|An electronic Servo Position Controller and a brushless DC servomotor power the EGV Gas Throttle.
The motor is connected to the gas throttle valve through a gearbox.
Fuel Flow is regulated using a variable orifice with well-defined characteristics.
Together with throttle effective area, fuel flow is a function of:-
In either case Fuel Flow to the gas turbine can be determined from throttle valve position.
- gas specification (summarised as Wobee Index)
- supply pressure
- discharge pressure if throttle is de-choked
A Brushless DC Servo Motor is used to position the valve in response to a control signal from the governor.
The motor drives the valve through a low backlash.
High driving torque and the self-cleaning nature of the valve results in low sensitivity to contamination.
Trunion gas valve bearings are not exposed to fuel gas.
Valve position is determined using a position resolver mounted on the motor shaft.
A limit switch is used to provide independent indication that the valve is nominally at light-off position.
Motor winding temperature transmitter is included.
The valve characteristic has been chosen to give more progressive and accurate control at lower flows and can be expressed as a polynomial.