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engineering
introduction to electrical power

Questions and Answers of Introduction To Electrical Power

Explain the subtransient and transient reactance of the synchronous generator.
Between the two rough estimates of fault current as per the IEEE standard, which multiplier with the generator rated current, 8.5 or 10, should you use in the structural design of the bus bars and
Transformer A has 5% impedance and transformer B has 7% impedance. Which one will see greater fault current at the LV terminals?
Describe in your own words how the motor load contributes to the fault current.
What trade-offs are involved in using and selecting the current-limiting series reactor?
Which mathematical method is used to analyze unsymmetrical (L-G, L-L, and L-L-G) faults?
Summarize in a paragraph the simple determination of the circuit breaker’s symmetrical fault current interruption rating.
Determine the general-purpose fuse rating for a single-phase, 120-V, 2-kW load circuit in the boiler room uptake, which has an ambient air temperature of 65°C. Assume the load equipment efficiency
Determine the time-delay fuse rating for a three-phase, 208-V, 5-hp motor branch circuit in the engine room, which has an ambient air temperature of 55°C. Assume the motor efficiency of 92% and
The 8.25-kV circuit breaker in Table 9.4 can be used for rated fault current interruption of 33 kA at a rated 8.25-kVLL system voltage. Determine the range of system voltage and interruption current
The 4.76-kV circuit breaker in Table 9.4 can be used for a rated fault current interruption of 41 kA at a rated 4.76 kVLL system voltage. Determine the range of system voltage and interruption
Identify equipment and reasons that may require time-delay fuse and fast acting fuse.
Why must each load branch circuit have an overload protection, in addition to the fuse?
Determine the continuous current rating and the rms fault current interruption rating of circuit breakers or fuses on both sides of a 100-kVA, 480-V Δ/208-V Y, three-phase transformer that has 5%
Determine the continuous current rating and the rms fault current interruption rating of a circuit breaker or fuse on both sides of a 300-kVA, 600-V Δ/ 208-V Y, three-phase transformer that has 6%
In the figure below, a three-phase, 1000-kVA, 480-V, Y-connected generator with ungrounded neutral has armature resistance Ra = 1% and subtransient reactance Xʺd = 10%. It feeds a three-phase,
How is the arcing prevented at the relay contacts while breaking the current?
In a health monitoring scheme for power factor correction capacitors shown in Figure 9.23, the three capacitor banks in phase A, B, and C draw 12 Arms each when healthy. Determine the neutral
Why do the circuit breaker contacts see arcing when the current is interrupted, and how is it blown away in circuit breakers?
What is the differential relay, and how does it work?
Describe the working of alternative ways of protecting major electrical equipment from lightning over voltages.
What does the protection coordination mean, and how is it achieved?
Briefly describe the arc flash analysis and the end product of it.
Identify three alternative ways an insulation between HV and LV conductors can break down, leading to flashover.
A 1000-kVA transformer is open for procurement. Vendor A offers 97% efficiency at $90,000 price, and vendor B offers 98% efficiency at $100,000 price.Determine the profitability of buying the
A 2-MVA transformer is open for procurement. Vendor A offers 96.5% efficiency at $160,000 price, and vendor B offers 97.8% efficiency at $180,000 price. Determine the present worth of buying the
Explain the difference between the terms interest rate and discount rate used in the economic analysis for determining a profitability of investment in a capital project.
In a large motor drive application under consideration, either a 5000-hp induction motor or a 5000-hp synchronous motor can be used. The estimated system efficiency of the synchronous motor with LCI
A 5000-hp variable-frequency motor drive is under consideration using either an induction motor or a synchronous motor. The estimated system efficiency of the synchronous motor with drive is 92%, and
What is the difference between simple payback period and discounted payback period?
A new 10-hp motor is required to replace an old one. It will run 500 h per month, and the energy cost is $0.15/kWh. You have two options available: (1) A standard motor with 90% efficiency at $1500
A new 25-hp motor is required to replace an old one. It will run 500 h per month, and the energy cost is $0.15/kWh. You have two options available:(1) A standard motor with 90% efficiency at $3000
Why is the power loss capitalization rate more important for the transformer and generator than for the motor?
The electrical power usage in a factory is shown in the table below. The utility contract calls for energy charge of $0.15/kWh and demand charge of $15 per peak kilovolt-ampere over any 15-min period
The table below shows a factory’s electrical power usage pattern. The utility contract calls for energy charge of $0.12/kWh and demand charge of $14 per peak kilovolt-ampere over any 15-min period
Differentiate clearly between poor power factor and poor efficiency, and their causes and remedies.
The daily power consumption profile of a customer is tabulated below, where the kilowatt loads are average over the period listed and kilovoltampere demand meter readings are peak over 15-min
Explain the difference between regenerative braking and dynamic braking and at what speed they take place.
Identify a few more candidates for RGB (other than those listed in the book).
Determine the capacitor rating in kVAR and also in farad to improve the load pf from 0.70 lagging (i.e., θ1 = 45.6°) to 0.90 lagging (i.e., θ2 = 25.8°) at a three-phase, 60-Hz, 460-V distribution
Determine the capacitor rating in kVAR and also in farads to improve the load pf from 0.75 lagging to 0.95 lagging at a three-phase, 60-Hz, 480-V distribution point delivering 2400-kW real power.
A 200-kVAR, 3300-V, 60-Hz, three-phase, American-made capacitor bank is operating at 2400 V, 50 Hz in Europe. Determine its new kVAR capacity in the European power system.
Why does RGB of the dc motor require variable voltage and variable field resistance, whereas the ac motor requires variable frequency and variable voltage?
A 200-kVAR, 2400-V, 50-Hz, three-phase European-made capacitor bank is connected to 3300-V, 60-Hz lines in the United States. Determine its new kVAR capacity in the United States.
A three-phase, four-pole, 60-Hz induction motor is running at 1746 rpm under full load. Determine the regenerative braking torque at the instant of frequency suddenly reduced to 95% using variable
What is a rough estimate of % energy that can be saved using RGB in city metro trains with stations only 1 mi. apart?
A three-phase, 100-hp, four-pole, 60-Hz induction motor is running at 1740 rpm under full load. Determine the RGB torque at the instant of reducing frequency to 96% using a variable-frequency drive
Name the types of energy storage systems you can use for large-scale energy storage, say, for a wind farm or a solar park.
What is the present worth of $1000 coming at the end of(1) The 6th month, (2) The 24th month, and (3) 30 years at the discount rate of 1% per month?
Your plant needs to buy a 1000-hp motor for a new conveyor belt. You have the following information:(1) A standard motor having 90% efficiency costs $96,000. (2) A high-efficiency motor having 95%
The plant you are working uses three-phase, 30-MW, 60-Hz power at 6.6 kV, 0.80 pf lagging. Determine (1) The size of a three-phase Y-connected capacitor bank that will improve the pf to 0.95
A battery with an internal resistance of 0.01 Ω/cell needs to deliver 10-A current at 120 V at the load terminals. Determine the number of cells in series if the electrochemical voltage is 1.25
A battery with an internal resistance of 0.015 Ω/cell needs to deliver 20-A current at 240 V to the load. Determine the number of cells in series if the electrochemical voltage is 2.0 V/cell.
If a 100-Ah battery is being charged at C/5 rate, how long will it take to get fully charged?
You have two options in procuring 100-Ah battery cells for a large battery assembly in an industrial plant, which requires frequent charging and discharging. Cell A has an average cell voltage of 1.2
Select the favorable cell from two options available in procuring 100-Ah battery cells. It is for a large battery assembly in an industrial plant, which requires frequent charging and discharging.
If you have used or designed any type of battery, would you replace it with another electrochemistry, and for what reason?
A battery lasts 2000 charge/discharge cycles of 100% DoD. Determine its approximate cycle life at 40% DoD and at 25% DoD.
A battery lasts 3000 charge/discharge cycles of 100% DoD. Determine its approximate cycle life at 30% DoD and at 20% DoD.
Design the battery for an industrial application that requires 10-kWh energy in 1.5 h for a dc load at 120 V three times daily for 250 days every year. The battery must be completely recharged in 2.0
Identify the battery type that has the highest volumetric and gravimetric energy densities: (1) In the secondary battery group and(2) In the primary battery group.
Design the battery for an industrial application that requires 20-kWh energy in 2 h for a dc load at 240 V four times daily for 300 days every year. The battery must be completely recharged in 2.5 h
What is the difference between charge efficiency and energy efficiency?
A large 240-V battery is assembled from 12-V, 110-Ah battery modules commercially available off the shelf. Determine the air ventilation requirement for each room.
A large 240-V battery is assembled from 2-V, 160-Ah lead–acid battery cells commercially available off the shelf. The maximum charging rate is C/4, and the charging rate during gas formation is
Describe the memory effect in the NiCd battery and the remedy for minimizing it.
Discuss the key performance requirement for a battery for an electric car.
A new electrochemical cell has an average charge voltage of 4.5 V, an average discharge voltage of 3.0 V, and a c/d ratio of 1.15. Determine its roundtrip energy efficiency.
The winter temperature of your car battery when parked outdoors on a street in Alaska can fall to −40°F at midnight. Determine the minimum SoC you must maintain in your battery to avoid
When using two or more batteries in parallel, why should each battery have a separate charger and diode in the discharge path?
Design a NiCd battery for a 10-year calendar life, which is required to (1) power 10-kW load at 240 Vdc for 1 h three times every day (once every 8 h) and (2) charge it back in 6 h, allowing 2-h
A battery in your plant lasts 7 years when repeatedly discharged to 50% DoD. Determine its approximate life if the repeated DoD is increased to 75%.
Name alternatives to a battery for large-scale energy storage, say, for a wind farm or a solar park.
Argue for and against the electric car in solving: (1) The environment problem and(2) The energy problem.
Give your thoughts on the impact of the battery on the energy shortage problem many nations face today. Will it solve it or aggravate it?
Identify alternatives to the battery in (1) The marine industry, (2) The commercial industry, and (3) Consumer electronics.

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