CONOCIMIENTOS GENERALES DE NUTRICION

The liquid fuel system consists of fuel handling components and electrical control components. Some of the fuel handling components are: primary fuel oil filter (low pressure), fuel oil stop valve, fuel pump, fuel bypass valve, fuel pump pressure relief valve, secondary fuel oil filter (high pressure), flow divider, combined selector valve/pressure gauge as- sembly, false start drain valve, fuel lines, and fuel nozzles. The electrical control components are: liq- uid fuel pressure switch (upstream) 63FL–2, fuel oil stop valve limit switch 33FL, fuel pump clutch sole- noid 20CF, liquid fuel pump bypass valve servo- valve 65FP, flow divider magnetic speed pickups 77FD–1, –2, –3 and SPEEDTRONIC control cards TCQC and TCQA. A diagram of the system show- ing major components is shown in Figure 15. The fuel bypass valve is a hydraulically actuated valve with a linear flow characteristic. Located

Figure 14 Servo Positioning Loops <QTBA> ANALOG OUTPUT POSTION FEEDBACK FUEL HYDRAULIC ACTUATOR HIGH PRESSURE OIL TORQUE MOTOR EXCITATION SERVO VALVE LVDT LVDT EXCITATION POSTION FEEDBACK <R> <S> <T> REF REF REF D/A D/A D/A 3.2KHZ 3.2KHZ TBQC ANALOG INPUT id0026 TCQC TCQC TCQC 3.2KHZ

GE Power Systems

15 FUNDAMENTALS OF SPEEDTRONIC

MARK V CONTROL SYSTEM A00100

between the inlet (low pressure) and discharge (high pressure) sides of the fuel pump, this valve bypasses excess fuel delivered by the fuel pump back to the fuel pump inlet, delivering to the flow divider the

fuel necessary to meet the control system fuel de- mand. It is positioned by servo valve 65FP, which receives its signal from the controllers.

63FL-2

Figure 15 Liquid Fuel Control Schematic

id0031V DIFFERENTIAL PRESSURE GUAGE COMBUSTION CHAMBER FLOW DIVIDER ACCESSORY GEAR DRIVE

MAIN FUEL PUMP FQROUT

BY-PASS VALVE ASM.

TYPICAL FUEL NOZZLES OFV FSR1 TNH L4 L20FLX OH HYDRAULIC SUPPLY FUEL STOP VALVE _VR4 OLT- CONTROL OIL FALSE START DRAIN VALVE CHAMBER OFD TO DRAIN FQ1 <RST> <RST> OF P R 65FP 33FL PR/A <RST>

CONN. FOR PURGE WHEN REQUIRED ATOMIZING AIR 40µ 77FD-3 AD 77FD-1 77FD-2 TCQA TCQC TCQA

The flow divider divides the single stream of fuel from the pump into several streams, one for each combustor. It consists of a number of matched high volumetric efficiency positive displacement gear pumps, again one per combustor. The flow divider is driven by the small pressure differential between the inlet and outlet. The gear pumps are mechanically connected so that they all run at the same speed, making the discharge flow from each pump equal. Fuel flow is represented by the output from the flow divider magnetic pickups (77FD–1, –2 & –3). These are non–contacting magnetic pickups, giving a pulse signal frequency proportional to flow divider speed, which is proportional to the fuel flow deliv- ered to the combustion chambers.

The TCQA card receives the pulse rate signals from 77FD–1, –2, and –3 and outputs an analog signal which is proportional to the pulse rate input. The

TCQC card modulates servovalve 65FP based on in- puts of turbine speed, FSR1 (called–for liquid fuel flow), and flow divider speed (FQ1).

Fuel Oil Control – Software

When the turbine is run on liquid fuel oil, the control system checks the permissives L4 and L20FLX and does not allow FSR1 to close the bypass valve unless they are ‘true’ (closing the bypass valve sends fuel to the combustors). The L4 permissive comes from the Master Protective System (to be discussed later) and L20FLX becomes ‘true’ after the turbine vent timer times out. These signals control the opening and closing of the fuel oil stop valve. The fuel pump clutch solenoid (20CF) is energized to drive the pump when the stop valve opens.

The FSR signal from the controlling system goes through the fuel splitter where the liquid fuel re-

quirement becomes FSR1. The FSR1 signal is mul- tiplied by TNH, so fuel flow becomes a function of speed – an important feature, particularly while the unit is starting. This enables the system to have bet- ter resolution at the lower, more critical speeds where air flow is very low. This produces the FQROUT signal, which is the digital liquid fuel flow command. At full speed TNH does not change, therefore FQROUT is directly proportional to FSR. FQROUT then goes to the TCQA card where it is changed to an analog signal to be compared to the feedback signal from the flow divider. As the fuel flows into the turbine, speed sensors 77FD–1, –2, and –3 send a signal to the TCQA card, which in turn outputs the fuel flow rate signal (FQ1) to the TCQC card. When the fuel flow rate is equal to the called– for rate (FQ1 = FSR1), the servovalve 65FP is moved to the null position and the bypass valve re- mains “stationary” until some input to the system changes. If the feedback is in error with FQROUT, the operational amplifier on the TCQC card will change the signal to servovalve 65FP to drive the by- pass valve in a direction to decrease the error. The flow divider feedback signal is also used for system checks. This analog signal is converted to digital counts and is used in the controller’s software to compare to certain limits as well as to display fuel flow on the CRT. The checks made are as follows: 1. L60FFLH:Excessive fuel flow on start–up 2. L3LFLT1:Loss of LVDT position feedback

(MS7–1 & MS9–1)

3. L3LFBSQ:Bypass valve is not fully open when the stop valve is closed.

4. L3LFBSC:Servo current is detected when the stop valve is closed.

5. L3LFT:Loss of flow divider feedback

If L60FFLH is true for a specified time period (nom- inally 2 seconds), the unit will trip; if L3LFLT1 through L3LFT are true, these faults will trip the unit during start–up and require manual reset.