The insulation monitor continuously supervises the insulation resistance of an unearthed IT system against the protective conductor. In an IT system the first earth fault does not disconnect the supply and stays unnoticed until a second fault occurs; the relay detects it earlier, signals it on two independently adjustable thresholds - pre-alarm and alarm - and leaves time to clear the fault during a planned stop. DOLD lists preventive fire and plant protection and the detection of symmetrical and asymmetrical insulation faults as the benefits; selective earth-fault detection on the positive or negative pole shortens fault localisation.
The measuring circuit works in AC, DC and mixed systems, also with the large leakage capacitance typical of circuits with converters and filters. With the external coupling devices RL 5898, RP 5898 or RR 5898 it covers systems with higher voltages. Settings are made with two rotary switches on the front, the display shows the measured value and the mains voltage, and a sealable transparent cover protects the settings against manipulation. The trigger output starts the insulation fault location system RR 5886 / RR 5887.
Applications listed by DOLD in the datasheet: unearthed AC, DC and AC/DC systems, UPS systems, networks with frequency inverters, battery networks, networks with DC drives, hybrid and battery-powered vehicles, mobile generator sets. For railways we propose it for battery-fed onboard networks and for auxiliary circuits of substations and trackside cabinets operated as IT systems. The datasheet contains a classification to EN 50155 and test data according to the DNV class guideline for shipboard equipment.
Parameters (RN 5897.12/010/61, from the datasheet):
