What causes low insulation resistance?
Low insulation resistance may be due to the age of the installation, or alternatively it may be caused by an individual circuit, which would merit further investigation. In summary, insulation resistance testing should be undertaken at relevant times during and on completion of an installation.
How do you increase insulation resistance?
one thumb rule is: For every 10°C increase in temperature, halve the resistance; or, for every 10°C decrease, double the resistance. For example, a two-megohm resistance at 20°C reduces to 1/2 megohm at 40°C. each type of insulating material will have a different degree of resistance change with temperature.
Why excessive insulation is harmful to a coil?
Insulation breakdown commonly occurs due to high current and voltage which are high above the rated values. The breakdown of the insulation results in the flashover of the winding turns and cause a short circuit. The windings are usually of copper. Due to the copper line resistance, thermal losses occur.
How can you tell if insulation is failing?
Using a resistor divider is a simple way to measure the insulation resistance. Figure 5 shows a TINA-TI™ simulated circuit for this approach, where two series resistors (R12 and R2) are connected in parallel with the insulation resistance (Riso).
What causes insulating oil to deteriorate in a transformer?
The insulating oil deteriorates gradually with use. The main cause is the absorption of the moisture in the oil. Each time the moisture is doubled in a transformer, the life of the insulation is cut by one-half. Failures due to moisture are the most common causes of transformer failures.
Why are there so many faults in Transformers?
The major reasons for the insulation breakdown are, ageing of insulation, Partial discharges in the insulation, Transient over voltages due to lightning or switching in the network, Current forces on the windings due to external faults with high current. Insulation Breakdown of the windings will cause short circuits and /or earth faults.
What can cause a transformer to heat up?
Insulation Breakdown of the windings will cause short circuits and /or earth faults. These faults cause severe damaging on the windings and the transformer core. The overexcited transformer flux is forced through metal tank and other un-laminated parts of the transformer and result in heating up.
What causes a dielectric fault in a transformer?
Dielectric faults occur in the winding due to turn-to-turn insulation breakdown. These are the insulation between the turns of the winding. Insulation breakdown commonly occurs due to high current and voltage which are high above the rated values.