The (product) life cycle of an electrical system or an item of equipment can essentially be divided into the phases given in Table 1. Depending on the specific phase, (high) voltage testing, insulation measurement or insulation monitoring are required.
In unearthed power supplies, the monitoring can be undertaken using an insulation monitoring device. In earthed power supply systems the monitoring can be undertaken indirectly using fault current monitoring. By detecting impending insulation faults at an early stage, these devices are an important tool for the timely planning of maintenance tasks.
Conversely, the insulation measurement is only an instantaneous snapshot of the insulation resistance. In principle the insulation resistance is dependent on
- The nature of the electrical installation or equipment
- The operating conditions
- The type of usage.
Here attention is to be paid to the safety risk and the protection goal.