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The main characteristics of a Direct Current – or DC – is that the electrons within the current always flow in the same direction, from the side with a deficit to the side with a surplus. This is the kind of current supplied via the chemical effect by batteries, or via the photovoltaic effect by solar panels. The terminals are marked + and – to show the polarity of the circuit or generator. The voltage and current are constant in time.





Current

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  • Advantages: batteries can supply DC directly and it is possible to add the sources in parallel or series.
  • Disadvantages: In reality, the use of the batteries limits the voltage to a few volts (up to 24 volts in some vehicles). Those low voltages prevent the transportation of this type of current.
Things That Use DC Current

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Alternating Current (AC)

In alternating current – or AC - the electrons reverse direction at a given frequency. As the current continually alternates there is no fixed + or –, but “phase” and “neutral”. Voltage and current follow a sinusoidal curve. While voltage and current continually vary between a maximum and minimum value, measurement masks this variation and shows a stable average value—such as 220V.





Current

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The frequency is defined as number of sinusoidal oscillations per second:

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  • Advantages: Can be transported over long distances without too much loss using high tension lines. It is easy to produce.
  • Disadvantages: AC current cannot be stored; it must be created. AC current can also pose a greater health hazard for living organisms that come into contact with it.
Things That Use AC Current

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There are two types of AC:

Single-Phase

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A single-phase current is the most common type of current, and thus is usually the configuration delivered by public networks, but also by a single-phase generator. A single-phase AC current is supplied via two lines (phase and neutral), usually with a 220 V voltage difference between them. Plugs can be inserted in both ways.

Because the voltage of a single-phase system reaches a peak value twice in each cycle, the instantaneous power is not constant and is mainly use for lighting and heating but cannot work with industrial motors.

A single-phase load may be powered from a three-phase distribution transformer allowing single-phase lighting to be connected phase-to-neutral and three-phase motors to be connected to all three phases. This eliminates the need of a separate single-phase transformer.

Three-Phase

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Once Power needs are increased, in the use of large electrical motor for example, constancy and balance pay a key role. Three-phase is the common current configuration for electricity companies, and can also be produced with a three-phase generator. A three-phase current is the combination of three single phase currents.

To carry a given power with 3 separate single-phase cables, 9 wires are needed. To carry the same power in a three-phase cable, only 5 wires are required (3 phase, 1 neutral, 1 ground), which it is why there can be significant savings when properly planning a three-phase current: saving on wires, cables, and also in apparatus using or producing electricity: three phase motor or alternator will be smaller than the same power produced by three single phase equivalent units.

Grouping Circuit Components

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