Classification Electric Motors according to application, technology and NEMA

Electric Motors, Generators and Drives

Classification of electric motors according to application and technology

Alternating Current Motors:
Alternating-current motors are of three general types: induction, synchronous, and series-wound and are defined as follows.

NEMA Induction Motor:
An induction motor is an induction machine in which a primary winding on one member (usually the stator) is connected to the power source, and a polyphase secondary winding or a squirrel-cage
secondary winding on the other member (usually the rotor) carries induced current.

NEMA Squirrel-Cage Induction Motor:
A squirrel-cage induction motor is an induction motor in which the secondary circuit (squirrel-cage winding) consists of a number of conducting bars having their extremities connected by metal rings or
plates at each end.

NEMA Wound-Rotor Induction Motor:
A wound-rotor induction motor is an induction motor in which the secondary circuit consists of a polyphase winding or coils whose terminals are either short-circuited or closed through suitable circuits.

NEMA Synchronous Motor:
A synchronous motor is a synchronous machine for use as a motor.

NEMA Direct-Current-Excited Synchronous Motor:
Unless otherwise stated, it is generally understood that a synchronous motor has field poles excited by direct current.

NEMA Permanent-Magnet Synchronous Motor:
A permanent-magnet synchronous motor is a synchronous motor in which the field excitation is provided by permanent magnets.

NEMA Reluctance Synchronous Motor:
A reluctance synchronous motor is a synchronous motor similar in construction to an induction motor, in which the member carrying the secondary circuit has a cyclic variation of reluctance providing the effect of salient poles, without permanent magnets or direct-current excitation. It starts as an induction motor, is normally provided with a squirrel-cage winding, but operates normally at synchronous speed.

Design Letters of Polyphase Squirrel-Cage Medium Motors

NEMA Design A:
A Design A motor is a squirrel-cage motor designed to withstand full-voltage starting and developing locked-rotor torque at 60 hertz and 50 hertz and having a slip at rated load of less than 5 percent.

NEMA Design B:
A Design B motor is a squirrel-cage motor designed to withstand full-voltage starting, developing locked rotor, breakdown, and pull-up torques adequate for general application at 60 hertz and 50 hertz and having a slip at rated load of less than 5 percent.

NEMA Design C:
A Design C motor is a squirrel-cage motor designed to withstand full-voltage starting, developing locked rotor torque for special high-torque application for 60 hertz and 12.35.2 for 50 hertz, and having a slip at rated load of less than 5 percent.

NEMA Design D:
A Design D motor is a squirrel-cage motor designed to withstand full-voltage starting, developing high locked rotor torque for 60 hertz and 50 hertz, and having a slip at rated load of 5 percent or more.

Single Phase NEMA Motors

NEMA Design N:
A Design N motor is a single-phase small motor designed to withstand full-voltage starting and with a locked-rotor current.

NEMA Design O:
A Design O motor is a single-phase small motor designed to withstand full-voltage starting and with a locked-rotor.

Single-phase medium motors include the following:

NEMA Design L:
A Design L motor is a single-phase medium motor designed to withstand full-voltage starting and to develop a breakdown torque with a locked-rotor current.

NEMA Design M:
A Design M motor is a single-phase medium motor designed to withstand full-voltage starting and to develop a breakdown torque with a locked-rotor current.

Single-phase squirrel-cage induction motors are classified and defined as follows:

NEMA Split-Phase Motor:
A split-phase motor is a single-phase induction motor equipped with an auxiliary winding, displaced in magnetic position from, and connected in parallel with, the main winding. Unless otherwise specified, the auxiliary circuit is assumed to be opened when the motor has attained a predetermined speed. The term “split-phase motor,” used without qualification, describes a motor to be used without impedance other than that offered by the motor windings themselves, other types being separately defined.

NEMA Resistance-Start Motor:
A resistance-start motor is a form of split-phase motor having a resistance connected in series with the
auxiliary winding. The auxiliary circuit is opened when the motor has attained a predetermined speed.

NEMA Capacitor Motor:
A capacitor motor is a single-phase induction motor with a main winding arranged for direct connection to a source of power and an auxiliary winding connected in series with a capacitor. There are three types of capacitor motors, as follows.

NEMA Capacitor-Start Motor:
A capacitor-start motor is a capacitor motor in which the capacitor phase is in the circuit only during the starting period.

NEMA Permanent-Split Capacitor Motor:
A permanent-split capacitor motor is a capacitor motor having the same value of capacitance for both starting and running conditions.

NEMA Two-Value Capacitor Motor:
A two-value capacitor motor is a capacitor motor using different values of effective capacitance for the starting and running conditions.

NEMA Shaded-Pole Motor:
A shaded-pole motor is a single-phase induction motor provided with an auxiliary short-circuited winding or windings displaced in magnetic position from the main winding.

NEMA Single-Phase Wound-Rotor Motors:
Single-phase wound-rotor motors are defined as follows:

NEMA Repulsion Motor:
A repulsion motor is a single-phase motor which of power and a rotor winding connected to a and are so placed that the magnetic axis of winding. This type of motor has a varying-speed

NEMA Repulsion-Start Induction Motor:
A repulsion-start induction motor is a single- but at a predetermined speed the rotor winding equivalent of a squirrel-cage winding. This type induction motor with constant speed characteristics.

NEMA Repulsion-Induction Motor:
A repulsion-induction motor is a form of repulsion addition to the repulsion motor winding.

NEMA Universal Motors:
A universal motor is a series-wound motor designed to operate at approximately the same speed and output on either direct-current or single-phase alternating-current of a frequency not greater than 60 hertz and approximately the same rms voltage.

Series-Wound Motor:
A series-wound motor is a commutator motor in which the field circuit and armature circuit are connected in series.

Compensated Series-Wound Motor:
A compensated series-wound motor is a series-wound motor with a compensating field winding. The compensating field winding and the series field winding shall be permitted to be combined into one field winding.

Alternating Current Generators:
Alternating current generators are of two basic types, induction and synchronous, and are defined as follows:

Induction Generator:
An induction generator is an induction machine driven above synchronous speed by an external source of
mechanical power for use as a generator.

Shunt-Wound Generator:
A shunt-wound generator is a direct-current generator in which the field circuit is connected either in parallel with the armature circuit or to a separate source of excitation voltage.

Compound-Wound Generator:
A compound-wound generator is a direct-current generator which has two separate field windings—one, usually the predominating field, connected as in a shunt-wound generator, and the other connected in series with the armature circuit.

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