Electrical Power Quality Experiments

This paper describes several experiments that can be performed with a second generation power harmonics analyzer, such as the Fluke 43, or with an oscilloscope. Two of the experiments described herein involve transient phenomena, while the third demonstrates the capabilities of inexpensive UPS devices. Introduction Power quality problems may arise due to a variety of phenomena that occur on time scales ranging from less than a millisecond to steady-state. Each of these phenomenon cause different effects in the power system and require different solutions to avoid problems. A previous paper demonstrated several power quality experiments that could be performed with a first generation power harmonics analyzer, such as the Fluke 41. Those experiments concentrated primarily on harmonics. This paper describes several additional experiments that can be performed with a second generation power harmonics analyzer, such as the Fluke 43, or with an oscilloscope. Two of the experiments described herein involve transient phenomena, while the third demonstrates the capabilities of inexpensive UPS devices. The emphasis on these experiments was to keep the cost relatively low and to provide the student with a good demonstration of the applicable phenomena. The paper will show typical lab setups, procedures, and results. Induction motor starting current and system voltage drop The first experiment demonstrates the starting current and system voltage drop of a three-phase induction motor. Figure 1 illustrates the set-up for this experiment. Two power sources are provided for the induction motor. The first is the three-phase supply from the bench (stiff source), while the second places a three-phase transformer between the bench supply and the motor (weak source). The stiff source is rated substantially higher than the motor, while the weak source is rated only slightly higher than the motor. By using the transformer, the effect of starting a large motor in a plant is obtained. The first part of this experiment is the observation of the starting current of the motor. It is well known that induction motors draw six to eight times rated current when starting. Furthermore, the duration of the starting current is affected both by the load on the motor and by the voltage that is applied to the motor. The load for the motor consisted of a DC generator that could be connected to the shaft of the motor as shown in Figure 1. A resistive load allows the generator load to be varied. The generator and resistive load were set to provide somewhat above rated motor load at normal operating speed. Of course the output of the generator is a function of