Abstract:
A method of detecting a single point of failure 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.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to failure prevention and, in particular, systems and methods to avoid single point failures. 
         [0002]    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&#39;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. 
         [0003]    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&#39;s are used to measure the position of the valve. The VDT&#39;s can be either linear VDTs (LVDTs) or rotary VDTs (RVDTs) VDT&#39;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&#39;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. 
         [0004]    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. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]    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: 
           [0010]      FIG. 1  is a power supply system according to one embodiment; 
           [0011]      FIG. 2  is a flow chart illustrating a method of avoid single point failures according to one embodiment; and 
           [0012]      FIG. 3  is a power supply system according to another embodiment 
       
    
    
       [0013]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    As discussed above, the IGV and valves in a turbine can include two or more monitoring devices (e.g., VDT&#39;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. 
         [0015]    To further illustrate the problem, assume that all of the VDT&#39;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&#39;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&#39;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. 
         [0016]      FIG. 1  illustrates a power supply system  100  that supplies power to devices  102 ,  104 ,  106 . The power supply system  100  could supply power to any number of devices greater than two and the three devices  102 ,  104 ,  106  shown in  FIG. 1  are merely illustrative. The devices  102 ,  104 ,  106  can be sensors or other types of devices. In one embodiment, the devices  102 ,  104 ,  106  are position sensors that are implemented as either LVDTs or RDVTs. 
         [0017]    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  FIG. 1 . The power supply units  108 ,  110 ,  112  can be selected to provide either direct current (DC) or alternating current (AC) power depending on the requirements of the devices  102 ,  104 ,  106 . 
         [0018]    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  FIG. 1 , the terminal block  114  is shown as including three terminal block sections  116 ,  118  and  120 . Each of the power supply units  108 ,  110 ,  112  is connected to a different one of the terminal block sections  116 ,  118 ,  120 , respectively. 
         [0019]    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. 
         [0020]    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 . 
         [0021]    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. 
         [0022]    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 . 
         [0023]      FIG. 2  is a block diagram showing a method for determining if more than one (or a desired number) of devices are drawing power from a single power supply unit. In this example it shall be assumed that the devices are VDTs used to measure the position of a flow control or pressure control valve in a turbine. Of course, the method could be applied to any system when two or more sensors are measuring an operational parameter of a machine. For example, the sensors could be measuring the position of an IGV. 
         [0024]    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. 
         [0025]    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  FIG. 1 , if three power supply units  108 ,  110 ,  112  are providing power, during a first stroking of the valve, the current drawn from the first power supply unit  108  is measured, during a second stroking of the valve, the current drawn from the second power supply unit  110  is measured, and during a third stroking of the valve, the current drawn from the third power supply unit  112  is measured. 
         [0026]    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. 
         [0027]    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  ( FIG. 1 ). Of course, the minimum value could be zero in one embodiment. In another embodiment, the minimum value is the value that a particular device draws when in an idle state. In the even that the current drawn does not exceed the minimum, an alarm is generated indicating a connection error at block  210 . For example, if during one of the stroking cycles one of the power supply units had no power drawn from it, it can be concluded that two of the VDT&#39;s are drawing power from a single one of the power supply units. Of course, other algorithms could be utilized to determine if the two or more VDT&#39;s are drawing power from a single power supply unit. For example, if the current drawn from one of the power supply units when one of the valves is stroked exceeds a threshold that is equal the maximum current that can be drawn by a single VDT, it can be concluded that two or more VDT&#39;s are drawing power from the power supply unit  FIG. 3  illustrates an alternative embodiment of a power supply system  300 . This embodiment includes a switching element  150  disposed between the power supply units  108 ,  110 ,  112  and the terminal block  114 . The switching element  150  can be used to select the power supply unit that provides power to a particular terminal block section. The configuration shown in  FIG. 3  has device  106  coupled via connection  126  to terminal block section  302  rather than terminal block section  120 . 
         [0028]    In  FIG. 3 , one or more of the power supply units  108 ,  110 ,  112  can include the capability of providing output to two different devices  102 ,  104 ,  106 . As illustrated, power supply unit  108  is providing power to both terminal block section  116  and terminal block section  302 . As such, both devices  102  and  106  are connected to power supply  108 . Accordingly, the second connection  308  is incorrect and is shown as a dashed line. Performing the testing described above will indicate that power supply unit  112  is not providing power and that power supply unit  108  is providing power to two devices. This situation can be rectified, my varying the switch configuration in the switch element  150  to couple power supply  112  to terminal block  302  as shown by dashed connection  310 . This embodiment can be useful because it allows for switching power supply-to-device connections without requiring changing the wiring between the terminal block  114  and the devices  102 ,  104 ,  106 . 
         [0029]    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.