Engineering Answers

Problem 18.

A 400 kVA transformer has a

primary winding resistance of 0.5 and a

secondary winding resistance of 0.001. The iron

loss is 2.5 kW and the primary and secondary

voltages are 5 kV and 320 V, respectively. If the

power factor of the load is 0.85, determine the

efficiency of the transformer (a) on full load, and

(b) on half load.

Problem 9.

A single-phase, 50 Hz transformer

has 25 primary turns and 300 secondary turns. The

cross-sectional area of the core is 300 cm2. When

the primary winding is connected to a 250 V supply,

determine (a) the maximum value of the flux

density in the core, and (b) the voltage induced in

the secondary winding.

Problem 5.

A 5 kVA single-phase transformer

has a turns ratio of 10:1 and is fed from a 2.5 kV

supply. Neglecting losses, determine (a) the full

load secondary current, (b) the minimum load

resistance which can be connected across the

secondary winding to give full load kVA and (c) the

primary current at full load kVA.

A machine of mass 500kg is mounted through four rubber mountings that exhibit linear elasticity and viscous damping.in the installation of the machine ,each pad was observed to undergo a compression of 15mm. During the trial run of the machine ,the system was observed to execute free samples vibration such that it made 50 oscillations in 15 seconds.For this system,find;

a)the stiffness and damping coefficient of each mounting.

b)the minimum number of oscillations and consequently the time it will take for the amplitude of oscillations to be reduced to 1%.

what is thermal constancy?

Two glass tubes diameter 2 and 4 mm respectively, are attached to the side of a water tank to measure the level inside the tank, (surface tension = 0.074N/m)

Use this information to express the c apillary rise in the tube in the form h= mr + c where m and c are constants and r is the tube radius and hence determine the ideal tube diameter

2.1. Classify the following process as batch, continuous, semi – batch and identify if the process is an unsteady or steady state; 2.1.1. A balloon is filled with air at a steady rate of 4 g/ min. (2) 2.1.2. A bottle of milk is taken from the refrigerator and left on the kitchen table. (2) 2.1.3. Water is boiled in an open flask. (2) 2.1.4. Water is boiled in a closed flask. (2) 2.1.5. Filling an empty swimming pool with water. (2)

Suppose each year 60 000 people move into Gauteng province, 85000 people move out, 32000 are born and 18000 die. Write a balance equation on the population in Gauteng province accumulated per year. (Let P denote people)

One thousand kilograms per hour of a mixture of benzene (B) and Toluene (T) containing 60% benzene by mass is separated by distillation into two fractions. The mass flowrate of the benzene (B) in the top stream is 500 kg (B) /h and that of toluene in the bottom stream is 485 kg (T) / h. The unit operates at steady state. 3.1.1. Draw a schematic diagram showing all the relevant streams in the distillation unit. (8) 3.1.2. Write the basis for calculation.