Maintenance of Traction Motor - PART 2

Ref: - 1) HQ L/No. Diesel/Maintenance/HQs & Shed/30 dtd.7.1.2010.

         2) HQ L/No. Diesel/Maintenance/HQs & Shed/30 dtd.17.09.2010.

      An action plan to arrest high incidences of Traction Motor failures on line was issued by HQ vide ref. 1 & 2. Implementation of action plan by sheds, though partially, has resulted in some reduction in line failure cases.

Traction Motor Line failure incidences are as follows:

SN	Shed	09-10	10-11 (Up to Aug)
1	L	15	5
2	M	14	5
3	N	19	3
4	S	12	3
Total		60	16(5 months)

Action plan had emphasized and introduced following major points:

1.            Overhauling and testing of Traction Motor as per revised format.

2.            Measurement of manomatric pressure during every trip schedule.

3.            Condition monitoring of Traction Motor as per Traction Motor bearing temperature, IR value, MV drop, premature wear of Carbon brush, colour of carbon film and sign of flash over. Monitoring as per exception list.

4.            Securing of Pig Tail by adhesive/Nylon tag.

5.            Field IR should remain constant at 500 mega ohm 3 days after baking for 8 hrs.

6.            Armature cooling hole to be air cleaned by long perforated copper pipe.

7.            Fitment of additional 0.38mm Nomex paper at corner of Pole Shoes and 0.76mm nomex paper in backside of Pole Shoes, replacement of mica inspection during overhauling.

8.            UST of armature shaft.

9.            During no load test temp. rise of both side bearing to be kept below 9 degree Celsius at pinion end & 16 degree Celsius at commutator end strictly. Motor to be run both clockwise and anticlockwise. An efficient Traction Machine produces least temperature rise.

10.         Dominant frequency to be measured on vibration test bed.

11.         Use of SPM and Engineers Stethoscope. Traction Motor sound should be deep, continuous and regular without any break.

12.         ZYGLO testing and profile checking of pinion.

13.         Replacement of Arc Ring bolts and use of thread locking compound.

14.         Use of single unit epoxy tight brush holder and spring tension checking of holder pocket.

15.         Provision of sleeve over cable, Provision of Rubber cushioning under cleat joint, securing of cable and MV drop of terminals.

16.         Compilation of Tell Tale sign compendium for visual checking of Traction Motor.

         Each shed should carry-out audit and report present status of compliance of above technical instructions.

         In order to further improve reliability of Traction Motors, following instructions should be incorporated in schedule maintenance.

1.            Handling: Only Nylon rope/ sling should be used for lifting Traction Motor armature to avoid damage of PTFE band and poly glass binding.

2.           Armature:

2.1         Check both side bandings for any looseness by tapping gently with nylon mallet, examine thoroughly for rubbing marks, damaged insulation, overheating, loose wedge, shaft defects etc.

2.2         Mica residues inside the commutator slots should be removed by special tool. Cover the teflon band so that the teflon band is not damaged while removing mica.

2.3         Check for any welding cracks in balancing pieces by tapping them gently

2.4         Bar to bar resistance measurement should be done. The permissible difference between values is + / -3 standard deviation.

2.5         Clean the armature with compressed air and heat it in oven at100°c for 4 hours cover the commutator with rexin and varnish the armature to avoid ‘ V ’ ring failure.

         Apply araldite in ½ axial length of teflon ring base from bearing side & apply RTV on ¼ portion from segment side, then provide teflon ring. Apply varnish in the dust proof area.

2.6         Inspect armature shaft for straightness, size (including 4 points) on each bearing seat for ovality or taper, length of shaft, overall and critical sections) and surface integrity or wear. The difference between the outside diameter of inner race after and before fitment should be recorded. It should be around 0.06 to 0.08 mm.

2.7         Visually check commutator for any bar pattern, grooving, high bars or high micas. If evident, investigate cause and arrange appropriate corrective action.

3.            Commutator roundness Position dial gauge to touch the commutator surface. Rotate armature slowly by hand and measure the commutator eccentricity and run out. Commutator run out 0.01 mm (max) Commutator eccentricity 0.025 mm (max).

4.            Magnet frame:

4.1         Examination of magnet frame: Check for any potting cracks, dislocated clamp, rubbing mark on main poles and inter poles,   insulation damage or overheating marks.

4.2         Conduct DPT in the following locations MSU seating area, TM gear case lugs, TM nose, TM safety lug. Apply RTV sealant over the holding bolt heads after tightening.

4.3         Check all the eight axle cap bolt fixing bores for any broken bolt pieces inside or any damage to the threads.

4.4         Clear the threads of end shield fixing holes, terminal cover fixing holes etc with original size taps.

4.5         Tighten the IP fixing bolts at a torque of 24 kgm after removing the sealant tighten the mp fixing bolts at a torque value of 42kgm after removing the sealant. Apply “M” seal over the bolt heads.

4.6         Check up the gap between top and bottom nose liners. Replace them if worn out.

4.7         Measure the diameter and length of yoke and Varnish the yoke with gun.

4.8         Provide suitable gasketting compound with high insulation resistance in all vulnerable areas where chances of power ground are possible.

5.            Air bellow openings

5.1         After testing is completed, the motor air bellow opening shall be sealed with a cardboard plate to prevent foreign material entering the motor.

6.            Check and correct nose suspension lug and wear plate as per Manufacturer's Maintenance Manual.

7.            Spray the interior of the machine with red air drying insulating varnish.

8.            Testing for insulation condition

8.1         When the motor has been received in the working area it shall be tested prior to dismantling and cleaning to determine the quality of the insulation.

8.2         Polarisation index test.

          This test is much like the Meg-Ohm Test, but it is performed for 10 minutes. Over this time period, the molecules in the slot liner paper polarize. When the molecules polarize, the insulation resistance values should increase over the10- minute period.

          Megger the motor at 500 volts for ten (10) minutes. Record the insulation resistance after 1 minute (IR1) and after ten (10) minutes (IR10). Digital mega Ohm meter should be used.

8.3         Polarisation Index P.I. = IR10 / IR1.

8.4         A P.I. greater than or equal to one (1) is an initial indication of good quality insulation providing there have been no recorded failures or bookings in service.

          Note - there shall be a discharge time allowance of 40 minutes after completion of the P.I. test.

9.            Two voltage test.

9.1         Megger the motor at 500 volts for one (1) minute and record the Insulation Resistance (R1). Then megger at 1000 volts for one (1) minute and record (R2).

·         The variation in values ΔR = R1 – R2.

·         ΔR / R1 should be less than 0.25.

·         PI = 1 and ΔR / R1 = 0.25 indicates that the insulation is in good condition and normal servicing should be satisfactory.

·         PI < 1 and ΔR / R1 > 0.25 indicates contaminated insulation and additional cleaning can be anticipated, perhaps to the extent of having to remove the armature bands.

·         PI < 1 and ΔR / R1 < 0.25 indicates deteriorated or worn insulation and major work, either armature rewinding or field replacement can be anticipated. This should be sent to DMW.

9.2         Measure armature resistance, Series field resistance and Inter pole coil resistance by digital micro ohm meter.

MV drop testing of various brazing joints and terminals should be conducted.

Trend monitoring of IR: Long term IR trend must be monitored and any reduction of IR of 25% is cause of serious alarm. At least 12 individual reading graphs should be available and scrutinized before doing TM overhauling. Individual traction motor IR reading should be taken during M4 and above.

9.3         Tan Delta Test: Sheds should use Tan Delta machine for finding out insulation quality of Traction Machines. Trend monitoring of Tan Delta value of the particular Traction Machine should be done and in case of any deviation of more than 10% from previous Tan Delta value of the traction machine, corrective action should be taken for improving/replacing insulation.

9.4         Leakage current:  Cut off value and trend should be monitored.

10.     Performance Testing:

10.1      Apply 700 amps for 30 minutes and then measure the temperature rise at the brazed joints of MP and IP by using non-contact type thermometer. Keep the thermometer at a distance of about 25cms away from the joint for measurement. Normally the temperature rise will be up to 50°c. But in case of any defect in brazing, the temperature will increase to 100°c.

10.2      Ensure air tight fitment of inspection cover Test between F-FF and conduct continuity between IP coils and cable ensure continuity of windings.

10.3   Measure the IR value of MP, IP and ‘A’ cable with 1000 V.

10.4   Measurement of temperature rise in all vulnerable location (brazing joint, terminal leads, cable joints, suitable points on poles, commutator etc.) during no load test bench checking.

10.5   Inject 500amp from dc high current injecting set to main field circuit    ‘F-FF’ and measure the voltage drop at motor terminals and also record the same.

11.0   Road Ahead

11.1   Endoscope monitoring of Traction Motor condition during schedule inspection.

11.2   Thermal imaging during Test Bench checking.

11.3   Advance Winding Analyser for conducting step voltage testing and surge testing.