Questions and Answers of Electrical Systems For Buildings

Consider an MCC with six identical motors, each motor rated at 60 HP, three-phase, 60 Hz, 460 V, 1760 RPM, a service factor of 1.00, and a power factor of 90%. All the motors are protected by
Consider an MCC with nine identical motors, each motor rated at 50 HP, three-phase, 60 Hz, 460 V, 1175 RPM, a service factor of 1.00, and a power factor of 90%. All the motors are protected by
A motor control center has three induction motors each rated at 40 HP and 480 V and 4 induction motors each rated at 30 HP and 480-V. Each 40-HP motor has an efficiency of 0.92, 1172 rpm, a power
For this problem, consider the single-line diagram for a building power system shown in Figure 8.34. In particular, the utility system short-circuit kVA capability is 850,000 kVA with X/R = 6.0.
Using the radial electrical distribution system of Figure 8.34, determine the unit substation specifications and the electrical room size. The primary feeder is protected by a fused switch.(a)
A homeowner is considering adding a sunspace to his home. The project is completed during 4 years and requires \($20,000\) to be spent the first year, \($15,000\) the second year,(\($10,000\)\) the
An energy audit indicates that a home consumption is 20,000 kWh/year. By using Energy Star appliances and CFLs, a savings of 20% can be achieved for the electrical energy use. The cost for the home
An air conditioner (AC) consumes 7500 kWh annually with an overall efficiency of COP = 3.0. If this AC is replaced by a more energy-efficient AC (COP = 3.7) at a cost of $3500.(a) Determine the
Two air conditioner systems are proposed to cool a house. Each AC has a rated capacity of 5 tons and is expected to operate 500 full-load equivalent hours per year. Air conditioner A has a standard
A company has contacted you regarding their rate schedule. The company is on the rate schedule defined in Problem 9.11 as service level 3 (secondary service), but are near transmission lines and so
For an apartment building with a total of 20 incandescent lamps rated at 60 W. Determine the energy-saving potential if these lamps are replaced with 13 W CFLs. The lifespan of incandescent lamp and
For a house with a total 20 of incandescent lamps rated at 60 W, determine the energy-saving potential if these lamps are replaced with(a) 13 W CFLs and(b) 7 W LED lamps. The lifespan of incandescent
Estimate the annual phantom load for a TV with a set-top box if the TV is operated 5 h/day. Determine the annual cost of the phantom load energy if the electricity cost is 0.12/kWh.
Estimate the annual phantom load for an audio mini-system operated 3 h/day. Determine the annual cost of the phantom load energy if the electricity cost is 0.10/kWh.
Consider a ranch house of 100 m2 located in Phoenix, CO, with a total window area of 15 m2 with double-pane glazing that has a visible transmittance of 0.35. The home has 20 incandescent lamps, each
Determine the energy and cost savings of daylighting harvesting to a thin two-story house building (each floor is 24 ft × 50 ft) with a window-to-floor area ratio of 30%. The building has clear
Based on the analysis of voltage measured for a lighting panel, it was found that the rms values for the fundamental, the third, the fifth, the seventh, and the ninth harmonics that make up the
Based on the analysis of current measured for a power panel, the rms values for the fundamental, the third, the fifth, and the seventh harmonics that make up the voltage waveform are estimated to be
Estimate the current THD of a desktop computer with its monitor. Use the data provided in Table 11.2. TABLE 11.2 Limits for Harmonic Currents for 120 V-69 kV Distribution Systems Set by IEEE
Determine the k-factor required for a transformer supplying a load made up of 245 A for fundamental harmonic, 115 A for the third harmonics, 75 A for the fifth harmonics, 50 A for the seventh
Determine AC resistance values for a 400 MCM copper conductor serving a lighting panel. Consider the fundamental as well as the third, the fifth, the seventh, and the ninth harmonics.
For the 400 MCM copper conductor, estimate the current rating factor q if the rms current values for the various harmonics are I1 = 310 A (fundamental harmonic), I3 = 120 A (third harmonics), I5 =
A 2500 kVA transformer rated at 13.8 kkVA–480Y/277 V with an impedance of 5%. Determine the resonance frequency as a function of the size in kVAR capacitor banks ranging from 100 to 1000 kVAR.

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