What were the advantages and disadvantages of DC power?

Answer 1

Currently, the transmission of electrical power from bulk power generators all the way to household, commercial and industrial consumers is made through high voltage alternating current (AC) transmission and distribution systems, and through a series of voltage transformations to reduce losses and minimize cost. Voltage levels used are of standard values.

AC system is used in the transmission of bulk power, instead of DC (Direct Current), because of its ability to transform voltage to various levels by using a transformer. The voltage transformation follows the faradays Law which states;The emf induced in a circuit is directly proportional to the time rate of change of magnetic flux through the circuit.

Note that, at higher voltage, the current was reduced thus line losses was also reduced.

Ability to transform voltage and to flow power in two opposite directions (bidirectional) are the only advantages of AC system over DC system.

DC transmission system on the other hand has more advantages over AC transmission system:

1. Reactance.

DC system does not introduce a reactance in the line.

2. Resistance

DC system reduces the amount of resistance in the line.

3. Power

In DC system, the power is just the real component.

4. Frequency

In DC system, the frequency is zero, thus no frequency variation to monitor. Connection will not also require synchronization.

5. Susceptance

DC system does not introduce susceptance in the line thus removing the effect of charging current.

6. Analysis

Analysis of AC system always involved complex numbers, while DC is only a real number, thus simplifying the analysis.

7.Number of conductors.

A DC system requires only two conductrs as compare to three for ac system.

8.Absence of inductance.

A DC system has no inductance as a result the voltage drop in DC system is less than that of AC system for same load and sending end voltages and hence a better voltage regulation.

9.NO skin effect.

A DC system has no skin effect so we can utilize entire cross section area of line conductor.

10.Less insulation require.

A DC system require less insulation than an AC system because of less potential stress for same working voltage.

11.absence of capacitance.

Absence of capacitance in DC system leads to less power loss because there will not be charging and discharging of capacitance.

If DC system has the ability to transform voltage into various levels, efficiently, the DC transmission system will the more efficient, stable, easy to monitor, and most importantly, easy to analyze than AC system.

Currently, the transformation of DC voltage into another level involves 3 steps;

1. AC to DC Rectification

2. AC to AC transformation, and

3. DC to AC Conversion

If compared to AC system voltage transformation, steps 1 and 3 are the only added steps. Unfortunately, these steps incur additional heavy losses. However, modern technology converter/inverter has attempted to reduce the amount of this loss. A 1000 MW, 230 KV AC - 450 KV DC/ 450 KV DC - 230 kV AC converter/inverter, for example, has a combine power loss of around 1.6 %.

The use of DC system in the transmission of power will be more economical if the price from its benefits is higher that the cost incurred from the addition of rectifier and converter.

Answer 2

DC is needed by electronic circuits so that they can process data or signals without the interruptions caused by alternating current 100 or 120 times each second. So radios/TVs/computers have to run on DC power and they have a transformer/rectifier/smoother inside to derive it from the AC house supply.

Answer 3

One advantage of using direct current (DC) is its simplicity, which makes it ideal for use in vehicles to give power to engine ignition and management modules, interior and exterior lights, horn, etc.

Another advantage of using DC is that a relatively small rechargeable battery can be used on-board the vehicle to store electricity to power the engine's starter motor to get the engine turning again after it has been switched off.

There are serious disadvantages in using DC for many other applications - such as supplying power to homes, offices, factories, etc. - because DC cannot be easily transformed up or down in voltage (and, correspondingly, either down or up in current).

Alternating current (AC) is very much easier to use instead of DC where the ability to transform voltage and current is essential, such as for the distribution of the power produced by generating stations out to consumers using a National Grid and for producing the low voltages used by the chargers needed by small appliances such as electric shavers, mobile phones, mp3 players, etc.