Design of Electrical Machines Mcqs

Q:

The frame size is designated by a number which is its centre height expressed in mm.

A) true B) false
 
Answer & Explanation Answer: A) true

Explanation: The IEC 72 lists a coherent range of main dimensions with the central heights ranging between 56-1000 mm. The frame size is designated by a number which is its centre height expressed in mm. The frame designated 180 has a centre height of 180 mm.

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7
Q:

What is the range of the central heights used in the standard frames?

A) 50-1000 mm B) 90-1000 mm
C) 100-1000 mm D) 56-1000 mm
 
Answer & Explanation Answer: D) 56-1000 mm

Explanation: The modern motors of small and medium sizes are built with standard frame sizes as specified in IEC 72. The IEC 72 lists a coherent range of main dimensions with the central heights ranging between 56-1000 mm.

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8
Q:

What is the value of the alternative core lengths below which variation in rating can be obtained?

A) 0.7 * length B) 0.4 * length
C) 0.3 * length D) 0.7 * length or 0.5 * length
 
Answer & Explanation Answer: D) 0.7 * length or 0.5 * length

Explanation: The variation in the ratings can be obtained using alternative core lengths. The value of the alternative core lengths below 0.5 * length or 0.7 * length provides the variation in the ratings.

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8
Q:

How can the variation in ratings be obtained?

A) alternative windings B) alternative core lengths
C) alternative pole pitch D) alternative pole length
 
Answer & Explanation Answer: B) alternative core lengths

Explanation: The frame is a mechanical structure required to house a stator of given outside diameter, housing the bearings, end covers, terminal box and maximum length. The variation in the ratings can be obtained using alternative core lengths.

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7
Q:

What is the frame used in the standard frames?

A) set of standard values B) mechanical structure required to house a rotor of given outside diameter
C) mechanical structure required to house a stator of given outside diameter D) mechanical structure required to house a stator of given outside length
 
Answer & Explanation Answer: C) mechanical structure required to house a stator of given outside diameter

Explanation: The frame is a mechanical structure required to house a stator of given outside diameter. The frame also includes housing the bearings, end covers, terminal box and maximum length.

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10
Q:

What is the factor which is by modern motors which are into a series of standard frames?

A) current rating B) voltage rating
C) power rating D) output rating
 
Answer & Explanation Answer: C) power rating

Explanation: The modern motors for industrial applications is concentrated into a series of standard frames. The standard frames are used to cover a wide range of power ratings.

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9
Q:

The core length should be high to obtain high short circuit ratio.

A) true B) false
 
Answer & Explanation Answer: A) true

Explanation: The core length is directly proportional to the short circuit ratio. If high short circuit ratio is required, high core length should be used.

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8
Q:

What is the relationship between the diameter and number of poles?

A) diameter is directly proportional to the number of poles B) diameter is indirectly proportional to the number of poles
C) diameter is directly proportional to the square of the number of poles D) diameter is indirectly proportional to the square of the number of poles
 
Answer & Explanation Answer: A) diameter is directly proportional to the number of poles

Explanation: The number of poles is one of the factors involved in the separation of D and L in the synchronous machines. The number of poles is directly proportional to the diameter.

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