ELE2004M Electrical Power And Machines

From the circuit diagram, we notice that the supply voltage is 240V at a frequency of 50Hz. We are further told that the power factor is raised to 0.9. We will therefore calculate the value of the PFC capacitor as shown below.

Using the supply current, we can calculate the reactive power, Q as shown below;

But we also know that

Also,  

Therefore,

Therefore the value of the PFC capacitor is

The above value for the PFC capacitor is slightly higher than the practical value. This variation could be as a result of the power loses that are experienced within the circuit components.

Application of a PFC in the Industry

Power factor is usually corrected by inserting an additional load to the circuit. This load should draw the same amount of reactive power but in the opposite direction to help cancel out any effects of the inductive reactance of the load. It is important to note that only a capacitive reactance can cancel out inductive reactance (Billings & Morey, 2011). The power factor correction unit is therefore just a capacitor that is connected in parallel as the additional load.

The PFC is commonly applied in the industries because most industries run on reactive loads. It furnishes the required magnetizing current for both the induction motors and transformers and thus reduci9ng the current drawn from the supply. It is important to note that a reduction in current will cause a decrease in the load on the transformers and feeder circuits (Billings & Morey, 2011). Also, it is evident that there is a reduction of the electrical current in the line which implies that the  losses will also reduce. This decrease in losses leads to an improvement of the efficiency which helps in eliminating the unnecessary blackouts. Another reason as to why PFC is used in the industry is because it reduces the wear and tears in the motor since the motor draws a reduced amount of current (Billings & Morey, 2011). As a result, the life of the appliance is improved, and the motor develops an improved immunity against any fluctuations in the current.

Distribution Topology

Lamp 3 and the  are parallel to one another and therefore the voltage drop across them is the same. Therefore the current across the  resistor can be calculated as follows;. The ratings of the lamps indicate that the current through the lamps is 0.2A. Following Kirchhoff’s laws, the current through CD will be  

Kirchhoff’s principles still help us to calculate the other currents as follows.

Current through BC will be

Current through AB will be

The voltage drops in the circuit are calculated as shown below.

The drops across the  is

The drop across each lamp is 24V thus according to Kirchhoff’s voltage law, the potential drops across BC

Consequently the drops across CD

There are differences between the predicted and the experimental results. We notice that our experimental values are slightly lower than the predicted values. This could be caused by many factors as outlined below.

Firstly, there could be drifts in the instruments used for measurements. It is worth noting the readings in most electronic measuring devices always drift after some time. The amount of drift will determine the extent of the error, and even though it is rarely significant, sometimes the drift could just be enough to influence the reading. Another possible cause of the difference could be due to drops along the circuit. The circuit components carry internal resistances that cause potential to drop as current moves throughout it. Other errors and differences arise from poorly calibrated measuring devices. Calibration is very crucial when precision and accuracy is desired. Additionally, the difference in measurements can also result from personal errors. This could be due to carelessness and poor technique by the individual carrying out the experiment. It is therefore imperative to handle this experiment with the seriousness it deserves to achieve accurate and precise results.  

Question 6: Advantages and Disadvantages of Radial and Ring Circuits

The radial system of distribution has the following advantages (Brown, 2017).

1. It is a simple system of distribution since it is only fed at one end.
2. The maintenance cost of a radial system is relatively lower when compared to the ring circuit.

• It works perfectly with stations that are located centrally to the loads.

1. The initial cost of setting up this system is relatively lower than that of the ring topology.
2. The number of cables required in this system is less as compared to the other systems.

Despite all the advantages mentioned above, it is worth noting that the radial system also has its disadvantages. These disadvantages are as listed below.

1. The end of the distributor that is close to the substation is normally very loaded.
2. The whole of the radial system goes off in the event of a fault.

The ring system also has its advantages and disadvantages. The advantages include;

1. The power in this system is supplied from both ends.
2. The voltage drop in a ring topology is less along the distribution line when compared to radial system.

• The clients witness fewer voltage fluctuations at their terminals.

The disadvantages of this system include;

1. The cost of maintenance usually is very high.
2. It is not applicable for clients located at the center of the load.

• The initial cost of a ring system is very high.

References

Billings, K. H., & Morey, T. (2011). Switchmode power supply handbook. McGraw-Hill.

Brown, R. E. (2017). Electric power distribution reliability. CRC press.