Commercial Electrical Study Guide - DC Motors

Vocabulary practice flashcards covering DC motor types, field windings, terminal identification, speed regulation, and operating principles based on the commercial electrical study guide.

Shunt field in differential compound motors

The field winding that determines the direction of rotation of a differential compound motor at no load or light load when the series field is weak.

Field loss relay in compound DC motor control circuits

A relay that disconnects power to the armature if power is lost to the shunt field, preventing the motor from dangerously overspeeding.

Compound motor field windings

A combination of both series and shunt field windings in a single motor, combining high starting torque with speed regulation.

Series motor no-load operation restriction

The rule that a series motor must never be operated without a load connected, because it will accelerate to dangerously high speeds and potentially destroy itself.

Shunt motor

A DC motor known as a 'constant speed motor' because its speed varies very little between no-load and full-load conditions.

Transistors in converters

Power components that act as electronic switches turned on or off in a proper sequence to route current through stator windings.

Permanent magnet field pole efficiency

An efficiency characteristic of permanent magnet DC motors where no electrical power is consumed to generate the magnetic field of the pole pieces.

Torque

The pushing or turning force created by the magnetic field of the pole pieces and the magnetic field of the loop or armature.

Motor

A device that converts electrical energy into mechanical energy.

Permanent magnet motor efficiency relative to field-wound motors

Higher efficiency resulting from zero electrical power required to generate a magnetic field in the stator.

Brushless DC motor

A motor that relies on an external electronic controller for commutation and does not contain a wound armature, commutator, or brushes.

Brushless DC motor armature/rotor magnets

Permanent magnets contained within the armature or rotor of a brushless DC motor.

DC machine terminal leads labeling

Standardized labeling used so leads can be correctly identified and wired when brought outside the motor housing to the terminal box.

Terminals A1 and A2

Terminal designations specifically used to identify armature leads in DC machines.

Shunt motor connection configuration

A DC motor design where the field winding is connected in parallel with the armature.

DC motor and DC generator terminal markings

Identical standardized NEMA terminal identification markings shared by both DC motors and DC generators.

Counter-electromotive force (CEMF)

The voltage induced into the rotating armature of a DC motor that opposes the applied source voltage (also called back-EMF).

Base speed

The speed at which a motor operates when full line voltage is applied to both the armature and the shunt field (also referred to as normal speed).

Terminals S1 and S2

Terminal markings designated specifically for series field windings in the connection box.

Compound motor

A DC motor constructed with both a series field winding and a shunt field winding.

Speed regulation

The differential in speed measured from a no-load condition to a full-load condition in a motor.

Field Loss Relay (FLR) function

A protection device intended to disconnect a motor from the power line if shunt field current is interrupted or drops below an acceptable level.

Shunt field winding resistance

A high electrical resistance exhibited by shunt field windings, constructed using many turns of fine wire.

Constant speed motor

A common name given to shunt motors due to their stable speed characteristics across varying loads.

Degree of compounding

The term used to indicate the relative strength between the series and shunt fields in a compound motor.

DC motor rotation reversal method

The most common method of reversing a direct current motor's direction of rotation by reversing current flow through the armature.

Frogleg wound armatures

Armature windings typically used in large, high-current DC machines to provide better commutation rather than in small machines.