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motors II
lesson 4 DC Motors and Generators
| Question | Answer |
|---|---|
| A ? motor is a DC motor that has the field wiring connected in parallel with the armature. | shunt |
| The interpoles are connected in series with the ? windings. | armature |
| ? motors are used in moderate starting conditions and where constant or adjustable speed is required. | Shunt |
| DC shunt motors can develop about ? to ? of full-load torque upon starting. | 250% / 300% |
| With a(n) ? shunt field, the speed can be regulated by varying the field current, the armature current, or both | self-excited |
| 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 |
| true/false DC compound motors have shared characteristics of series motors and shunt motors. | true |
| DC ? motors are used mostly for special applications that require constant speed under load and high starting torque. | compound |
| what are examples of a common DC compound motor | DC cumulative-compounded motor and DC differential-compounded motor |
| true/false DC permanent-magnet motors use magnets and coils of wire for the field windings. | false not coils of wire |
| Negative voltage regulation occurs only with ? generators. | series |
| A DC ? -wound generator provides a source of positive and zero voltage regulation to the load. | shunt |
| 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 |
| ? voltage regulation occurs when the countervoltage at no load is greater than the terminal voltage at full load. | Positive |
| When connected to 240 volts, a DC motor that has a winding resistance of 3.2 ohms at standstill draws ? . | 75A |
| 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 |
| An external ? applies mechanical torque to the armature and series field circuit, which induces voltage and current in the generator. | prime mover |
| 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 |
| 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 |
| 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 |
| 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 |
| Interpoles reduce sparking at the ? of some DC motors. | brushes |
| A(n) ? connects a brush to either the positive or negative terminal of the DC source. | pigtails |
| The function of a(n) ? is to keep armature windings in the correct polarity to interact with the main fields of a motor. | commutator |
| The ? rule gives the direction of motion for current-carrying wire interacting with a stationary magnetic field. | right-hand motor |
| The neutral plane is ? to the field flux when there is no current in the armature. | perpendicular |
| 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 |
| true/false The fields in a DC motor often change in polarity. | false |
| When the power is removed, DC ? motors provide some self-braking and produce relatively high torque at low speeds. | permanent-magnet |
Created by:
Yusosweet1