Peculiarities of Operation Modes of A.C. Machine with Short-Circuited Rotor Windings at Nonsinusoidal Power Supply

Abstract

This chapter deals with peculiarities of losses distribution in rotor short-circuited loops obtained based on the investigation of their currents distribution.

Appendices

Appendix 15.1

See Table 15.1.

Brief Conclusions

By operation in nonlinear networks:

• 1. In an induction machine without cage damage, all its bars are practically in equal thermal and mechanical state: the same refers to ring portions. This state is violated if there is a damage in cage.

• 2. In salient-pole machines thermal condition of damper winding is caused by uneven distribution of currents and losses in its elements. The law of currents distribution depends on the ratio of amplitudes of “adjacent” harmonics and on the difference of initial phases T_U. If the amplitude of one of these harmonics is much less than the second, the law of currents distribution in nonlinear network approaches that of currents distribution in asynchronous mode.

• 3. Besides known measures on the reduction of additional losses and overheats in damper winding structural elements given in Chap. 3, reduction of losses can be achieved by a difference increase of “adjacent” harmonics initial phases T_U within the range π/2 ≤ T_U ≤ π.

List of Symbols

m:

Order of stator MMF spatial harmonics

m_PH :

Number of stator winding phases

N:

Bar number (ring portion or segment) of damper winding or cage rotor

N₀ :

Number of bars of damper winding per pole or number of bars in squirrel cage

N = N₁, N₂, …, N₀ :

Numbers of bars and ring portions (segments) on pole

${\text{P}}(\upomega_{{{\text{ROT}},1}} ), \ldots ,{\text{P}}(\upomega_{{{\text{ROT}},2}} ) \ldots$ :

Losses in squirrel cage from currents with frequencies $\upomega_{{{\text{ROT}},1}} ,\upomega_{{{\text{ROT}},2}} \ldots$

P_CAG.RES :

Total losses in squirrel cage from rotor currents with frequencies $\upomega_{{{\text{ROT}},1}} ,\upomega_{{{\text{ROT}},2}} , \ldots$

P_D.RES :

Total looses in damper winding with frequencies $\upomega_{{{\text{ROT}},1}} ,\upomega_{{{\text{ROT}},2}} , \ldots$

p:

Number of pole pairs

Q:

Order of stator current time harmonic

T_U :

Difference of initial phases of two higher “adjacent” voltage harmonics

ω₁ :

Network circular frequency (frequency of stator current first harmonic)

ω_REV :

Angular speed of rotor rotation

ω_ROT,1, ω_ROT,2,…:

Circular frequencies of rotor currents