lesson 4 DC Motors and Generators
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| A ? motor is a DC motor that has the field wiring connected in parallel with the armature. | shunt
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| The interpoles are connected in series with the ? windings. | armature
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| ? motors are used in moderate starting conditions and where constant or adjustable speed is required. | Shunt
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| DC shunt motors can develop about ? to ? of full-load torque upon starting. | 250% / 300%
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| With a(n) ? shunt field, the speed can be regulated by varying the field current, the armature current, or both | self-excited
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| A ? winding is a small series field winding that improves stability of the fields while running with reduced current in the field circuit. | stabilizing field
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| true/false DC compound motors have shared characteristics of series motors and shunt motors. | true
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| DC ? motors are used mostly for special applications that require constant speed under load and high starting torque. | compound
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| what are examples of a common DC compound motor | DC cumulative-compounded motor
and DC differential-compounded motor
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| true/false DC permanent-magnet motors use magnets and coils of wire for the field windings. | false
not coils of wire
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| Negative voltage regulation occurs only with ? generators. | series
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| A DC ? -wound generator provides a source of positive and zero voltage regulation to the load. | shunt
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| A DC ? operates on the principle that voltage is induced in a coil of wire when the coil is rotated in a magnetic field. | generator
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| ? voltage regulation occurs when the countervoltage at no load is greater than the terminal voltage at full load. | Positive
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| When connected to 240 volts, a DC motor that has a winding resistance of 3.2 ohms at standstill draws ? . | 75A
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| The field windings in a ? -wound generator consist of a few turns of low-resistance wire because the large load current flows through them. | series
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| An external ? applies mechanical torque to the armature and series field circuit, which induces voltage and current in the generator. | prime mover
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| True/false In a compound-wound generator, the series field is normally stronger than the shunt field. | false
the shunt filed is normally the stronger of the two
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| When a DC motor connected to 235 volts accelerates to a speed that generates a countervoltage of 115 volts, the total voltage in the motor is ? . | 120 volts
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| A motor connected to 280 volts has a resistance of 7 ohms. When the motor accelerates to full speed, the counter voltage is 245 volts; the total voltage in the motor is 35 volts and the current drawn is ? . | 5.0 A
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| true/false Connecting voltage directly to the field and armature windings of a DC motor allows the motor to produce higher torque in a smaller frame than with an AC motor. | true
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| Interpoles reduce sparking at the ? of some DC motors. | brushes
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| A(n) ? connects a brush to either the positive or negative terminal of the DC source. | pigtails
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| The function of a(n) ? is to keep armature windings in the correct polarity to interact with the main fields of a motor. | commutator
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| The ? rule gives the direction of motion for current-carrying wire interacting with a stationary magnetic field. | right-hand motor
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| The neutral plane is ? to the field flux when there is no current in the armature. | perpendicular
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| Torque is exerted on the ? when the plane of the armature loop is parallel to the field and the armature loop sides are at right angles to the magnetic field. | armature
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| true/false The fields in a DC motor often change in polarity. | false
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| When the power is removed, DC ? motors provide some self-braking and produce relatively high torque at low speeds. | permanent-magnet
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