RELIABILITY
1. Action Plan for Improving the Reliabilty of 6FRA 6068 Traction Motors , used in
WAG9/WAP7 Locomotives
a. Stators : RDSO has studied various available literatures on the three phase traction
motor and manufacturing practices of leading motor manufacturers and had interaction
with some of the designers of these motors. It has been established that unsupported
overhangs of stator windings and inadequate insulation at the outlet of the core and in
knuckle points, not commensurate with the prevailing shocks and vibration level in
service are the main reasons of failure of stator windings. The problem gets aggravated
due to excessive shock and vibration level with worn out gears , where maximum
vibration of 89g has been recorded by BT while carrying out vibration trial in Sept’2002.
Worldwide all the manufacturers of traction motors are supporting the overhangs when its
length exceeds 100mm at a vibration level at 30g and above.
Based on the above study two schemes were proposed and stators were physically
modified accordingly. Subsequently these stators were rewound without any problem.
After ensuring successful implementation of the proposed schemes, both the schemes
were got validated through Finite Element Analysis by SIDBI Innovation and Incubation
Center of IIT ,Kanpur. RDSO has prepared a detail proposal to improve the reliability of
Stators RDSO’s proposal has been accepted by the Board , vide its letter no.
2005/Elect(TRS)440/18/53-phase) , dt. 21.01.2008. Accordingly , RDSO has prepared
Modification Sheets No 355 and 356, which gives the details of action to be taken to carry
out the proposed modification of supporting of overhangs during rewinding and new
manufacturer, respectively and CLW and Zonal Railways were informed , vide this office
letter no.EL/3.2.182 dt. 07.02.2008. So far 37 stators have been repaired with this
scheme.
b. Rotors: Similar studies have been taken up for the rotors of this traction motors. It has
been concluded that the present design of rotors are not able to withstand a larger
number of cycles of starts and stops , stalling while hauling high inertial loads at graded
sections of coal sidings. The problem gets further aggravated due to excessive shock
and vibration level achieved with worn out gears, when the maximum vibration level
reaches upto 300 g which was recorded by M/s Bombardier Transportation (BT) while
carrying out trials in Sept. 2002.
RDSO has accordingly prepared a detailed action plan to improve reliability of rotors,
which has been validated by Finite Element Analysis at SIDBI Incubation and Innovation
Center at IIT, Kanpur. This action plan recommends two schemes, which has been sent
to Railway Board on 10.04.2008:
1. Shaft Mounted Copper Stamping type Resistance Ring
2. Resistance Ring Mechanically Interlocked to Endplate Design
Shaft Mounted Copper Stamping type Resistance Ring Mechanically
Resistance Ring Interlocked to Endplate Design
2. Winding Scheme for Oil Cooling Blower Motors of different makes used on 3-Phase
Drive Locomotives
The reliability of Oil Cooling Blower motors (OCBs) of WAG9/WAP5/WAP7 class of 3-phase
Locomotives has been a cause of concern. The investigations have shown that failures are
mainly attributable to inter turn shorts and other winding failures caused by voltage surges
present in Auxiliary Converter output. The quality of rewinding done through trade on these
motors has not been up to the mark. In order to consolidate the winding schemes of different
makes to facilitate easy reference and use by rewinding workshops and other agencies, an SMI(
ELRS/SMI/0239 Rev ‘0’) containing winding scheme for OCBs has been issued vide letter
no.EL/3.2.176/1 dated 8.9.2006. So far 30 motors have been re-wound with these wires and are
in service for last 10 months with satisfactory performance.
3. Rewinding Facilities for Auxiliary Motors of Electric Locomotives:
RDSO vide letter No. EL/3.2.70 dt. 08.3.07 had circulated the Schedule of Technical
Requirements no. ELRS/STR/Aux/0014 of March 2006 for sources for rewinding of Auxiliary
motors of Electric Locos to Zonal Railways for evaluation and feedback for preparation of list of
approved sources.
RDSO identified 17 sources with feedback from Railways and sent the same to Railway Board
with a request to nominate committees of officers from Railways assisted by RDSO
representatives to visit the firms and submit the the report to RDSO. Three (3) committees were
nominated for covering all the 17 sources. The committees completed their evaluation in June
2007 and submitted its report to RDSO. The recommendations of RDSO has been sent to
Railway Board vide this office letter no. EL/3.2.70 dt. 22.6.2007.
4. Adoption of Comet makes Timers CM1L-110V DC in place of defective Syrelec timers
working on PC8 relays.
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In the 31 MSG meeting it was discussed that Syrelec timers fitted with ABB/BBC make PC-8
relays for Q44/Q118 are failing prematurely. Some of the Railways mentioned that Comet make
timers used in place of syrelec timers are functioning much better and recommended that RDSO
should examine the adoption of comet make timers on PC-8 relays. Based on study &
performance feed back, it has been recommended to the Railways that defective syrelec timers
may be replaced with Comet make timers type CM1L-110V DC used in Q44/Q118 application of
PC-8 relays vide this office letter no. EL/3.2.10/Gen dated 22-6-2007.
5. Provision of Nief Smitt plug in relays of M/s. Concord Automation, Faridabad:
st
As per decision of 31 MSG meeting, CLW has been advised to provide above relays on 10 loco
sets (except for Q45 locations) for gaining more experience vide this office letter no.
EL/3.2.10/Gen. dated 17-5-2007
6. Conversion of single bottle VCBs supplied by M/s. AAL:
st
As per decision of 31 MSG meeting, M/s. AAL and M/s. BT were advised vide letter dated 11-5-
2007 to submit their proposal for conversion of VCBs for improving reliability. The proposal of
M/s. AAL received vide their letter dated 23-05-2007 and 30-05-2007 has been examined by
RDSO and the same has been sent to Railway Board vide this office letter no. EL/3.2.61/3 dated
7-6-2007 and 22-6-2007 for approval and advising Railways for undertaking the conversion work
during POH of coaching locos and IOH of freight locos.
7. Surge Suppressors for protection of auxiliary machines & battery:
RDSO, vide letter EL/2.2.3 dated 19-12-2000, advised Railways for procurement of secondary
surge arrestors of Joslyn make for fitment on locomotives for field trials to assess their
effectiveness. In terms of para 3.2 of ML’s inspection note no. 2005/Elect(G)/145/1 dated 24-4-
2007, performance feed back received from Railways of Joslyn make surge arrestors, being cost
effective and having additional feature to detect the health of arrestors, Railways/PUs have been
advised vide this office letter no. EL/2.2.23 dated 22-6-2007 for following course of action:-
• Failed LTBAs should be replaced by Joslyn make LTBAs. 25% of the local requirements
of LTBAs at CLW for new locomotives should be made with Joslyn make LTBAs.
• Railways have also been requested to give performance feed back of Joslyn make
surge suppressors provided across transformer auxiliary winding and Arno converter.
8. Reliability improvement of control circuit:
Proposal of WR received vide letter no. EL/91/36/8 dated 07/05/2007 for Paralleling of interlock
of relay Q50, Q51, Q52 and SMGR interlock 61 & 62 in AC Tap Changer Locomotive control
Circuit has been examined. A draft modification sheet has been prepared and issued to Zonal
Railways for their comments and suggestions vide letter no. EL/3.1.3 dated 06-11-2007.