Impact of voltage impurity and load fluctuation on induction-motor current

Impact of voltage impurity and load fluctuation on induction-motor current

spectrum, with accounting for eccentricity, slotting and cage damage

J. Rusck

AGH University

Chair of Electrical Machines

Al. Mickiewicza 30, 30-059 Krakow, Poland

phone: (48 12) 6172897 - fax: (48 12) 6341096 - e-mail: gcrusck@cyf-kr.edu.pl

Приведеная статья была одним из докладов на 15-ой международной конференции по электрическим машинам "ICEM - 2002". Список статей которые докладывались на конференции, среди которых находится и данная статья находятся по адресу: http://icem.metu.edu.tr/icem2002content.htm
Печатный вариант приведенной статьи находится по адресу: http://www.bpp.agh.edu.pl/bpp.phtml

Frequencies of slot harmonics are concluded from the specific harmonic-balance model, having the form of algebraic equations included in the paper. Scrutiny of derivative of the frequency of the first slot harmonic, with respect to the rotor speed, allowed to judge about the number of rotor slots, prior to receiving the data from manufacturer. To this end the machines' categories, from website http://galaxv.uci.agh.edu.pl/~gerusek/Caiegorv2.htm were made use of. The necessary current spectra have been measured. Making use of the machine's geometrical dimensions and of the model accounting for slotting and eccentricity, current spectra have been calculated for the supply voltages containing 50, 150, 250 and 350 Hz contributions, and for fluctuating loading.

Fig. la presents registered current by no-load operation.

Fig. I. Measured current of the no-loaded 4 - kW, p = 2, Δ, 220 V - fed machine, a– waveform., b – spectra: 10000 samples over 5 s.

The spectrum in Fig. I b contains the slot harmonic of 645.66 Hz, which is associated with fundamental or 50 Hz current component. The reason for the 150, 250 and 350 Hz components is the pollution of the supply system. The sidebands around 50 Hz are caused by load fluctuation due to stiff but imperfect clutching of several machines.

Calculations consist in numerical integration of differential equations. Inductances of separate circuits were established in a numerical way, accounting for rotor bars' skew. One of these inductances is presented in Fig. 2. These inductances allowed to calculate the waveforms of the currents in Fig. 3 (no-load operation) and 4 (loading).

Fig.2.Calculated mutual inductance: 1^st stator phase – 1^st rotor mesh (accounting for rotor bars' skew).

Fig.3. Calculated supply current. No-load. 380 V, Δ, 50 Hz, plus: 1.52 V of 150 Hz, 11.4 V of 250 Hz, 3.8 V, of 350 Hz plus: 7.986 Nm (30% of T_N) of the fluctuating torque.

Fig.4. Calculated supply current. Loading, a – static + dynamic eccentricity, b – no eccentricity + 0.3 Nm of fluctuating torque.

Similarity of the current spectra in Figures 4b and e allows to conclude that the rotor-angle dependable, fluctuating load component has similar impact on the current spectrum as the mixed (static + dynamic) eccentricity.

References

[1] K. Oberretl, “Parasitaere synchrone Dreh- und Pendelmomen-te in Asynchronmotoren, Einfluss von Asugleichsvorgaengen und Eisensaettigung. Teil I: Stationaerer Zustand,” in Archiv fuer Elektrotechnik, No. 77, pp. 79-190, 1994.

[2] J. Rusek, Computer analysis of the induction machine

utilizing harmonic balance (in Polish), AGH Uczelniane Wydawnictwa Naukowo–Dydaktyczne, Krakow (2000).

[3] http://galaxy.uci.agh.edu.pl/~gerusek/Category2.htm

[4] P. Dybowski, Measurements and modelling of current

symptoms of induction machines’ ailments (in Polish), AGH– WEAIE Doctor Thesis, Krakow (2001).

[5] J. Rusek, “Reflection of eccentricities in spectral composition of currents of induction machines,” in Proc. ICEM1996 (Vigo), Vol. II, pp. 470-475.