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08/05/2024

The autotransformer was flooded with sea water. Emergency fire pump problem

Today we got low insulation of 440V on the main switchboard megohmmeter when starting the emergency fire pump. Checking the power part of the circuit showed an insulation resistance relative to the electric motor housing of 0 MOhm. Has the motor burned out or is there a chance to restore normal operation of the mechanism?

The autotransformer was flooded with sea water. Emergency fire pump problem

Checking the power part of the circuit (main contactor and autotransformer) with a portable megohmmeter showed 0 MOhm. Have to climb into the pump shaft and measure the insulation resistance of the electric motor at the terminal box with disconnecting of the power cable.

This procedure is standard when looking for low motor insulation. It is necessary to find out whether this is a problem with the electric motor or the power part, for example, a cable.

Emergency fire pump starter panel
Emergency fire pump starter panel
Motor terminal box
Motor terminal box
0 MΩ at terminal box with cable
0 MΩ at terminal box with cable
Low insulation of the power part of the circuit
Low insulation of the power part of the circuit

A test without cable showed that the electric motor gives infinity, so the problem is only in the power part of the circuit (cable, contactors and autotransformer).

Electrical diagram of the emergency fire pump
Electrical diagram of the emergency fire pump

Visually, there is increased humidity in the starter panel. Perhaps the panel was flooded with sea water, because... it is located in the steering gear compartment opposite the aft exit. In such a situation, you can try to dry out the electrical circuit inside the panel.

For this, a regular incandescent light bulb is suitable, which we install and connect inside the switchboard next to the autotransformer.

Lamp for drying the panel
Lamp for drying the panel
Drying the starter panel
Drying the starter panel

Also, several bags of silica gel were placed in the panel so that the moisture that evaporates is absorbed by the silica gel and does not settle on the walls inside.

Checking the insulation during drying
Checking the insulation during drying

During drying, the circuit insulation rose significantly to almost 50 MΩ.

Salt deposits on the power cableSalt deposits on the power cable

Salt deposits on the power cableSalt deposits on the power cable
Salt deposits on the power cable

On the walls of the shield and on the cable, salt formations are visible, which have settled after the moisture evaporates. Remove the salt using contact cleaner and continue drying. It is advisable to replace the silica gel with a new or dried one over time.

In this way, the insulation of the power part of the electric motor was restored and the problem of low insulation, which could lead to burnout of the circuit, was eliminated.

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