H
Hugo Caballero Figueroa
Guest
Hi! I have a question regarding the use of isolation transformers in
control cabinets. I have seen many diagrams in which an isolation
transformer is used to provide 230V AC control voltage although the
cabinets are endowed with a neutral potential from the source (3
phases+N+PE).
I have read that this is sometimes used in order to avoid ground loops,
to increase safety operation by ensuring a galvanic isolation or even to
increase the availability of this supply in case of a failure of the
neutral conductor (why is it assumed that it fails more often than any
other phase? Because it's independent from the source or the
transmission system?).
Sometimes, however, the secondary winding is earthed, thus cancelling
the benefits of the galvanic isolation.
I have also read that it is used in order to reduce the effect caused by
the switching of the different control devices (relays, contactors,
etc.) on the rest of the consumer loads, filtering out (undesired)
harmonics.
Could you please explain how this transformer filters out these
artifacts? Do I have to size the winding (number of turns) for the
reactance to be high enough from the desired frequency upwards (for
example, from the first harmonic to be filtered)?
If it had a turns ratio of 1, would it still have a significant effect
on shortcircuit current? Why? Is it because of the impedance of the
transformer? Where does the main contribution to this limiting effect
come from?
Thank you very much for your answers!
--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---
control cabinets. I have seen many diagrams in which an isolation
transformer is used to provide 230V AC control voltage although the
cabinets are endowed with a neutral potential from the source (3
phases+N+PE).
I have read that this is sometimes used in order to avoid ground loops,
to increase safety operation by ensuring a galvanic isolation or even to
increase the availability of this supply in case of a failure of the
neutral conductor (why is it assumed that it fails more often than any
other phase? Because it's independent from the source or the
transmission system?).
Sometimes, however, the secondary winding is earthed, thus cancelling
the benefits of the galvanic isolation.
I have also read that it is used in order to reduce the effect caused by
the switching of the different control devices (relays, contactors,
etc.) on the rest of the consumer loads, filtering out (undesired)
harmonics.
Could you please explain how this transformer filters out these
artifacts? Do I have to size the winding (number of turns) for the
reactance to be high enough from the desired frequency upwards (for
example, from the first harmonic to be filtered)?
If it had a turns ratio of 1, would it still have a significant effect
on shortcircuit current? Why? Is it because of the impedance of the
transformer? Where does the main contribution to this limiting effect
come from?
Thank you very much for your answers!
--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---