ABB TP854 After sales service is provided for the control card of the power supply device

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).

The circuit-breaker for the protection of the generator shall be selected according
to the following criteria:
• the set current higher than the rated current of the generator: I
1 ≥ Irg;
• breaking capacity I
cu or Ics higher than the maximum value of short-circuit
current at the installation point:
– in the case of a single generator: Icu(Ics) ≥ Ikg;
– in the case of n identical generators in parallel: Icu(Ics) ≥ Ikg·(n-1);
– in the case of operation in parallel with the network: Icu(Ics) ≥ IkNet,
as the short-circuit contribution from the network is normally
greater than the contribution from the generator;
• for circuit-breakers with thermomagnetic releases: low magnetic trip threshold:
I
3
=2.5/3·In
;
• for circuit-breakers with electronic releases:
-trip threshold of the delayed short-circuit protection function (S),
set between 1.5 and 4 times the rated current of the generator, in
such a way as to “intercept” the decrement curve of the generator:
I
2
= (1.5÷4)·Irg; if the function S is not present, function I can be set
at the indicated values I3
= (1.5÷4)·Irg;