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Control Method for Compressor Stability Management

IP.com Disclosure Number: IPCOM000200592D
Original Publication Date: 2010-Oct-20
Included in the Prior Art Database: 2010-Oct-26
Document File: 6 page(s) / 202K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Modern gas turbine engines are often used for the balancing of energy distribution networks. In order to meet the therewith associated performance requirements, gas turbines have to have short start-up times. However, modern gas turbines have shown failures attributed to compressor stall and over-temperature during start-up, affecting their start reliability significantly. In state of the art gas turbine control systems, two start-up philosophies can be found: the closed loop and the open-loop start-up scheduling. The open loop strategy is based on a predetermined fuel schedule, where the rate at which the fuel increases is controlled by a set of parameters and breakpoints throughout the start-up procedure. In this procedure fuel flow is usually prescheduled as a function of gas generator speed. Engine closed loop start-up scheduling is achieved by monitoring given engine requirements and closing the loop on the monitored parameters as calculated to provide start-up scheduling by adjusting the fuel flow.

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Control Method for Compressor Stability Management

Idea: Vili Panov, Ph.D., UK-Lincoln

Modern gas turbine engines are often used for the balancing of energy distribution networks. In order to meet the therewith associated performance requirements, gas turbines have to have short start-up times. However, modern gas turbines have shown failures attributed to compressor stall and over- temperature during start-up, affecting their start reliability significantly.

In state of the art gas turbine control systems, two start-up philosophies can be found: the closed loop and the open-loop start-up scheduling. The open loop strategy is based on a predetermined fuel schedule, where the rate at which the fuel increases is controlled by a set of parameters and breakpoints throughout the start-up procedure. In this procedure fuel flow is usually prescheduled as a function of gas generator speed. Engine closed loop start-up scheduling is achieved by monitoring given engine requirements and closing the loop on the monitored parameters as calculated to provide start-up scheduling by adjusting the fuel flow.

Usually fuel flow is variable delivered to the engine with a governor controlled feedback loop arrangement maintaining engine speed. Acceleration or fuel flow is adjusted as a difference function between predetermined torque and measured torque.

During start up when stall occurs, the pressure ratio of the compressor initially exceeds some critical value at a given speed, resulting in a subsequent reduction of compressor pressure ratio and airflow delivered to the engines combustor. Two different stall compressor instabilities can be distinguish, namely progressive and abrupt stall. Progressive stall can be recognized as a gradual reduction in total pressure ratio after stall begins. Abrupt stall has a sharp discontinuity in the pressure ratio characteristic with sudden drop in pressure. If such condition is undetected and allowed to continue, the combustor temperatures and vibratory stresses induced in the compressor may become sufficiently high to cause damage to the gas turbine engine.

Different methods for starting gas turbine engines with minimized thermal stresses and achieving stall- free and repeatable engine acceleration have been developed in the past. A number of these methods have been developed to sense when stall is imminent and to initiate engine control system corrective actions to avoid or recover the gas turbine from compressor instabilities. These methods can alleviate instabilities by increasing the compressor stability margin, using corrective actions in one of the following ways:

• controlling the fuel flow schedule,

• adjusting the compressor variable vanes, and hence reducing compressor air flow,

• modulating the compressor (interstage/exit) bleed.

State of the art stall protection methods for gas turb...