Internal resistance of Generator

Before we discuss the internal resistance of generator, we will se the basic definition of a generator.

What is Generator?

Any source that produces voltage output continuously is called Generator. It may be a cell separating charges by chemical action or a rotary generator converting motion and magnetism into voltage output.

Internal Resistance of Generator:

Now we see about the internal resistance of generator. In any case, all generators have internal resistance. Which is labeled as ri in figures.

The internal resistance ri is important when a generator supplies load current because its internal voltage drop Iri subtracts from the generated emf, resulting in lower voltage across the output terminals.  Physically, ri may be the resistance of the wire in a rotary generator, or in a chemical cell ri is the resistance of the electrolyte between electrodes.  More generally, the internal resistance ri is the opposition to load current inside the generator.

Since any current in the generator must flow through the internal resistance, interest to note that, with just one load resistance connected across a generator they are in series with each other because RL is in series with ri.

Generator, What is Generator, Definition of Generator, Resistance of Generator, Internal Resistance of Generator, Diagram of Generator

(a) Physical Arrangement of Voltage Cell

If there is a short circuit across the generator, its ri prevents the current from becoming infinitely high.  As an example, if a 1.5 V cell is temporarily short-circuited, the short-circuit current Isc could be about 15 A.  The ri is V/Isc, which equals 1.5/15, or 0.1 ohm for the internal resistance.  These are typical values for a carbon-zinc D-size cell.

Generator, What is Generator, Definition of Generator, Resistance of Generator, Internal Resistance of Generator, Diagram of Generator

(b) Schematic symbol of ri (c) Equivalent circuit of ri in series with VG

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