Peculiarities of rotation frequency ACS of stationary GTU, which operates on the gas-type fuel
1) In most stationary gas turbine units ACS agrigates are set up not on the case of the engine, but are placed in special modular box and partially on local control desk .
As SE in ACS stationary gas turbine speed is often used centrifugal oil pump - impeller, which is installed on the rotor shaft, and rotation frequency of which is used as the controlled parameter.
The task of impeller is to create a control signal in the form of oil pressure head which is supplied tothe input of the speed rotor rotation regulator.Thus, the oil head from the impellerdepends on the shaft speed where it is installed. For this purpose theoiltoimpeller supplied from the oil engine system at constant pressure.
The servomechanism of regulating valve that acts as control device in the control system of GTP working with gasious fuel, can be used as a membrane-pneumatic amplifier of the signas, lcoming from the speed regulator. In this case for control signal (pulse) transmission from the regulator to the speed regulating valve pneumatic connection is used.
As control device of rotational speed ACS the as a regulating valve or gas metering needle is usually used (see Fig. 5.6).
In the considered ACS as the working fluid the compressed air is used . This air comes from the compressor station manifold. For this purpose air is taken from operating GTU. Air pressure in the manifold is suppored at constant lelel (approximately 0.4 MPa.) At not working GTU for the initial filling ofthe collector used piston compressor with electric drive. Then after running out at least one gas turbine the compressor is turned off.
On the fig 5.6. 2 air lines are shown: constant air pressure line ðïîâ const (more often ðïîâ = 0,14 ìPà) and govern flowing line with air pressure ðïð.
Flowing line connected both the frequency rotation regulator and the regulating valve. The pressure in the flowing line ðïðis determined by the passing sectionarea between bush2 and slide 3, size of which depends on their mutual position relatively to each other.
Size of regulating valve opening, and thus the amount of fuel gas entering into the combustion chamber depends on air pressure that is created in the running line.
Fig 5.6. Rotation frequency ACS of GTU 10-4:
1 – casing of the regulator; 2 – bush; 3 – slider; 4 – rod; 5 – spring; 6 – piston; 7 – impeller; 8 – jet; 9 –slide governor; 10 – bush; 11 – slide membrane; 12- slide spring; 13 – valve spring; 14 – controlling valve; 15 – SM regulative valve membrane; ðì.³ – oil pressure after impeller; ðïîâ– air pressure in constant pressure line; ðïð– air pressure in flowing line; –––– –air constant pressure line; –- –- – flowing line
Firstly, the pressure in the flowing line and therefore requires rotation speed of GTU, is set up by operator with the help of setting up device SD by sleeve 2 replacement. Further support for a given pressure ðïðin flowing line, and subsequently given speed is occurred automatically.
In the case of rotation speed GTP decreasing induced by external conditions changes or load on the power turbine we will have oil pressure decreasing after impeller, and therefore before the piston 6 regulator. Violation of effort equality of on the pistons associated with the presence ðì.³and the efforts from the spring 5, will move the piston 6 and the spool 3, rigidlyinterconnected by means of the rod 4.
As it’s shown on the figure, with decreasing of speed rotation the valve 3 will fall down relative to bushing 2, which will increase air pressure in a flowing line. In turn, increased pressure in the flowing line will move the control valve 9 downward relative to bushing 10, causing air from the line of constant pressure ðïîâwill come to the membrane 15 of SM regulating valve. When the force on the membrane from the pressure ðïîâwill be greater than efforts by the spring 13, then will occur regulating valve 14 removing in the upper position to increase the supply of fuel gas. As a result, supply of fuel gas into the combustion chamber will increase and, accordingly, will increase the engine speed to the original value. In the case of increasing the frequency of rotation of the rotor of a set value, the process control will proceed similarly, but in reverse.
The following scheme regulator spring 12, which is installed between the diaphragm control valve 9 and themembrane15servomechanismregulatingvalveservesizodromfeedbackandwarningclaimsspeedof the rotorin transient conditions, trying to establish managingspool 9 in the neutral position.Jet8preventsfluctuations in air pressure in the line of constant pressure when you change the air flow through the flowing line.
Change in rotation speed with aim to change the mode of GTP achievedpermutationrespectivelydown orup bush 2 on the slide 3 in the device ST. For example, to convert GTP to a higher mode of slider 2 it is necessary to move into the top position, leading to increased pressure in the flowing line, thus increasing the opening regulating valve. As a result the speed of the rotor GTU will increase to a new value, required mode.
During studying speed rotation frequency of SAC firstly we should clarify the definition of ACS, which emphasizes the need for consistency of elements performance that make up the system. Then you should consider that typical items which are the part of regulators to learn ways of elements’ representation on the diagram and to figure out an action principles of the most common elements.
You must also understand the principles of regulators classification. Further it is recommended tostudythe principle of direct action regulator processing, to analyze the static and dynamic characteristics of theregulator.
In a similar manner it is recommended to consider the principle of action, functional diagram,staticanddynamiccharacteristics of the indirect action speed regulator without feedback.
Further it’s recommendedto study the indirect actions regulator with rigid and isodromic feedback. It’s necessary to pay attention to the features of frequency rotation ACS of gas turbine, operating on gaseousfuels. However, as an example should be considered frequency rotation ACS of SCC-10-4gas turbine.
To consolidate the material it’s recommended to draw functional schemes of each type regulators and to analyze their operating principles.
1. Name the basic requirements to the frequency rotation ACS?
2. Whatparameters do characterize the quality of frequency rotation ACS?
3. Name the controlling principles, which are used in frequency rotation ACS of GTU?
4. Name the elements, which belong to frequency rotation regulator, and their designation?
5. Give the comparison estimation for static and dynamic characteristics of frequency rotation ACS of direct and indirect action with the simplest schemes.
6. Give the comparative analysis of static and dynamic characteristics of the indirect actionof regulators with RFB and indirect action regulators with IF (isodromic feedback).
7. What influence on static and dynamic characteristics does the indirect action regulator cause after putting into it the RFB?
8. What influence on static and dynamic characteristics does the indirect action regulator cause after putting into it the FFB?
9. Name the peculiarities of frequency rotation ACS of GTU, which operates on the gaseous fuel.