Patent Application
20120286820
The subject matter disclosed herein relates to failure prevention and, in particular, systems and methods to avoid single point failures.
Gas turbines, used in the generation of power, draw in air from the atmosphere and a fuel as inputs. The fuel can be gas, liquid or a combination of gas/liquid fuel. The fuel and air are combined and combusted to provide the driving force causing the turbine's rotor to rotate. As is known in the art, the power generated from gas turbines can be controlled by controlling a rate at which the fuel and air are provided to the turbine.
Inlet air from the atmosphere passes through an inlet guide vane (IGV) and then enters a compressor. Inlet airflow rate can be adjusted by changing a vane angle of the IGV. Fuel flow is controlled by a set of flow control and pressure control valves. The flow control and pressure control valve position can be measured by two or more variable differential transformers (VDTs) per valve depending on configuration. In general, the VDT's are used to measure the position of the valve. The VDT's can be either linear VDTs (LVDTs) or rotary VDTs (RVDTs) VDT's, in general, include an excitation (primary) coil and one or more output coils. In some cases, when the configuration uses two VDTs, the highest value is considered in control and protection algorithms. In cases where three VDT's are used to monitor the position of a single valve (i.e., a triple modular redundant (TMR) system) it is common to use a median value of the three reported positions in control and protection algorithms.
In order to operate the turbine in a desired manner, the user specifies a power output level. From this level, control algorithms determine the fuel and air required to meet the output level. The fuel and air requirements can be converted to valve and IGV positions and the positions are monitored by the VDTs. Of course, the valve and IGV positions can be changed to more closely tune the turbine to a desired power output.
According to one aspect of the invention, method of detecting a single point of failure is disclosed. The method of this aspect includes: placing a portion of a machine being monitored by a plurality of monitoring devices in a first position; causing the portion to cycle to a second position during a first cycle; measuring a component of electrical power provided by a first power supply unit while the portion cycles during the first cycle; returning the portion to the first position; causing the portion to cycle to the second position during a second cycle; measuring the component of electrical power provided by a second power supply during the second cycle; determining that an amount of the component of electrical power provided during either the first or second cycle is equal to or less than a minimum value; and generating an alarm.
According to another aspect of the invention a method of detecting a single point of failure is disclosed. The method of this embodiment includes: placing a portion of a machine being monitored by a plurality of monitoring devices in a first position; causing the portion to cycle to a second position during a first cycle; measuring a component of electrical power drawn from a first power supply unit and a second power supply unit while the portion cycles during the first cycle; determining that an amount of the component of electrical power drawn from either the first power supply unit or the second power supply unit is equal to or less than a minimum value; and generating an alarm.
According to another aspect of the invention, a method of detecting a single point of failure is disclosed. The method of this aspect includes: placing a portion of a machine being monitored by a plurality of monitoring devices in a first position; causing the portion to cycle to a second position during a first cycle; measuring a component of electrical power provided by a first power supply unit while the portion cycles during the first cycle; determining that an amount of the component of electrical power provided by the first power supply unit during the first cycle exceeds a threshold; and generating an alarm that indicates that more than one monitoring device is coupled to the first power supply.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
As discussed above, the IGV and valves in a turbine can include two or more monitoring devices (e.g., VDT's) used to monitor their operational positions. It has been discovered that when two or more of the monitoring devices receive power from a single power source, that power source can represent a single point of failure capable of disabling all of the monitoring devices to which it is coupled. It is a technical effect of one embodiment that a determination of whether such a single point of failure exists can be made.
To further illustrate the problem, assume that all of the VDT's monitoring the position of a flow control valve receive power from a single power supply. If this power supply fails, all of the VDT's fail and a trip occurs. Such trips can be costly and should be avoided. One approach to avoid such a single point of failure is to power each VDT from a different power source. However, human wiring errors can still occur. Embodiments disclosed herein can detect such errors. While the description herein focuses on VDT's used in turbines, it shall be understood that the teachings are applicable to any situation where two or more sensors are monitoring a parameter of a machine.
The power supply system 100 includes two or more power supply units illustrated as first power supply unit 108, second power supply unit 110, and third power supply unit 112. The power supply units 108, 110, 112 are each capable of powering one or more of the devices 102, 104, 106. According to one embodiment, the power supply system 100 includes only the first and second power supply units 108, 110. In another embodiment, the power supply system 100 includes more than the three power supply units illustrated in
As illustrated, the system 100 also includes an optional terminal block 114 that serves as a convenient connection location for both the power supply units 108, 110, 112 and the devices 102, 104, 106. In
In operation, and as described above, it is desirable to configure the system 100 such that each power supply unit 108, 110, 112 powers a different one of the devices 102, 104, 106. When so configured, the failure of one of the power supply units 108, 110, 112 will not cause the failure of devices not connected to it.
Connections 122, 124 and 126, respectively, connect the first terminal block section 116 to the first device 102, the second terminal block section 118 to the second device 104, and the third terminal block section 120 to the third device 106. When the system 100 is connected utilizing connections 122, 124, 126, each device 102, 104, 106 is receiving power from a different one of the power supply units 108, 110, 112, respectively. As such, there is not a single point of failure for all of the devices 102, 104, 106.
Conversely, when two or more of the devices 102, 104, 106 are coupled to a single power supply unit, that power supply unit is a single point of failure for all of the devices to which it is connected. Such a configuration is shown by dotted line connections 128, 131, 132 which illustrate an alternative configuration of the system 100. In such a configuration, of course, connections 122, 124 and 126 are not present.
The power supply system 100 also includes shunts 130 coupled between the power supply units 108, 110, 112 and the devices 102, 104, 106 they supply power to. One or more of these shunts 130 can include a meter that measures a voltage (or other power component) across the shunt 130. This voltage can be used by a tester 140 to determine if more than one device 102, 104, 106 is coupled to and drawing power from the power supply unit to which the particular shunt 130 is attached. Any or all of the shunts 130 can be coupled to the tester 140.
At block 202 the current being drawn from each power supply unit is measured. The measurement can be continuous or discrete. If discrete, the measurement can be made periodically in one embodiment.
At block 204, the valve is/are all closed. Then, at block 206, the valve is cycled from its fully closed position to its fully open position (i.e., stroked) as the current drawn through the VDTs is monitored. In one embodiment, the current drawn from each power supply unit is measured at the same time. In another embodiment, the process of block 204 and 206 are repeated and, during each repetition, the current drawn by a different one of the power supply units is monitored. For example, and referring again to
Regardless of when the currents are measured, at block 208 it is determined if the current drawn changed for all of the power supply units as the valve was stroked. If so, the connection of the devices is correct and the process ends.
In contrast, if the current drawn is less than or equal to a minimum value during any of the cycles, this indicates that one of the power supply units is not providing power to any of the devices 102, 104, 106 (
In
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
