The Y&F fuel regulator is a very sophisticated control device. It has a “minimum value gate” that protects the gas turbine from adverse operation. The MVG compares fuel limits, turbine speed and exhaust temperature on a continuous basis. The sub-system that “calls for” the least amount of fuel, as determined by variable control oil (VCO) output pressure, will be “in charge.” This is the internal decision maker that ultimately sends a signal VCO pressure to the fuel pump or gas control valve, as applicable, to regulate flow. Thus, the fuel regulator has a comparator and method of “calculating” the correct amount of fuel required by the gas turbine. The MVG is thus a computer with some variable inputs and one limit upper limit at any given time. See the chart below for typical values. In these early gas turbines, fuel flow was not measured directly by the control system; on the contrary, fuel flow was simply “limited” indirectly by measuring speed, exhaust temperature and rate of change of temperature.
- Zero Fuel prevents flow until specific firing conditions are met, namely: minimum speed and system purge. Sparking is also restricted to the appropriate time for a specific period time (usually one minute).
- Fuel Limits are pre-adjusted settings (approximate ranges for adjustment shown).
|Regulator Setting||Range (psig)||Comments|
|Zero Effective VCO||Less than 40 psig||Zero pump stroke|
|Maximum VCO||170 – 200 psig||Maximum Fuel (load)|
|Firing VCO||80 – 100 psig||Firing fuel limit|
|Accelerating VCO||100 – 130 psig||Accelerating fuel limit|
|Minimum VCO||50 – 75 psig||Minimum (shutdown) fuel|
- Speed Control is set by the governor in an operating range of 95 to 107 percent of rated speed.
- Minimum Fuel is a setting that permits shutdown of the gas turbine under flame.
- Average Turbine Exhaust Temperature is monitored, as a way of controlling the turbine firing (inlet) temperature.
FUEL REGULATOR APPLICATIONS
TYPE OF UNIT
|3500 KW &
HP Compressor Inlet Pressure
|100 ohms||None||None||None||100 ohms|
Chart 7-1: Several fuel regulator designs for various applications (data circa 1950)
The person responsible for assembling these fuel regulators over the past 40 years has been a man known as Mr. Fuel Regulator, the late Bill Brooks of Y&F.
Over the first two decades when the fuel regulator was offered as a control system ending in 1969, many improvements were made without changing the basic functions of the device. Fig.4 shows a fuel regulator that was reconditioned to be reinstalled on a gas turbine still located in Pennsylvania (installation circa 1967). There are some obvious physical changes to the one in Fig. 1; however there are no functional differences.
Over the past six decades, electrical systems have changed and evolved. Many of the support devices to the fuel regulator have become obsolete, extinct or impossible to obtain. The manufacturers no longer offer replacement units. No longer can you get spare parts or modules. These include: GE/MAC temperature control, Fisher electro-pneumatic transducer and the Fairchild flame detector. Yet, the fuel regulator itself can be replaced or reconditioned. These, along with their ancillary components (Y&F hydraulic positioning servos, Y&F gas control valves, Y&F VCO dividers and OilGear fuel pumps) can be recycled by the manufacturers of companies like PAL Turbine Services, LLC.
Fig. 7-4 shows some gentlemen who were very active in the Product Service Department of the Gas Turbine Division of General Electric during the Fuel Regulator era. Left to right include Larry Mitter and the late George Kennedy and Geoff Jarvis. Mr. Mitter went to work for Y&F in the 1970s and became a vice president in engineering with the firm. George Kennedy was very involved in the GT Start-up Program, training numerous field engineers on fuel regulator control and protection systems. Mr. Jarvis was a mechanical “guru” who was very supportive to clients owners and GE field engineers during his product service days. Kennedy and Jarvis both died in the late 1990s.
The GE/MAC system had two slide-out modules (See Fig. 5 below) that allowed testing and calibration. The millivolt-to-current (MV/I) amplifier is on the left and the programmer is on the right. The output signal (10 to 50 milliamperes) was sent to an electro-pneumatic transducer (not shown) that, in turn, sent a proportional air signal (3 to 27 psig) to the fuel regulator. If the fuel regulator MVG determined that the exhaust temperature was “too high,” it would limit or reduce the output VCO pressure and internal reduce fuel flow.
Flame detection was done by a Fairchild Thermocouple Flame Relay like the one shown in Fig. 7-6. Like the GE/MAC, it took a millivolt signal from an averaging cabinet that represented the turbine exhaust temperature.
Modern programmable logic controllers (PLC) have been employed to replace these devices while retaining the fuel regulator and all its intended functions. A few external improvements and features have been made but the fuel regulator is still “in charge” of fuel flow to the gas turbine combustors. Sequencing lights on the right give the operator indications as event occur in the normal starting, loading, unloading and shutdown of the gas turbine.
The PLC below can continuously monitor such variables as:
- Time of operation, hours/minutes
- Turbine Speed, Ts, revolutions per minute (rpm)
- Fuel Flow, FF, gallons per minute (gpm)
- Average Exhaust Temperature, Txa, in degrees Fahrenheit (˚F)
- Fuel Pressure, FP, in pounds per square inch-gage (psig)
- Fuel Demand Signal: Vco in pounds per square inch-gage (psig)
- Bypass valve position, LVDT, in percent (% stroke)
The fuel regulator is alive and well in many gas turbine power plants. It is an ingenious device that has proven its worth and reliability in gas turbine operations for over 60 years. Few computer systems have lasted as long or performed as well as the Young & Franklin fuel regulator.