Answer / kapil mishra

PI is a variation of the IR test. It is the ratio of IR
measured after voltage has been applied for 10 minutes (R10)
to the IR measured after one minute (R1), i.e.

PI = R10/R1
Low value of PI indicates that the winding may have been
contaminated with oil, dirt etc or absorbed moistures. In
the test, a relatively high DC voltage is applied between
the copper conductor and the stator or rotor core usually
between the winding and ground as the machine core & body
are grounded)

Answer / v.senthilkumar - skpcl

The ratio between IR value for 10 minutes to 1 minute.

Formula (PI) = Resistance Value 10 Min after
start/Resistance value 1 Min after start. (IR 10min / IR
1min)

The recommended minimum values for PI are based on the
thermal class of the insulating materials and apply to all
insulating materials regardless of application per IEC
60085-01:1984. The PI test is not applicable to non-
insulated field winding. The recommended minimum value for
PI are as follows:

Class A Termal Class Rating = Min PI is 1.5
Class B Termal Class Rating = Min PI is 2.0
Class F Termal Class Rating = Min PI is 2.0
Class F Termal Class Rating = Min PI is 2.0

Answer / sridhar

It is the ratio of Insulation Resistance value of 1st
minute and 10th minute for any Electrical equipment.
Equipment is said to be sound if the ratio is greater than
one.

Answer / santhoshkumar

The ratio between IR value for 10 minutes to 1 minute.
It proves the healthiness of the insulation. Best value
will be above 1.2

Answer / rajpalsing rajput

It is the ratio of IR value at 10 min to the IR value at 1
min.It is measure of condition of insulation system wether
it is clean or dirty.If it is greater than 2 indicat the
good condition of insulation system and if it is greatore
than 6 indicate that insulation system is thermally degrade.

Answer / md. robiul islam

Polarization Index is an indicator which gives an idea of
the cleanliness of the windings. It is a ratio of the
Insulation Resistance Measured for 10 minutes to the
insulation resistance value measured after 1 minute. Since
it is a ratio; it does not have any units.

Polarization Ratio = Insulation Resistance after 10 minutes/
Insulation Resistance after 1 minute

The Polarization Index should be above 2.0 to be
permissible. Machines having PI below 2.0 cannot be operated.

Answer / karthikeyan

Polarisation intex test is used for find out the IR value at
a particular temperature

if a 3phase 100kva distribution transformer , 400 v,50 hz, 4-wire system is loaded at 160 k.w mostly 1-phase Lighting & Airconditioning split a.c load what will be the net effect on the power system in terms of voltage, powerfactor, current , efficiency of xformer

1 Answers  

what is first pole to clear factor

1 Answers  

What is negative sequence over voltage element?

0 Answers   Green T&D,

What is size 00, 01, 1 etc., in HRC fuse types?

0 Answers   Jaypee,

why ups in kva ratings?

2 Answers  

why there is no short circuit when any resistance is used between phase and neutral?

3 Answers  

What are the difference between off-load tap changer and on-load tap changer in transformer?

2 Answers   HCL,

How do we measure earth fault current in Generator Transformer(20/420kv),Station Transformer(20/11 kv) and Unit Transformers(20/11kv) for our plant system, since these don't have any Neutral earth Fault relay connected to their Neutral Earth? But for Unit Service transformers(11/.433 Kv) we have an Earth Fault Relay connected to its neutral earth.Why is such so?

1 Answers   NTPC,

PID controller details

1 Answers  

why fault current always calculated for 1 seconds?

3 Answers   Coca Cola,

why gravels is used in transformer yard?

6 Answers  

what is the deference between watt and KVA

3 Answers   IAF,