The digitally controlled KCM161Mx series monitors insulation level between a non-grounded (IT) AC mains and its protective earth, regardless of whether the mains is live or non-live (standby) in marine and offshore installations.

IDV MEASURING PRINCIPLE
Insulation is measured between the complete galvanically interconnected AC network and its protective earth. The unit injects a sequentially coded measuring signal to the monitored system. The signal flows to ground via the path of the insulation fault, the level of flow indicates the insulation resistance. The measuring accuracy is not influenced by any normal kind of load attached to the AC network.

An AC or DC auxiliary voltage is required for the unit, if powered from a separate source the network can also be monitored during standby conditions. Only ONE KPM161Mx can be connected to each IT-system. The ohmmeter and the triple-zone status LEDs give at a glance the clear safety message:

• ALARM
• WARNING
• HEALTHY

HIGH ENERGY DC VOLTAGE IN YOUR AC MAINS, AN UNKNOWN AND NEGLECTED PROBLEM
Experience has confirmed that full cycle half-wave and partial cycle full-wave rectifier/regulator loads, or a semiconductor failure in heavy power rectifiers/inverters may impose high energy DC voltage on the AC supply line voltages. Intermittent or ENDURING imposed DC voltage is reported to be up to several hundred volts with positive or negative polarity relative to protective earth.

This DC voltage will distort insulation measurements, and may cause breakdown of protective guards The uncontrolled DC energy can cause functional problems by saturating magnetic cores and influence performance of current and voltage transformers, reactors, motors, regenerative drives, generators and regulators.

It is also a fact that this serious malfunction normally remains undetected and unknown to the crew. The M-variant therefore includes a unique DC voltage detection function with an alarm output.

When a "foreign" positive DC voltage exceeding 17V or a negative DC voltage exceeding 3V are detected on the monitored AC supply the DC detection function will within 20 seconds disable the insulation measuring function to avoid false readings, isolate the unit input, activate LED "DC EXPOSURE" and trip relay 3. In this mode unit will sustain continuos high-energy exposure up to +/- 800VDC. The "pathfinder" function identifies polarity of imposed DC. At 10 minutes intervals the unit senses if DC is still present and will reset automatically and restore normal operation when DC exposure ends.


NOTE
The standard Insulation Guards KCM161x and KCM163x are protected against sporadic AC and DC voltage surges imposed on the monitored AC network.

Exposure to enduring  high energy DC voltage (reported to be up to several hundred volts with positive or negative polarity) will instantaneously cause the meter to read false insulation value and may destroy the unit.