Download Three-Phase ac Measurements - Experiment #1 | ECE 469 and more Lab Reports Electrical and Electronics Engineering in PDF only on Docsity! ECE 431 Experiment #1 Three-Phase ac Measurements PERFORMED: 26 January 2005 WRITTEN: 28 January 2005 Jason Wells LEADER: Jason Wells RECORDER: Nathaniel Hakes 2 1 Introduction The primary objectives of the experiment on three-phase ac measurement include becoming familiar with the laboratory equipment as well as reviewing three-phase voltage, current, and complex power relationships studied in previous courses. These objectives were met by investigating a wye-connected resistive load, a delta-connected complex load, and an induction motor operating under no load conditions. This experiment also introduced the one-wattmeter and two-wattmeter methods for measuring reactive and real power, respectively. 2 Discussion and Results 2.1 One-Wattmeter and Two-Wattmeter Method Although equipment exists than can directly analyze three-phase real and reactive power, it is often expensive and delicate. As such, it is occasionally desirable to utilize relatively inexpensive single-phase power meters to determine these quantities in the field. This experiment introduced two such methods which are described in [1] on page 22. In the two-wattmeter method, the total three-phase real power of the load is determined by 3 1 2P P Pφ = + (1) where P1, P2, and φ , the power factor angle, are given by 1 3 cos(30 )l lP V I φ= + (2) 2 3 cos( 30 )l lP V I φ= − + (3) V Iφ θ θ= − (4) Notice that P2 will be equal to zero if whenever the voltage, current, or cos(-30+φ ) is equal to zero. This will occur when the power factor angle, φ , is equal to either -60 degrees or +120 degrees. Additionally, P1 will equal P2 if the power factor angle is equal to zero or 180 degrees (i.e. a purely resistive load). In the one-wattmeter method, the total three-phase reactive power is determined from the observed power by 3 3 obsQ Pφ = (5) 2.2 Balanced Wye-Connected Resistive Load With the one-wattmeter and two-wattmeter methods established, a wye-connected resistive load was tested to observe basic three-phase relationships according to the procedure in [1]. With a wye-connected load, the line-to-line, line, and phase relationships are described theoretically by 3ln llV V Vφ = = (6) lI Iφ = (7)
