Patent Application
20100265816
This application relates to monitoring switching networks as used, for example, in high power regulation devices.
Static VAR correctors, also referred to as static VAR compensators (SVCs), are electrical devices that provide reactance compensation to power transmission networks. SVCs are commonly used in various applications, including, for example, regulating utility line voltage, improving network steady-state stability, and establishing near unity power factor on transmission lines.
Typically, an SVC includes a bank of controllable capacitors and reactors that can be individually switched into and out of a utility power network (e.g., a transmission or a distribution line) by a set of semiconductor switches (e.g., thyristors). Each switch is driven by electrical gating signals generated based on line conditions, allowing the corresponding capacitors or inductors to discharge or conduct in a controlled manner. When using thyristors that are capable of responding to gating signals within a sub-cycle (e.g., on the order of several milliseconds), an SVC is able to provide near-instantaneous reactance flow to compensate voltage or current fluctuations on utility networks. After extended use, thyristors can fail, rendering the SVC inoperable and leading to power service interruptions and costly replacements. For this reason, thyristors are monitored to prevent failure of the SVC.
In a general aspect of the invention, a sensing circuit is configured for use with a switching network including a plurality of switches. The sensing circuit includes a plurality of detecting networks, the plurality of detecting networks being fewer in number than the plurality of switches, and each detecting network providing signals indicative of a failure of at least one of the switches.
Implementations of the sensing circuit may include one or more of the following features.
The detecting networks are configured to send a warning signal if the failed switches are greater in number than zero and fewer than or equal to a number of redundant switches in the switching network.
The detecting networks are configured to send a trip signal to disable the switching network if the failed switches are greater in number than the number of redundant switches.
In a general aspect of the invention, a sensing circuit is configured for use with a switching network that includes a plurality of switches and has a number of redundant switches. The sensing circuit includes a plurality of detecting networks configured to send a warning signal indicating that a number of failed switches is greater than zero and is also fewer than or equal to the number of redundant switches. At least one of the detecting networks in the sensing circuit is configured to disable the switching network if a number of failed switches is greater than the number of redundant switches.
Implementations of the sensing circuit may include one or more of the following features.
The plurality of detecting networks is fewer than the number of switches.
In a general aspect of the invention, a sensing circuit is configured for use with a switching network that includes a plurality of switches and has a number of redundant switches. The sensing circuit includes a plurality of detecting networks that are fewer than the plurality of switches. The detecting networks are configured to send a warning signal indicative of a number of failed switches greater than zero and fewer than or equal to the number of redundant switches. At least one of the detecting networks disables the switching network if a number of failed switches is greater than the number of redundant switches.
Implementations of the sensing circuit may include one or more of the following features.
Each of the plurality of detecting networks monitors, at most, a number of switches equaling all the switches in the switching network divided by the number of detecting networks.
A number of detecting networks equals at least two more than the number of redundant switches.
The switches of the switching network are in series.
The number of redundant switches is two or more.
The switches include one or more high-power semiconductor switch-diode pairs or one or more high-power semiconductor switch-switch pairs.
The detecting networks detect voltage.
The detecting networks include dropping networks, which may also include one or more of a resistor divider, a transformer, a set of reactors, or a set of capacitors.
The plurality of detecting networks includes a differential amplifier.
The plurality of detecting networks includes a processor that compares voltages across one or more of the plurality of switches.
In a general aspect of the invention, a method of monitoring a switching network containing a plurality of switches, includes: obtaining signals from each of a plurality of detecting networks, wherein at least one detecting network monitors two or more switches; determining a number of failed switches in the switching network based on the received signal; and performing one or more actions depending on the number of failed switches in the switching network.
Implementations of the method may include one or more of the following features.
Obtaining signals includes measuring voltages across one or more switches using a dropping network or a differential amplifier.
Determining includes comparing the received signals to stored signals representative of a known number of failed switches.
Performing one or more action depending on the number of failed switches in the switching network includes sending a warning signal indicative of the number of failed switches if the number of failed switches is greater than zero and fewer than or equal to a number of redundant switches in the switching network. Performing one or more action depending on the number of failed switches in the switching network also includes disabling the switching network if the number of failed switches is greater than the number of redundant switches in the switching network.
The above-described systems and methods may include one or more of the following advantages.
Switches in a switching network can be monitored efficiently and effectively. A switching network having a redundant number of switches can be monitored so that the network continues normal operation even after a number of switches up to and including the redundant number of switches have failed. In this scenario, a warning is sent to alert that switches have failed so that maintenance can be scheduled.
In the event that more than the redundant number of switches fails, the monitoring system and methods disable the switching network, preventing damage to the network.
The switch monitoring systems and methods are efficient and cost-effective because the status of each switch is inferred without having to employ a separate monitor for each switch.
Other features and advantages of the invention are apparent from the following description, and from the claims.
Referring to
Generally, each of the monitors 120 receives signals related to associated groups of thyristors 122 and report to a controller 108 how many of the thyristors have failed. When the number of failed thyristors is fewer than or equal to the number of redundant thyristors, the controller 108 sends a warning. For example, the warning can be received by an operator who then schedules a replacement of the failed thyristors.
When the monitor 120 reports that the number of failed thyristors is greater than the number of redundant thyristors, the controller 108 disables the SVC 104. As will be described in greater detail below, an arrangement of monitors 120 and a method of operation of the monitors permit an efficient, effective means for monitoring the thyristors 122 within an SVC 104.
The SVC 104 regulates voltage by controlling the amount of reactive power injected into or absorbed from the power network. For example, when the network voltage is low, as can happen when customer usage increases during summer months, the SVC generates capacitive reactive power. On the other hand, when the system voltage is high, the SVC absorbs inductive reactive power. A controller 108 measures a stepped-down voltage and includes or excludes multi-phase banks of capacitors 110 and banks of inductors 112 in the utility power system 100 as needed. Valves 114 include a series of thyristors and control the capacitor banks 110, which are referred to as thyristor-switched capacitors (TSCs) 116, and inductor banks, which are referred to as thyristor-switched reactors (TSRs) 118. Alternatively or in addition, inductors can be controlled by different phases, in which case they are referred to as thyristor-controlled reactors (TCRs, which are not shown in
Referring to
Thyristors within the valve 114 can fail, for example, because of over-voltage or over-current operating conditions, inadequate cooling, or mechanical damage. When a thyristor fails, it often shorts as its failure mode, causing the voltages to change across the thyristor-diode pair 200 as well as across the entire series of thyristor-diode pairs in the valve 114. To monitor for failure of the valve 114 and the SVC 104, the monitor 120 (shown within a dotted line) measures parameters (e.g., voltages) related to the functionality of the thyristors within the valves 114.
The monitor 120 is integrated between the valve 114 and a thyristor bank controller 204 either during initial construction or by retrofitting. The monitor 120 contains four detection groups (e.g., detection groups 206a-d) that each monitors a group (e.g., groups 208a-d) of three or four thyristor-diode pairs 200. In the example shown in
Referring to
Referring to
Referring to the other rows of table 400, measured voltages across the TSC groups 208a-d are listed, in which one, two, or three shorted thyristors are distributed among the groups. A negative voltage value indicates that the voltage across a group has decreased and the group contains one or more shorted thyristors. For example, the top row of table 400 lists voltages measured when one failed thyristor is distributed among groups 208a-d. A voltage of 7.7% is measured across each of groups 208a, 208c, and 208d, and a voltage of −19.2% is measured across group 208b. As such, the failed switch is localized to group 208b. Because of the noted symmetry in the groups 208b and 208c, if the failed switch were instead in group 208c, the voltage across each of groups 208a, 208b, and 208d would be 7.7% and the voltage across group 208c would be −19.2%.
The sixth row of table 400 lists voltages measured when one failed thyristor is located in group 208a. In this scenario, a voltage of 7.7% is measured across each of groups 208b, 208c, and 208d, and a voltage of −28.2% is measured across group 208a. Because of the noted symmetry in the groups 208a and 208d, if the failed switch were instead in group 208d, the voltage across each of groups 208a, 208b, and 208c would be 7.7% and the voltage across group 208d would be −28.2%. The remaining rows of table 400 list the measured voltages across the groups 208a-d, in which two or three shorted thyristors are distributed among the groups.
Referring to
It is to be understood that the configurations of the monitor 120 shown in
A standard design practice is for the voltage rating across the valve to be two times the peak voltage rating, or 13,200×2×sqrt(2)˜37,336 volts. Using thyristors that are each rated at 6,500 volts, six thyristor-thyristor pairs 602 are needed. If a redundancy of two pairs is desired, eight thyristor-thyristor pairs 602 are needed. The level of redundancy can be higher or lower. At higher voltages or different thyristor ratings, the number of thyristor-thyristor pairs 602 is changed as needed.
As in the previous implementation, the monitor 120 is integrated between the valve 114 and a thyristor bank controller 204. The integration can be performed during initial construction or by retrofitting. The monitor 120 contains four detection groups (e.g., detection groups 606a-d) that each monitors a group (e.g., group 608a-d) of two thyristor-thyristor pairs 602. In the example shown in
Referring to
Referring to the other rows of table 450, measured voltages across the groups 608a-d are listed, in which one, two, or three shorted thyristors are distributed among the groups. A negative voltage value indicates that the voltage across a group has decreased and the group contains one or two shorted thyristors. For example, the top row of table 450 lists voltages measured when one failed thyristor is distributed among groups 208a-d. A voltage of 14.3% is measured across each of groups 608a, 608c, and 608d, and a voltage of −42.9% is measured across group 608b. As such, the failed switch is localized to group 608b. Because of the noted symmetry in the groups, the voltage across any group that contains one failed switch would be −42.9%, and the voltage across the remaining groups that each has two properly-functioning thyristors would be 14.3%. This is confirmed in the fifth row of table 450, in which group 608a contains the failed switch.
The remaining rows of table 450 list the measured voltages across the groups 608a-d, in which two or three shorted thyristors are distributed among the groups.
While the above examples have described monitoring thyristors within SVCs, the methods and systems described can also be applied to monitor other switches or switching devices, including but not limited to silicon controlled switches, rectifiers, transistors, and bi-directional triode thyristors (also called “triacs”).
The techniques described herein can be implemented in one or more of digital electronic circuitry, computer hardware, firmware, or software. The techniques can be implemented as logic gates or a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.
Method steps of the techniques described herein can be performed by one or more programmable processors executing a computer program to perform functions of the invention by operating on input data and generating output. Method steps can also be performed by and apparatus of the invention can be implemented as special purpose logic circuitry, e.g., a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). Modules can refer to portions of the computer program and/or the processor/special circuitry that implements that functionality.
Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., random access memory (RAM), magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in special purpose logic circuitry.
To provide for interaction with a user (e.g., a warning that alerts of failed thyristors), the techniques described herein can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer (e.g., interact with a user interface element, for example, by clicking a button on such a pointing device). Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.
It is to be understood that the foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the appended claims. Other embodiments are within the scope of the following claims.
