Measuring insulation resistance on ships. Factors affecting Insulation Resistance

A part from the fact that good insulation resistance is an essential condition for maintaining service, the regular recording of insulation resistance values is undoubtedly the best method of detecting deterioration and of indicating when remedial action is desirable, or perhaps essential, in order to prevent complete failure.

Insulation resistance (IR) should accordingly be measured and recorded at regular intervals, the recording being preferably on a separate log-sheet for each important machine or circuit, so that each fresh reading can be compared with previous values and any downward trend immediately observed. It cannot be too strongly emphasised that, subject of course to reasonable minimum values being maintained, trends are more important than actual values; a single value is of comparatively little significance. The intelligent interpretation of results is therefore of great importance and a general appreciation of the factors involved is essential.

What is a DC Voltage Transducer?

DC Voltage Transducer delivers an output voltage proportional to the armature voltage or induced voltage. The output signal is mathematically isolated from the input voltage. The armature current signal is used to compensate the output signal for armature current variations in such a way that the output signal is approximately proportional to the induced EMF.

Where accurate EMF measurement is required, the measuring circuit also has an input which may be connected to the terminal of the machine. The voltage drop across the commutation winding of the machine is then used for IR compensation, and this arrangement therefore compensates to a considerable degree for the dependence of winding resistance on temperature.