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WorksheetsRME Review - Autotransformer Motor Starter
Total questions: 20
Worksheet time: 10mins
What is the primary function of an autotransformer starter in motor control?
To increase the voltage applied to the motor
To reduce the inrush current during motor startup
To reverse the direction of the motor
To control the motor speed
How does an autotransformer starter reduce the starting current?
By introducing resistance into the rotor circuit
By supplying a reduced voltage to the motor through transformer taps
By supplying a reduced voltage to the motor changing transformer power rating
By using a timer to delay the application of full voltage
What is the typical percentage of voltage reduction provided by an autotransformer starter?
50%, 65%, 80%
10%, 20%,30%
25%, 50%, 75%
70%, 85%, 90%
What is the key difference between an autotransformer starter and a wye-delta starter in motor control?
Autotransformer starters are simpler and cheaper than wye-delta starters.
Wye-delta starters provide higher starting torque than autotransformer starters.
Autotransformer starters allow more precise voltage reduction and provide higher starting torque than wye-delta starters.
Wye-delta starters use transformer taps for voltage reduction during startup.
In an autotransformer starter, how does the torque change if the voltage is reduced to 80% of the line voltage?
Torque is reduced to 64% of full-load torque.
Torque is reduced to 33% of full-load torque.
Torque is reduced to 80% of full-load torque.
Torque is unaffected by the voltage reduction.
Which type of motor is most suitable for starting with an autotransformer starter?
Single-phase motor
Small three-phase induction motor
Large three-phase induction motor with high starting torque requirements
Stepper motor
What happens when the motor transitions from the reduced voltage to full voltage in an autotransformer starter?
The motor stops momentarily
The motor operates at reduced torque
The autotransformer is bypassed, and full voltage is applied to the motor
The motor reverses its direction
What is the main advantage of using an autotransformer starter over a wye-delta starter?
It is simpler to install
It provides better control of starting torque
It is more cost-effective for small motors
It eliminates the need for overload protection
In which industrial application is an autotransformer starter commonly used?
) Lighting circuits
Conveyor systems with heavy starting loads
Fans and blowers
Low-power domestic appliances
What is a major disadvantage of an autotransformer starter?
It is not suitable for high-torque applications
It causes high inrush current
It is more expensive and complex compared to other starters
It does not reduce starting voltage
How many contactors are typically used in an autotransformer starter?
1
2
3
4
An autotransformer is preferred to a conventional 2-winding transformer:
because it is much safer to use an auto-transformer
where large number of secondary taps are needed
where it is required to electrically isolate the two windings
where ratio of transformer is low
Which transformer has only one winding?
distribution
power
autotransformer
isolated winding transformer
Which of the statement given below is true about autotransformer?
It has two separate windings connected in series externally
It can only step down the voltage
It has only one winding
It is most suitable for power transformer
Each autotransformer 600 volts, nominal, or less shall be protected by ________device installed in series with each _____ input conductor. Such overcurrent device shall be rated or set at not more than 125 percent of the rated full-load input current of the autotransformer.
an individual overcurrent, ungrounded
disconnect, ungrounded
an individual overcurrent, grounded
disconnect, grounded
An overcurrent protective device of adequate short-circuit rating that will open simultaneously all ungrounded conductors when it operates shall be applied in the grounding autotransformer branch circuit and shall be rated or set at a current not exceeding 125 percent of the autotransformer continuous per-phase current rating or ___percent of the continuous-current rating of any series connected devices in the autotransformer neutral connection.
53
42
125
73
The common use for autotransformer in electrical power work is
Current-limiting reactor
Instrument current transformer
Starting compensator for motor
Insulating transformer
An autotransformer differs from other types of transformers in that ______.
Its primary winding is always larger than its secondary winding
It can be used only in automobile
Its primary and secondary windings are common to each othe
It must be wound with heavier wire
What is a primary limitation of autotransformers compared to conventional transformers?
They are not suitable for stepping up voltage.
They cannot be used for large power systems.
They do not provide electrical isolation between primary and secondary circuits.
They require a separate cooling system.
Answer: C
Why are autotransformers commonly used for motor starting?
They provide a fixed high starting torque.
They reduce the inrush current by supplying reduced voltage during startup.
They eliminate the need for overload protection.
They operate the motor at a constant reduced speed.
