Direct current is the form of the current that does not change with time. DC sources lead to circuit current, voltage, and power that are constant – unchanging with time. There are numerous applications for DC circuits but mostly used to supply power to electronic devices.
The so-called war of currents between alternating current (AC) and direct current (DC) has its roots from the very start of electricity. The pioneers of electricity generation Edison and Tesla both had their own views of the mode of electricity. Edison supported DC as a mode of electricity whereas Tesla supported AC. In the beginning, AC won the battle of currents due to the invention of transformers, an easy and cost-effective way of stepping up and stepping down voltages as required.
But DC has still some advantages over AC. Moreover, future industrial improvements of equipment could give DC a new future that could enhance the electric system. That’s why an increase in energy sources providing DC power is expected. Let’s see the benefits of direct current.
Advantages of direct current (DC)
A DC system has many advantages over an AC system. The benefits of the direct current are given below:
After the invention of the transistor in 1947, the electronic revolution started. The invention of high voltage power electronic devices, in particular, has made a comeback for direct current possible. Long high voltage direct current (HVDC) lines and cables are now used more often. In addition to HVDC, direct current is present in residential and urban grids from 230 V to 50 kV. PV panels produce a DC voltage. Wind turbines produce an AC output voltage with variable frequency; connection to the grid is only possible via power converter (AC-DC-AC) Almost all loads need DC as supply voltage.
Residential loads use DC
At the residential level, DC has entered our bedrooms, kitchen, and garage. Many residential loads are DC operated; our microwave ovens, computers, laptops, phones, lighting, and electric vehicles. The feasibility of DC distribution and its comparison with AC has been the interest of many researchers for years.
Many loads like consumer electronics, light-emitting diode (LED) lighting systems, appliances using a variable speed motor drive, etc., require DC power. Currently, major applications of DC distribution systems are in the ﬁelds of telecommunication systems, datacenters, DC buildings, and microgrids.
High power quality
It offers higher efﬁciency and reliability at an improved power quality. It does not create any power factor problem.
Reduced installation cost
It has reduced installation costs as it requires fewer power conversion stages, less copper, and smaller ﬂoor space.
Easy integration to renewables
DC distribution enables the simpler integration of renewable energy sources and energy storage systems.
No reactive power and skin effect
Since the power is distributed in DC, there is no reactive power or skin effect in the system. Unlike the AC distribution system, a DC distribution system facilitates plug-and-play features as it does not require any synchronization.
Telecommunication and data center usage
Telecommunication systems and data centers are among the few surviving examples of DC distribution systems. They are low voltage (48 Vdc) power systems that have characteristics similar to a conventional DC distribution system. The requirement of DC power for major consumer electronic loads and recent developments in renewable energy technology as well as increased penetration of distributed energy resources have prompted renewed interest in DC distribution systems among researchers and industry players.
In order to evaluate the personal protection and safety requirements of DC and AC systems, it is important to understand the effects of DC and AC currents on the human body. The effect of an electric shock depends on the current magnitude, the duration of current, the current path, and the type of voltage (AC or DC). Among all the possible effects of electric shock, ventricular ﬁbrillation is the most dangerous. Hence, in order to prevent any casualty proper protection needs to be provided. The graph below shows the characteristic curve of body current (AC and DC) vs. the duration of current ﬂow.
The graph is divided into four regions based on the effects on the human body:
- No effect
- A little pain but no dangerous effects
- Muscular contraction and respiratory compromise, which is reversible
- Critical effects such as ventricular ﬁbrillation
It can be observed from the ﬁgure that the magnitude of safe operating current limit for DC is higher compared to AC, thus making DC safer to operate than AC.
Popular in protection and switching technology
Many advantages of DC distribution systems are currently driving the market growth for DC technologies. Since equipment protection has been a major concern, many companies have been researching DC protection devices. Currently, major companies have started providing products used in DC distribution that follow existing standards for safety. Companies like ABB, Eaton, Carling Technologies, Schneider, Nader, Siemens, etc., provide DC circuit breakers and fuses to be used for safety and protection purposes in DC distribution systems.
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