• In Dc Machine The Number Of Slots Per Pole Usually Lies Across
• In Dc Machine The Number Of Slots Per Pole Usually Lies Beneath

The other thing to be aware of is that the more poles (magnets) there are on a motor the more work the ESC has to do per revolution. ESCs have a max RPM (usually somewhere between 120kRPM and 240kRPM for a 2 pole motor) that they can support, so a low magnet count high RPM motor will be compatible with more ESCs.

1. Lecture Notes Elements of Electrical Machines 8 Let, I flux per pole in weber z total number of armature conductors=no. Of conductors/slot P no. Of generator poles A no. Of parallel paths in armature N armature rotation in revolutions per minute (rpm) E emf induced in any parallel path in armature Generated emf, E g.
2. Total number of turns in these angles =m Z 360 2 Demagnetising amp – turns per pair of pole = m ZI 360 2 AT d per pole = m ZI 360 The conductors lying between angles AOD and BOC constitute what are known as distorting or cross-magnetising conductors. Their number is found as under.

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1. The number of parallel path in a simplex lap winding is equal to
(a)number of poles
(b)number of pole pairs
(c)two
(d)two times number of pole

2. The number of parallel path in a simplex wave windings are equal to
(a)two
(b)number of poles
(c)number of poles pairs
(d)no of coils

In Dc Machine The Number Of Slots Per Pole Usually Lies Across

3. The number of parallel path in a 8-pole duplex wave winding is equal to
(a)2
(b)4
(c)8
(d)16

4. The number of parallel path in a 8-pole duplex lap winding is equal to
(a)4
(b)8
(c)16
(d)32

5. In DC machine, the fractional pitch winding is used to
(a)produce vibration
(b)reduce sparking
(c)avoid hunting
(d)avoid magnetic locking

In Dc Machine The Number Of Slots Per Pole Usually Lies Beneath

6. In a DC machine, the sparking at the brushes is due to
(a)low contact resistance
(b)reactance voltage
(c)armature reaction
(d)over excitation

7. When the field excitation of a DC generator increases, its generated emf
(a)decreases
(b)increases
(c)remain same
(d)first increases then constant

8. The field coil of a DC machine are usually made of
(a)copper
(b)aluminium
(c)carbon
(d)mica

9. Then insulating material used between commutator segment is generally
(a)paper
(b)mica
(c)plastic
(d)fibre

You may also read
• Why all the voltage levels are multiples of 11 kV?
• Why Motor rated in kW instead of kVA?

10. The function of dummy coils in DC machines is to
(a)reduce armature reaction
(b)provide alternate flux
(c)reduce losses
(d)provide mechanical balancing

11. Permeability is reciprocal of
(a)susceptibility
(b)reluctivity
(c)permittivity
(d)conductivity

12. The purpose of using dummy coil in a DC machine is to
(a)reduce losses
(b)reduce armature reaction
(c)provide mechanical balance to armature
(d)improve power factor

13. The rotor part of a DC machine carries
(a)armature winding
(b)field winding
(c)either field or armature winding
(d)none of the above

14. If a field winding designed for series connection is connected in parallel, the machine will
(a)draw very high current
(b)stand still
(c)run normally
(d)run at slow speed

15. In the commutative compound machine, the mmf of the series field winding will ________ to the mmf of the shunt field winding.
(a)add
(b)minus
(c)same
(d)half

16. Which is the basic dominant factor in the production of the magnetic flux in a compound machine?
(a)Shunt field mmf
(b)Series field mmf
(c)Both shunt and series field mmf
(d)None of the above

17. The principle of dynamically induced emf is used in
(a)generator
(b)battery
(c)transformer
(d)all of the above

18. A dummy coil may required in a DC machine, if the machine is
(a)lap wound
(b)wave wound
(c)either lap or wave wound
(d)none of the above

19. In a DC Machine, the frog leg wound armature are designed for the use with
(a)high current high voltage
(b)high current low voltage
(c)moderate current and moderate voltage
(d)low current and low voltage

20. Which of the following is main factor to determine the size and rating of and electric machine?
(a)Current
(b)Temperature
(c)Speed
(d)Voltage

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Also Read :

• Why all the voltage levels are multiples of 11 kV? asked by Bahu
• What is the function of a choke in tube light? asked by varu
• What is the difference between Earthing and Grounding? asked by admin
• Why Motor rated in kW instead of kVA? asked by Guma

A Motor is a machine that converts electrical energy into mechanical energy. There is no difference between a DC motor and DC generator from a construction point of view. The only difference is that the generators are usually operated in more protected locations and, therefore, their construction is generally of the open type.

On the other hand, motors are generally used in locations where they are exposed to dust, moisture, fumes and mechanical damage. Thus, the motor requires protective enclosures.

For example – Motor requires drip-proof, fire-proof, etc. enclosure according to the requirement. The DC motors are very useful where a wide range of speeds and good speed regulation is required, such as in the electric traction system.

As the construction of DC Motor is similar to DC Generator, which is discussed in the topic Construction of DC Generator. Thus, for the construction of a DC motor refer the link given below. There are various types of DC Motors. They are Shunt motor, Series motor and Compound motor.

Also See:Construction of DC Generator

The EMF equation of DC Motor is given by the equation shown below:

Where,

• E_b is the induced emf of the motor
• N is the speed
• P is the number of poles
• ϕ is the flux per pole.
• Z is the total number of conductors
• A is the number of parallel paths

Equivalent Circuit of a DC Motor Armature

The armature of a DC Motor can be represented by an equivalent circuit. It can be represented by three series-connected elements E, Ra and Vb. The element E is the back emf, Ra is the armature resistance and Vb is the brush contact voltage drop.

The equivalent circuit of the armature of a DC motor is shown below:

In a DC motor, the current flows from the line into the armature, against the generated voltage. By applying KVL,

Where,

• V – Motor terminal voltage
• E_b – Back EMF
• I_a – Armature current
• R_a – Armature circuit resistance

The equation (1) written above is called the fundamental motor equation. It is seen that the Back EMF of the motor is always less than its terminal voltage V. The equation can also be written as shown below:

The equation (2) is considered or applicable when the voltage drop V_b in the brushes is also taken into account.