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FAILURE OF BARRING GEAR CLUTCH ASSLY COUPLING

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.

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FAILURE OF BARRING GEAR CLUTCH ASSLY COUPLING

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  1. FAILURE OF BARRING GEAR CLUTCH ASSLY COUPLING U#2,33MW TG. BORL,BINA PROJECT

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

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