41 + Interview Questions in Design Of Current Transformers (Ct) in Design Of Electrical Machines Page 1 InterviewSolution

1.	How many factors are present in the behavior of transformer under short circuit conditions?(a) 2(b) 3(c) 4(d) 5I got this question in a national level competition.Question is taken from Turns Compensation in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right ANSWER is (b) 3 Easy explanation: There are 3 FACTORS present in the BEHAVIOR of the transformer under short circuit conditions. They are temperature rise, current density, mechanical FORCES.

Discussion

2.	What is the dimension of the round copper wire made use of in the windings of current transformer?(a) 3 cm^2(b) 3 mm^2(c) 3 m^2(d) 3 cmThis question was posed to me during an online interview.This is a very interesting question from Turns Compensation topic in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right answer is (B) 3 mm^2 For explanation I would say: 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 mm^2.

Discussion

3.	The phase angle error is significantly affected by the small change in secondary turns.(a) true(b) falseI had been asked this question in an internship interview.The query is from Turns Compensation in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct answer is (B) false To ELABORATE: 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.

Discussion

4.	What is the range of current density in the windings of the current transformer?(a) 1-3 A per mm^2(b) 2-3 A per mm^2(c) 1-2 A per mm^2(d) 0.5-2 A per mm^2I got this question in homework.Question is taken from Turns Compensation in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct ANSWER is (C) 1-2 A per mm^2 To elaborate: The MINIMUM VALUE of the current DENSITY in the windings I A per mm^2. The maximum value of the current density is 2 A per mm^2.

Discussion

5.	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 ratioI had been asked this question in exam.My enquiry is from Turns Compensation in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» RIGHT answer is (C) 1 or 2 less than the number such that the turns ratio is EQUAL to the nominal current ratio 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.

Discussion

6.	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 currentI had been asked this question in a job interview.My question is from Turns Compensation topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The CORRECT option is (c) ACTUAL ratio = turns ratio + LOAD current / secondary current Explanation: The turns ratio is FIRST calculated. NEXT the load current and secondary current is calculated and on substitution gives the actual ratio.

Discussion

7.	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 reducedI got this question in an online interview.I'm obligated to ask this question of Turns Compensation topic in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right choice is (d) the transformation RATIO is reduced Best 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.

Discussion

8.	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 errorThis question was addressed to me in class test.My enquiry is from Turns Compensation topic in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct option is (B) to reduce the RATIO error The explanation is: There are 2 TYPES of errors in the current transformer. The TURNS compensation is USED to reduce the ratio error.

Discussion

9.	What is the rating of the primary current in the current transformer?(a) 200 A(b) 300 A(c) 400 A(d) 500 AI got this question in an international level competition.Origin of the question is Design Principles topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct option is (d) 500 A The BEST I can explain: 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.

Discussion

10.	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 lowThe question was posed to me by my school principal while I was bunking the class.Question is from Design Principles topic in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» RIGHT ANSWER is (d) ratio of EXCITATION mmf to PRIMARY mmf should be low To elaborate: The primary CURRENT rating depends on exciting mmf and primary mmf. The ratio of the exciting mmf to the primary mmf should be low.

Discussion

11.	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 costI had been asked this question in an interview.The origin of the question is Design Principles topic in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct answer is (d) high voltages and high cost For explanation I WOULD say: 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.

Discussion

12.	What is the value of the rated secondary current?(a) 1 A(b) 2 A(c) 3 A(d) 5 AThis question was addressed to me in a job interview.My question is taken from Design Principles in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct CHOICE is (d) 5 A The best 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.

Discussion

13.	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 highI got this question in quiz.My query is from Design Principles in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct option is (a) LENGTH of the MAGNETIC path in core should be low For EXPLANATION: The length of the magnetic path in core should be as small as possible. This REDUCES the core reluctance of the current transformer.

Discussion

14.	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 sectionsI got this question in an interview for job.This key question is from Design Principles in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct answer is (c) RECTANGULAR strips or c-shaped sections The best 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.

Discussion

15.	The ring shaped cores are made use of in the reduction of the secondary winding leakage reactance and secondary impedance.(a) true(b) falseThis question was addressed to me in class test.I want to ask this question from Design Principles in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right option is (a) true The best I can explain: 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.

Discussion

16.	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 impedanceThe question was posed to me in an interview for internship.Query is from Design Principles in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct option is (a) secondary winding leakage REACTANCE is DIRECTLY proportional to the secondary CIRCUIT impedance The best 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.

Discussion

17.	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 coresThis question was posed to me in a job interview.Question is from Design Principles in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct choice is (a) MUMETAL CORES Easiest 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.

Discussion

18.	How many classifications are the magnetic alloys used in the current transformers classified into?(a) 3(b) 2(c) 4(d) 5The question was posed to me in an online interview.I need to ask this question from Design Principles in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct choice is (a) 3 Easiest 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.

Discussion

19.	To reduce the peak voltage between layers, the secondary winding is being sectionalized.(a) true(b) falseThe question was asked during an interview.Enquiry is from Current Transformers Construction in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct CHOICE is (a) true To elaborate: 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.

Discussion

20.	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 highThis question was addressed to me by my college professor while I was bunking the class.I want to ask this question from Design Principles topic in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The CORRECT ANSWER is (c) the exciting mmf is to be kept low The 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.

Discussion

21.	How many design principles are present in the current transformers?(a) 2(b) 3(c) 4(d) 5This question was addressed to me in unit test.Asked question is from Design Principles topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct choice is (d) 5 For explanation I would say: 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.

Discussion

22.	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 currentI had been asked this question in an interview.I would like to ask this question from Current Transformers Construction topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» RIGHT choice is (a) reluctance of the interleaved corner is directly proportional to the magnetizing CURRENT Easy 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.

Discussion

23.	The current transformers are assembled on to the secondary conductors “on site” for either permanent or temporary duty.(a) true(b) falseThis question was addressed to me in class test.I want to ask this question from Current Transformers Construction in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct answer is (b) false Best explanation: The current TRANSFORMERS are assembled on to the primary CONDUCTORS. They are assembled “on site” for the PERMANENT or temporary duty.

Discussion

24.	What is the other name of the ring type current transformer?(a) brush transformer(b) cloud transformer(c) circular transformer(d) bushing transformerI got this question in examination.I'm obligated to ask this question of Current Transformers Construction in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer»

Discussion

25.	How many faces are present in the split core current transformer?(a) 2(b) 3(c) 4(d) 5This question was posed to me in exam.The origin of the question is Current Transformers Construction topic in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct ANSWER is (a) 2 To EXPLAIN I would say: The split CORE transformer consists of a split core. The split half consists of 2 finely grounded or lapped gap FACES.

Discussion

26.	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 resinThe question was asked during an online interview.This intriguing question originated from Current Transformers Construction topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right option is (d) bakelized paper tube or resin For 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.

Discussion

27.	How many commonly used shapes of current transformer are present?(a) 1(b) 2(c) 3(d) 4The question was asked in an interview for internship.This key question is from Current Transformers Construction in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct option is (C) 3 To explain: The current transformers CONSIST of 3 commonly used shapes. They are STADIUM, CIRCULAR, RECTANGULAR orifices.

Discussion

28.	What is the insulation material used in the current transformer?(a) elephantide(b) presspahn(c) elephantide and presspahn(d) elephantide or presspahnI had been asked this question during an interview for a job.I'd like to ask this question from Current Transformers Construction topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right option is (d) elephantide or PRESSPAHN Easy explanation: The insulation in current TRANSFORMER is by means of end collars and circumferential WRAPS. The insulation MATERIAL used in elephantide or presspahn.

Discussion

29.	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 damageI have been asked this question in an online quiz.This intriguing question originated from Current Transformers Construction in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right option is (c) to protect secondary winding CONDUCTOR from mechanical damage The best 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.

Discussion

30.	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 ironThis question was addressed to me during an interview for a job.This is a very interesting question from Current Transformers Construction topic in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct choice is (b) hot rolled steels The explanation is: The current TRANSFORMER CONSISTS of stacks of LAMINATIONS. The LAMINATION used in the current transformer is hot rolled steel.

Discussion

31.	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 materialI had been asked this question in my homework.I want to ask this question from Current Transformers Construction in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» CORRECT choice is (b) PRIMARY WINDING consists of a BAR of suitable size and material The BEST 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.

Discussion

32.	How many types are the current transformers classified into?(a) 2(b) 3(c) 4(d) 5I have been asked this question in class test.This question is from Current Transformers Construction in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» RIGHT choice is (a) 2 For explanation: The CURRENT transformers are classified into 2 types. They are wound TYPE and bar type.

Discussion

33.	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 coreI got this question during an online interview.The above asked question is from Current Transformers Construction topic in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct answer is (b) PRIMARY winding having more than one full turn wound on CORE The best I can EXPLAIN: 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.

Discussion

34.	The ratio of active conductor section to total conductor section is called space factor.(a) true(b) falseI have been asked this question in class test.The query is from Errors topic in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Correct option is (a) true The EXPLANATION: The space factor is a TERM that is USED in the design of the magnet coils. It is the ratio of the active CONDUCTOR SECTION to the total conductor section.

Discussion

35.	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 * regulationThis question was posed to me by my school principal while I was bunking the class.Question is taken from Errors topic in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The CORRECT answer is (a) ratio error = turns ratio – REGULATION / regulation For explanation I would say: First the turns ratio is CALCULATED. NEXT the regulation of the current transformer is obtained and on substitution GIVES the ratio error.

Discussion

36.	How many types of errors are present in the current transformers?(a) 1(b) 2(c) 3(d) 4The question was posed to me during an interview.This is a very interesting question from Errors topic in section Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The CORRECT CHOICE is (B) 2 Explanation: There are 2 types of errors present in the current transformers. They are ratio error and phase ANGLE error.

Discussion

37.	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)I got this question by my college director while I was bunking the class.The doubt is from Errors in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer» RIGHT CHOICE is (a) phase angle of secondary load circuit = TAN^-1 * (reactance of the external burden/resistance of the external burden) The best I can explain: 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.

Discussion

38.	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)]I have been asked this question during an interview.I want to ask this question from Errors topic in portion Design of Current Transformers (CT) of Design of Electrical Machines
Answer»

Discussion

39.	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 relationshipThis question was addressed to me during an interview for a job.I'd like to ask this question from Errors topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right CHOICE is (a) the primary and SECONDARY windings are in exact RATIO and same phase relationship Explanation: The primary and secondary WINDING ratio are same. The phase relationship of the windings are also same.

Discussion

40.	How many classifications are present for the current transformers?(a) 1(b) 2(c) 3(d) 4The question was asked in an international level competition.My question is from Errors in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» Right choice is (B) 2 The BEST explanation: The current transformers is DIVIDED into 2 types. They are I) measuring current transformer and II) protective current transformer.

Discussion

41.	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 currentI had been asked this question in homework.This is a very interesting question from Errors in division Design of Current Transformers (CT) of Design of Electrical Machines
Answer» The correct CHOICE is (c) it is used for measuring high current The EXPLANATION is: For the measuring of high currents, the current transformer is MADE use of. The measured current is SCALED down to lower values equivalently.

Discussion

Explore topic-wise InterviewSolutions in .

How many factors are present in the behavior of transformer under short circuit conditions?(a) 2(b) 3(c) 4(d) 5I got this question in a national level competition.Question is taken from Turns Compensation in section Design of Current Transformers (CT) of Design of Electrical Machines

The phase angle error is significantly affected by the small change in secondary turns.(a) true(b) falseI had been asked this question in an internship interview.The query is from Turns Compensation in chapter Design of Current Transformers (CT) of Design of Electrical Machines

What is the rating of the primary current in the current transformer?(a) 200 A(b) 300 A(c) 400 A(d) 500 AI got this question in an international level competition.Origin of the question is Design Principles topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines

What is the value of the rated secondary current?(a) 1 A(b) 2 A(c) 3 A(d) 5 AThis question was addressed to me in a job interview.My question is taken from Design Principles in chapter Design of Current Transformers (CT) of Design of Electrical Machines

To reduce the peak voltage between layers, the secondary winding is being sectionalized.(a) true(b) falseThe question was asked during an interview.Enquiry is from Current Transformers Construction in section Design of Current Transformers (CT) of Design of Electrical Machines

How many design principles are present in the current transformers?(a) 2(b) 3(c) 4(d) 5This question was addressed to me in unit test.Asked question is from Design Principles topic in chapter Design of Current Transformers (CT) of Design of Electrical Machines

How many faces are present in the split core current transformer?(a) 2(b) 3(c) 4(d) 5This question was posed to me in exam.The origin of the question is Current Transformers Construction topic in portion Design of Current Transformers (CT) of Design of Electrical Machines

How many commonly used shapes of current transformer are present?(a) 1(b) 2(c) 3(d) 4The question was asked in an interview for internship.This key question is from Current Transformers Construction in division Design of Current Transformers (CT) of Design of Electrical Machines

How many types are the current transformers classified into?(a) 2(b) 3(c) 4(d) 5I have been asked this question in class test.This question is from Current Transformers Construction in chapter Design of Current Transformers (CT) of Design of Electrical Machines

The ratio of active conductor section to total conductor section is called space factor.(a) true(b) falseI have been asked this question in class test.The query is from Errors topic in portion Design of Current Transformers (CT) of Design of Electrical Machines

How many types of errors are present in the current transformers?(a) 1(b) 2(c) 3(d) 4The question was posed to me during an interview.This is a very interesting question from Errors topic in section Design of Current Transformers (CT) of Design of Electrical Machines

How many classifications are present for the current transformers?(a) 1(b) 2(c) 3(d) 4The question was asked in an international level competition.My question is from Errors in division Design of Current Transformers (CT) of Design of Electrical Machines