Combustion Gas Turbines - Turbine Hydraulic Oil Trip System PDF Print E-mail
Written by Norrie   
Wednesday, 13 January 2010 10:12
Article Index
Combustion Gas Turbines
Principles and Operation
The Air Compressor
The Combustion Chamber
The Compressor (HP) Turbine
The Variable-Angle Nozzles Load Turbine
Turbine/Compressor Lube Control Oil System
Turbine Hydraulic Oil Trip System
Turbine Overspeed Trip Mechanisms
Turbine System Details
All Pages

TURBINE HYDRAULIC OIL & TRIP SYSTEM

CONTROL OIL
A flow of oil to the accessory gear also goes to the FUEL GAS REGULATOR which is a device incorporating a pump. This pump increases the oil pressure from 25 Psi to 300 psi which is called the Constant Control Oil (CCO). A Variable Control Oil (VCO) is also put out from the fuel gas regulator, the pressure of which depends on the signal coming from the Turbine Speed Controller. This variable pressure oil (VCO) operates and controls the Fuel Gas Control valve. The 300 psi CCO goes to the NOZZLE REGULATOR where another variable oil pressure is produced - ( NCO ) Nozzle Control Oil, which passes through the 'NCO Dump' valve to the 2nd stage turbine, ( Load turbine ), nozzle control cylinder. This cylinder controls the variable angle nozzles which direct the superheated air leaving the HP turbine blades onto the blades of the load turbine. In this way the load turbine speed is controlled depending on the load on the turbine produced by the driven machine. (Generator, Compressor…etc). A load change will tend to change the turbine speed. The control system adjusts the angle of the L.P. turbine nozzle-vanes to maintain the speed. The control system is inter-connected to the Fuel Gas regulator and the HP & LP turbine control systems to maintain the balance between the HP & LP turbines as mentioned earlier.

HYDRAULIC OIL
The 120 Psi Hydraulic oil from the lube oil pump discharge is filtered by one of two filters and passes to the hydraulic oil system through a restriction orifice. The hydraulic oil is piped to :-

  1. A manual emergency trip valve
  2. The Solenoid trip valve
  3. The HP and LP turbine overspeed trips
  4. The NCO dump valve
  5. The Fuel gas stop valve

The system operates as follows: -
The pressure of the hydraulic oil is holding the NCO dump valve and the Fuel Gas Stop Valve (4 & 5 above), in the 'GO' position - The NCO dump valve is allowing the NCO to pass to the nozzle control cylinder. The fuel gas stop valve is also held open to allow the fuel gas to flow to the combustion chambers. When any trip is activated, (1, 2 or 3 above), the hydraulic oil pressure is dumped to the lube oil tank and drops to zero psi. This causes the Fuel Gas Stop valve to close shutting off the fuel to the combustion chambers. At the same time the NCO dump valve operates to close the NCO supply and open the dump line from the control cylinder which takes the nozzle control ring to zero setting (nozzles fully open). The turbine shuts down. The flow of hydraulic oil through the restriction orifice is less than the flow to the dump, keeping the pressure at zero. Before re-starting the machine, speed controls have to be put on manual and set to zero, compressor recycles to manual and fully open and the trip condition has to be corrected and cancelled. As the trip condition is corrected and cancelled, the hydraulic pressure is restored slowly to normal and the operating start up procedure followed to re-start the machine. (Figure. 23)

CONTROL & HYDRAULIC TRIP SYSTEMS
Figure. 23

Various trip conditions which will activate the electrical trip circuit to the solenoid valve include the following: -

  • Low lube oil pressure
  • Low seal oil overhead tank level
  • High shaft vibration
  • High temperature in the lube and seal oil return lines
  • High compressor discharge temperature
  • High turbine exhaust temperature
  • High compressor suction drum liquid level etc.

The activation of any trip will dump the hydraulic oil to zero Psi and the oil will return to the lube oil reservoir. Before tripping the machine, the high turbine exhaust temperature operates to cut back the fuel to the machine which of course reduces the machine capability. If this fails to cool the exhaust, the machine will trip. In very hot summer weather, particularly in hot climates, the high ambient temperature of the inlet air to the turbine air compressor causes these conditions.



Last Updated on Wednesday, 24 February 2010 20:06