Overview
ABSTRACT
The use of three-phase AC power for the distribution electricity networks requires balance between generators and loads and introduction of security systems with inverters. But DC power may also be used. The DC network is often desirable, because the interconnections and the management of power are simpler with choppers. In this first article, the several possibilities for using AC and DC networks are examined, and how the power from one to the othercan be transfered. In the second article, smart associations AC ?DC are suggested, especially in Brittany.
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Read the articleAUTHOR
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Michel PINARD: Professeur agrégé Hors Classe - Professor at the Conservatoire National des Arts et Métiers and ESIEE
INTRODUCTION
What is an electrical power distribution network? A set of lines connecting a large number of generators, usually three-phase AC, to receivers (or loads) via transformers or converters, since transmission requires the use of high voltage.
At the load (or consumer) level, it is imperative to :
that the rms voltage value is constant;
that the frequency is constant.
The operator managing the three-phase alternative network must, at all times :
ensure that the production of active power balances consumption on loads and lines: this is the production-consumption balance;
ensure that reactive power generation is equal to consumption on loads and lines;
the three-phase system is balanced, and phase shifts between generators are controlled for parallel connection;
that the network is able to carry out power transfers regardless of the vagaries of consumption;
cope with possible malfunctions in power routing, particularly in the event of a fault (short-circuit or open circuit), and plan safety systems accordingly.
The arrival of new energies (wind turbines, tidal turbines, photovoltaics, etc.) and static power converters (with IGBT transistors) is prompting installers to reconsider the use of DC current and voltage for electricity transmission. This new situation led electricians to reflect on the advisability of using high-voltage DC networks alongside AC networks. This approach is now referred to as HVDC (High-Voltage Direct Current) or even Smart Grid or Super Grid...
The advantages of direct current (compared with three-phase) include :
there is no reactive power;
that the frequency setting does not exist;
there is no phase imbalance;
control of short-circuit transients is simpler;
that it is possible to store energy in accumulators (batteries, etc.), but only for small or medium quantities of energy;
that many generators from new energies are DC;
that voltage control is easy thanks to digital controls acting on the power converters.
The disadvantages of direct current include :
that the current's non-zero crossing makes it difficult to interrupt;
that a chopper needs to be...
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KEYWORDS
Chopper | Inverter | Power transfer | Power filter
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Conversion of electrical energy
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