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WorksheetsEE8353 ELECTRICAL DRIVES AND CONTROL
Total questions: 45
Worksheet time: 3600secs
Which of the following type electric drive is used in cranes?
Individual
Multimotor
Group
None of the Above
Which of the following is the basic elements of a electric drive?
Control system
Electric motor
Both
None of the above
The selection of an electric motor for any application depends on which of the following factors?
Electrical Characteristics
Mechanical Characteristic
Size and rating of the motors
All
The load cycle for a motor driving a power press will be
Variable load.
Continuous load
Continuous but periodic.
Intermittent and variable load.
Example for continuous duty ______
Paper mill drive
Conveyers
Fan
All
Example for short time duty_______
Crane drive
Pressing
Cutting
Drilling
What will happen if DC shunt motor is connected across AC supply?
Will run at normal speed
Will not run
Will Run at lower speed
Burn due to heat produced in the field winding
What will happen if the back emf of a DC motor vanishes suddenly?
The motor will stop
The motor will continue to run
The armature may burn
The motor will run noisy
What will happen, with the increase in speed of a DC motor?
Back emf increase but line current falls.
Back emf falls and line current increase.
Both back emf as well as line current increase.
Both back emf as well as line current fall.
Which part will surely tell that given motor is DC motor and not an AC type?
Winding
Shaft
Commutator
Stator
Direction of rotation of motor is determined by
Faraday’s law
Lenz’s law
Coulomb’s law
Fleming’s left-hand rule
Why is this circuit not working?
Because it does not work.
Because the crocodile clip is not touching the bulb holder.
Because the battery has no power.
Because the bulb is broken.
The consideration involved in the selection of the type of electric drive for a particular application depends upon
Speed control range and its nature
Starting Nature
Environmental condition
All of the above
__________ drive is also called as Line shaft drive
Individual drive
Multimotor drive
Group Drive
None of the above
In __________ drive each machine is driven by its own separate motor with the help of gears and pulley
Individual drive
Multimotor drive
Group Drive
None of the above
Electric drive is becoming more and more popular because
all of below.
it provide smooth and easy control
it is cheaper in cost.
it is simple and reliable.
The basic elements of a electric drive are
electric motor.
control system.
electrical motor and control system.
none of the above
List the sensing unit-----------------
Speed Sensing
Current Sensing
Speed and current sensing
Voltage and speed sensing
The process of converting Fixed DC voltage into variable DC Voltage is called as-------------------------
Chopper
Inverter
Rectifier
Cycloconverter
More than one motor with single load is called----------drive.
Group
Individual
Multimotor
Motor
Heating time constant is defined as the time taken by the machine to attain ------ of its final steady temperature rise.
62.3%
61.3%
36.7%
63.2%
Variable speed control is possible in ------
AC Drives
DC Drives
Basic classification of duty----
2
3
1
The load, which is applied continuously without any break is known as--------- duty. I.e the drive motor always run with some load.
Continuous
Short time
House hold appliances, Automatic lock gates and bridges example for--------
Continuous duty
Short time duty
Cycloconverter converts ----------
Fixed DC to Variable DC
Fixed AC to Variable AC
Types of AC motors----
single and three phase induction motor
single and three phase induction motor,Synchronous motor
What kind of motor used in electric traction--------
DC Series motor
AC Series motor
The function of power modulator isregulate the power flow from source to the motor to enable the motor todevelop the torque speed characteristics required by the load
True
False
Cooling time constant is, therefore, defined as the time required cooling the machine down to-------- times the initial temperature rise above ambient temperature
36.7%
37.6%
In cumulatively cascade method for speed controlling, if PA is the number of poles of main motor and PB is the number of poles of auxiliary method. Then the speed of the rotor B is given
120f / PA + PB
120f / PA - PB
120f / PA
120f / PB
The loads are too short to allow the motor to reach its final steady value while periods of rest are too small to allow the motor to cool down to the which temperature.
a) ambient temperature
b) Room temperature
c) Nominal temperature
d) None of the above
In regenerative braking of dc shunt motor
Eb=V
Eb<V
Eb>V
None of the above
Why starters are required in a DC motor?
a) Back emf of these motors is zero initially
b) These motors are not self-starting
c) These motors have high starting torque
d) To restrict armature current as there is no back emf at starting
In a manual shunt motor starter relay positions are ________________________
a) Over load relay is connected in series and no volt relay in parallel with the load
b) Over load relay is connected in parallel and no volt relay in series with the load
c) Over load relay and no volt relay are both connected in series with the load
d) Over load relay and no volt relay are both connected in parallel with the load
The drawback of speed control of a slip ring induction motor with the help of resistance in the circuit is that
a) It is applicable only to motors having power of more than 100 kW
b) It results in high losses
c) With reduction in speed, the torque decreases significantly
d) The speed can be controlled only very broadly
The field of an induction motor rotor rotates relative to the stator at
a) Rotor speed
b) Synchronous speed
c) Slip speed
d) Very low speed
Ward-Leonard system of system of speed control is not recommended for _________
a) constant speed operation
b) Wide speed
c) frequent-motor reversed
d) very slow speed
Ward Leonard method is ___________
a) Armature control method
b) Field control method
c) Combination of armature control method and field control method
d) Totally different from armature and field control method
In kramer system when the field resistance is changed the back e.m.f of motor
remains constant
zero
changes
None of the above
At full load of a 10 h.p the temperature rise of a motor is 25
° c after one hour and 40 ° c after two hours.Find heating time constant of motor.2.365 hrs
1.9576 hrs
6.022 hrs
9.336 hrs
In cascade control method of two induction motor if the torques produced both act in the same direction cascading is called as
a) Differential cascading
b) single cascading
c) Cumulative cascading
None of the above
. In the rotor voltage injection method, when an external voltage source is in opposite phase with the main voltage then speed will _________
a) Increase
b) Decrease
c) Remain unchanged
d) First increases then decrease
In the rotor voltage injection method, when an external voltage source is in phase with the main voltage then speed will ___________
a) Increase
b) Decrease
c) Remain unchanged
d) First increases then decrease
Armature voltage control works for speeds _____ base speed and field resistance control works well for speed _____ base speed.
a) below, above
b) above, below
c) above, above
d) below, below
