Trip Oil [PDF]

Zitiervorschau

Gas Turbine Training Manual

TRIP OIL SYSTEM The hydraulic trip oil system is the primary protection interface between turbine control panel and the components on the turbine which admit or shut off fuel to the turbine. Lube oil (oil) from the turbine bearing header is used for trip functions (abnormal and emergency shutdown of the turbine) as well as the hydraulic signal to the fuel stop valve for normal startup and shutdown. See the schematic diagram FUNCTIONAL DESCRIPTION The low-pressure lube oil (oil) functions in this system as trip oil to cause component devices to trip. Lube oil is passed through a piping orifice to become the trip oil (OLT). This orifice is sized to limit the flow of lube oil into the trip oil system and ensure an adequate capacity for all tripping device operations without causing starvation of the lube system when the trip oil system is activated. The resultant low-pressure oil (OLT) is then at proper capacity for the trip functions. This low pressure trip oil is supplied to the inlet guide vane trip device, 20TV-1, and passes through the flow limiting parallel check valve/orifice arrangement to the turbine over speed trip device. Trip oil then flows through a second flow limiting parallel check valve/orifice piping arrangement to the turbine fuel system (fuel stop valve arrangement) parallel to the trip system solenoid operated fuel dump valve 20FG-1. Operation of the solenoid valve permits use of the fuel system for turbine operation and turbine stop action when required. The system also provides a direct connection to the 12 HA over speed trip device for turbine shutdown whenever an over speed condition occurs. A fuel system trip or an over speed trip will not trip the inlet guide vane system. The IGVs will close under normal control under these conditions. The devices that cause a turbine shutdown through the trip system do so by dumping fluid pressure from the system either directly or indirectly through solenoidoperated dump valves 20FG-1 or 20FL-1. When oil in the trip oil line is dumped, fuel stop valves close by spring return action. When the turbine is started, the dump valve is energized to reset at the desire point in the starting sequence, permitting oil pressure to open the fuel stop valves. The fuel stop valves remain open until some trip action occurs or until the unit is shut down.

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Scheme For Trip Oil System

Pressure switches 63HG-1,-2 and -3 are also installed in the low pressure trip and fuel control systems to provide redundant pressure monitoring and feedback to the turbine control system insuring required trip oil pressure levels for turbine operations. If the pressure levels for turbine operations. If the pressure of the fuel system becomes too low for reliable operation, one or more switches will trip ;the unit and cause an alarm indication of “Low trip oil pressure”. A direct reading pressure gauge and test valves are installed with the pressure switches to facilitate required inspection and maintenance.

Gas Turbine Training Manual

TRIP DEVICES Over Speed Trip Mechanism ( for FR-5 only)

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Gas Turbine Training Manual An over speed trip mechanism, mounted on the Accessory gear, is the second trip device in the system. This totally mechanical device, located in the Accessory gear, is Actuated automatically by the over speed bolt should the turbine speed exceed the bolt setting . As a result, a rapid decay of trip oil pressure(OLT) occurs, ultimately stopping the flow of fuel to the turbine by action of the fuel oil stop valve. When activated, the over speed bolt assembly trips the latching trip fingers of the over speed trip mechanism. The action release the trip valve in the mechanism and dumps the OLT trip system pressure to atmosphere. In turn, this causes the oil in the fuel stop valve cylinder to return to atmosphere pressure, thus allowing spring pressure to close the valve. An additional feature included in the over speed trip mechanism is a limit switch (12HA) which signals an alarm and trips the turbine and a manual trip push. Once the trip is actuated, the system remains open and drains until it is reset manually by pulling the reset rod. Hydraulic Dump Solenoid Valves 20 FL-1 and 20FG-1 Solenoid-operated spring return hydraulic dump valves 20FL-1 for Liquid Fuel and 20 FG-1 for gas fuel are used to trip the system operation by a signal form the master control and protection circuit. The valves are energized when the turbine is running depending upon the fuel currently in use. Fuel Stop solenoid (dump) valve 20 FG-1 relieves trip oil pressure going to the gas fuel stop valve. By dumping the trip oil to the gas fuel stop valve, it causes the fuel system to shut down. This solenoid valve is spring biased to trip and, therefore protects the turbine during all normal situations as well as for loss of DC power. 20 FG-1 is shown in its de-energized state in the schematic diagram. Similarly , 20 FL-1 valve is used to relieve trip oil pressure going to Liquid Fuel stop valve. The stop valve , based on the spring tension , closes upon dumping of the trip oil and thus causes fuel system to shut down. Hydraulic Dump Valve for IGV - 20TV-1 Functionally it dumps trip oil pressure to the inlet guide vane dump valve, VH3-1, and stops the flow in a manner similar to the over speed trips mentioned above.

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