What Is the DC Power System and How Does it Work?

What is Direct Current (DC)?

DC or direct current can be defined as the flow of electric charge in one direction. DC, an electrochemical cell is considered as one of the main examples of a DC power system. It may flow through a conductor or semiconductor, vacuum, ion beams, or insulators.

The electric current is known for flowing in a constant direction which distinguishes it from the alternating current or AC. This current was formerly known as the galvanic current. These terms are often referred to by their abbreviations AC and DC referring to alternating and direct current.

The alternating current supply might be used for converting direct current supply with the help of a rectifier. This consists of electrochemical or electronic elements which allow the flow of current in one direction. With the help of an inverter, direct current may be converted into an alternating current.

DC as a term is used for denoting the power systems which are known for using one polarity of current or voltage and refers to the zero frequency, constant or lesser varying the local mean value of current or voltage.

It has been observed that the voltage across the DC voltage source is constant as the current passes through a DC current source. The DC solution of an electric circuit is the solution consisting of constant currents and voltages. A stationary voltage or current waveform may be said to be decomposed in a sum comprising of a DC component and a zero-mean time-varying component.

The DC power system value here is defined as the expected value, all-time current, and average value of the voltage. DC is generally referred to as the constant polarity, here the DC voltages vary in time as observed in the raw output of the fluctuating voice signal on a phone line or a rectifier.

Why Is DC Now Used?

Electrical power is known to be generated, transmitted, and distributed in the alternating current form. Power is used in numerous applications and in some, direct power is necessary. Variable speed machinery incorporated by DC motors and critical areas that requires storage battery is a few areas of its requirement.

It has been observed that the advancements in power electronics have made the transformation of DC voltage levels and conversion from AC to DC swifter. The distribution of solar and wind energy has been increasing rapidly, both these sources are essentially DC.

A huge number of household and office appliances need DC with low voltage for their internal requirements. These appliances are fed with alternating current and further transformed into low voltage DC by the internal circuitry.

Currently, direct current is free from phase balancing problems, skin effects, and harmonic issues. This type of energy may be easily stored in fuel cells and batteries which can be in the future in case of power supply failure.

Direct current or DC power system has multiple uses, it can be used for the charging of batteries to supplying large power for the electronic systems, motors, etc. Large quantities of electrical energy which is delivered by the direct current are used in electrochemical processes, smelting of aluminum, and in railways.

DC of high voltage is used for transmitting huge power to interconnect AC power grids or from remote generation sites. Direct current is generally found in low-voltage and extra-low voltage applications. This happens mostly where these are powered by solar power systems or batteries.

Usually, the domestic DC installations have various types of connectors, fixtures, sockets, and switches from the ones which are suitable for AC. This happens mainly because of the usage of lower voltages which results in higher currents for producing the same amount of power.

Many automotive applications are known for using DC; an automotive battery provides power for lighting, ignition system, and starting. DC power system is used in a device with the circuit board, this happens because the chips present within these devices need a unidirectional and steady flow of electrons for operating and storing data.

Every home’s power circuit has an in-built DC inverter system which provides DC-style power to the devices present inside the case. Laptops are another example as they too contain a battery that delivers power in the DC format.

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DC power is mostly produced by sources such as thermocouples, batteries, and solar cells. It is used in low voltage applications such as automotive applications, charging batteries, aircraft applications, and other low voltage/current applications. All the solar panels produce DC power these days.

It has common applications in the PV industry which comprises off-grid appliances and portable solar systems. Nonusage of a solar inverter for converting direct current into alternating current keeps the cost down of these types of systems.                                                                       

Detail About DC Power System

DC power system consists of an electrical circuit which is a combination of resistors and constant current sources. The circuit current and voltages are independent of any time factor. A circuit current or voltage does not depend on the past value of the circuit current or voltage.

This means that the equational system which represents the DC circuit does not possess derivatives or integrals in relation to time. Once an inductor or capacitor is added to the DC circuit, it resulting circuit is not a DC circuit. However, it does have a DC solution that delivers circuit currents and voltages once the circuit reaches DC steady state.

This type of circuit is being represented by a system consisting of differential equations. The solution applied to these types of equations generally consists of a transient or time-varying part in addition to the steady or constant state part. This steady-state part is the DC solution.

There are some circuits that don’t have a DC solution for example a constant voltage source connected to an inductor and a constant current source connected to a capacitor. A circuit that is powered by a DC voltage source such as the output of a DC power supply or a battery is generally referred to in electronics. This occurs even when what is meant here is that the circuit is powered by a DC power system.

At the end of the 19^th century, the first electrical distribution network built by Edison was based on DC technology. However, later with the invention of transformers, the AC system was recognized as much better than the DC system. The AC systems were adopted globally for the generation of transmission, power, and distribution.

Types of DC Power Distribution

AC power can be rectified from the transmission network at a substation by utilizing the conversion equipment and feeding the DC distribution system. This happens wherever the DC power distribution is needed. By using the DC to AC inverter, the AC consumers may be connected to the DC system.

There are many types of DC power distribution; the low voltage DC distribution system is divided into two types which are unipolar DC distribution system and bipolar DC distribution system. Let’s read about both these types in detail.

Unipolar DC Distribution System

A unipolar DC distribution system is also known as 2 – wire DC system. This system utilizes two conductors as indicated in the name among which one is the positive one while the other is a negative conductor. The energy is passed on to all the consumers by using this system at a single level only.

Bipolar DC Distribution System

A bipolar DC distribution system is also known as the 3 – wire DC system. It can be identified as a combination of two series which are interconnected unipolar DC systems. It consists of two outer conductors among which one is the positive one while the other is negative, three conductors, and a middle conductor which is neutral.

Under this type, the consumer has numerous connection choices which include the following. The connection can be created between the positive conductor & neutral, between the negative & neutral, between positive & negative with double voltage, and positive to negative neutral.

It is observed that the DC to AC inverter or a DC-to-DC converter may be installed at the user’s premises as per his/her or the requirement of the load. The consumers may be also be connected directly with the DC distributors in case the distribution voltage level is the same according to the requirement.

Types of DC Distributors

DC distributors are divided on the basis of the way they are been fed. There are four types of DC distributors which are as follows: distributor fed at one end, distributor fed at both ends, distributor fed at the center, and ring distributor. Let’s read about all these in detail.

Distributor Fed at One End

In distributor fed at one end, the distributor is connected to the supply at one end. The loads are being tapped at various points along its length. The current in different sections of the distributor which is away from the feeding point continues to decrease.

The voltage continues to decrease away from the feeding point. In the scenario of a fault found in any of the sections of the distributor, the complete distributor requires to be disconnected from the supply. This is the reason that the supply continuity gets interrupted.

Distributor Fed at Both Ends

When it comes to this one, here the distributor is connected to the supply at both ends. The voltages available at the feeding points may or may not be at equal levels. The minimum voltage occurs at a load point which is seen shifted by the variation of load on various sections of the distributor.

In case a fault is found at the feeding point, it is made sure that the continuity of supply occurs from the other feeding point. If the fault is observed in the section of the distributor, it is made sure that the supply continues on both sides of the fault along with their respective feeding points.

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Here, the conductor cross-section area needs a double distributor which double fed and is lesser compared to the requirement for a distributor at one feeding.

Distributor Fed at the Center

As per the name, under this type, the distributor is supplied at the center point as the voltage drops at the farthest ends. This voltage drop is not as large as it might be in a distributor which is fed at one end. This one is equivalent to the two distributors which are fed individually. Under this, each distributor has a commonly used feeding point with a length that is half of the total.

Ring Main DC Distributor

This type of distributor exists in the form of a closed ring which is being fed at one point. It is equivalent to a straight distributor which feeds at both ends consisting of equal voltages. In this type, the two ends are bought together in order to form a closed ring. These types of different DC distributor rings can be fed at various points.                     

What Is the Main Function of a DC Power Supply?

DC power supply produces an output DC voltage which is known for delivering power to one or many loads. Under it, the output is generated by converting the input signals into the output. A basic DC power supply is built with four sections or circuits with each block representing a specific circuit that performs a particular function.

How Does a DC Power Supply System Work?

Let’s read about the function of the DC power supply. A basic DC power supply may be built with four sections with each one representing a specific circuit performing a unique task. It consists of different parts such as a transformer, rectifier, filter, and regulator.

Transformer

An AC signal is provided as an input to the transformer which is generated using a line voltage like power from an electric outlet. The main function of a transformer comprises of stepping down or stepping up of a signal to produce the desired DC level needed at the output of the power supply.

It plays the role of an isolator as in numerous applications, it is important to isolate these input signals from the one generated internally by the device itself.

Rectifier

The signal received as output from the rectifier is further introduced as an input to the rectifier. A rectifier may be a half-wave or a full-wave rectifier and consists of a rectified pulsating DC signal.

In this, the pulsating signal is a signal which is voltage or current that doesn’t change its polarity and has a magnitude as a function of time. The typical ones are constructed by using resistors and diodes.

Filter

A filter is required for converting the pulsating DC signal into a non-pulsating DC signal. Generally, a capacitor filter suffices and the output generated by it is DC voltage consisting of minor AC variations and ripples.

Regulator

A regulator generally has two functions which include smoothening the signal from the filter by producing a DC signal without any ripple and production of constant voltage at the output. The voltage available at the output of the regulator is constant even in the presence of variations. These variations may be present in the variations in the load or in the input voltage.

Advantages and Disadvantages of Direct Current (DC)

DC has its own set of advantages and disadvantages, let’s read about these.

Advantages of DC

Although the DC power system has numerous advantages, the biggest advantage of DC is that it is easier to store in comparison to the alternating current. This happens when it is being stored on a small scale.  Storing electricity for later use is considered critical for a hybrid independent power plant.

When electricity is stored, it can be used whenever required as storing it increases the density. Power can be thus used as per the requirement for operating high-powered equipment.  The generator set may be turned off once the electricity is stored as it helps in saving fuel.

When DC electricity is used for an independent power plant, the advantage is that electricity for AC mains can be generated efficiently by utilizing a diesel DC generator and converting DC electricity into main style AC electricity. After this, the main style AC electricity is directly generated using a petrol AC synchronous generator.

For a direct current generator, the characteristics of the main-style electricity are determined by using the DC to AC conversion process. No field winding and variable speed makes a DC generator highly efficient than a synchronous AC generator.

Disadvantages of DC

Let’s read about the disadvantages of DC. There is difficulty in generating direct current at high voltage as it has commutation problems. The voltage in the DC system is not stepped up for high voltage transmission easily. Also, the DC circuit switches and breakers are known for offering more limitations.