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WorksheetsDC Machines
Total questions: 17
Worksheet time: 15mins
DC generator can convert
DC Electrical energy into mechanical energy only
Mechanical energy into dc electrical energy only
Either dc electrical energy into mechanical energy or mechanical energy into dc electrical energy
Only increase the voltage level of electrical energy
The basic law for the working of dc motor is based on
Right hand palm rule
Faraday law
Biot Savert law
Fleming left hand rule
The relation that depicts the basic law for dc generator is
Which are main parts of a DC machine?
Yoke (frame)
Commutator
Slip rings
Brushes
Which one is not a part of the field system of dc machines?
Pole shoe and pole core
Yoke or frame
Exciting winding
Armature
In a dc machine, if number of parallel path is equal to number of poles this implies
The armature winding is wave connected.
The armature winding is open.
The armature winding is lap connected.
The armature winding is short circuited.
In a dc machine, if number of parallel path is equal to 2 this implies
The armature winding is lap connected.
The armature winding is open.
The armature winding is wave connected.
The armature winding is short circuited.
The emf induced in the dc machine is given by,
DC Shunt generator
DC Series generator
DC Shunt motor
DC Series motor
The induced emf in a DC machine is directly proportional to
Armature speed
Flux per pole
Number of poles
All of the above
The device that converts AC induced in armature to DC at terminals in a DC generator is (a) .
Which type of DC motor is typically used in applications requiring high starting torque, such as electric trains and cranes?
Shunt motor
Series motor
Compound motor
Separately excited motor
The purpose of using brushes in a DC machine is to:
Provide a path for the flow of field current
Collect current from the commutator or feed current to the commutator
Control the speed of the motor
Reduce eddy current losses
A 220V DC shunt motor is running at 1000 RPM and drawing a current of 10A. The armature resistance
𝑅𝑎 is 0.5 Ω and the field resistance 𝑅𝑓 is 220Ω. What is the back EMF generated by the motor?
205 V
220 V
210 V
215 V
A DC series motor is operating under heavy load. If the load is suddenly removed, what is the likely consequence?
The motor stops immediately due to lack of load torque.
The motor speed stabilizes at a safe, slightly higher speed.
The motor speed increases dangerously (runs away) and may destroy itself mechanically.
The motor reverses its direction of rotation.
In a working DC generator, reversing the direction of rotation while keeping the field polarity the same will cause the output voltage polarity to reverse.
True
False
17.
Answer the questions below after watching the video
Sparking at brushes usually indicates:
Good commutation
Poor commutation
Correct brush setting always
Motor running at zero speed
