Radovan Radosavljevic

A novel approach for temperature estimation in squirrel-cage induction motor without sensors

In this paper, the authors present a coupled thermal and electromechanical model for squirrel-cage induction motor simulation and analyses. The effect of iron saturation, rotor parameter variation due to current displacement (skin-effect) and temperature variations of both stator and rotor resistances are taking into account simultaneously. A new device for the temperature measurement in the stationary as well as rotating parts of electric machines is built. The unique construction of the device for continuous rotor temperature monitoring is briefly described. This device is a part of a complete acquisition system, which is used for precise testing and investigating of a coupled thermal and electromechanical phenomena. An original thermal observer based on the direct stator temperature measurement under normal running condition with no additional sensors is proposed.

Calculation of impulse characteristics for gas-insulated systems with homogenous electric field

The possibility of generating a statistical sample of the pulse breakdown voltage random variable numerically is examined for arbitrary shaped pulses. Impulse characteristics are then determined on the basis of the generated statistical sample. Numerically generated statistical samples of the pulse breakdown voltage random variable are compared to the corresponding experimentally obtained statistical samples. Impulse characteristics obtained from the numerically generated statistical samples are compared to the corresponding impulse characteristics derived from the semi-empirical Area Law and the Time Enlargement Law. The set of impulse characteristics obtained in this way is compared to the results obtained experimentally for different shapes of the pulse voltage load. Gases used in the experimental and numerical models include SF6, N2 and Ar. Gas pressures range from 1 × 102 Pa to 6 × 102 Pa, and inter-electrode gaps from 0.1 to 10 mm. A homogenous electric field is considered.

On the determination of characteristic temperatures in power oil transformers during transient states

ContentsUnder usual assumptions the equations describing thermal phenomena in a transformer are established. Without neglecting any substantially important factor, algorithms are developed for predicting the temperatures in critical spots in non-stationary states occurring either in practice or in load/time diagrams. This paper suggests the determinaton of conductances dependent on temperature and constant capacitances of equivalent thermal circuits of a transformer. They are based on a small number of experiments (as simple as possible) and on a parameter estimation procedure. In such a way the temperatures of transformer parts in different transient states can be determined by computer simulation established on equivalent circuits, so the operators in power and sub-stations will be able to load their transformers close to the permitted limit. It is felt that this paper may give a stimulation for a possible revision of IEC rules.ÜbersichtDie Gleichungen des Temperaturverhaltens eines Transformators werden unter den üblichen Annahmen aufgestellt. Es werden Algorithmen entwickelt, welche die Vorausbestimmung der Temperatur an kritischen Stellen bei nichtstationärem Betrieb erlauben. Vorgeschlagen wird die Bestimmung der temperaturabhängigen und-unabhängigen Parameter auf Grund von wenigen und einfachen Messungen. Damit kann das Personal in Verteilerstationen in die Lage versetzt werden, mit Hilfe von PCs die Belastung der Transformatoren bis zu den zulässigen Grenztemperaturen auszudehnen. Die Autoren möchten damit einen Anstoß zu einer möglichen Überarbeitung von IEC-Vorschriften geben.

A new thermal observer for squirrel-cage induction motor

In the present paper the authors built a device for the temperature measurement in the stationary as well as rotating parts of electric machines. The effectiveness of the device is tested in real working condition on squirrel cage induction machine. The unique construction of the device for continuous rotor temperature monitoring is briefly described. This device is a part of a complete acquisition system which is used for precise testing and investigating of a thermal process. A new thermal observer based on direct stator temperature measurement under normal running condition with no additional sensors is proposed.

Measurement of the transient electrical and shaft torques in an induction motor drive by the indirect two-speed method

ContentsThis paper presents a new method, called Indirect Two-Speed Method (ITSM), for obtaining electrical and shaft torques in an induction motor drive by means of measuring the speeds of both lumped-inertia elements assigned to a second order model. The measuring is realized by using high-resolution digital tachometers (represented by incremental encoders), two frequency measurement systems based on the Double-Buffered Method, digitalfiltering of the raw speed data and numerical differentiation of the filtered speed data.ÜbersichtIm Beitrag wird ein neues Verfahren zur Ermittlung des elektrischen Moments und des Wellen-Drehmoments eines Induktionsmotor-Antriebs vorgestellt. Das als Indirekte Zwei-Drehzahlen-Methode (ITSM) bezeichnete Verfahren geht aus von einem mechanischen Modell zweiter Ordnung und mißt die Drehzahlen beider als konzentrierte Parameter betrachteten Drehmassen. Für die Durchführung werden hochauflösende digitale Tachometer eingesetzt. Die Frequenzmessung erfolgt durch ein Verfahren mit doppelter Pufferung, und es werden die Rohdaten nach digitaler Filterung numerisch differenziert.