary mmf should be high
b) ratio of secondary mmf to primary mmf should be low
c) ratio of excitation mmf to primary mmf should be high
d) ratio of excitation mmf to primary mmf should be low
Answer: d
Explanation: The primary current rating depends on exciting mmf and primary mmf. The ratio of the exciting mmf to the primary mmf should be low.
12. What is the rating of the primary current in the current transformer?
a) 200 A
b) 300 A
c) 400 A
d) 500 A
Answer: d
Explanation: The rating of the primary current is minimum 500 A. If the rating is less than 500 A, then multiturn primary windings and rating is above than 500 A, then single turn winding is enough.
Turns Compensation
1. What is the use of the turns compensation in current transformer?
a) to increases the ratio error
b) to reduce the ratio error
c) to increase the phase angle error
d) to reduce the phase angle error
Answer: b
Explanation: There are 2 types of errors in the current transformer. The turns compensation is used to reduce the ratio error.
2. What is the formula of the actual ratio?
a) actual ratio = turns ratio + load current * secondary current
b) actual ratio = turns ratio * load current * secondary current
c) actual ratio = turns ratio + load current / secondary current
d) actual ratio = turns ratio / load current * secondary current
Answer: c
Explanation: The turns ratio is first calculated. Next the load current and secondary current is calculated and on substitution gives the actual ratio.
3. What happens if the number of secondary turns is reduced?
a) the primary turns is reduced
b) the output is reduced
c) the efficiency is reduced
d) the transformation ratio is reduced
Answer: d
Explanation: The reduction of the number of secondary turns reduces the transformation ratio. If the number of secondary turns reduces by 1 percent the actual transformation ratio reduces by equal percentage.
4. What is the best number of secondary turns of the current transformer?
a) 1
b) 2
c) 1 or 2 less than the number such that the turns ratio is equal to the nominal current ratio
d) 1 or 2 more than the number such that the turns ratio is equal to the nominal current ratio
Answer: c
Explanation: The best number of secondary turns of the current transformer is 1 or 2 less than the number such that the turns ratio is equal to the nominal current ratio. For example in a 1000/5 current transformer, the secondary turns number would be 198 or 199 rather than 200.
5. The phase angle error is significantly affected by the small change in secondary turns.
a) true
b) false
Answer: b
Explanation: There are 2 types of errors which is the ratio error and phase angle error. The phase angle error is not significantly effected by a small change in secondary turns.
6. What is the dimension of the round copper wire made use of in the windings of current transformer?
a) 3 cm2
b) 3 mm2
c) 3 m2
d) 3 cm
Answer: b
Explanation: Copper strip is used for primary windings. The dimension of the round copper wire made use of in the windings of current transformer is 3 mm2.
7. What is the range of current density in the windings of the current transformer?
a) 1-3 A per mm2
b) 2-3 A per mm2
c) 1-2 A per mm2
d) 0.5-2 A per mm2
Answer: c
Explanation: The minimum value of the current density in the windings I A per mm2. The maximum value of the current density is 2 A per mm2.
8. How many factors are present in the behavior of transformer under short circuit conditions?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: There are 3 factors present in the behavior of the transformer under short circuit conditions. They are temperature rise, current density, mechanical forces.