WorksheetsSiemens Level 1 Mechanical #1
Total questions: 11
Worksheet time: 22mins
Which component has to be maintained most often in a small DC machine?
Armature
Brushes
Permanent Magnets
Bearings
Commutator
ow could you change the direction of rotation for an asynchronous machine (ASM) with squirrel cage?
Use secondary shaft on opposite side.
Exchange three terminals with each other.
Exchange two terminals with each other
Possible only with mechanical solutions (gear box and clutch).
Apply negative voltage to the terminals.
A pump is connected with a clutch to a series-wound DC machine. What happens with the machine if the clutch is suddenly opened during operation?
The speed could get very high and probably destroy the machine.
The machine gets very hot.
The speed breaks down to zero.
The motor’s voltage will directly increase.
Nothing; the machine will continue to run at the rated speed.
An electrical DC machine gets too hot during operation. What could be the cause? Two answers are correct.
There is malfunction in the cooling system.
The load increased.
The supply voltage broke down.
The load decreased.
The brushes broke and have to be maintained.
The switching frequency of a power electronic for a DC machine is set to 2 kHz. This could cause:
Torque ripples.
Annoying noise.
More losses than necessary.
High armature currents.
Nothing; 2 kHz is an appropriate switching frequency and often used in industries.
The ideal rotating magnetic field in the stator of a three-phase machine is deformed by: Two answers are correct.
High no-load speed.
Non-symmetrical stator windings.
Wrong direction of rotation.
Non-ideal net situation.
Alternating voltages and currents.
The speed of a synchronous machine is higher than written in the data sheet. What could be the reason?
The amplitude of the three-phase voltage is too high.
The frequency of the three-phase voltage is too high.
The load connected to the machine is too small.
The load connected to the machine is too high.
The excitation of the machine is too low.
A frequency inverter has a malfunction: one low-side switch is broken and as a result always opens. Result for the driven asynchronous machine: Two answers are correct.
Half of the speed.
More torque ripple and more noise.
Less maximum torque.
Much less no-load speed.
The maximum torque will increase and possibly break the machine.
Which components are used for energy transport between different machine units of a system? Two answers are correct.
Timing Belts
Washers
Bearings
Screws
Power Screws
Which of the following rolling contact bearings are able to absorb thrust forces at least from one side?
Bearing b and e.
Bearing a, c and d.
Bearing a and d.
All bearings.
None of the answers given.
Which of the following statements about the gear train shown in the picture below is not correct?
The module of both gears has to be the same.
The pictured gears are used to lower the noise in operation.
The gear train exerts thrust (axial) forces.
The rotation speed of the upper shaft is smaller than the speed of the lower shaft.
The torque of the upper shaft is smaller than the torque of the lower shaft.
