ABB 800PP846A High performance touch screen

Description

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The need to guarantee an ever greater continuity of service has led to an increase
in the use of emergency supply generators, either as an alternative to, or in
parallel with the public utility supply network.
Typical configurations include:
• “Island supply” (independent functioning) of the priority loads in the case of a
lack of energy supply through the public network;
• Supply to the user installation in parallel with the public supply network.
Unlike the public supply network, which has a constant contribution, in case of
a short-circuit, the current supplied by the generator is a function of the
parameters of the machine itself, and decreases with time; it is possible to
identify the following successive phases:
1. a subtransient phase: with a brief duration (10÷50 ms), characterized
by the subtransient reactance X”d (5÷20% of the rated impedance value),
and by the subtransient time constant T”d (5÷30 ms);
2. a transitory phase: may last up to some seconds (0.5÷2.5 s), and is
characterized by the transitory reactance X’d (15÷40% of the rated
impedance value), and by the transitory time constant T’d (0.03÷2.5 s);
3. a synchronous phase: may persist until the tripping of external protection,
and is characterized by the synchronous reactance Xd (80÷300% of
the rated impedance value).