1 - System Description

GEK106910 April 1998 Replaces VARIGV00

GE Power Systems Gas Turbine

Variable Inlet Guide Vane System

I. GENERAL Variable compressor inlet guide vanes (VIGV) are installed on the turbine to provide compressor pulsation protection during startup and shutdown and also to be used during operation under partial load conditions. The variable inlet guide vane actuator is a hydraulically actuated assembly having a closed feedback control loop to control the guide vanes angle. The vanes are automatically positioned within their operating range in response either to the control system exhaust temperature limits for normal loaded operation, or to the control system pulsation protection limits during the start-up and shutdown sequences. On DLN units, the IGV angle is modulated to control air flow to the combustors for DLN operation modes. II. GUIDE VANE ACTUATION The modulated inlet guide vane actuating system includes the following components: servo valve 90TV, position sensors (LVDT) 96TV-1 and 96TV-2, and hydraulic dump valve VH3. These are shown on the trip oil and IGV schematic diagrams in Volume III. When the inlet guide vane dump solenoid valve 20TV in the trip oil circuit is energized, its drain ports are blocked thus allowing the trip oil to operate the dump valve VH3. Actuation of the dump valve allows hydraulic oil to flow through servo valve 90TV. Control of 90TV will port hydraulic oil through the dump valve to operate the variable inlet guide vane actuator. For normal shutdown, inlet guide vane actuation is the reverse of the startup sequence; the compressor bleed valves will open when the generator breaker is opened. The inlet guide vanes will ramp to the full closed position as a function of temperature corrected speed. In the event of a turbine trip, the compressor bleed valves will open and the inlet guide vanes will ramp to the closed position as a function of temperature corrected speed. III. PULSATION PROTECTION CONTROL The inlet guide vanes are automatically positioned during a start-up and a shutdown sequence to avoid gas turbine compressor pulsation. The pulsation limit is expressed as a function of IGV angle and corrected speed, shown by the broken line on Figure 1. Corrected speed is a compressor design parameter that is a function of the actual running speed of the compressor and the inlet air temperature. The control system utilizes the measured variables of turbine speed and ambient temperature to determine the IGV angle and automatically modulate them to that position.

These instructions do not purport to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection with installation, operation or maintenance. Should further information be desired or should particular problems arise which are not covered sufficiently for the purchaser’s purposes the matter should be referred to the GE Company.  1998 GENERAL ELECTRIC COMPANY

GEK106910

Variable Inlet Guide Vane System

IGV Angle Degrees (CSRVPS)

Full Open (Max. Angle)

Minimum Full Speed Angle

Rotating Stall Region

Corrected Speed % (TNHCOR)

100 0

Load %

Figure 1. IGV Angle vs Corrected Speed and Load.

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100

Variable Inlet Guide Vane System

GEK106910

IV. EXHAUST TEMPERATURE CONTROL For applications such as a regenerative cycle or where there is a steam generator (boiler) in the gas turbine exhaust, it is desirable to maximize the exhaust temperature. The control program for such turbines includes an exhaust temperature control which automatically holds the IGV at a minimum angle during part-load operations. A switch is provided to permit the operator to select this mode of operation. V. OPERATION During a normal start-up, the inlet guide vanes are held in the full-closed position (see the Control Specifications in this service manual for settings) until the proper temperature-corrected speed is reached. At this time, the guide vanes will begin to open. A graphic representation of this action is shown in Figure 1. The compressor bleed valves, which must operate in conjunction with the VIGVs to maintain compressor surge margin during startup, will close when the generator breaker is closed. When the VIGV temperature control mode is not activated, the guide vanes are held at the minimum fullspeed angle until the simple cycle VIGV exhaust temperature is reached. This temperature is the constant CSKGVSSR. As the exhaust temperature rises, a value computed as the product of constant CSKGVTPG times the difference between the actual exhaust temperature TTXM and CSKGVSSR is added to the minimum angle, causing the VIGVs to open until they reach the maximum angle. This sets a minimum load which the unit must reach before the VIGVs are allowed to open. This is necessary to avoid combustion resonance and must not be changed. For applications which require part load exhaust temperature control operation, the guide vanes are switched to the “IGV temp control On” with a soft switch. In this mode the VIGVs remain at the minimum full operating position until the base exhaust temperature limit is reached. At this point, they begin to open to hold the exhaust temperature at this limit until they are full open when the exhaust temoerature control reverts to fuel modulation. In order to keep the fuel control and IGV control from trying to act simultaneously, a fuel control bias is added to keep the fuel line slightly above the VIGV line. This bias is the product of constant CSKGVBG times the difference between the maximum VIGV angle (constant CSKGVMAX) and the VIGV reference CSRGV. This bias becomes zero when the VIGVs are fully open and the fuel temperature control takes over. The operator can activate or deactivate the VIGV temperature control mode at any time via the panel soft switches. The control system will automatically reprogram the VIGVs to the correct position at a controlled rate. Manual open/close soft switches are provided to allow the operator to manually position the VIGVs between the minimum full speed angle and full Open. This control should only be used in special circumstances to limit the travel (amount opened). The manual control is limited to command an angle only when less than that being called for by the automatic control system. In normal operation, the manual control is set at full open. For applications requiring steam turbine warmup, the operator can select a desired exhaust temperature and the IGV’s will modulate to achieve the setpoint. Refer to the control sequence program for a detailed representation of the VIGV software. VI. FAULT PROTECTION The guide vane protection system will trip solenoid valve 20TV, initiate a fast normal shutdown and annunciate if there is low hydraulic supply pressure, or the LVDT feedback is different from command, or IGV position trouble is indicated. Should the inlet guide vane system be tripped under and one of the above conditions, the SPEEDTRONIC sequencing logic generates a signal which is used in the start check circuit to prevent any attempt to restart the turbine prior to eliminating the cause for the trip.

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GEK 106910

Variable Inlet Guide Vane System

The primary IGV fault signal is generated by the “IGV not following CSRGV” algorithm, L86GVT. This algorithm compares the difference between the VIGV position feedback CSGV and the reference signal CSRGV to generate alarm signal, L86GVA if the IGV is not following the reference within the value of LK86GVA1 given in the Control Specifications Settings. The alarm signal is annunciated if the difference persists for time LK86GVA2 specified in the Control Specifications Settings. During part speed operation, a trip signal L86GVT is generated if the VIGV position feedback CSGV does not agree with the speed reference CSRGV within the value of LK86GVT1 and for a time of LK86GVT2 given in the Control Specifications Settings. Trip signal L86GVT will deenergize 20TV, trip the turbine and annunciate an alarm. During full-speed operation, trip logic L4GVTX will alarm and trip the turbine if the VIGV feedback CSGV falls below a minimum allowable full-speed value LK4IGVTX.

GE Power Systems General Electric Company One River Road, Schenectady, NY 12345 518 • 385 • 2211 TX: 145354