It must be removed from the motor and may adversely affect longevity. The heat is an undesired byproduct of this conversion. Some of the electric energy is lost to heat, another form of energy, due to I2R losses (also called copper losses) in the motor windings. Unfortunately, electric motors are not 100% efficient. Such has been the case with diesel-electric locomotives on a smaller scale for many years.Īt the system level, (Figure above) a motor takes in electrical energy in terms of a potential difference and a current flow, converting it to mechanical work. The figure above shows the family tree of the AC motors described in this chapter.Ĭruise ships and other large vessels replace reduction geared driveshafts with large multi-megawatt generators and motors. And, the stepper motor, a digital version of the motor, is driven by alternating current square waves, again, generated by solid-state circuitry. The brushless DC motor, actually an AC motor, is replacing the conventional brushed DC motor in many applications. Modern solid-state electronic circuits drive brushless DC motors with AC waveforms generated from a DC source. Above one horsepower (750 W), the Tesla motor reigns supreme. Yet small brushed AC motors, similar to the DC variety, persist in small appliances along with small Tesla induction motors. Its ruggedness and simplicity make for long life, high reliability, and low maintenance. His new type of motor, the AC induction motor, is the workhorse of the industry to this day. Nikola Tesla envisioned an entirely new type of motor when he visualized a spinning turbine, not spun by water or steam, but by a rotating magnetic field. Steinmetz contributed to solving these problems with his investigation of hysteresis losses in iron armatures. Figure 5.1 AC electric motor family diagramĬharles P.
Initially, AC motors were constructed like DC motors, but numerous problems were encountered due to changing magnetic fields. However, motors were a problem with alternating current. Transmission of electrical energy covered longer distances at a lower loss with alternating current. The lighting worked as well on AC as on DC. For the iTIG III Model D the leads are the high voltage output leads so the micro Ohm winding resistance measurement can be part of an automatic sequence of motor tests including high voltage tests.After the introduction of the DC electrical distribution system by Edison in the United States, a gradual transition to the more economical AC system commenced. It eliminates the lead resistance and is typically more accurate.Īll winding resistance measurements done with Electrom Instruments motor testers are done with a four lead system. This type of resistance measurement will include the tester’s leads in the winding resistance test’s measurement. Resistance can be measured with two leads connected to a DUT. The difference in percent to the target resistance value is then calculated.Ī temperature correction factor can automatically be applied to correct the measurement to a standard temperature so results can be more accurately tracked over time with the winding analyzer. Using Ohm’s law the resistance is calculated in µΩ (micro Ohms) or mΩ (milli Ohms) by the winding analyzer.įor a 3-phase motor, 3 resistance measurements are normally done between the phases, and the balance or imbalance between the 3 measurements is calculated and displayed along with the measurement values.įor single coils and sometimes for motors, the resistances measured may be compared to a resistance value instead of having a balance calculated.
Winding resistance tests are a measurement of the applied DC voltage and current to the device under test -DUT. Some of these are the wire gauge issues, resistive connections, and blown or disconnected magnet wires in hand. Winding resistance is an important measurement because other tests and measurements will not find some of the problems a resistance measurement will find.
The winding resistance test is used to find open windings, shorts to ground, wrong turn count, wrong wire gauge, resistive connections, round wires in hand that are not connected in a coil, some connection mistakes, the resistance balance between phases, and in some cases shorted turns.