Abstract

Induction motors are the most predominant motors used in the industry. They use two-thirds of the total electrical energy generated in the industrialized countries. Motors fail due to many reasons and many are rewound two or more times during their lifetimes. It is generally assumed that a rewound motor is not as efficient as the original motor. Precise estimation of efficiency of a refurbished motor or any existing motor is crucial in industries for energy savings, auditing and management. Full-load and partial load efficiency can be determined by using the dynamometer procedure which is a highly expensive way and available only in well-equipped laboratories. An inexpensive and easily applied procedure for efficiency estimation is therefore a target of researchers and engineers in the field. In this Ph.D. work, two novel methods for estimating repaired, refurbished, or any existing induction motors’ efficiency are proposed. The two methods (named Method A and Method B) require only a DC test (including temperature measurement), nameplate details, and RMS readings of no-load input power, input voltage, and input current. Experimental and field results of testing a total of 196 induction motors by using Method A are presented and the degree of accuracy is shown by comparing the estimated efficiencies to the measured values. Method B was validated by testing 8 induction motors with acceptable accuracy. To provide the necessary credits to the proposed techniques, an error analysis study is conducted to investigate the level of uncertainty through testing three induction motors, and the results of uncertainty of the direct measurements and no-load measurements using the proposed technique are declared.
Derating is a necessary procedure to protect induction motors from overheating which is the main reason of motor failures. The overheating is caused by operating induction motors with unbalanced voltages, over or undervoltage, or harmonics rich power supplies. To derate a machine, its full-load efficiency with balanced undistorted voltages and with unbalanced or distorted voltages must be measured.
In many situations in industry and due to critical processes, it is not allowed to interrupt induction machines operation. Hence, an in situ efficiency estimation technique is most required.
In this thesis, three novel in situ efficiency estimation algorithms are proposed. The first algorithm is to estimate the full-load and partial loads efficiency of induction motors operating with balanced undistorted voltages. The algorithm is validated by testing 30 induction motors with acceptable accuracy.
The second proposed algorithm is for full-load efficiency estimation of induction motors operating with unbalanced voltages. The technique is evaluated by testing 2 induction motors with different levels of voltage unbalance. The results showed an acceptable accuracy.
The third proposed algorithm is for full-load efficiency estimation of induction motors operating with distorted unbalanced voltages where the harmonics effect is added. The technique is evaluated by testing 2 induction motors with different levels of voltage unbalance. The results showed an acceptable accuracy.
The three novel algorithms are designed by using Genetic Algorithm, pre-tested data, and IEEE Method F1 calculations.