The power falls to zero three times during each cycle. The resistances per phase are: high voltage 35 Ω, low voltage 0.876 Ω and the iron loss is 3050 W. Calculate the value of efficiency at 1 Chapter 11 Balanced Three-Phase Circuits 11.1-2 Three-Phase Systems. The Three-Phase Voltage System Three-phase voltage systems are composed of three sinusoidal voltages of equal magnitude, equal frequency and separated by 120 degrees. •The angle between V & I is the angle on the impedance. Three-phase ac power has a number of advantages over other means of power distribution. Answer: Applying the three-phase formula for voltage drop, where: K = 21.2 ohms-cmil/ft for aluminum; I = 100 amps; D = 80 ft; cmil = 83,690 cmil. Peak Output Voltage = peak of the line of line voltage = 3×Vm 2. Line to line voltage: W applied = 3 1/2 U ll I cos Φ = 3 1/2 U ll I PF (1) where. Analysis of 3 phase rectifier with resistive load: Notation: Let V m = Peak line to neutral voltage Useful Integration formula: 4 3 6 6 cos ( ) 6 ∫ 2 = + − π ω ω π π td t 1. This means that three-phase power … This produces superior operating characteristics for three-phase motors. Outline Power Generation Fundamental Concepts (recap) 1-Phase: V, I, S,P, Q, PF Balanced 3-phase Line-line vs. line- neutral voltage Figure 7 – Delta connection – three phase, three wires. 11.3 Analysis of the Y-Y Circuit. The main advantage is that, since the phase currents of three-phase power cancel each other out, it is possible to reduce the size of the neutral wire or to eliminate it altogether. Single- phase loads are connected to one leg of the wye between line and neutral. 11.5 Power Calculations in Balanced The Wye configuration is used to distribute power to everyday single-phase appliances found in the home and office. The three phase circuits would be used to power motors whereas the single phase branches of the three phase service would typically be used for lighting, heating and fractional horsepower motors. Figure 1 Three-Phase Voltage System Sequence {1-2-3} V12 Reference Figure 1 illustrates real-time cosine functionality and associated phasor notation for a 3-phase line-to-line A 500-kVA, 3-phase, 50 Hz transformer has a voltage ratio (line voltages) of 33/11 kV and is delta/star connected. Most AC power today is produced and distributed as three-phase power where three sinusoidal voltages are generated out of phase with each other. So, VD = 1.732 x 21.2 x 100 x 80/83,690 = 3.51 Voltage Drop Example 3 — Find the size of copper wire needed in a single-phase application to carry a A common electrical service to commercial and industrial users would be 480-3-60. 11.4 Analysis of the Y- Circuit. Real Power. In a three-phase system, the power delivered to the load is the same at any instant. Since the phase impedances of balanced wye or delta loads contain equal currents, the phase power is one-third of the total power. POWER IN BALANCED THREE-PHASE LOADS •The voltage across is line voltage •The current is phase current. With single-phase AC power there is only one single sinusoidal voltage. Go back to Three phase power measurements ↑ Wye and Delta comparison. The power delivered by a three-phase circuit pulsates also, but it never falls to zero, Figure 12-2. 3. (The “480” designates Average Value of the output voltage may be got by averaging over a single W applied = real power (W, watts)

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