Engineering Answers

Multiple Choo questions

Question 10 

Question 8 

The economic dispatch problem describes: 

(1) How the real power output of a controlled generating unit is selected to meet a 

given load and to minimize the total operating cost 

(2) How the reactive power output of a controlled generating unit is selected to meet 

a given load and to minimize the total operating cost 

(3) How the levels of power generation can be adjusted to maximise the total 

operating cost. 

(4) How power plants can be built economically. Question 7 

The regulator: 

(1) Supplies current to the rotor. 

(2) Converts ac to dc from voltage transformer. 

(3) Controls generator terminal voltages.

Multiple Choo questions

Question 10 

Th goal of the equal area criteria in transient stability is to determine whether a system 

is stable or not without having to completely integrate the system response. The 

system will be stable after the fault if: 

(1) The acceleration area is greater than 1.0 per unit. 

(2) The acceleration area is greater than the deceleration area. 

(3) The deceleration area is smaller than the acceleration area. 

(4) The deceleration area is greater than the acceleration area.

Carry out a series of calculations on the same diatomic molecule you were assigned in class. The sequence of steps is given below. Do this for two semi-empirical methods (AM1 and PM3) and then two ab initio methods. For the two ab initio methods choose the Small(3-21G) and Large(6- 31G**) basis sets. In all cases just use the other default settings. (a) Draw the molecule. (b) Select a method (semi-empirical or ab initio). (c) Optimize the geometry and note the bond length. (d) Do a single point calculation. (e) Do a vibrational calculation. (f) Display the vibrational results and note the vibrational frequency. Use the NIST database to obtain experimental values of the bond length and vibrational frequency. Compare these with your calculated results. Turn in a summary of your findings.

Liquid ethanol (C2 H5 OH) is burned with 150% theoretical oxygen in a steady-state, steady-flow process. The reactants enter the combustion chamber at 25 ◦ C and the products leave at 65 ◦ C. The process takes place at 1 bar. Assuming complete combustion (i.e. CO2 and H2 O as products along with any excess O2 ), calculate the heat transfer per kmole of fuel burned.

6.2 Gaseous propane at 25 ◦ C is mixed with air at 400 K and burned. 300% theoretical air is used. What is the adiabatic flame temperature? Again, assume complete combustion.

6.3 Repeat Problems 6.1 and 6.2 using CEA2. Compare the product composition using CEA2 with the assumption of complete combustion. What do you observe?

Using CEA2, calculate the equilibrium composition of a mixture of 1 mol of CO2 , 2 mol of H2O, and 7.52 mol of N2 at 1 bar and temperatures ranging from 500 to 3000 K in steps of 100 K. Then plot the mole fraction of NO as a function of temperature.

Power station A delivers 640 MVA to its consumers at a power factor of 0.766 lagging.

Power station B delivers 560 MVA to its consumers at a power factor of 0.7071 lagging.    

Two three-phase generating power stations A and B work at (86.077+j18.296) kV and (131.277+j13.798) kV respectively.The two power stations are inter-connected via a transmission line with an impedance of (6.59+j16.672) Ω/phase. The phase-regulator at power station A is adjusted such as to reduce the loading at power station A by 82 MW.

Take machine A as leading machine.

Use standard formulae to the following calculations.

Determine the total active power delivered or received by Power station A (P_i) in MW

QUESTION 1 GEARS [40]

1.1 Write a problem statement to verify spur gear set material selected from Table 

6.9, page 127 of the prescribed textbook.

(3)

1.2 Elaborate on the product design specification for the design of the spur gear 

set (Figure 1 above) referring to the performance aspect, consider the 

transmission of power, the gear ratio, and efficiency.

(6)

1.3 Verify the suitable material for pinion and gear (Figure 1 above) based on 

Lewis’ formula if both the pinion and gear were selected from Table 6.9, page 

127.

(31)

QUESTION 2 MINIMUM DIAMETER OF THE OUTPUT SHAFT [10]

2.1 The output solid steel shaft is supported by the ball bearings, as shown in 

Figures 1 & 2 above. The shaft operates at room temperature. Determine the 

minimum allowable diameter of the output shaft based on ASME CODE and 

select the standard size of the shaft from the Macsteel catalogue, provided 

with the question paper.

In an unbalanced, three-phase, star-delta system has a frequency of 50 Hz, and CBA phase rotation.The phase impedances

of the load are as follows:

 Z_ab =29.41∠ 54.69°Ω ;      Z_bc=25.61∠-38.66° Ω ;    Z_ca =17.8 ∠ 51.84° Ω

The emf of the source is represented by:e_c(t)=221.831 𝐬𝐢𝐧 (𝛚𝐭 +(𝟓𝝅/𝟏𝟖) ) V

Calculate the phase current,( I_ab, Ibc & Ica) of the load in polar form.

Calculate the active power( P_ab, P_{bc ,} Pca) in phase AB of the load in phasor form.

Determine the line current,( I_a, I_{b &} I_c) in polar form.

If two wattmeters are connected in lines a and b respectively of the above circuit to

measure the active power, 

Determine the reading of the wattmeter,(W_a) connected in line a.

Determine the reading of the wattmeter,(W_b) connected in line b.