Bhoruka Power ,Neria Report

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Date: 01/03/2012

FINAL GEARBOX INSPECTION REPORT

SITE: BHORUKA POWER CORPORATION LIMITED.,

Neria Mini Hydel Scheme,

Village: Nidle, Taluk: Belthangady,

South Canara Dist.,

KARNATAKA

EQUIPMENT: TG Gearbox.

Power: 5050 KW. Unit Number: 1

Ratio: 2.885 Speed: 260 / 750 rpm.

Oil recommended: ISO-VG-320 Teeth Design: Single Helical

Oil Quantity: 147 Lpm Service Factor: 2.00

Driving Equipment: Hydel Turbine

Driven Equipment: Alternator

Further to the Preliminary report dated 28.12.2011, the gearbox tooth mesh was

inspected at site after decoupling the turbine and following observations made.

OBSERVATIONS:

a) Static blue teeth condition checked by decoupling both low speed and high speed

couplings.

Only 40% contact found towards alternator side.

Mesh Pattern in Both HS& LS Shaft Decoupled

Condition



b) MOP dismantled from pinion NDE side and all gearbox foundation bolts were

Loosened and blue contact pattern was rechecked. Mesh pattern found same asabove.

c) Further pinion NDE thrust housing was loosened and blue contact recheckingwas done.

MOP Dismantled

Mesh Pattern

Mesh Pattern while foundation

bolts & thrust housing in loose Mesh Pattern in Non-active flank



Contact pattern found towards pinion DE side for around 20% length of the total face

width.

d) Mesh Pattern checked on non-active flank and contact found towards pinion

DE for around 30% of the total face width.

After checking mesh contact pattern at different conditions at site, it was decided to take

the gearbox for TEIL works repair & rectification.

PRE RECEIPT CHECKS.

Before receipt of gearbox following in house checks were carried out on gearbox

performance data, quality, manufacturing and testing records

i. Review of raw material records did not show any deviation as regards to

ultrasonic, cleanliness, grain size, inclusions, chemical composition and

mechanical properties from standard requirements.

ii. Review of manufacturing processes confirmed that the subject pinion shaft has

gone through the standard processes and in- process checks. Records of no load

full speed test at Mysore also did not reveal any deviations.

To analyze this problem gearbox was brought back to TEIL works on 30.01.2012 and

Gearbox tooth mesh was checked using foundation stools to simulate site foundation

condition.

Casing Joint

Line



Blue contact checked and found towards pinion DE side for around 35% length of the

total face width which was similar to what was found at site.

To understand the fragileness of casing the gearbox was then placed on the foundation

master using gearbox tank as support and mesh contact was checked.

Teeth Mesh contact found at the Centre for around 75-80% of the total face width as

Below.

Oil tray



CONCLUSIONS:

From the detailed observations of the pattern of failure of pinion teeth, various tests,

checks and studies carried out, following conclusions have been deduced.

1. Raw material of pinion shaft is found to meet the design specifications.

2. The manufacturing processes followed are found in line with design

requirements. The tooth quality such as profile, helix, and PCD run out,

accumulated pitch error found confirming to the required DIN class

of accuracy.

3. The heat treatment processes followed have met the requirements of case

depth, microstructure and case hardness.

4. The review of MRT report suggests that the gearbox running parameters

such as casing vibration, noise and bearing temperatures were well within

the permissible limits during shop testing. The blue contact during open

inspection found 80-90% of the face width.

5. The tooth contact of gearbox at site during 2011 off season was observed

to be 40% as against 80-90% achieved at TEIL works during shop testing.

The tooth contact check carried out at TEIL works on receipt back of the

gearbox from site indicated contact pattern similar to that of site.

6. The teeth mesh was found improving from 40% to 80% when gearbox was

positioned on oil tray indicating presence of possible fragileness in the

casing.



To summarize the tooth contact of the gearbox was found very sensitive to the gearbox

positioning. The casing bore coaxiality found varying depending on the method of gearbox positioning. This fragileness of casing is the most probable cause for the

tooth contact shift and pitting in the pinion.

The gearbox is provided with mesh adjustment mechanism for such eventualities at site

and usage of the same at site during installation could have avoided such end loading

and teeth damage if commissioning work was entrusted to TEIL. It is a general practice

to check the tooth contact pattern after erection of the gearboxes at site. Nevertheless

this mesh check will be carried out for this supply.

CORRECTIVE ACTION:

Teeth contact at site will be ensured to 80-90%(as obtained during testing at TEIL

facility) by TEIL service engineer after gearbox erection at site.

This check will surely eradicate the root cause of end loading due to which previous

failure had occurred.

Bhoruka Power ,Neria Report

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