Which checks and routines to be conducted for ensuring the proper running condition of turbo generator?
The Basic Primary requirement of the efficient and stable running of turbo-generator is a steady steam condition. To achieve this condition the following equipment is to be in good order:
1.1 Boiler combustion control.
1.2 Exhaust boiler condition.
1.3 Boiler excess steam control at predetermined set pressure.
1.4 Dumping steam control into Vacuum / Turbine Exhaust steam condenser system.
1.5 Avoid low-pressure steam / wet steam running conditions. Impingement occurs when the steam quality decreases to the point that steam condensate exists in the turbine. Water droplets impinging on turbine blades contribute to wear by causing erosion of the blades. At varying steam and varying load conditions, when D/G and T/G are running in parallel, the governor motors will be subjected to excessive movements lead to failure of the governor motors.Exhaust steam/vacuum condition: The Efficiency of the plant is depending on the vacuum condition of the condenser. In order to run at its maximum capacity, even up to 100% load running condition, optimum steam consumption, the vacuum of the condenser should be around 690 – 720 mm Aq. or the makers suggested value as per load trial run report. In order to achieve above condition, the following equipment should be in very good condition:
2.1 Vacuum control unit (ejector operating unit or vacuum pump unit).
2.2 Vacuum condenser water level control.
2.3 Condensate extraction pumps.
2.4 Cooling control of Air ejector condenser, if ejector type
2.5 Nozzle / Flow line filters
2.6 Condensate re-circulating valves and controllers
2.7 Water ring pump units and its associated valves.
2.8 Water ring pump condenser and circulation.
2.9 Vacuum side lines and valves/ breaker valves.
2.10 Vacuum condenser mountings and associated connections integrity
2.11 The controller valves pneumatic control equipment.
Gland steam condition:
3.1 The gland steam should always on and maintained at 0.1 -0.2 bars, normal operating ranges.
3.2 The gland steam make-up controller, pressure gauge and positioner valve operation.
3.3 The gland steam Spill control valve controller, pressure gauges and its positioner valve operation.
3.4 Gland steam receiver, pressure gauges, drain condensate valves, safety valve, set at 0.20 bar, normally.
3.5 Gland steam return to condenser, extraction fan, cooling water system and control.
3.6 TLV float controllers, if ejector system is applicable.
Lube oil condition: The important requirement is steady lube oil operating condition
4.1 Steady lube oil temperature about 45 +/- 2° Cel.
4.2 Failure to maintain correct lube oil properties may cause:
a) Deteriorates from oxidizing, polymerization results acids formation.
b) An increase in viscosity and foaming properties forms gummy residues and accumulations in oil passages.
c) Increases bearing temperatures and break down oil film.
d) Acids promote corrosion of working components.
4.3 Water content and impurities levels causes:
a) Corrosion
b) Emulsion
c) causes poor circulation and lubrication
e) Oxidation and sludge formation
4.4 Oil cooler oil temp controller and positioner valve operation:
a) Low oil temperature leads to the uneven supply of lubricating oil and has a greater possibility of local overheating of the bearings and malfunctioning of governing devices.
b) Oil temperature has to be maintained 45°C by means of the controller.
c) IN practice, it is easy to achieve low oil temperature by blanking on bypass line, DO NOT blank the oil by pass, at lower sea water temperatures cools down lube oil temperature too low and supply will be reduced due to increase in viscosity can cause major damages to the gear box.
4.5 Filters and change over valves, st-by lube pump auto operation.Other Important Checks:
5.1 Main stop valve- free operation is required. Any sedimentation will lead to unexpected trouble.
5.2 Accumulations from boiler steam- drop in OUT PUT and abnormal steam thrust lead to whipping of the bearings
5.3 After the suspension of turbine operation, completely drain for condensate and close the drains for infiltration of moisture.
5.4 In stop condition, do not allow steam to leak, the leaking steam can corrode blades and rotor, remarkably. 5.5 Vacuum condenser - S.W cooling system is not provided with recirculation system at low sea water temperatures. When temperatures changing to below 15°C, cooling water flow to be reduced with overboard or condenser outlet valve control to prevent the cracking of condenser tubes. 5.6 Salinity indicator system to be in good operational condition. 5.7 Load characteristics - It is not desirable to run the turbine in NO load condition for a long time since some times temperature rise excessively at each stage. Avoid sudden heavy loading in short span of time. 5.8 Over-speeding of the turbine is a catastrophic failure. Experiences and records indicated that deposits have caused the STEM of the both the governor and the trip valve to stick when there was a loss of load. Of course destructive over-speeding results from loss of load.
5.9 Turning gear operation - when the turbine is not operating, heat must be prevented from warping the rotors, a motor driven or air driven turning device is engaged to rotate the turbine to allow uniform cooling.Trip devices: Should be tried at regular intervals and operational at all times.
6.1 Over- speed emergency trip
6.2 Low lube oil pressure
6.3 High back pressure trip
6.4 Excess vibration trip
6.5 Aux lube oil pump auto start/stop
