Electrical Machine Design — Part 1 MCQs with Explanations

The insulation between windings and the grounded core, as well as the insulation between the windings of the same phase, is referred to as major insulation . Major insulation is designed to withstand higher voltage stresses as it separates the high-voltage components from the grounded core and ensures the safety and reliability of the electrical machine. In contrast, minor insulation is used for low voltage insulation, such as between adjacent turns in a winding, where the voltage stress is comparatively low. Therefore, Option B is the correct answer.

Copper is universally used for windings of electrical machines due to several reasons: 1. Easily workable: Copper is a highly malleable and ductile metal, making it easy to form into wires and windings without the risk of fracturing. 2. Conductivity: Copper has excellent electrical conductivity, which is crucial for efficient energy transfer and reducing losses in electrical machines. 3. Thermal properties: Copper has good thermal conductivity, allowing it to dissipate heat effectively, which is important for maintaining the temperature of electrical windings. Option A: Fracture is incorrect because copper does not fracture easily due to its ductility. Option B: Silver is incorrect because while silver is highly conductive, it is not commonly used in electrical machines due to its high cost. Option C: Steel is incorrect because steel is not as conductive as copper and is less suitable for electrical windings. Option D: Aluminium is incorrect because although aluminum is used in some applications, copper is preferred in electrical machines due to its superior conductivity and other properties. Therefore, the correct answer is Copper .

better ventilation is the correct answer to “D.C. machines designed with a large value of air gap length have”. This question is standard in competitive examination syllabi for Electrical Machine Design.

Portative is the correct answer to “_________ electromagnets generally function as holding magnets.”. This question is standard in competitive examination syllabi for Electrical Machine Design.

All of the above is the correct answer to “By which of the following methods motor rating for variable load drives can be determined”. This question is standard in competitive examination syllabi for Electrical Machine Design.

hollow is the correct answer to “In direct cooled system using hydrogen both stator and rotor conductors are made”. This question is standard in competitive examination syllabi for Electrical Machine Design.

All of the above is the correct answer to “On which of the following variables heat convected depends”. This question is standard in competitive examination syllabi for Electrical Machine Design.

induction instrument is the correct answer to “An instrument transformer is used to extend the range of”. This question is standard in competitive examination syllabi for Electrical Machine Design.

All of the above is the correct answer to “The value of exciting or magnetizing current depends upon which of the following factors”. This question is standard in competitive examination syllabi for Electrical Machine Design.

All of the above is the correct answer to “The voltage control in electric supply networks in required on account of which of the following reasons”. This question is standard in competitive examination syllabi for Electrical Machine Design.

by pass the current is the correct answer to “The function of shunt in an ammeter is to”. This question is standard in competitive examination syllabi for Electrical Machine Design.

Drysdale potentiometer is the correct answer to “A phase shifting transformer is used in conjunction with”. This question is standard in competitive examination syllabi for Electrical Machine Design.

increase is the correct answer to “The weight of copper of both armature and field windings decreases with _____ in number of poles.”. This question is standard in competitive examination syllabi for Electrical Machine Design.

Indicating instruments is the correct answer to “Which of the following instruments indicate the instantaneous value of the electrical quantity being measured at the time at which it is being measured”. This question is standard in competitive examination syllabi for Electrical Machine Design.

bus-bars is the correct answer to “In Weston synchronoscope the moving coil is connected across”. This question is standard in competitive examination syllabi for Electrical Machine Design.

Forced winding is the correct answer to “The winding where dummy coils are used is sometimes called”. This question is standard in competitive examination syllabi for Electrical Machine Design.

Any of the above is the correct answer to “By which of the following methods the temperature rise of windings and other parts may be determined”. This question is standard in competitive examination syllabi for Electrical Machine Design.

120° is the correct answer to “In a dynamometer 3-phase power factor meter, the planes of the two moving coils are at”. This question is standard in competitive examination syllabi for Electrical Machine Design.

200 MW is the correct answer to “With conventional hydrogen cooling it is possible to increase the rating of a single unit to”. This question is standard in competitive examination syllabi for Electrical Machine Design.

All of the above is the correct answer to “Which of the following is the commonly used type of electromagnets”. This question is standard in competitive examination syllabi for Electrical Machine Design.

hydrogen is the correct answer to “The noise produced by a ______ cooled machine is less as the rotor moves in a medium of smaller density.”. This question is standard in competitive examination syllabi for Electrical Machine Design.

10° is the correct answer to “If the current in a capacitor leads the voltage by 80°, the loss angle of the capacitor is”. This question is standard in competitive examination syllabi for Electrical Machine Design.

0.5 is the correct answer to “In a 3-phase power measurement by two wattmeter method the reading of one of the wattmeter was zero. The power factor of the load must be”. This question is standard in competitive examination syllabi for Electrical Machine Design.

moving iron instrument is the correct answer to “Wattmeter cannot be designed on the principle of”. This question is standard in competitive examination syllabi for Electrical Machine Design.

not necessary to standardise the potentiometer is the correct answer to “To measure a resistance with the help of a potentiometer it is”. This question is standard in competitive examination syllabi for Electrical Machine Design.

dynamometer instrument is the correct answer to “A Weston synchronoscope is a”. This question is standard in competitive examination syllabi for Electrical Machine Design.

0.07 is the correct answer to “The density of hydrogen is _____ times the density of air.”. This question is standard in competitive examination syllabi for Electrical Machine Design.

10 mm is the correct answer to “In D.C. machines the width of the duct is usually”. This question is standard in competitive examination syllabi for Electrical Machine Design.

high is the correct answer to “The efficiency of a machine should be as ______ as possible to reduce the operating cost.”. This question is standard in competitive examination syllabi for Electrical Machine Design.

All of the above is the correct answer to “Which of the following methods is used for air cooling of turbo-alternators”. This question is standard in competitive examination syllabi for Electrical Machine Design.

Perpendicular is the correct answer to “In a Weston frequency meter, the magnetic axes of the two fixed coils are”. This question is standard in competitive examination syllabi for Electrical Machine Design.

5 + 0.9 kV mm is the correct answer to “A practical formula for determining the thickness of insulation between low voltage and high voltage windings is”. This question is standard in competitive examination syllabi for Electrical Machine Design.

5.4 to 6.2 A/mm2 is the correct answer to “A current density of _________ is used for large power transformers with forced circulation of oil or with water cooling coils.”. This question is standard in competitive examination syllabi for Electrical Machine Design.

high is the correct answer to “The resistance in the circuit of the moving coil of a dynamometer wattmeter should be”. This question is standard in competitive examination syllabi for Electrical Machine Design.

Natural graphite is the correct answer to “_______ brushes are fragile and cause excessive wear of commutator,”. This question is standard in competitive examination syllabi for Electrical Machine Design.

magnetic screening is the correct answer to “To avoid the effect of stray magnetic field in A.C. bridges we can use”. This question is standard in competitive examination syllabi for Electrical Machine Design.

D.C. potentiometer is the correct answer to “It is required to measure the true open circuit e.m.f. of a battery. The best device is”. This question is standard in competitive examination syllabi for Electrical Machine Design.

1.5 is the correct answer to “Hydrogen has a heat transfer co-efficient _____ times that of air”. This question is standard in competitive examination syllabi for Electrical Machine Design.

7 is the correct answer to “The thermal conductivity of hydrogen is ______ times that of air”. This question is standard in competitive examination syllabi for Electrical Machine Design.

high is the correct answer to “The design of mechanical parts is particularly important in case of _____ speed machines.”. This question is standard in competitive examination syllabi for Electrical Machine Design.