6.4 Monitoring mobile power professional generators Electrical safety is often difficult to assure on mobile power gene-rators. • In very few cases does the ground/environment permit an earthing system to be installed (stones, rubble, rock, asphalt, etc. would have to be penetrated).• Time is of the essence, there is not enough time to measure and check the protective measure.• The relevant expertise is lacking. However, the ability to respond immediately and appropriately is vital in an emergency situation. It is for this reason that mobile power generators feature the protective measure "Protection by electrical separation with insulation monitoring and disconnec- tion" in accordance with IEC 60364-5-51/DIN VDE 0100-551. Technical aspects affecting the use of insulation monitoring devices A-ISOMETER® 6.3 Monitoring a disconnected load Many loads are only switched on in an "emergency" (e.g. fire pumps, slides, all types of heating, etc.). Whilst they are offline, however, moisture or other factors can cause insulation faults in the associated supply cable or on the load itself. When these loads are switched on, the protective device will respond or fires will start, thereby preventing operation.The insulation monitoring device, also known as the offline moni-tor, monitors insulation resistance during offline periods and signals insulation faults immediately. When the load is switched on, insulation measurement based on the K contactor is deactiva- ted. The fault memory is also able to detect transient insulation faults. If it can be assured that all poles on the load will be taken offline, this monitoring can also be used in TN and/or TT systems.Response value of the insulation monitoring device: The insulation monitoring device must signal insulation faults ≤ 1 MΩ, this is because motors are frequently rendered non-operatio- nal at an insulation resistance of ≤ 500 kΩ.
Figure 6.7 Mobile power generator with the protective measure "Protection by electrical separation with insulation monitoring and disconnection"” Figure 6.6 Monitoring an offline motor Annex 1.9.1 Annex 1.9.1 Main catalogue part 1 – 08.2007/Insulation monitoring 171