Technological Institute of the Philippines

• ELECTRICAL 857

• 1. A dc generator has a no-load output voltage rating of 120 Volts. Its armature circuit resistance is 0.95 ohm and its field coils are separately energized. If a load rated at 2 kW at 115 Volts is connected across the terminals, neglecting the effect of armature reaction and line drop, what power would be absorbed by the load? A. 1,670 Watts C. 2,000 Watts B. 2,180 Watts D. 1,518 Watts Answer: Given: 𝑅𝑎 = 0.95Ω 𝑉 = 120 V 𝑊 = 2 kW 𝑉𝐿 = 115 V Solution: 𝑅𝐿 = (𝑉𝐿) 2 𝑊 = 1152 2000 = 6.613Ω Then, 𝑅 = 𝑅𝐿 + 𝑅𝑎 𝑊𝐿 = 𝐼2𝑅𝐿 𝑅 = 6.613 + 0.95 = 7.563Ω 𝑊𝐿 = (15.867) 2 (6.613) By using Ohm’s Law, 𝑾𝑳 = 𝟏𝟔𝟔𝟒. 𝟗𝟎𝟎 𝐖 𝐼 = 𝑉 𝑅 = 120 7.563 = 15.867A 2. A shunt generator when running light as a motor at 1000 rpm takes 12 Amp from 115- Volt mains. The field current is 7 Amp, and the armature resistance is 0.03 ohm. Determine stray-power loss of the machine at this particular value of flux and speed. A. 574.25 W C. 575.25 W B. 576.25 W D.