Transcript jjjjj - BHEL PSWR

FAILURE OF BARRING GEAR
CLUTCH ASSLY COUPLING
U#2,33MW TG. BORL,BINA PROJECT
DESCRIPTION
 Unit-2 TG is provided with a motorised
barring gear unit which drives the turbine
at 150 rpm barring speed.
 The barring gear unit comprises mainly
of one electric motor(37KW), worm
reducer, SSS clutch assly ,worm gear and
a soft starter.
 Drive is transmitted from motor through
worm gear, clutch assly to Gear box
pinion shaft and then to main turbine.
The clutch assly is connected to the
pinion shaft of the gear box with a
coupling consisting 8nos studs.
 When Barring gear is switched on, the worm
shaft rotates the input assly. As input assly
start rotating , the helical sliding assly
moves axially towards drive end. This results
in engagement of gear teeth of sliding assly
and output assly. Thus barring gear gets
engaged.
The m/c was first put on Barring Gear
operation on 03.07.10 and was running on
BG for about an hour.
 Before steam rolling while m/c was
being put on Barring Gear on 12.08.10
suddenly all the 8nos coupling bolts of
output assly got sheared off and motor
got disengaged.
 Before starting the motor, JOP header pr
and lift of rotor was checked and found in
order. Rotor was also free in hand
rotation.
ACTION TAKEN
 The failure occurred just before steam rolling
program of the unit. The barring gear
operation was possible only after replacement
of the sheared studs of output assly.
 A complete barring gear unit was available for
U#3. It was dismantled and studs were
removed from the coupling and fitted in the
affected clutch assly.
 Barring gear could be restored in 15 hrs which
otherwise could have taken 5-7 days for
procurement of coupling bolts.
ANALYSIS
 As per opinion of M/s Triveni Engg , the
supplier of the Barring Gear unit, the studs
have sheared-off due to excessive loading of
the turbine rotor probably caused due to drop
in JO pressure at the time of switching on the
motor.
 M/s Triveni also suggested the signal of min
JOP which is a start permissive for BG motor,
should be taken from individual brg instead of
JOP header as per existing scheme.
REMARKS
 With soft starter and overload relay in
service, Barring gear motor is well protected
against any overloading.
 Failure of coupling bolts of M/s Triveni
supplied Barring gear unit was reported from
few other sites.
 In view of the above BHEL site feels that bolts
are to be designed for higher capacity.