CU400 for Electromagnets 

The Thyristor converters DCREG series now offers the possibility to manage highly inductive loads such as electromagnets.

The load’s typology, assimilable to an ohmic resistor placed in series to a very high inductance, creates some applicative problems which have been efficaciously solved inside the DCREG by means of a control algorithm especially developed for this aim. The fact that the load has a high inductance level causes some functional safety problems which show themselves when, for failures or critical installation, an interruption on one of the main supply meshes is possible. Such interruption, along with the high inductive level of the magnet, can provoke strong sudden overvoltages which may even reach some thousands of Volts. It is not anyway possible to protect the converter against such overvoltages, except if you take specifi c measures while installing it. The most effi cacious method consists in providing a closing mesh on the magnet’s current, thanks to a special system called CU400.
The energy accumulated into the magnet is “absorbed” and stocked into a clamping circuit of RC type, in which the function of overcurrent limiting is ensured by the inner capacitor, while the subsequent dissipation of such energy is ensured by the inner resistor. If a power supply conducting mesh is physically interrupted (because of wiping contacts or other) or the connecting cables between magnet and converter open, the voltage arc generated by the current interruption is limited by the clamping circuit able to limit overvoltage, taking it to safe values. For this reason, the above confi guration is necessary in case of electromagnets installed on bridge cranes on which the 3phase power supply comes the main supply by means of wiping brushes which might occasionally open.