توضیحاتی در مورد رابطه گشتاور در موتور هیسترزیس

[سمندون 19437]

Hysteresis Motor

Construction. The stator of hysteresis motors is produced in the same types

of construction as motors with magnet rotor, i. e. with slots, with claw poles

or with split poles. The rotor has a ring of hysteresis material. This is similar

to permanent-magnetic materials; the hysteresis loop, however, is less broad

and not prepolarized.

Mode of functioning. The ampere turns of the stator generate a field

rotating with synchronous speed (Eq. 2.99). They permanently reverse the

magnetization of the hysteresis rotor, so long as it stops or rotates slower

as the rotating field. The magnetic state of the rotor elements runs through

the whole hysteresis loop. The hysteresis losses PH generated by that are

proportional to the remagnetizing frequency

f2 = s · f1 (2.112)

with the slip s of the rotor with regard to the rotating field according to

Eq. (2.100). In the hysteresis material hysteresis losses arise analogously to

the rotor losses in asynchronous motors (Fig. 2.138, left):

PH = PV2 = s · Pδ (2.113)

and at the shaft, the output power is given by

P = (1 − s)Pδ . (2.114)

Neglecting first the eddy currents generated by the rotating field, no currents

flow in the rotor, which are reacting upon the air-gap field. The stator current

does not depend on the load, because there is no armature reaction. Therefore,

the power losses of the stator PV1 and the input power coming from the power

supply P1 are constant. As a result, the air-gap power is constant, too:

Pδ = P1 − PV1 . (2.115)

Therefore, the torque generated by the hysteresis is constant according to

Eq. (2.105):

T = P

2πn

= Pδ

2πns

. (2.116)

The above statements are valid for ideal motors. In reality, eddy-current

losses arise in every hysteresis rotor proportional to the square of the rotor

frequency sf1. The eddy-current torque TE is inversely proportional to the

slip. Therefore, it decreases linearly with the slip or with increasing speed

(Fig. 2.138, middle). The torque characteristic of real hysteresis motors is

2 Motors for Continuous Rotation 151

Fig. 2.138. Powers and torques of hysteresis motors. a, b Ideal motor. c Real motor

shown in Fig. 2.138 on the right side for three-phase or AC operation. Caused

by leakage fluxes and a generally high harmonic content of the air-gap field,

the real torque characteristic differs from that of an ideal motor. It is typical

for a hysteresis motor that it starts independently without swinging in and

pulls softly into synchronism. In the synchronism poles are formed. Now the

hysteresis motor acts like a magnet-rotor motor, but it creates a torque, which

is 20 to 30 times smaller. Therefore, gearings with a great reduction ratio are

used, in order to get sufficiently great torques for the respective application

case. Due to the low utilization hysteresis drives have considerably lost in

importance today.

 

 

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