Motor and Drive Examination 2019 1. Single-choice questions (number of questions: 25, total 50.0 points) 1 When the current through the coil is rated, the armature of the overcurrent relay ((2.0 points) A, action B, No action C, Uncertain My answer: B 2 Press the color and symbolic mark of the twist cap to be used ((2.0 points) A, Caution! B, Arouse vigilance C, Distinguishing function My answer: C 3 The rated current of the fuse shall be () the rated current of the melt contained.(2 points) A, greater than B, Greater than or equal to C, less than My answer: B 4 In the relay contact control circuit of motor, the function of zero voltage protection is (). (2 points) A, Prevent power supply voltage from burning down motor B, Alarm in case of power outage C, Preventing motor self-starting when power supply is restored after power failure D, Prevent motor speed from being too low My answer: A 5 The transformer has the highest efficiency at ().(2 points) A, Operation under rated load B, No-load operation C, Light load operation D, Operation over rated load My answer: A 6 Fuse series connection is mainly used in circuit ((2.0 minutes) A, Short circuit protection B, overload protection C, Undervoltage protection My answer: A 7 DC motor in series resistance speed regulation process, if the load torque remains unchanged, then () (2.0 minutes) A, Input power remains unchanged B, Constant output power C, The total loss power remains unchanged D, Electromagnetic power remains unchanged ____________ My answer: B 8 The starting current of three-phase asynchronous motor can be reduced to () when starting directly by Y-commutation. (2 points) A, B, C, D, My answer: B 9 A three-phase transformer has a capacity of 3000 KVA. If the primary voltage is 10 KV, the primary current is about () A (2.0 minutes). A, 300 B, 86.6 C, 173.2 D, 60 My answer: C 10 A DC motor 2P=4, S=K=Z=17, then its synthetic pitch Y=() (2.0 points) A, 4 B, 2 C, 6 D, 8Inside My answer: A 11 Three-phase asynchronous motors operating at rated voltage, such as load changes near rated load, motor speed ().(2 points) A, Unchanged B, Great changes C, Slightly changed D, Instable My answer: A 12 The change ratio of autotransformer is general to that of Ka ().(2 points) A, More than 2 B, Less than 2 C, More than 10 D, Less than 10 My answer: A 13 The ratio of transformer to original and auxiliary side () (2.0 points) A, Voltage is inversely proportional B, The current is proportional. C, Turns are inversely proportional D, Voltage is proportional My answer: C 14 The iron loss and copper loss of DC motor are respectively ().(2 points) A, Change with load, change with load B, No change with load, no change with load C, Change with load, not with load D, No change with load, no change with load My answer: D 15 By changing the power supply phase sequence of the motor stator winding to generate braking torque, the method of forcing the motor to stop quickly is ((2.0 points) A, Energy consumption brake B, Capacitive braking C, Reverse braking My answer: C 16 When a DC motor starts, the excitation circuit should be () (2.0 points) A, Connect with armature circuit at the same time B, After the armature circuit is connected C, Access prior to armature circuit D, No sequence My answer: A 17 The main flux_in transformer core varies according to sinusoidal law and the induced potential in winding ().(2 points) A, Sinusoidal Variation and Phase Consistency B, Sinusoidal change, opposite phase C, Sinusoidal variations and phases are related to the specified positive direction D, Sinusoidal variations and phases are independent of the specified positive direction My answer: B 18 To make the starting torque equal to the maximum torque response () (2 points) A, Change the Voltage Size B, Changing power supply frequency C, Increasing Rotor Loop Resistance D, Reducing Air Gap of Motor My answer: C 19 In the case of equal voltage, if an AC electromagnet is connected to DC current for use, it will occur (). (2 points) A, Coil current increases, heating, and even burns out B, noise C, Suction reduction D, Increased iron losses My answer: A 20 Auxiliary circuits are used from top to bottom and from left to right according to equipotential principle ((2.0 points) A, number B, Letter C, Numbers or letters My answer: A 21 Electrical appliances working at 1000V AC are called () (2.0 points) A, High voltage apparatus B, L