Turbine Core Auxiliary Equipment; Variable Guide Vane (Vgv) Actuator; Interstage Bleed Valve; P2 Blow-Off Valves - Siemens SGT-400 Operator's Manual

Turbine Package Operators Manual
Chapter 1
Turbine Package System Overview

Turbine Core Auxiliary Equipment

Variable Guide Vane (VGV) Actuator

The purpose of the variable guide vane (VGV) system is to vary the flow through the gas
generator to optimize starting and running conditions. This is achieved by altering the angles at
which the inlet guide vanes and the first three stages of compressor blades are presented to the
airflow. The position of the blades is altered by the operation of the mechanically linked VGV
actuator.
The electrical VGV actuator (ZZ8) consists of an actuator and servo positioner assembly. The
assembly is mounted on the turbine to vary the position of the inlet guide vanes and the first,
second, third and fourth stages of compressor stator blades.
The actuator position is controlled by the servo positioner, which reacts to drive signals (ZC4)
from the unit control panel. The unit control panel monitors the position of the VGS blades/inlet
guide vanes using a proportional feedback signal (ZT9) from the VGS actuator.

Interstage Bleed Valve

To prevent gas generator surge during starting, it is necessary to reduce the compressor delivery
air pressure. This is achieved by the use of the interstage bleed valve, mounted on the upper
low-pressure compressor stator casing.
During the turbine starting sequence, as the compressor speed increases, control air is bled from
the delivery stage of the compressor and routed through a pilot valve (XV60) onto the piston of
the interstage bleed valve (XV59). As the air pressure increases, the piston is pushed to its full
extent of travel, thus closing off the air being vented to atmosphere.
Operation of the pilot valve is achieved by instrument air controlled by a solenoid mounted in the
instrument air pipeline.

P2 Blow-off Valves

Blow-off valves (XV267 and XV268) are mounted on the port and starboard sides of the turbine
to modulate engine compressor air during starting and to enable a rapid discharge of air during
engine over-speed conditions.
This is achieved by bypassing engine air from upstream of the power turbine through the blow-
off valves into the exhaust diffuser.
The blow-off valves are operated by solenoid valves (port - SOL625, SOL627 and starboard -
SOL626, SOL628). The solenoids direct P2 air to either side of the valve actuators (XV267 and
XV268). The solenoid valves are operated by a drive signal (ZC43, ZC44) from the unit control
panel. The unit control panel monitors the position of the P2 blow-off valves using a proportional
feedback signal (ZT141, ZT142) from the P2 blow-off valve butterfly spindles.

Waterwash Nozzles

Waterwash nozzles are mounted in the engine air inlet to facilitate the supply of wash and rinse
fluids into the turbine during engine hot and cold wash operations. A last chance filter (XF27)
ensures filtration of the wash/rinse fluids.
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