# Design of Electrical Machines Questions and Answers – Design of Field Winding – 1

This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Design of Field Winding – 1”.

1. What type of coils are made use of for machines with small number of poles?
a) iron wound coils
b) wire wound coils
c) rectangular coils
d) square coils

Explanation: Different type of coils are being made use of for the machines as per the quantity of number of poles. For small number of poles the wire wound coils are made use of.

2. What type of strips is made use of for field coils of small alternators?
a) wood covered rectangular strips
b) bare copper strips
c) glass covered rectangular strips
d) iron strips

Explanation: The glass covered rectangular strips are made use of for the field coils of small alternator. The bare copper strips are being used are made use of for the field coils of large alternator.

3. What should be the maximum width of the edge conductors used in the large alternators?
a) 6 mm
b) 5 mm
c) 4 mm
d) 3 mm

Explanation: The field coils of the large alternators use strip on edge winding wherein the bare copper strips are insulated from each other by interturn insulation. The width of the edge conductors does not exceed 6 mm.

4. For machines with Class B insulation, how many layers of inter turn insulation is made use of and what is the distance between the layers?
a) 4, 0.18 mm
b) 3, 0.25 mm
c) 2, 018 mm
d) 2, 0.25 mm

Explanation: The machines using Class B insulation makes use of 2 layers of inter turn insulation. The distance between the insulation is given to be 0.18 mm.

5. What material is the paper strips stuck with?
a) synthetic resin varnish
b) shellac
c) synthetic resin varnish and shellac
d) synthetic resin varnish or shellac

Explanation: The paper strips used in the Class B insulation machines are stuck on with shellac. They are also made of the synthetic resin varnish materials.

6. What is the thickness of the flanges and what material is used in the flanges?
a) 10 mm thick, resins
b) 10 mm thick, asbestos
c) 15 mm thick, asbestos
d) 10 mm thick, bakelized asbestos

Explanation: The flanges used in the Class B insulation is made up of 10 mm thickness. The flanges are made up of the bakelized asbestos.

7. Current is passed simultaneously through the conductors to raise the temperature of the field coil.
a) true
b) false

Explanation: The current is passed simultaneously through the conductors to raise the temperature of the field coil. The temperature should be high enough so that polymerization of interturn insulation is complete.

8. During the pressing and consolidation by how much is the thickness of the interturn insulation reduced to?
a) 0.36 mm to 0.26 mm
b) 0.36 mm to 0.25 mm
c) 0.30 mm to 0.25 mm
d) 0.32 mm to 0.25 mm

Explanation: The thickness of the interturn insulation before the pressing and consolidation is 0.36 mm. After the process of pressing and consolidation the thickness of the interturn insulation is reduced to 0.26 mm.

9. How many layers does the machine with Class F insulation consists of?
a) 2
b) 3
c) 4
d) 5

Explanation: The machines with Class B insulation consists of 2 layers. The machines with Class F insulation consists of 3 layers.

10. What is the thickness of the layers of Class F insulation and what material is layers made of?
a) 0.18 mm, asbestos paper
b) 0.10 mm, asbestos paper
c) 0.18 mm, thick epoxy treated asbestos paper
d) 0.10 mm, thick epoxy treated asbestos paper

Explanation: The thickness of the layers is 0.18 mm. The layers are made up of thick epoxy treated asbestos paper.

11. What is the lamination material of the pole body and the thickness of the pole body insulation?
a) epoxy resin, 5 mm thick
b) epoxy resin. 4 mm thick
c) asbestos, 4 mm thick
d) asbestos 5 mm thick

Explanation: The pole body insulation is made up of the epoxy resin laminations. The thickness of the pole body insulation is 4 mm thick.

12. What is the range of the pressure under which the field coils are consolidated?
a) 4-10 MN per m2
b) 3-10 MN per m2
c) 4-12 MN per m2
d) 4-15 MN per m2

Explanation: The minimum pressure under which the field coils are consolidated is 4 MN per m2. The maximum value of the pressure under which the field coils are 12 MN per m2.

13. What is the range of the exciter voltage in the field coils?
a) 50-100 V
b) 150-300 V
c) 200-400 V
d) 50-400 V

Explanation: The minimum value of the exciter voltage across the field coils is 50 V. The maximum value of the exciter voltage is 400 V.

14. The field winding should be designed for a voltage from 15-20% less than the exciter voltage.
a) true
b) false

Explanation: The field winding should be designed for a voltage from 15-20% less than the exciter voltage. This is because to allow for the drop in voltage between field and exciter and to allow for variations in the reluctance of the magnetic field.

15. What is the formula for the voltage across each field coil?
a) voltage across each field coil = (0.8-0.85)*exciter voltage/number of poles
b) voltage across each field coil = (0.8-0.85)*exciter voltage*number of poles
c) voltage across each field coil = (0.8-0.85)/exciter voltage*number of poles
d) voltage across each field coil = (0.8-0.85)/exciter voltage/number of poles

Explanation: The exciter voltage value is first set up for the particular machine. Then with the number of poles, the voltage across each field coil is calculated.

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