Load Losses In Induction Machines Research Articles

When loads stray: Evaluation of Different Measurement Methods to Determine Stray Load Losses in Induction Machines

The efficiency data provided by manufacturers are measured or calculated according to different national and international standards. These standards use different means to incorporate the stray load losses; thus the efficiency values obtained from different testing standards can differ by several percent. This leads to problems in competition and to a potentially confusing situation for the manufacturers and customers. This paper evaluates different measurement methods to determine stray load losses in induction machines.

Comparison of Different Evaluation Methods to Determine Stray Load Losses in Induction Machines With Eh-Star Method

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The eh-star method is a simple and economical alternative test for stray-load-loss assessment in induction machines, also for higher efficiency above 96%. It is an asymmetrical circuit where two machine phases are connected in parallel through an auxiliary <emphasis emphasistype="boldital">ohmic</emphasis> resistance <formula formulatype="inline"><tex Notation="TeX">$R_{\rm eh}$</tex></formula> without coupling of the machine and without needing any dynamometer. This resistance shall be adjusted, so that the positive sequence current <formula formulatype="inline"><tex Notation="TeX">$I_{1}$</tex></formula> stays below 30% of negative sequence current <formula formulatype="inline"><tex Notation="TeX">$I_{2}$</tex></formula>. If this pure “<emphasis emphasistype="boldital"> ohmic</emphasis>” resistance is not available, the eh-star measurement can be done with an impedance <formula formulatype="inline"><tex Notation="TeX">$\underline{Z}_{\rm eh}$</tex></formula>, preferably <emphasis emphasistype="boldital">ohmic</emphasis> inductive. The determination of stray load losses must be done from the measured losses by decomposition into positive and negative sequence losses. Negative sequence losses at slip <formula formulatype="inline"><tex Notation="TeX">$2 - s \approx 2$</tex></formula> correspond to stray load losses similar to the standardized reverse-rotation test (RRT). For this evaluation, the phase angles of measured currents and voltages must be known. This can be done by calculation with three different methods A, B, and C, which yield identical results for ideal <emphasis emphasistype="boldital">ohmic</emphasis> resistance <formula formulatype="inline"><tex Notation="TeX">$R_{\rm eh}$</tex></formula>. Method A is only useful for an <emphasis emphasistype="boldital">ohmic</emphasis> resistance <formula formulatype="inline"><tex Notation="TeX">$R_{\rm eh}$</tex> </formula> for determination of loss separation. Method B is based on the measured two line-to-line motor-input-power values <formula formulatype="inline"><tex Notation="TeX">$P_{{\rm e}, {\rm in}\_{\rm UV}}$</tex></formula> and <formula formulatype="inline"><tex Notation="TeX">$P_{{\rm e}, {\rm in}\_{\rm WV}}$</tex></formula>. Instead of <formula formulatype="inline"><tex Notation="TeX">$R_{\rm eh}$</tex></formula>, also an impedance <formula formulatype="inline"> <tex Notation="TeX">$\underline{Z}_{\rm eh}$</tex></formula> (inductor, capacitor, or resistor) may be used. Method C is similar to method B, but only the measured total motor input power <formula formulatype="inline"><tex Notation="TeX">$P_{{\rm e}, {\rm in}}$ </tex></formula> is needed. A comparison of evaluated stray load losses with the three evaluation methods is given with theoretical examples and measurements. This is compared to stray load losses and measured with RRT and input–output method according to IEEE-112. </para>

When Loads Stray: Evaluation of Different Measurement Methods to Determine Stray Load Losses in Induction Machines

When Loads Stray: Evaluation of Different Measurement Methods to Determine Stray Load Losses in Induction Machines

Stray Load Losses in Induction Machines A Review of Experimental Measuring Methods and a Critical Performance Evaluation

Stray Load Losses in Induction Machines A Review of Experimental Measuring Methods and a Critical Performance Evaluation

Thermal effects of stray load losses in induction machines

Additional heat produced in induction machines due to stray load losses could influence the plant rating, winding insulation design, operating limit and the machine protection design. Quantifying this additional heat and stray load losses accurately and, hence, investigating the extent of some of these influences are the concerns of this paper. Two experimentally verified models, electrical and thermal, are presented. Results of a practical exercise on the measurement of stray load losses by different test methods are reported. The study, thereafter, gives insight into the relationship between stray load losses and the influences mentioned above and contribute results, which are useful to the design and operation of this machine and its protection.

Stray Losses in Induction Machines: Part I, Definition, Origin and Measurement

The state of the art of stray load losses in induction machines is discussed with respect to definition, origin and effects, and measurement techniques. The historical search for a definitive evaluation technique for these losses is discussed together with the recognized criticisms of each approach. It is noted that although this subject has been the object of intensive investigations for more than seventy years there is still very little agreement on either the origin or evaluation of stray load loss. This paper discusses the major works in the area with the objective of delimiting the problem so that a rational approach for future work may be promulgated.

Stray Losses in Induction Machines: Part II, Calculation and Reduction

The definition, origin and measurement of stray load losses in induction machines have already been addressed in a companion paper. This paper completes the study by examining the mechanisms for prediction of those losses as well as some techniques for reduction. It also suggests some directions for future work.