The insulation resistance value of the armature of 1250KW DC motor is 1.5 M.ohm. The reading of same type another armature is 20 M.ohm. We cleaned the armature, heated up to 80C for two days but the reading of IR is not increasing than 1.5 M ohm. Any suggestion is requested please.

 

Short of getting it rewound or vacuum impregnated, might be time for a new motor.

Regards
cww

 

carbon particles will be accumulted in the commutator and on continuous rotation the spacing between the slots gets uneven which leads to decrease of IR value. clean the commutator and the cut the mica sheet with a depth of 3 mm

 

Phil Corso please any guide line from you? One of local motor armature winder is going to remove external insulation and wants to rebind and insulate the armature. We don't know IR value shall be increased by this process or not.

Regards
Shaheed

 

Shaheed... before "cutting out" suspected wiring please answer the following:

1) What is the motor's rated voltage?

2) What is driven-machine?

3) What is Enclosure-type?

4) What is Insulation-Class?

5) How long has it been in service?

6) When was IR last measured?

7) What makes you suspicious of wires connecting winding to terminal box?

8) Was IR measured with motor "cold"? Or shortly after having been shut down?

9) Have you determined Polarization Index,i.e., Ratio of 10-minute to 1-minute Meggar reading?

Regards, Phil

 

Sir,
1- Motor rated voltage are DC 690 excitation voltage 220VDC.
2- Driven machine is sugar cane shredder
3- Enclosure type is IP-54
4- Insulation class is F
5- Service years are 6 Y
6- IR Not taken before
7- Question as I understood, Motor brought to routine maintenance first time and IR value create confusion conflicting IEEE std 43-2000 minimum recommended aramture IR 100 Megohm.
8- IR measured with cold motor
9- PI not determined.

Regards
Shaheed

 

Shaheed.. If you haven't already done so search the Control.Com archives! Specifically:

o 1001509379 !

o 1026224486 !

o 1239792210 !

My suggestions are:

1) Perform the Polarization-Index test just after the motor has been de-energized, that is, with the motor "Hot" !

2) Use a Megger Instrument with a rating < = 500Vdc ! 300Vdc is preferred !

3) Do Not, repeat Do Not, perform a Dielectric Absorption Test !

4) Make sure the Armature winding is separated from the slip-rings, or from the source of power if the machine "Brushless" !

Phil

 

Shaheed... correction to my earlier post. Last Archive Thread should have been:

o 1239772210!

Phil

 

Shaheed... one more quesion:

10) what was IR reading of stator-winding?

Phil

 

Shaheed... I apologize for my incorrect identification of components: I should have said "brush-gear" instead of "slip-rings" and "field" instead of "stator!"

Phil Corso

 

Sir

Thanks for your expert suggestions.

1-The motor is in workshop hot PI is difficult but in the same condition PI is 1.

2- I am worried that our hand driven mager is 1000VDC for testing.

3- It was new experience for me that we placed three room heater rods 1000W each inside the space of armature and heated for 3 days. I am much surprised today the IR reading (cold) found 20Megohm that was 1.6 some days before.

4-The field and excitation IR is 5 and 10 Megohm and drying process is running.

5- Archive 101509379 I need some more information how to search this specific number.

Regards
Shaheed

 

Shaheed...

What is the motor's rated voltage?

Were the brushes "lifted" so that there is no contact with the commutator?

Phil

 

Shaheed...

Has the problem been solved?

Regards,
Phil Corso

 

Sir

Yes the problem has been solved. Armatures dried out for about 5 days, one insulating stick in slot was also giving low resistance that replaced. washed the armature with CTC Carbon tetra chloride and again HT varnished. Now readings are more than 80 megohms.

Regards
Shaheed