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.
