1. Introduction to Cable Insulation Monitoring Device
          A Cable Insulation Monitoring Device is an online monitoring instrument designed for the real-time supervision of the main insulation condition of power cables. It is a critical piece of equipment for ensuring the safety of distribution networks, particularly in systems with ungrounded or resonant-grounded (via arc suppression coils) neutral points.

2. Key Role of Cable Insulation Monitoring
          The primary role of cable insulation monitoring is to continuously evaluate the health of the cable insulation. It provides early warning before the insulation resistance drops to a dangerous level, thereby preventing insulation degradation from escalating into phase-to-phase short circuits or ground faults. This helps avoid unplanned power outages and equipment damage.

3. Main Functions of the Insulation Monitor
Real-time Monitoring: Continuously measures the insulation resistance value of each cable phase to ground.
Threshold Alarms: Generates alerts when the insulation resistance falls below preset warning or alarm thresholds.
Fault Recording: Logs the time and relevant parameters of insulation anomalies and events.
Communication Capability: Supports interfaces like RS485 and Ethernet for data transmission to a central monitoring system.

4. Working Principle of Insulation Monitoring
The device operates by injecting a weak, specific-frequency AC signal between the monitored cable core and the ground (or screen). It then measures the resulting current flowing through the insulation resistance. Based on Ohm’s Law (R=U/I), it calculates the precise insulation resistance value. The deterioration or health of the insulation is assessed by continuously tracking the trend of this resistance value.