PM820-1 PM820-2 ABB Control system module spare parts

Product Details

Product Description

Product Description
PM820-1 PM820-2 ABB Control system module spare parts
PM820-1 PM820-2 ABB Control system module spare parts
Our Email: 2235954483@qq.com
contact number:13313705507
contacts：HE
Main applications of direct current:
• Emergency supply or auxiliary services:
the use of direct current is due to the need to employ a back-up energy
source which allows the supply of essential services such as protection
services, emergency lighting, alarm systems, hospital and industrial services,
data-processing centres etc., using accumulator batteries, for example.
• Electrical traction:
the advantages offered by the use of dc motors in terms of regulation and of
single supply lines lead to the widespread use of direct current for railways,
underground railways, trams, lifts and public transport in general.
• Particular industrial installations:
there are some electrolytic process plants and applications which have a
particular need for the use of electrical machinery.
Typical uses of circuit-breakers include the protection of cables, devices and
the operation of motors.
Considerations for the interruption of direct current
Direct current presents larger problems than alternating current does in terms
of the phenomena associated with the interruption of high currents. Alternating
currents have a natural passage to zero of the current every half-cycle, which
corresponds to a spontaneous extinguishing of the arc which is formed when
the circuit is opened.
This characteristic does not exist in direct currents, and furthermore, in order to
extinguish the arc, it is necessary that the current lowers to zero.
The extinguishing time of a direct current, all other conditions being equal, is
proportional to the time constant of the circuit T = L/R.
It is necessary that the interruption takes place gradually, without a sudden
switching off of the current which could cause large over-voltages. This can be
carried out by extending and cooling the arc so as to insert an ever higher
resistance into the circuit.
The energetic characteristics which develop in the circuit depend upon the
voltage level of the plant and result in the installation of breakers according to
connection diagrams in which the poles of the breaker are positioned in series
to increase their performance under short-circuit conditions. The breaking
capacity of the switching device becomes higher as the number of contacts
which open the circuit increases and, therefore, when the arc voltage applied is
larger.
This also means that when the supply voltage of the installation rises, so must
the number of current switches and therefore the poles in series.

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