Monitoring the status of ungrounded IT networks is a precondition for ensuring network safety and continuous operation, as required, in particular, in the health sector and in the heavy industries. The insulation monitoring devices monitor the insulation condition of the IT network and inform the operators immediately by acoustic or optical alarms about any insulation resistance decrease below the preselected Rcrit level (against the PE protective conductor).
The insulation monitoring devices (IMD) offered by Hakel are used for easy application in ungrounded IT power supply systems in metallurgy, civil engineering, shipbuilding, in hospitals, the transport environment, underground and surface mine
IT POWER SUPPLY NETWORK
IT power supply system is an insulated system that has all active parts isolated from the earth or one point of the network grounded via high impedance. Inactive parts of the electrical installation are grounded. Ungrounded system increases the operational reliability and human safety. Therefore it is used in the metallurgy, mechanical engineering, shipbuilding, traction systems, public transport and hospitals. The advantage of the ungrounded system is that the device connected to this system can work continuously even in the case of first fault (so-called earth fault). The phase voltage of the undamaged phase (or phases in the three-phase system) is increased to the value of the delta voltage during the first fault. The system is safe if inactive parts are properly grounded. The reason is that there occur no bigger than safe current levels. The relevant responsible person must be informed about this failure and the first fault must be eliminated as soon as possible. However, the second fault (double earth fault) must result in immediate disconnection of the power supply system. The insulation monitoring devices or residual current relays are used for monitoring of the ungrounded system. These devices indicate the insulation level decrease below the set value.