Low insulation 440V and refrigeration chambers on a ship

Greetings! Low insulation 440V has appeared, but this time it is difficult to detect because insulation appears for a short time and disappears. After two days of observations, it turned out that low insulation comes out twice a day, usually at lunchtime and at night.

Low insulation 440V and refrigeration chambers on a ship

We also noticed that when low insulation 440V comes out, the temperature of the meat refrigeration (freezer) chamber goes to INHIB in the alarm monitoring system in the ECR. 

The temperature alarm goes off while the meat chamber is being defrosted.

INHIB meat chamber temperature

Thus, the search circle narrowed significantly, and it settled on meat refrigeration cooler heaters.

Control panel for provision (refrigeration) chambers

Panel circuit breakers and contactors

Ice on the evaporator (heater tube)

During defrosting of the freezer, electric heaters (heating elements) are turned on to defrost ice that can accumulate on the evaporative part of the cooler.

Circuit diagrams of operation of provisional ref chambers

Cooler controller

Defrost turns on once every 11 hours for 20 minutes

Three heaters

Three heaters connected in a star

Three electric heaters are connected in a star, so in order to check each of them it is necessary to remove the wire ends from the terminal box. There are also separate heaters in the sump and drain pipe, they were checked immediately (they are clean).

Terminal box cooler unit

After disconnecting all the wire ends, we begin checking the each heating element.

Checking insulation resistance of heating elements

Low insulation of one heating element

One of the heating elements (heaters) turned out to have low insulation - 0 MOhm. We replace the broken heating element and thus restore the safe operation of the defrost system of the meat freezer.

It may not be possible to find the source of low insulation on a ship right away, because... some systems and mechanisms turn on for a short time. Heating elements may have different insulation resistance relative to the ground, depending on the temperature of their heating. 

The insulation resistance of heating elements in a cold state can be 100 MOhm, and in a hot state can be 0 MOhm (if the heating element is broken).

AMS model: Alarm monitoring & control system Kongsberg K-Chief 500.

Articles about finding low insulation 440V on a ship:

1. Low insulation 440V. First actions of the ETO
2. Abnormal Fire. The boiler does not start. Troubleshooting
3. The autotransformer was flooded with sea water. Emergency fire pump problem
4. Motor Fault on the crane. Troubleshooting 
5. Problems with cargo cranes. Some problems with cargo cranes that occur on the ship