Virtual instruments (VIs) for study of asynchronous motor functional characteristics

In this paper, using Lab View graphical programming environment are implemented the virtual instrumentation´s concept, realizing three virtual instruments which are been used at the study of asynchronous motor functional characteristics. In this study, the asynchronous motor is in case of steady state regime. It starts from the per phase equivalent diagram in T for these Virtual Instruments designed. In this diagram the sinusoidal time dependent quantities (U₁, I₁ are voltage and current of the stator circuit; I´₂ is current of the rotor circuit, with respect to the stator and I₀ is no-load current in synchronism) are represented by complex functions. With these virtual instruments, it can obtain the functional motor´s characteristics such as: the principal parameters (input current I₁, input power P₁, power factor PF, developed power P₂, developed torque T, motor efficiency RAND) depending by motor´s slip s or by his mechanical speed n₂. These quantities result from formulas, using the motors parameter (R₁, X₁ represent the stator resistance and the inductive leakage reactance; R´₂, X´₂ represent the rotor resistance and the inductive leakage reactance per phase of the rotor circuit, referred to the stator; R_Fe represent resistance stands for core losses; X_m represent magnetizing reactance); all of these motor´s parameters are easily entered as numerical values, following their effect on each characteristic separately. The rated frequency and supply voltage (U_1n and f_1n), the losses (p_{f, v} and p_sFe2) or the number of machine pole pairs (p) as constructive parameter of the motor can be also numerical entered. Each of the three Virtual Instruments allows setting three different values of supply voltage, frequency, suplimentary rotor´s resistance and displays four functional characteristics.