What is polarization index in transformer?

Polarization Index, or PI, is a ratio of the megohms after 10 minutes divided by the megohms after 1 minute. An instrument records megohm data over the 10 minutes, and the resulting graph and PI ratio can provide additional information about the winding insulation beyond the megohm number itself.

What is polarized index?

The polarization index (PI) is used as an indicator of motor insulation health, and is useful in identifying accumulation of contaminants as well as physical change in the insulation. From a standpoint of physics, to polarize is to cause something to obtain polarity.

What should be the pi value of transformer?

Interpretation of Polarisation Index results
PI	Condition of item under test
1 – 1.5	Bad
1.5 – 2.0	Doubtful
2.0 – 3.0	Adequate

What does a high polarization index mean?

The Polarization Index (PI) is used to determine the fitness of a motor or generator for use. The polarization index gives an indication of the buildup of dirt or moisture, the deterioration of insulation and the suitability for operation of the motor or generator.

What is pi and Dar test?

DAR measurement is a diagnostic test similar to the Polarization Index (PI), but DAR takes the ratio of the Insulation Resistance usually measured at 30 sec and 1 min (other time settings are possible) instead of 1 min and 10 min typically of the PI.

What is the polarization index value for a class B type insulation?

2.0
prescribed in Table 1 for a Class B insulation system is 2.0.

What is polarization index and dielectric absorption ratio?

The polarization index is defined as the ratio of the 10 minute resistance value to the 1 minute resistance value. Dielectric absorption ratio is referred to the ratio of the 60 second resistance value to the 30 second resistance value.

How do you test pi on a transformer?

In PI test, ratio of insulation resistance at different times after starting of test is recorded. The DC voltage is applied between conductors and insulating part, and the insulation resistance value is recorded after 1 minute, then test is continued and the insulation resistance value after 10 minutes is recorded.

What is duration of drying out for 400 kv transformer?

kVA,400 kVA,630 kVA,800 kVA). continued for 36 hours.

What is Dar value of transformer?

What is the polarization index value for Class A type insulation Mcq?

Polarization index (PI) The IEEE Std 43-2000 recommends the minimum value of PI for AC and DC rotating machinery in thermal class B, F and H as 2.0, and the minimum PI value for class A equipment is 1.5. Table 1.

What is meant by the polarisation index of a transformer?

Originally Answered: What is meant by the polarisation index of a transformer? Polarisation index is the ratio of megger value taken for 10 minutes to the megger value taken for 1 minute.

What is the polarization index test?

Polarization Index (PI) Test The polarization Index is nothing but the ratio of insulation resistance after 10 minutes and after 1 minute. How PI Test is Performed? In PI test, ratio of insulation resistance at different times after starting of test is recorded.

What is the relation between IC and Megger value in polarization index?

Polarization index is the ratio of Megger value taken for 10 minutes to the Megger value taken for 1 minute. Let I = Total initial current during Polarization Index Test or PI test. IC = Charging current due to Capacitance of Insulator.

What does a high polarization index of an insulator imply?

This equation indicates that high polarization index of an insulator implies healthiness of insulator. For good insulator resistive leakage current I R is very tiny. It is always desired to have polarisation index of an electrical insulator more than 2.