Electrical Machines Set 1

How can the direction of a capacitor start single phase motor be reversed?

• Reverse the connection to the capacitor

• Reverse the connection to the start winding

• Reverse the polarity of the supply

• Reverse the connection of the start and run windings

How can the direction of a capacitor start single phase motor be reversed?

• Reverse the connection to the capacitor

• Reverse the connection to the start winding

• Reverse the polarity of the supply

• Reverse the connection of the start and run windings

When are single phase series universal motors used?

• When high starting torque is required

• When starting on no-load is required

• When constant speeds are required

• When low speed drives are required

When is the stator winding of a three phase squirrel-cage induction motor connected in star?

• when in full load

• when running at rated speed

• when on light load

• when starting the motor

What is the percentage slip of a motor at full load speed where the nameplate details are: f= 50Hz, poles = 4, full load speed = 1440 rpm?

• s = 3%

• s = 4%

• s = 5%

• s = 6%

What is the shape of the laminations used in the magnetic circuit of a single phase shell-type transformer?

• LL

• TT

• LE

• EI

What type of transformer is used for interconnecting high voltage transmission systems operating at different voltage levels?

• Current transformer

• wound transformer

• Voltage transformer

• Autotransformer

What conditions must be satisfied before connecting two transformers in parallel to share a common load?

• Same inductance, same kVA rating

• Same polarity, same phase sequence

• Same polarity resistance, same current ratio

• Same number of polarity turns, same voltage regulation

What is the relationship between the VA rating of a transformer and the internal percentage impedance Z?

• VA ∝1/ Z

• VA ∝Z

• VA ∝2Z

• VA ∝ Z/2

What two power losses occur in a transformer when operating on no-load?

• Mechanical losses, core losses

• Frictional losses, heat losses

• Rotational losses, copper losses

• Copper losses, core losses